Compare revisions

Ben Gamari · Marge Bot · Ben Gamari · Marge Bot · Finley McIlwaine · Marge Bot
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -433,6 +433,7 @@ hadrian-multi:
      - cabal-cache
  rules:
    - if: '$CI_MERGE_REQUEST_LABELS =~ /.*full-ci.*/'
+    - if: '$CI_MERGE_REQUEST_LABELS =~ /.*marge_bot_batch_merge_job.*/'

 ############################################################
 # stack-hadrian-build
@@ -511,7 +512,7 @@ doc-tarball:
      optional: true
    - job: nightly-x86_64-windows-validate
      optional: true
-    - job: release-x86_64-windows-release+no_split_sections
+    - job: release-x86_64-windows-release
      optional: true

  tags:
@@ -535,7 +536,7 @@ doc-tarball:
        || mv "ghc-x86_64-linux-deb10-release.tar.xz" "$LINUX_BINDIST" \
        || true
      mv "ghc-x86_64-windows-validate.tar.xz" "$WINDOWS_BINDIST" \
-        || mv "ghc-x86_64-windows-release+no_split_sections.tar.xz" "$WINDOWS_BINDIST" \
+        || mv "ghc-x86_64-windows-release.tar.xz" "$WINDOWS_BINDIST" \
        || true
      if [ ! -f "$LINUX_BINDIST" ]; then
        echo "Error: $LINUX_BINDIST does not exist. Did the Debian 9 job fail?"
@@ -831,6 +832,7 @@ perf-nofib:
    - if: '$CI_COMMIT_BRANCH == "master"'
    - if: '$CI_COMMIT_BRANCH =~ /ghc-[0.9]+\.[0-9]+/'
    - if: '$CI_MERGE_REQUEST_LABELS =~ /.*full-ci.*/'
+    - if: '$CI_MERGE_REQUEST_LABELS =~ /.*marge_bot_batch_merge_job.*/'
  tags:
    - x86_64-linux
  before_script:
@@ -898,6 +900,7 @@ perf:
      - out
  rules:
    - if: '$CI_MERGE_REQUEST_LABELS =~ /.*full-ci.*/'
+    - if: '$CI_MERGE_REQUEST_LABELS =~ /.*marge_bot_batch_merge_job.*/'

 ############################################################
 # ABI testing
@@ -938,6 +941,7 @@ abi-test:
      - out
  rules:
    - if: '$CI_MERGE_REQUEST_LABELS =~ /.*full-ci.*/'
+    - if: '$CI_MERGE_REQUEST_LABELS =~ /.*marge_bot_batch_merge_job.*/'


 ############################################################

--- a/.gitlab/generate-ci/gen_ci.hs
+++ b/.gitlab/generate-ci/gen_ci.hs
@@ -921,8 +921,8 @@ job_groups =
     -- This job is only for generating head.hackage docs
     , hackage_doc_job (disableValidate (standardBuildsWithConfig Amd64 (Linux Fedora33) releaseConfig))
     , disableValidate (standardBuildsWithConfig Amd64 (Linux Fedora33) dwarf)
-     , fastCI (standardBuildsWithConfig Amd64 Windows (splitSectionsBroken vanilla))
-     , disableValidate (standardBuildsWithConfig Amd64 Windows (splitSectionsBroken nativeInt))
+     , fastCI (standardBuildsWithConfig Amd64 Windows vanilla)
+     , disableValidate (standardBuildsWithConfig Amd64 Windows nativeInt)
     , standardBuilds Amd64 Darwin
     , allowFailureGroup (addValidateRule FreeBSDLabel (validateBuilds Amd64 FreeBSD13 vanilla))
     , fastCI (standardBuilds AArch64 Darwin)

--- a/.gitlab/jobs.yaml
+++ b/.gitlab/jobs.yaml
@@ -3577,7 +3577,7 @@
      "XZ_OPT": "-9"
    }
  },
-  "release-x86_64-windows-int_native-release+no_split_sections": {
+  "release-x86_64-windows-int_native-release": {
    "after_script": [
      "bash .gitlab/ci.sh save_cache",
      "bash .gitlab/ci.sh save_test_output",
@@ -3587,7 +3587,7 @@
    "artifacts": {
      "expire_in": "1 year",
      "paths": [
-        "ghc-x86_64-windows-int_native-release+no_split_sections.tar.xz",
+        "ghc-x86_64-windows-int_native-release.tar.xz",
        "junit.xml",
        "unexpected-test-output.tar.gz"
      ],
@@ -3626,8 +3626,8 @@
    ],
    "variables": {
      "BIGNUM_BACKEND": "native",
-      "BIN_DIST_NAME": "ghc-x86_64-windows-int_native-release+no_split_sections",
-      "BUILD_FLAVOUR": "release+no_split_sections",
+      "BIN_DIST_NAME": "ghc-x86_64-windows-int_native-release",
+      "BUILD_FLAVOUR": "release",
      "CABAL_INSTALL_VERSION": "3.8.1.0",
      "CONFIGURE_ARGS": "",
      "GHC_VERSION": "9.4.3",
@@ -3636,11 +3636,11 @@
      "LANG": "en_US.UTF-8",
      "MSYSTEM": "CLANG64",
      "RUNTEST_ARGS": "",
-      "TEST_ENV": "x86_64-windows-int_native-release+no_split_sections",
+      "TEST_ENV": "x86_64-windows-int_native-release",
      "XZ_OPT": "-9"
    }
  },
-  "release-x86_64-windows-release+no_split_sections": {
+  "release-x86_64-windows-release": {
    "after_script": [
      "bash .gitlab/ci.sh save_cache",
      "bash .gitlab/ci.sh save_test_output",
@@ -3650,7 +3650,7 @@
    "artifacts": {
      "expire_in": "1 year",
      "paths": [
-        "ghc-x86_64-windows-release+no_split_sections.tar.xz",
+        "ghc-x86_64-windows-release.tar.xz",
        "junit.xml",
        "unexpected-test-output.tar.gz"
      ],
@@ -3689,8 +3689,8 @@
    ],
    "variables": {
      "BIGNUM_BACKEND": "gmp",
-      "BIN_DIST_NAME": "ghc-x86_64-windows-release+no_split_sections",
-      "BUILD_FLAVOUR": "release+no_split_sections",
+      "BIN_DIST_NAME": "ghc-x86_64-windows-release",
+      "BUILD_FLAVOUR": "release",
      "CABAL_INSTALL_VERSION": "3.8.1.0",
      "CONFIGURE_ARGS": "",
      "GHC_VERSION": "9.4.3",
@@ -3699,7 +3699,7 @@
      "LANG": "en_US.UTF-8",
      "MSYSTEM": "CLANG64",
      "RUNTEST_ARGS": "",
-      "TEST_ENV": "x86_64-windows-release+no_split_sections",
+      "TEST_ENV": "x86_64-windows-release",
      "XZ_OPT": "-9"
    }
  },

--- a/.gitlab/merge_request_templates/Default.md
+++ b/.gitlab/merge_request_templates/Default.md
@@ -25,6 +25,10 @@ If you have any questions don't hesitate to open your merge request and inquire
 in a comment. If your patch isn't quite done yet please do add prefix your MR
 title with `WIP:`.

+By default a minimal validation pipeline is run on each merge request, the ~full-ci
+label can be applied to perform additional validation checks if your MR affects a more
+unusual configuration.
+
 Once your change is ready please remove the `WIP:` tag and wait for review. If
 no one has offerred review in a few days then please leave a comment mentioning
 @triagers and apply the ~"Blocked on Review" label.

--- a/compiler/GHC/Builtin/Names.hs
+++ b/compiler/GHC/Builtin/Names.hs
@@ -716,14 +716,6 @@ ltTag_RDR               = nameRdrName  ordLTDataConName
 eqTag_RDR               = nameRdrName  ordEQDataConName
 gtTag_RDR               = nameRdrName  ordGTDataConName

-eqClass_RDR, numClass_RDR, ordClass_RDR, enumClass_RDR, monadClass_RDR
-    :: RdrName
-eqClass_RDR             = nameRdrName eqClassName
-numClass_RDR            = nameRdrName numClassName
-ordClass_RDR            = nameRdrName ordClassName
-enumClass_RDR           = nameRdrName enumClassName
-monadClass_RDR          = nameRdrName monadClassName
-
 map_RDR, append_RDR :: RdrName
 map_RDR                 = nameRdrName mapName
 append_RDR              = nameRdrName appendName
@@ -750,41 +742,10 @@ enumFromTo_RDR          = nameRdrName enumFromToName
 enumFromThen_RDR        = nameRdrName enumFromThenName
 enumFromThenTo_RDR      = nameRdrName enumFromThenToName

-ratioDataCon_RDR, integerAdd_RDR, integerMul_RDR :: RdrName
-ratioDataCon_RDR        = nameRdrName ratioDataConName
-integerAdd_RDR          = nameRdrName integerAddName
-integerMul_RDR          = nameRdrName integerMulName
-
-ioDataCon_RDR :: RdrName
-ioDataCon_RDR           = nameRdrName ioDataConName
-
-newStablePtr_RDR :: RdrName
-newStablePtr_RDR        = nameRdrName newStablePtrName
-
-bindIO_RDR, returnIO_RDR :: RdrName
-bindIO_RDR              = nameRdrName bindIOName
-returnIO_RDR            = nameRdrName returnIOName
-
-fromInteger_RDR, fromRational_RDR, minus_RDR, times_RDR, plus_RDR :: RdrName
-fromInteger_RDR         = nameRdrName fromIntegerName
-fromRational_RDR        = nameRdrName fromRationalName
-minus_RDR               = nameRdrName minusName
+times_RDR, plus_RDR :: RdrName
 times_RDR               = varQual_RDR  gHC_NUM (fsLit "*")
 plus_RDR                = varQual_RDR gHC_NUM (fsLit "+")

-toInteger_RDR, toRational_RDR, fromIntegral_RDR :: RdrName
-toInteger_RDR           = nameRdrName toIntegerName
-toRational_RDR          = nameRdrName toRationalName
-fromIntegral_RDR        = nameRdrName fromIntegralName
-
-fromString_RDR :: RdrName
-fromString_RDR          = nameRdrName fromStringName
-
-fromList_RDR, fromListN_RDR, toList_RDR :: RdrName
-fromList_RDR = nameRdrName fromListName
-fromListN_RDR = nameRdrName fromListNName
-toList_RDR = nameRdrName toListName
-
 compose_RDR :: RdrName
 compose_RDR             = varQual_RDR gHC_BASE (fsLit ".")


--- a/compiler/GHC/Builtin/Names/TH.hs
+++ b/compiler/GHC/Builtin/Names/TH.hs
@@ -1147,29 +1147,7 @@ bndrInvisKey = mkPreludeMiscIdUnique 801
 ************************************************************************
 -}

-lift_RDR, liftTyped_RDR, mkNameG_dRDR, mkNameG_vRDR, mkNameG_fldRDR,
-  unsafeCodeCoerce_RDR :: RdrName
+lift_RDR, liftTyped_RDR, unsafeCodeCoerce_RDR :: RdrName
 lift_RDR     = nameRdrName liftName
 liftTyped_RDR = nameRdrName liftTypedName
 unsafeCodeCoerce_RDR = nameRdrName unsafeCodeCoerceName
-mkNameG_dRDR = nameRdrName mkNameG_dName
-mkNameG_vRDR = nameRdrName mkNameG_vName
-mkNameG_fldRDR = nameRdrName mkNameG_fldName
-
-- data Exp = ...
-conE_RDR, litE_RDR, appE_RDR, infixApp_RDR :: RdrName
-conE_RDR     = nameRdrName conEName
-litE_RDR     = nameRdrName litEName
-appE_RDR     = nameRdrName appEName
-infixApp_RDR = nameRdrName infixAppName
-
-- data Lit = ...
-stringL_RDR, intPrimL_RDR, wordPrimL_RDR, floatPrimL_RDR,
-    doublePrimL_RDR, stringPrimL_RDR, charPrimL_RDR :: RdrName
-stringL_RDR     = nameRdrName stringLName
-intPrimL_RDR    = nameRdrName intPrimLName
-wordPrimL_RDR   = nameRdrName wordPrimLName
-floatPrimL_RDR  = nameRdrName floatPrimLName
-doublePrimL_RDR = nameRdrName doublePrimLName
-stringPrimL_RDR = nameRdrName stringPrimLName
-charPrimL_RDR   = nameRdrName charPrimLName
--- a/compiler/GHC/Builtin/primops.txt.pp
+++ b/compiler/GHC/Builtin/primops.txt.pp
@@ -1929,6 +1929,14 @@ primop  UnsafeFreezeByteArrayOp "unsafeFreezeByteArray#" GenPrimOp
   with
   has_side_effects = True

+primop  UnsafeThawByteArrayOp "unsafeThawByteArray#" GenPrimOp
+   ByteArray# -> State# s -> (# State# s, MutableByteArray# s #)
+   {Make an immutable byte array mutable, without copying.
+
+    @since 0.12.0.0}
+   with
+   has_side_effects = True
+
 primop  SizeofByteArrayOp "sizeofByteArray#" GenPrimOp
   ByteArray# -> Int#
   {Return the size of the array in bytes.}

--- a/compiler/GHC/CmmToAsm/Ppr.hs
+++ b/compiler/GHC/CmmToAsm/Ppr.hs
@@ -245,6 +245,10 @@ pprGNUSectionHeader config t suffix =
      OtherSection _ ->
        panic "PprBase.pprGNUSectionHeader: unknown section type"
    flags = case t of
+      Text
+        | OSMinGW32 <- platformOS platform
+                    -> text ",\"xr\""
+        | otherwise -> text ",\"ax\"," <> sectionType platform "progbits"
      CString
        | OSMinGW32 <- platformOS platform
                    -> empty

--- a/compiler/GHC/Core.hs
+++ b/compiler/GHC/Core.hs
@@ -451,7 +451,7 @@ TL;DR: we relaxed the let/app invariant to become the let-can-float invariant.
 Note [Core top-level string literals]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 As an exception to the usual rule that top-level binders must be lifted,
-we allow binding primitive string literals (of type Addr#) of type Addr# at the
+we allow binding primitive string literals (of type Addr#) at the
 top level. This allows us to share string literals earlier in the pipeline and
 crucially allows other optimizations in the Core2Core pipeline to fire.
 Consider,
@@ -629,7 +629,7 @@ Note [Representation polymorphism invariants]
 GHC allows us to abstract over calling conventions using **representation polymorphism**.
 For example, we have:

-  ($) :: forall (r :: RuntimeRep) (a :: Type) (b :: TYPE r). a -> b -> b
+  ($) :: forall (r :: RuntimeRep) (a :: Type) (b :: TYPE r). (a -> b) -> a -> b

 In this example, the type `b` is representation-polymorphic: it has kind `TYPE r`,
 where the type variable `r :: RuntimeRep` abstracts over the runtime representation
@@ -662,14 +662,14 @@ Note that these two invariants require us to check other types than just the
 types of bound variables and types of function arguments, due to transformations
 that GHC performs. For example, the definition

-  myCoerce :: forall {r1 r2} (a :: TYPE r1) (b :: TYPE r2). Coercible a b => a -> b
+  myCoerce :: forall {r} (a :: TYPE r) (b :: TYPE r). Coercible a b => a -> b
  myCoerce = coerce

 is invalid, because `coerce` has no binding (see GHC.Types.Id.Make.coerceId).
 So, before code-generation, GHC saturates the RHS of 'myCoerce' by performing
 an eta-expansion (see GHC.CoreToStg.Prep.maybeSaturate):

-  myCoerce = \ (x :: TYPE r1) -> coerce x
+  myCoerce = \ (x :: TYPE r) -> coerce x

 However, this transformation would be invalid, because now the binding of x
 in the lambda abstraction would violate I1.

--- a/compiler/GHC/Core/Rules.hs
+++ b/compiler/GHC/Core/Rules.hs
@@ -888,9 +888,6 @@ So we must add the template vars to the in-scope set before starting;
 see `init_menv` in `matchN`.
 -}

-rvInScopeEnv :: RuleMatchEnv -> InScopeEnv
-rvInScopeEnv renv = ISE (rnInScopeSet (rv_lcl renv)) (rv_unf renv)
-
 -- * The domain of the TvSubstEnv and IdSubstEnv are the template
 --   variables passed into the match.
 --
@@ -1271,7 +1268,16 @@ match renv subst e1 (Let bind e2) mco

 ------------------------  Lambdas ---------------------
 match renv subst (Lam x1 e1) e2 mco
-  | Just (x2, e2', ts) <- exprIsLambda_maybe (rvInScopeEnv renv) (mkCastMCo e2 mco)
+  | let casted_e2 = mkCastMCo e2 mco
+        in_scope = extendInScopeSetSet (rnInScopeSet (rv_lcl renv))
+                                       (exprFreeVars casted_e2)
+        in_scope_env = ISE in_scope (rv_unf renv)
+        -- extendInScopeSetSet: The InScopeSet of rn_env is not necessarily
+        -- a superset of the free vars of e2; it is only guaranteed a superset of
+        -- applyng the (rnEnvR rn_env) substitution to e2. But exprIsLambda_maybe
+        -- wants an in-scope set that includes all the free vars of its argument.
+        -- Hence adding adding (exprFreeVars casted_e2) to the in-scope set (#23630)
+  , Just (x2, e2', ts) <- exprIsLambda_maybe in_scope_env casted_e2
    -- See Note [Lambdas in the template]
  = let renv'  = rnMatchBndr2 renv x1 x2
        subst' = subst { rs_binds = rs_binds subst . flip (foldr mkTick) ts }

--- a/compiler/GHC/Core/Type.hs
+++ b/compiler/GHC/Core/Type.hs
@@ -828,7 +828,7 @@ runtimeRepLevity_maybe rep
 --  Splitting Levity
 --------------------------------------------

-- | `levity_maybe` takes a Type of kind Levity, and returns its levity
+-- | `levityType_maybe` takes a Type of kind Levity, and returns its levity
 -- May not be possible for a type variable or type family application
 levityType_maybe :: LevityType -> Maybe Levity
 levityType_maybe lev

--- a/compiler/GHC/HsToCore/Foreign/JavaScript.hs
+++ b/compiler/GHC/HsToCore/Foreign/JavaScript.hs
@@ -58,7 +58,6 @@ import GHC.Builtin.Types.Prim
 import GHC.Builtin.Names

 import GHC.Data.FastString
-import GHC.Data.Pair
 import GHC.Data.Maybe

 import GHC.Utils.Outputable
@@ -83,7 +82,7 @@ dsJsFExport

 dsJsFExport fn_id co ext_name cconv isDyn = do
    let
-       ty                              = pSnd $ coercionKind co
+       ty                              = coercionRKind co
       (_tvs,sans_foralls)             = tcSplitForAllTyVars ty
       (fe_arg_tys', orig_res_ty)      = tcSplitFunTys sans_foralls
       -- We must use tcSplits here, because we want to see
@@ -242,7 +241,7 @@ dsJsImport
  -> Maybe Header
  -> DsM ([Binding], CHeader, CStub)
 dsJsImport id co (CLabel cid) cconv _ _ = do
-   let ty = pFst $ coercionKind co
+   let ty = coercionLKind co
       fod = case tyConAppTyCon_maybe (dropForAlls ty) of
             Just tycon
              | tyConUnique tycon == funPtrTyConKey ->
@@ -272,7 +271,7 @@ dsJsFExportDynamic :: Id
                 -> DsM ([Binding], CHeader, CStub)
 dsJsFExportDynamic id co0 cconv = do
    let
-      ty                            = pFst (coercionKind co0)
+      ty                            = coercionLKind co0
      (tvs,sans_foralls)            = tcSplitForAllTyVars ty
      ([Scaled arg_mult arg_ty], fn_res_ty)  = tcSplitFunTys sans_foralls
      (io_tc, res_ty)               = expectJust "dsJsFExportDynamic: IO type expected"
@@ -342,7 +341,7 @@ dsJsCall :: Id -> Coercion -> ForeignCall -> Maybe Header
        -> DsM ([(Id, Expr TyVar)], CHeader, CStub)
 dsJsCall fn_id co (CCall (CCallSpec target cconv safety)) _mDeclHeader = do
    let
-        ty                   = pFst $ coercionKind co
+        ty                   = coercionLKind co
        (tv_bndrs, rho)      = tcSplitForAllTyVarBinders ty
        (arg_tys, io_res_ty) = tcSplitFunTys rho


--- a/compiler/GHC/Parser.y
+++ b/compiler/GHC/Parser.y
@@ -751,7 +751,7 @@ TH_QQUASIQUOTE  { L _ (ITqQuasiQuote _) }

 -- Exported parsers
 %name parseModuleNoHaddock module
-%name parseSignature signature
+%name parseSignatureNoHaddock signature
 %name parseImport importdecl
 %name parseStatement e_stmt
 %name parseDeclaration topdecl
@@ -4416,18 +4416,29 @@ pvL :: MonadP m => m (LocatedAn t a) -> m (Located a)
 pvL a = do { av <- a
           ; return (reLoc av) }

-- | Parse a Haskell module with Haddock comments.
-- This is done in two steps:
+-- | Parse a Haskell module with Haddock comments. This is done in two steps:
 --
 -- * 'parseModuleNoHaddock' to build the AST
 -- * 'addHaddockToModule' to insert Haddock comments into it
 --
-- This is the only parser entry point that deals with Haddock comments.
-- The other entry points ('parseDeclaration', 'parseExpression', etc) do
-- not insert them into the AST.
+-- This and the signature module parser are the only parser entry points that
+-- deal with Haddock comments. The other entry points ('parseDeclaration',
+-- 'parseExpression', etc) do not insert them into the AST.
 parseModule :: P (Located (HsModule GhcPs))
 parseModule = parseModuleNoHaddock >>= addHaddockToModule

+-- | Parse a Haskell signature module with Haddock comments. This is done in two
+-- steps:
+--
+-- * 'parseSignatureNoHaddock' to build the AST
+-- * 'addHaddockToModule' to insert Haddock comments into it
+--
+-- This and the module parser are the only parser entry points that deal with
+-- Haddock comments. The other entry points ('parseDeclaration',
+-- 'parseExpression', etc) do not insert them into the AST.
+parseSignature :: P (Located (HsModule GhcPs))
+parseSignature = parseSignatureNoHaddock >>= addHaddockToModule
+
 commentsA :: (Monoid ann) => SrcSpan -> EpAnnComments -> SrcSpanAnn' (EpAnn ann)
 commentsA loc cs = SrcSpanAnn (EpAnn (Anchor (rs loc) UnchangedAnchor) mempty cs) loc


--- a/compiler/GHC/Rename/Module.hs
+++ b/compiler/GHC/Rename/Module.hs
@@ -39,6 +39,7 @@ import GHC.Rename.Names
 import GHC.Tc.Errors.Types
 import GHC.Tc.Gen.Annotation ( annCtxt )
 import GHC.Tc.Utils.Monad
+import GHC.Tc.Types.Origin ( TypedThing(..) )

 import GHC.Types.ForeignCall ( CCallTarget(..) )
 import GHC.Unit
@@ -574,10 +575,13 @@ rnClsInstDecl (ClsInstDecl { cid_poly_ty = inst_ty, cid_binds = mbinds
             -- class type constructor...
             eith_cls = case hsTyGetAppHead_maybe head_ty' of
               Just (L _ cls) -> Right cls
-               Nothing        -> Left
-                 ( getLocA head_ty'
-                 , TcRnIllegalInstanceHeadDecl head_ty'
-                 )
+               Nothing        ->
+                  Left
+                   ( getLocA head_ty'
+                   , TcRnIllegalInstance $
+                       IllegalClassInstance (HsTypeRnThing $ unLoc head_ty') $
+                       IllegalInstanceHead $ InstHeadNonClass Nothing
+                   )
         -- ...finally, attempt to retrieve the class type constructor, failing
         -- with an error message if there isn't one. To avoid excessive
         -- amounts of error messages, we will only report one of the errors
@@ -721,7 +725,9 @@ rnFamEqn doc atfi
               && not (cls_tkv `elemNameSet` pat_fvs)
                    -- ...but not bound on the LHS.
             bad_tvs = filter improperly_scoped inst_head_tvs
-       ; unless (null bad_tvs) (addErr (TcRnBadAssocRhs bad_tvs))
+       ; unless (null bad_tvs) $ addErr $
+           TcRnIllegalInstance $ IllegalFamilyInstance $
+             FamInstRHSOutOfScopeTyVars Nothing bad_tvs

       ; let eqn_fvs = rhs_fvs `plusFV` pat_fvs
             -- See Note [Type family equations and occurrences]

--- a/compiler/GHC/StgToCmm/Prim.hs
+++ b/compiler/GHC/StgToCmm/Prim.hs
@@ -371,6 +371,10 @@ emitPrimOp cfg primop =
  UnsafeFreezeByteArrayOp -> \[arg] -> opIntoRegs $ \[res] ->
    emitAssign (CmmLocal res) arg

+--  #define unsafeThawByteArrayzh(r,a)       r=(a)
+  UnsafeThawByteArrayOp -> \[arg] -> opIntoRegs $ \[res] ->
+    emitAssign (CmmLocal res) arg
+
 -- Reading/writing pointer arrays

  ReadArrayOp -> \[obj, ix] -> opIntoRegs $ \[res] ->

--- a/compiler/GHC/StgToJS/Prim.hs
+++ b/compiler/GHC/StgToJS/Prim.hs
@@ -652,6 +652,7 @@ genPrim prof bound ty op = case op of
  ShrinkMutableByteArrayOp_Char     -> \[]    [a,n]      -> PrimInline $ appS "h$shrinkMutableByteArray" [a,n]
  ResizeMutableByteArrayOp_Char     -> \[r]   [a,n]      -> PrimInline $ r |= app "h$resizeMutableByteArray" [a,n]
  UnsafeFreezeByteArrayOp           -> \[a]   [b]        -> PrimInline $ a |= b
+  UnsafeThawByteArrayOp             -> \[a]   [b]        -> PrimInline $ a |= b
  SizeofByteArrayOp                 -> \[r]   [a]        -> PrimInline $ r |= a .^ "len"
  SizeofMutableByteArrayOp          -> \[r]   [a]        -> PrimInline $ r |= a .^ "len"
  GetSizeofMutableByteArrayOp       -> \[r]   [a]        -> PrimInline $ r |= a .^ "len"

--- a/compiler/GHC/Tc/Deriv/Generate.hs
+++ b/compiler/GHC/Tc/Deriv/Generate.hs
@@ -34,7 +34,7 @@ module GHC.Tc.Deriv.Generate (
        gen_Newtype_fam_insts,
        mkCoerceClassMethEqn,
        genAuxBinds,
-        ordOpTbl, boxConTbl, litConTbl,
+        ordOpTbl, boxConTbl,
        mkRdrFunBind, mkRdrFunBindEC, mkRdrFunBindSE, error_Expr,

        getPossibleDataCons,
@@ -2363,7 +2363,7 @@ box ::         String           -- The class involved
            -> Type             -- The argument type
            -> LHsExpr GhcPs    -- Boxed version of the arg
 -- See Note [Deriving and unboxed types] in GHC.Tc.Deriv.Infer
-box cls_str arg arg_ty = assoc_ty_id cls_str boxConTbl arg_ty arg
+box cls_str arg arg_ty = nlHsApp (assoc_ty_id cls_str boxConTbl arg_ty) arg

 ---------------------
 primOrdOps :: String    -- The class involved
@@ -2403,23 +2403,22 @@ ordOpTbl
    ,(doublePrimTy, (ltDouble_RDR, leDouble_RDR
     , eqDouble_RDR, geDouble_RDR, gtDouble_RDR)) ]

-- A mapping from a primitive type to a function that constructs its boxed
-- version.
-boxConTbl :: [(Type, LHsExpr GhcPs -> LHsExpr GhcPs)]
+-- A mapping from a primitive type to a DataCon of its boxed version.
+boxConTbl :: [(Type, LHsExpr GhcPs)]
 boxConTbl =
-    [ (charPrimTy  , nlHsApp (nlHsVar $ getRdrName charDataCon))
-    , (intPrimTy   , nlHsApp (nlHsVar $ getRdrName intDataCon))
-    , (wordPrimTy  , nlHsApp (nlHsVar $ getRdrName wordDataCon ))
-    , (floatPrimTy , nlHsApp (nlHsVar $ getRdrName floatDataCon ))
-    , (doublePrimTy, nlHsApp (nlHsVar $ getRdrName doubleDataCon))
-    , (int8PrimTy,   nlHsApp (nlHsVar int8DataCon_RDR))
-    , (word8PrimTy,  nlHsApp (nlHsVar word8DataCon_RDR))
-    , (int16PrimTy,  nlHsApp (nlHsVar int16DataCon_RDR))
-    , (word16PrimTy, nlHsApp (nlHsVar word16DataCon_RDR))
-    , (int32PrimTy,  nlHsApp (nlHsVar int32DataCon_RDR))
-    , (word32PrimTy, nlHsApp (nlHsVar word32DataCon_RDR))
-    , (int64PrimTy,  nlHsApp (nlHsVar int64DataCon_RDR))
-    , (word64PrimTy, nlHsApp (nlHsVar word64DataCon_RDR))
+    [ (charPrimTy  , nlHsVar $ getRdrName charDataCon)
+    , (intPrimTy   , nlHsVar $ getRdrName intDataCon)
+    , (wordPrimTy  , nlHsVar $ getRdrName wordDataCon)
+    , (floatPrimTy , nlHsVar $ getRdrName floatDataCon)
+    , (doublePrimTy, nlHsVar $ getRdrName doubleDataCon)
+    , (int8PrimTy,   nlHsVar int8DataCon_RDR)
+    , (word8PrimTy,  nlHsVar word8DataCon_RDR)
+    , (int16PrimTy,  nlHsVar int16DataCon_RDR)
+    , (word16PrimTy, nlHsVar word16DataCon_RDR)
+    , (int32PrimTy,  nlHsVar int32DataCon_RDR)
+    , (word32PrimTy, nlHsVar word32DataCon_RDR)
+    , (int64PrimTy,  nlHsVar int64DataCon_RDR)
+    , (word64PrimTy, nlHsVar word64DataCon_RDR)
    ]


@@ -2443,26 +2442,6 @@ postfixModTbl
    ,(word64PrimTy, "#Word64")
    ]

-litConTbl :: [(Type, LHsExpr GhcPs -> LHsExpr GhcPs)]
-litConTbl
-  = [(charPrimTy  , nlHsApp (nlHsVar charPrimL_RDR))
-    ,(intPrimTy   , nlHsApp (nlHsVar intPrimL_RDR)
-                      . nlHsApp (nlHsVar toInteger_RDR))
-    ,(wordPrimTy  , nlHsApp (nlHsVar wordPrimL_RDR)
-                      . nlHsApp (nlHsVar toInteger_RDR))
-    ,(addrPrimTy  , nlHsApp (nlHsVar stringPrimL_RDR)
-                      . nlHsApp (nlHsApp
-                          (nlHsVar map_RDR)
-                          (compose_RDR `nlHsApps`
-                            [ nlHsVar fromIntegral_RDR
-                            , nlHsVar fromEnum_RDR
-                            ])))
-    ,(floatPrimTy , nlHsApp (nlHsVar floatPrimL_RDR)
-                      . nlHsApp (nlHsVar toRational_RDR))
-    ,(doublePrimTy, nlHsApp (nlHsVar doublePrimL_RDR)
-                      . nlHsApp (nlHsVar toRational_RDR))
-    ]
-
 -- | Lookup `Type` in an association list.
 assoc_ty_id :: HasCallStack => String           -- The class involved
            -> [(Type,a)]       -- The table

--- a/compiler/GHC/Tc/Errors/Ppr.hs
+++ b/compiler/GHC/Tc/Errors/Ppr.hs
@@ -56,6 +56,7 @@ import GHC.Core.PatSyn ( patSynName, pprPatSynType )
 import GHC.Core.Predicate
 import GHC.Core.Type
 import GHC.Core.FVs( orphNamesOfTypes )
+import GHC.CoreToIface

 import GHC.Driver.Flags
 import GHC.Driver.Backend
@@ -91,7 +92,7 @@ import GHC.Types.Fixity (defaultFixity)

 import GHC.Iface.Errors.Types
 import GHC.Iface.Errors.Ppr
-import GHC.Iface.Syntax ( ShowSub(..), ShowForAllFlag(..), showToHeader )
+import GHC.Iface.Syntax

 import GHC.Unit.State
 import GHC.Unit.Module
@@ -140,9 +141,14 @@ instance Diagnostic TcRnMessage where
                  (diagnosticMessage opts msg)
    TcRnWithHsDocContext ctxt msg
      -> messageWithHsDocContext opts ctxt (diagnosticMessage opts msg)
-
    TcRnSolverReport msg _ _
      -> mkSimpleDecorated $ pprSolverReportWithCtxt msg
+    TcRnSolverDepthError ty depth -> mkSimpleDecorated msg
+      where
+        msg =
+          vcat [ text "Reduction stack overflow; size =" <+> ppr depth
+               , hang (text "When simplifying the following type:")
+                    2 (ppr ty) ]
    TcRnRedundantConstraints redundants (info, show_info)
      -> mkSimpleDecorated $
         text "Redundant constraint" <> plural redundants <> colon
@@ -385,13 +391,6 @@ instance Diagnostic TcRnMessage where
              2 (ppr sig)
    TcRnTupleConstraintInst _
      -> mkSimpleDecorated $ text "You can't specify an instance for a tuple constraint"
-    TcRnAbstractClassInst clas
-      -> mkSimpleDecorated $
-           text "Cannot define instance for abstract class" <+>
-           quotes (ppr (className clas))
-    TcRnNoClassInstHead tau
-      -> mkSimpleDecorated $
-           hang (text "Instance head is not headed by a class:") 2 (pprType tau)
    TcRnUserTypeError ty
      -> mkSimpleDecorated (pprUserTypeErrorTy ty)
    TcRnConstraintInKind ty
@@ -433,11 +432,8 @@ instance Diagnostic TcRnMessage where
            n_arguments | thing_arity == 0 = text "no arguments"
                        | thing_arity == 1 = text "1 argument"
                        | True          = hsep [int thing_arity, text "arguments"]
-    TcRnIllegalInstanceDecl cls tys reason
-      -> mkSimpleDecorated $
-           hang (hang (text "Illegal instance declaration for")
-                    2 (quotes (pprClassPred cls tys)) <> colon)
-              2 (pprIllegalInstanceReason cls tys reason)
+    TcRnIllegalInstance reason ->
+      mkSimpleDecorated $ pprIllegalInstance reason
    TcRnVDQInTermType mb_ty
      -> mkSimpleDecorated $ vcat
           [ case mb_ty of
@@ -465,18 +461,10 @@ instance Diagnostic TcRnMessage where
    TcRnIllegalConstraintSynonymOfKind kind
      -> mkSimpleDecorated $
           text "Illegal constraint synonym of kind:" <+> quotes (pprKind kind)
-    TcRnIllegalClassInst tcf
-      -> mkSimpleDecorated $
-           vcat [ text "Illegal instance for a" <+> ppr tcf
-                , text "A class instance must be for a class" ]
    TcRnOversaturatedVisibleKindArg ty
      -> mkSimpleDecorated $
           text "Illegal oversaturated visible kind argument:" <+>
           quotes (char '@' <> pprParendType ty)
-    TcRnBadAssociatedType clas tc
-      -> mkSimpleDecorated $
-           hsep [ text "Class", quotes (ppr clas)
-                , text "does not have an associated type", quotes (ppr tc) ]
    TcRnForAllRankErr rank ty
      -> let herald = case tcSplitForAllTyVars ty of
               ([], _) -> text "Illegal qualified type:"
@@ -790,18 +778,6 @@ instance Diagnostic TcRnMessage where
    TcRnArrowProcGADTPattern
      -> mkSimpleDecorated $
           text "Proc patterns cannot use existential or GADT data constructors"
-
-    TcRnSpecialClassInst cls because_safeHaskell
-      -> mkSimpleDecorated $
-            text "Class" <+> quotes (ppr $ className cls)
-                   <+> text "does not support user-specified instances"
-                   <> safeHaskell_msg
-          where
-            safeHaskell_msg
-              | because_safeHaskell
-              = text " when Safe Haskell is enabled."
-              | otherwise
-              = dot
    TcRnForallIdentifier rdr_name
      -> mkSimpleDecorated $
            fsep [ text "The use of" <+> quotes (ppr rdr_name)
@@ -1163,11 +1139,6 @@ instance Diagnostic TcRnMessage where
      -> mkSimpleDecorated $
        hsep [text "Class", quotes (ppr badMethodErrClassName),
          text "does not have a method", quotes (ppr badMethodErrMethodName)]
-    TcRnNoExplicitAssocTypeOrDefaultDeclaration name
-      -> mkSimpleDecorated $
-        text "No explicit" <+> text "associated type"
-          <+> text "or default declaration for"
-          <+> quotes (ppr name)
    TcRnIllegalTypeData
      -> mkSimpleDecorated $
        text "Illegal type-level data declaration"
@@ -1218,17 +1189,6 @@ instance Diagnostic TcRnMessage where
                  2 (hang (pprPrefixName name)
                        2 (dcolon <+> ppr hs_ty))
             ]
-    TcRnIllegalFamilyInstance tycon
-      -> mkSimpleDecorated $
-        vcat [ text "Illegal family instance for" <+> quotes (ppr tycon)
-             , nest 2 $ parens (ppr tycon <+> text "is not an indexed type family")]
-    TcRnMissingClassAssoc name
-      -> mkSimpleDecorated $
-        text "Associated type" <+> quotes (ppr name) <+>
-        text "must be inside a class instance"
-    TcRnNotOpenFamily tc
-      -> mkSimpleDecorated $
-        text "Illegal instance for closed family" <+> quotes (ppr tc)
    TcRnNoRebindableSyntaxRecordDot -> mkSimpleDecorated $
      text "RebindableSyntax is required if OverloadedRecordUpdate is enabled."
    TcRnNoFieldPunsRecordDot -> mkSimpleDecorated $
@@ -1359,14 +1319,6 @@ instance Diagnostic TcRnMessage where
          = vcat [ text "Starting from GHC 9.10, this warning will turn into an error." ]
        user_manual =
          vcat [ text "See the user manual, § Undecidable instances and loopy superclasses." ]
-    TcRnIllegalInstanceHeadDecl head_ty -> mkSimpleDecorated $
-      hang (text "Illegal head of an instance declaration:"
-              <+> quotes (ppr head_ty))
-        2 (vcat [ text "Instance heads must be of the form"
-                , nest 2 $ text "C ty_1 ... ty_n"
-                , text "where" <+> quotes (char 'C')
-                  <+> text "is a class"
-                ])
    TcRnUnexpectedStandaloneDerivingDecl -> mkSimpleDecorated $
      text "Illegal standalone deriving declaration"
    TcRnUnusedVariableInRuleDecl name var -> mkSimpleDecorated $
@@ -1385,11 +1337,6 @@ instance Diagnostic TcRnMessage where
        err = case errReason of
          UnboundVariable uv nis -> pprScopeError uv nis
          IllegalExpression -> text "Illegal expression:" <+> ppr bad_e
-    TcRnBadAssocRhs ns -> mkSimpleDecorated $
-      hang (text "The RHS of an associated type declaration mentions"
-                <+> text "out-of-scope variable" <> plural ns
-                <+> pprWithCommas (quotes . ppr) ns)
-              2 (text "All such variables must be bound on the LHS")
    TcRnDuplicateRoleAnnot list -> mkSimpleDecorated $
      hang (text "Duplicate role annotations for" <+>
            quotes (ppr $ roleAnnotDeclName first_decl) <> colon)
@@ -1506,9 +1453,6 @@ instance Diagnostic TcRnMessage where
                   <+> quotes (ppr ps_name) <> colon)
                2 (pprPatSynInvalidRhsReason reason)
           , text "RHS pattern:" <+> ppr lpat ]
-    TcRnMultiAssocTyFamDefaults name -> mkSimpleDecorated $
-      text "More than one default declaration for"
-      <+> ppr name
    TcRnTyFamDepsDisabled -> mkSimpleDecorated $
      text "Illegal injectivity annotation"
    TcRnAbstractClosedTyFamDecl -> mkSimpleDecorated $
@@ -1538,6 +1482,46 @@ instance Diagnostic TcRnMessage where
        (sort, name) = case reason of
          TyFamsDisabledFamily n -> ("declaration", ppr n)
          TyFamsDisabledInstance n -> ("instance", ppr n)
+    TcRnBadTyConTelescope tc -> mkSimpleDecorated $
+      vcat [ hang (text "The kind of" <+> quotes (ppr tc) <+> text "is ill-scoped")
+                2 pp_tc_kind
+           , extra
+           , hang (text "Perhaps try this order instead:")
+                2 (pprTyVars sorted_tvs) ]
+      where
+        pp_tc_kind = text "Inferred kind:" <+> ppr tc <+> dcolon <+> ppr_untidy (tyConKind tc)
+        ppr_untidy ty = pprIfaceType (toIfaceType ty)
+          -- We need ppr_untidy here because pprType will tidy the type, which
+          -- will turn the bogus kind we are trying to report
+          --     T :: forall (a::k) k (b::k) -> blah
+          -- into a misleadingly sanitised version
+          --     T :: forall (a::k) k1 (b::k1) -> blah
+
+        tcbs = tyConBinders tc
+        tvs  = binderVars tcbs
+        sorted_tvs = scopedSort tvs
+
+        inferred_tvs  = [ binderVar tcb
+                        | tcb <- tcbs, Inferred == tyConBinderForAllTyFlag tcb ]
+        specified_tvs = [ binderVar tcb
+                        | tcb <- tcbs, Specified == tyConBinderForAllTyFlag tcb ]
+
+        extra
+          | null inferred_tvs && null specified_tvs
+          = empty
+          | null inferred_tvs
+          = hang (text "NB: Specified variables")
+               2 (sep [pp_spec, text "always come first"])
+          | null specified_tvs
+          = hang (text "NB: Inferred variables")
+               2 (sep [pp_inf, text "always come first"])
+          | otherwise
+          = hang (text "NB: Inferred variables")
+               2 (vcat [ sep [ pp_inf, text "always come first"]
+                       , sep [text "then Specified variables", pp_spec]])
+
+        pp_inf  = parens (text "namely:" <+> pprTyVars inferred_tvs)
+        pp_spec = parens (text "namely:" <+> pprTyVars specified_tvs)
    TcRnTyFamResultDisabled tc_name tvb -> mkSimpleDecorated $
      text "Illegal result type variable" <+> ppr tvb <+> text "for" <+> quotes (ppr tc_name)
    TcRnRoleValidationFailed role reason -> mkSimpleDecorated $
@@ -1553,10 +1537,6 @@ instance Diagnostic TcRnMessage where
           text "give different types for field", quotes (ppr field_name)]
    TcRnClassExtensionDisabled cls reason -> mkSimpleDecorated $
      pprDisabledClassExtension cls reason
-    TcRnAssocNoClassTyVar cls fam_tc -> mkSimpleDecorated $
-      sep [ text "The associated type" <+> quotes (ppr fam_tc <+> hsep (map ppr (tyConTyVars fam_tc)))
-          , text "mentions none of the type or kind variables of the class" <+>
-                  quotes (ppr cls <+> hsep (map ppr (classTyVars cls)))]
    TcRnDataConParentTypeMismatch data_con res_ty_tmpl -> mkSimpleDecorated $
      hang (text "Data constructor" <+> quotes (ppr data_con) <+>
            text "returns type" <+> quotes (ppr actual_res_ty))
@@ -1581,16 +1561,6 @@ instance Diagnostic TcRnMessage where
        with_sig (tc_name, ksig) = ppr tc_name <+> dcolon <+> ppr ksig
    TcRnEmptyDataDeclsDisabled tycon -> mkSimpleDecorated $
      quotes (ppr tycon) <+> text "has no constructors"
-    TcRnFamilyCategoryMismatch family -> mkSimpleDecorated $
-      text "Wrong category of family instance; declaration was for a"
-      <+> kindOfFamily
-      where
-        kindOfFamily | isTypeFamilyTyCon family = text "type family"
-                     | isDataFamilyTyCon family = text "data family"
-                     | otherwise = pprPanic "wrongKindOfFamily" (ppr family)
-    TcRnFamilyArityMismatch _ max_args -> mkSimpleDecorated $
-      text "Number of parameters must match family declaration; expected"
-      <+> ppr max_args
    TcRnRoleMismatch var annot inferred -> mkSimpleDecorated $
      hang (text "Role mismatch on variable" <+> ppr var <> colon)
         2 (sep [ text "Annotation says", ppr annot
@@ -1609,11 +1579,6 @@ instance Diagnostic TcRnMessage where
    TcRnIncoherentRoles _ -> mkSimpleDecorated $
      (text "Roles other than" <+> quotes (text "nominal") <+>
      text "for class parameters can lead to incoherence.")
-    TcRnTyFamNameMismatch fam_tc_name eqn_tc_name -> mkSimpleDecorated $
-      hang (text "Mismatched type name in type family instance.")
-         2 (vcat [ text "Expected:" <+> ppr fam_tc_name
-                 , text "  Actual:" <+> ppr eqn_tc_name ])
-
    TcRnUnexpectedKindVar tv_name
      -> mkSimpleDecorated $ text "Unexpected kind variable" <+> quotes (ppr tv_name)

@@ -1869,6 +1834,8 @@ instance Diagnostic TcRnMessage where
      -> diagnosticReason msg
    TcRnSolverReport _ reason _
      -> reason -- Error, or a Warning if we are deferring type errors
+    TcRnSolverDepthError {}
+      -> ErrorWithoutFlag
    TcRnRedundantConstraints {}
      -> WarningWithFlag Opt_WarnRedundantConstraints
    TcRnInaccessibleCode {}
@@ -1957,10 +1924,6 @@ instance Diagnostic TcRnMessage where
      -> ErrorWithoutFlag
    TcRnTupleConstraintInst{}
      -> ErrorWithoutFlag
-    TcRnAbstractClassInst{}
-      -> ErrorWithoutFlag
-    TcRnNoClassInstHead{}
-      -> ErrorWithoutFlag
    TcRnUserTypeError{}
      -> ErrorWithoutFlag
    TcRnConstraintInKind{}
@@ -1975,8 +1938,8 @@ instance Diagnostic TcRnMessage where
      -> WarningWithFlag Opt_WarnSimplifiableClassConstraints
    TcRnArityMismatch{}
      -> ErrorWithoutFlag
-    TcRnIllegalInstanceDecl{}
-      -> ErrorWithoutFlag
+    TcRnIllegalInstance rea
+      -> illegalInstanceReason rea
    TcRnVDQInTermType{}
      -> ErrorWithoutFlag
    TcRnBadQuantPredHead{}
@@ -1989,12 +1952,8 @@ instance Diagnostic TcRnMessage where
      -> ErrorWithoutFlag
    TcRnIllegalConstraintSynonymOfKind{}
      -> ErrorWithoutFlag
-    TcRnIllegalClassInst{}
-      -> ErrorWithoutFlag
    TcRnOversaturatedVisibleKindArg{}
      -> ErrorWithoutFlag
-    TcRnBadAssociatedType{}
-      -> ErrorWithoutFlag
    TcRnForAllRankErr{}
      -> ErrorWithoutFlag
    TcRnMonomorphicBindings{}
@@ -2098,8 +2057,6 @@ instance Diagnostic TcRnMessage where
      -> ErrorWithoutFlag
    TcRnArrowProcGADTPattern
      -> ErrorWithoutFlag
-    TcRnSpecialClassInst {}
-      -> ErrorWithoutFlag
    TcRnForallIdentifier {}
      -> WarningWithFlag Opt_WarnForallIdentifier
    TcRnTypeEqualityOutOfScope
@@ -2206,8 +2163,6 @@ instance Diagnostic TcRnMessage where
      -> WarningWithoutFlag
    TcRnBadMethodErr{}
      -> ErrorWithoutFlag
-    TcRnNoExplicitAssocTypeOrDefaultDeclaration{}
-      -> WarningWithFlag (Opt_WarnMissingMethods)
    TcRnIllegalTypeData
      -> ErrorWithoutFlag
    TcRnIllegalQuasiQuotes{}
@@ -2222,12 +2177,6 @@ instance Diagnostic TcRnMessage where
      -> WarningWithFlag (Opt_WarnMissingMethods)
    TcRnMisplacedInstSig{}
      -> ErrorWithoutFlag
-    TcRnIllegalFamilyInstance{}
-      -> ErrorWithoutFlag
-    TcRnMissingClassAssoc{}
-      -> ErrorWithoutFlag
-    TcRnNotOpenFamily{}
-      -> ErrorWithoutFlag
    TcRnNoRebindableSyntaxRecordDot{}
      -> ErrorWithoutFlag
    TcRnNoFieldPunsRecordDot{}
@@ -2272,8 +2221,6 @@ instance Diagnostic TcRnMessage where
      -> ErrorWithoutFlag
    TcRnLoopySuperclassSolve{}
      -> WarningWithFlag Opt_WarnLoopySuperclassSolve
-    TcRnIllegalInstanceHeadDecl{}
-      -> ErrorWithoutFlag
    TcRnUnexpectedStandaloneDerivingDecl{}
      -> ErrorWithoutFlag
    TcRnUnusedVariableInRuleDecl{}
@@ -2282,8 +2229,6 @@ instance Diagnostic TcRnMessage where
      -> ErrorWithoutFlag
    TcRnIllegalRuleLhs{}
      -> ErrorWithoutFlag
-    TcRnBadAssocRhs{}
-      -> ErrorWithoutFlag
    TcRnDuplicateRoleAnnot{}
      -> ErrorWithoutFlag
    TcRnDuplicateKindSig{}
@@ -2322,8 +2267,6 @@ instance Diagnostic TcRnMessage where
      -> ErrorWithoutFlag
    TcRnPatSynInvalidRhs{}
      -> ErrorWithoutFlag
-    TcRnMultiAssocTyFamDefaults{}
-      -> ErrorWithoutFlag
    TcRnTyFamDepsDisabled{}
      -> ErrorWithoutFlag
    TcRnAbstractClosedTyFamDecl{}
@@ -2340,6 +2283,8 @@ instance Diagnostic TcRnMessage where
      -> ErrorWithoutFlag
    TcRnTyFamsDisabled{}
      -> ErrorWithoutFlag
+    TcRnBadTyConTelescope {}
+      -> ErrorWithoutFlag
    TcRnTyFamResultDisabled{}
      -> ErrorWithoutFlag
    TcRnRoleValidationFailed{}
@@ -2350,8 +2295,6 @@ instance Diagnostic TcRnMessage where
      -> ErrorWithoutFlag
    TcRnClassExtensionDisabled{}
      -> ErrorWithoutFlag
-    TcRnAssocNoClassTyVar{}
-      -> ErrorWithoutFlag
    TcRnDataConParentTypeMismatch{}
      -> ErrorWithoutFlag
    TcRnGADTsDisabled{}
@@ -2366,10 +2309,6 @@ instance Diagnostic TcRnMessage where
      -> ErrorWithoutFlag
    TcRnEmptyDataDeclsDisabled{}
      -> ErrorWithoutFlag
-    TcRnFamilyCategoryMismatch{}
-      -> ErrorWithoutFlag
-    TcRnFamilyArityMismatch{}
-      -> ErrorWithoutFlag
    TcRnRoleMismatch{}
      -> ErrorWithoutFlag
    TcRnRoleCountMismatch{}
@@ -2380,8 +2319,6 @@ instance Diagnostic TcRnMessage where
      -> ErrorWithoutFlag
    TcRnIncoherentRoles{}
      -> ErrorWithoutFlag
-    TcRnTyFamNameMismatch{}
-      -> ErrorWithoutFlag
    TcRnUnexpectedKindVar{}
      -> ErrorWithoutFlag
    TcRnNegativeNumTypeLiteral{}
@@ -2492,6 +2429,8 @@ instance Diagnostic TcRnMessage where
      -> diagnosticHints msg
    TcRnSolverReport _ _ hints
      -> hints
+    TcRnSolverDepthError {}
+      -> [SuggestIncreaseReductionDepth]
    TcRnRedundantConstraints{}
      -> noHints
    TcRnInaccessibleCode{}
@@ -2588,10 +2527,6 @@ instance Diagnostic TcRnMessage where
      -> noHints
    TcRnTupleConstraintInst{}
      -> noHints
-    TcRnAbstractClassInst{}
-      -> noHints
-    TcRnNoClassInstHead{}
-      -> noHints
    TcRnUserTypeError{}
      -> noHints
    TcRnConstraintInKind{}
@@ -2614,12 +2549,8 @@ instance Diagnostic TcRnMessage where
      -> noHints
    TcRnIllegalConstraintSynonymOfKind{}
      -> [suggestExtension LangExt.ConstraintKinds]
-    TcRnIllegalClassInst{}
-      -> noHints
    TcRnOversaturatedVisibleKindArg{}
      -> noHints
-    TcRnBadAssociatedType{}
-      -> noHints
    TcRnForAllRankErr rank _
      -> case rank of
           LimitedRank{}      -> [suggestExtension LangExt.RankNTypes]
@@ -2632,8 +2563,8 @@ instance Diagnostic TcRnMessage where
      -> noHints
    TcRnArityMismatch{}
      -> noHints
-    TcRnIllegalInstanceDecl _ _ reason
-      -> illegalInstanceHints reason
+    TcRnIllegalInstance rea
+      -> illegalInstanceHints rea
    TcRnMonomorphicBindings bindings
      -> case bindings of
          []     -> noHints
@@ -2727,8 +2658,6 @@ instance Diagnostic TcRnMessage where
      -> noHints
    TcRnArrowProcGADTPattern
      -> noHints
-    TcRnSpecialClassInst {}
-      -> noHints
    TcRnForallIdentifier {}
      -> [SuggestRenameForall]
    TcRnTypeEqualityOutOfScope
@@ -2852,8 +2781,6 @@ instance Diagnostic TcRnMessage where
      -> noHints
    TcRnBadMethodErr{}
      -> noHints
-    TcRnNoExplicitAssocTypeOrDefaultDeclaration{}
-      -> noHints
    TcRnIllegalTypeData
      -> [suggestExtension LangExt.TypeData]
    TcRnTypeDataForbids{}
@@ -2864,12 +2791,6 @@ instance Diagnostic TcRnMessage where
      -> noHints
    TcRnMisplacedInstSig{}
      -> [suggestExtension LangExt.InstanceSigs]
-    TcRnIllegalFamilyInstance{}
-      -> noHints
-    TcRnMissingClassAssoc{}
-      -> noHints
-    TcRnNotOpenFamily{}
-      -> noHints
    TcRnNoRebindableSyntaxRecordDot{}
      -> noHints
    TcRnNoFieldPunsRecordDot{}
@@ -2924,8 +2845,6 @@ instance Diagnostic TcRnMessage where
        cls_or_qc = case ctLocOrigin wtd_loc of
          ScOrigin c_or_q _ -> c_or_q
          _                 -> IsClsInst -- shouldn't happen
-    TcRnIllegalInstanceHeadDecl{}
-      -> noHints
    TcRnUnexpectedStandaloneDerivingDecl{}
      -> [suggestExtension LangExt.StandaloneDeriving]
    TcRnUnusedVariableInRuleDecl{}
@@ -2934,8 +2853,6 @@ instance Diagnostic TcRnMessage where
      -> [suggestExtension LangExt.StandaloneKindSignatures]
    TcRnIllegalRuleLhs{}
      -> noHints
-    TcRnBadAssocRhs{}
-      -> noHints
    TcRnDuplicateRoleAnnot{}
      -> noHints
    TcRnDuplicateKindSig{}
@@ -2978,8 +2895,6 @@ instance Diagnostic TcRnMessage where
      -> [SuggestExplicitBidiPatSyn name pat args]
    TcRnPatSynInvalidRhs{}
      -> noHints
-    TcRnMultiAssocTyFamDefaults{}
-      -> noHints
    TcRnTyFamDepsDisabled{}
      -> [suggestExtension LangExt.TypeFamilyDependencies]
    TcRnAbstractClosedTyFamDecl{}
@@ -2996,6 +2911,8 @@ instance Diagnostic TcRnMessage where
      -> noHints
    TcRnTyFamsDisabled{}
      -> [suggestExtension LangExt.TypeFamilies]
+    TcRnBadTyConTelescope{}
+      -> noHints
    TcRnTyFamResultDisabled{}
      -> [suggestExtension LangExt.TypeFamilyDependencies]
    TcRnRoleValidationFailed{}
@@ -3010,8 +2927,6 @@ instance Diagnostic TcRnMessage where
      -> [suggestExtension LangExt.FunctionalDependencies]
    TcRnClassExtensionDisabled _ ConstrainedClassMethodsDisabled{}
      -> [suggestExtension LangExt.ConstrainedClassMethods]
-    TcRnAssocNoClassTyVar{}
-      -> noHints
    TcRnDataConParentTypeMismatch{}
      -> noHints
    TcRnGADTsDisabled{}
@@ -3027,10 +2942,6 @@ instance Diagnostic TcRnMessage where
      -> [suggestExtension LangExt.KindSignatures]
    TcRnEmptyDataDeclsDisabled{}
      -> [suggestExtension LangExt.EmptyDataDecls]
-    TcRnFamilyCategoryMismatch{}
-      -> noHints
-    TcRnFamilyArityMismatch{}
-      -> noHints
    TcRnRoleMismatch{}
      -> noHints
    TcRnRoleCountMismatch{}
@@ -3041,8 +2952,6 @@ instance Diagnostic TcRnMessage where
      -> [suggestExtension LangExt.RoleAnnotations]
    TcRnIncoherentRoles{}
      -> [suggestExtension LangExt.IncoherentInstances]
-    TcRnTyFamNameMismatch{}
-      -> noHints
    TcRnUnexpectedKindVar{}
      -> [suggestExtension LangExt.PolyKinds]
    TcRnNegativeNumTypeLiteral{}
@@ -5817,21 +5726,74 @@ pprBootDataConMismatchErr dc1 dc2 = \case
 --------------------------------------------------------------------------------
 -- Illegal instance errors

-pprIllegalInstanceReason :: Class -> [Type] -> IllegalInstanceReason -> SDoc
-pprIllegalInstanceReason cls tys = \case
-  IllegalInstanceHeadTypeSynonym ->
+pprIllegalInstance :: IllegalInstanceReason -> SDoc
+pprIllegalInstance = \case
+  IllegalClassInstance head_ty reason ->
+    pprIllegalClassInstanceReason head_ty reason
+  IllegalFamilyInstance reason ->
+    pprIllegalFamilyInstance reason
+  IllegalFamilyApplicationInInstance inst_ty invis_arg tf_tc tf_args ->
+    pprWithExplicitKindsWhen invis_arg $
+      hang (text "Illegal type synonym family application"
+              <+> quotes (ppr tf_ty) <+> text "in instance" <> colon)
+         2 (ppr inst_ty)
+      where
+        tf_ty = mkTyConApp tf_tc tf_args
+
+pprIllegalClassInstanceReason :: TypedThing -> IllegalClassInstanceReason -> SDoc
+pprIllegalClassInstanceReason head_ty = \case
+  IllegalInstanceHead reason ->
+    pprIllegalInstanceHeadReason head_ty reason
+  IllegalHasFieldInstance has_field_err ->
+    with_illegal_instance_header head_ty $
+      pprIllegalHasFieldInstance has_field_err
+  IllegalSpecialClassInstance cls because_safeHaskell ->
+    text "Class" <+> quotes (ppr $ className cls)
+    <+> text "does not support user-specified instances"
+    <> safeHaskell_msg
+      where
+        safeHaskell_msg
+          | because_safeHaskell
+          = text " when Safe Haskell is enabled."
+          | otherwise
+          = dot
+  IllegalInstanceFailsCoverageCondition cls coverage_failure ->
+    with_illegal_instance_header head_ty $
+      pprNotCovered cls coverage_failure
+
+pprIllegalInstanceHeadReason :: TypedThing
+                             -> IllegalInstanceHeadReason -> SDoc
+pprIllegalInstanceHeadReason head_ty = \case
+  InstHeadTySynArgs -> with_illegal_instance_header head_ty $
    text "All instance types must be of the form (T t1 ... tn)" $$
    text "where T is not a synonym."
-  IllegalInstanceHeadNonTyVarArgs -> vcat [
+  InstHeadNonTyVarArgs -> with_illegal_instance_header head_ty $ vcat [
    text "All instance types must be of the form (T a1 ... an)",
    text "where a1 ... an are *distinct type variables*,",
    text "and each type variable appears at most once in the instance head."]
-  IllegalMultiParamInstance -> parens $
+  InstHeadMultiParam -> with_illegal_instance_header head_ty $ parens $
    text "Only one type can be given in an instance head."
-  IllegalHasFieldInstance has_field_err ->
-    pprIllegalHasFieldInstance has_field_err
-  IllegalInstanceFailsCoverageCondition coverage_failure ->
-    pprNotCovered cls tys coverage_failure
+  InstHeadAbstractClass clas ->
+    text "Cannot define instance for abstract class" <+>
+    quotes (ppr (className clas))
+  InstHeadNonClass bad_head ->
+    vcat [ text "Illegal" <+> what_illegal <> dot
+         , text "Instance heads must be of the form"
+         , nest 2 $ text "C ty_1 ... ty_n"
+         , text "where" <+> quotes (char 'C') <+> text "is a class."
+         ]
+    where
+      what_illegal = case bad_head of
+        Just tc ->
+          text "instance for" <+> ppr (tyConFlavour tc) <+> quotes (ppr $ tyConName tc)
+        Nothing ->
+          text "head of an instance declaration:" <+> quotes (ppr head_ty)
+
+with_illegal_instance_header :: TypedThing -> SDoc -> SDoc
+with_illegal_instance_header head_ty msg =
+  hang (hang (text "Illegal instance declaration for")
+           2 (quotes (ppr head_ty)) <> colon)
+      2 msg

 pprIllegalHasFieldInstance :: IllegalHasFieldInstance -> SDoc
 pprIllegalHasFieldInstance = \case
@@ -5846,8 +5808,8 @@ pprIllegalHasFieldInstance = \case
           , text "could unify with one of the field labels of" <+> ppr_tc <> dot ]
    where ppr_tc = quotes (ppr tc)

-pprNotCovered :: Class -> [Type] -> CoverageProblem -> SDoc
-pprNotCovered clas _tys
+pprNotCovered :: Class -> CoverageProblem -> SDoc
+pprNotCovered clas
  CoverageProblem
  { not_covered_fundep        = fd
  , not_covered_fundep_inst   = (ls, rs)
@@ -5879,17 +5841,72 @@ pprNotCovered clas _tys

 illegalInstanceHints :: IllegalInstanceReason -> [GhcHint]
 illegalInstanceHints = \case
-  IllegalInstanceHeadTypeSynonym ->
-    [suggestExtension LangExt.TypeSynonymInstances]
-  IllegalInstanceHeadNonTyVarArgs ->
-    [suggestExtension LangExt.FlexibleInstances]
-  IllegalMultiParamInstance ->
-    [suggestExtension LangExt.MultiParamTypeClasses]
+  IllegalClassInstance _ reason ->
+    illegalClassInstanceHints reason
+  IllegalFamilyInstance reason ->
+    illegalFamilyInstanceHints reason
+  IllegalFamilyApplicationInInstance {} ->
+    noHints
+
+illegalInstanceReason :: IllegalInstanceReason -> DiagnosticReason
+illegalInstanceReason = \case
+  IllegalClassInstance _ reason ->
+    illegalClassInstanceReason reason
+  IllegalFamilyInstance reason ->
+    illegalFamilyInstanceReason reason
+  IllegalFamilyApplicationInInstance {} ->
+    ErrorWithoutFlag
+
+illegalClassInstanceHints :: IllegalClassInstanceReason -> [GhcHint]
+illegalClassInstanceHints = \case
+  IllegalInstanceHead reason ->
+    illegalInstanceHeadHints reason
  IllegalHasFieldInstance has_field_err ->
    illegalHasFieldInstanceHints has_field_err
-  IllegalInstanceFailsCoverageCondition coverage_failure ->
+  IllegalSpecialClassInstance {} -> noHints
+  IllegalInstanceFailsCoverageCondition _ coverage_failure ->
    failedCoverageConditionHints coverage_failure

+
+illegalClassInstanceReason :: IllegalClassInstanceReason -> DiagnosticReason
+illegalClassInstanceReason = \case
+  IllegalInstanceHead reason ->
+    illegalInstanceHeadReason reason
+  IllegalHasFieldInstance has_field_err ->
+    illegalHasFieldInstanceReason has_field_err
+  IllegalSpecialClassInstance {} -> ErrorWithoutFlag
+  IllegalInstanceFailsCoverageCondition _ coverage_failure ->
+    failedCoverageConditionReason coverage_failure
+
+illegalInstanceHeadHints :: IllegalInstanceHeadReason -> [GhcHint]
+illegalInstanceHeadHints = \case
+  InstHeadTySynArgs ->
+    [suggestExtension LangExt.TypeSynonymInstances]
+  InstHeadNonTyVarArgs ->
+    [suggestExtension LangExt.FlexibleInstances]
+  InstHeadMultiParam ->
+    [suggestExtension LangExt.MultiParamTypeClasses]
+  InstHeadAbstractClass {} ->
+    noHints
+  InstHeadNonClass {} ->
+    noHints
+
+illegalInstanceHeadReason :: IllegalInstanceHeadReason -> DiagnosticReason
+illegalInstanceHeadReason = \case
+  -- These are serious
+  InstHeadAbstractClass {} ->
+    ErrorWithoutFlag
+  InstHeadNonClass {} ->
+    ErrorWithoutFlag
+
+  -- These are less serious (enable an extension)
+  InstHeadTySynArgs ->
+    ErrorWithoutFlag
+  InstHeadNonTyVarArgs ->
+    ErrorWithoutFlag
+  InstHeadMultiParam ->
+    ErrorWithoutFlag
+
 illegalHasFieldInstanceHints :: IllegalHasFieldInstance -> [GhcHint]
 illegalHasFieldInstanceHints = \case
  IllegalHasFieldInstanceNotATyCon
@@ -5901,6 +5918,17 @@ illegalHasFieldInstanceHints = \case
  IllegalHasFieldInstanceTyConHasFields {}
    -> noHints

+illegalHasFieldInstanceReason :: IllegalHasFieldInstance -> DiagnosticReason
+illegalHasFieldInstanceReason = \case
+  IllegalHasFieldInstanceNotATyCon
+    -> ErrorWithoutFlag
+  IllegalHasFieldInstanceFamilyTyCon
+    -> ErrorWithoutFlag
+  IllegalHasFieldInstanceTyConHasField {}
+    -> ErrorWithoutFlag
+  IllegalHasFieldInstanceTyConHasFields {}
+    -> ErrorWithoutFlag
+
 failedCoverageConditionHints :: CoverageProblem -> [GhcHint]
 failedCoverageConditionHints (CoverageProblem { not_covered_liberal = failed_cc })
  = case failed_cc of
@@ -5912,6 +5940,184 @@ failedCoverageConditionHints (CoverageProblem { not_covered_liberal = failed_cc
        then noHints
        else [suggestExtension LangExt.UndecidableInstances]

+failedCoverageConditionReason :: CoverageProblem -> DiagnosticReason
+failedCoverageConditionReason _ = ErrorWithoutFlag
+
+pprIllegalFamilyInstance :: IllegalFamilyInstanceReason -> SDoc
+pprIllegalFamilyInstance = \case
+  InvalidAssoc reason -> pprInvalidAssoc reason
+  NotAFamilyTyCon ty_or_data tc ->
+    vcat [ text "Illegal family instance for" <+> quotes (ppr tc)
+         , nest 2 $ parens (quotes (ppr tc) <+> text "is not a" <+> what) ]
+    where
+      what = ppr ty_or_data <+> text "family"
+  NotAnOpenFamilyTyCon tc ->
+    text "Illegal instance for closed family" <+> quotes (ppr tc)
+  FamilyCategoryMismatch tc ->
+    text "Wrong category of family instance; declaration was for a" <+> what <> dot
+    where
+      what = case tyConFlavour tc of
+        OpenFamilyFlavour IAmData _ -> text "data family"
+        _                           -> text "type family"
+  FamilyArityMismatch _ max_args ->
+    text "Number of parameters must match family declaration; expected"
+    <+> ppr max_args <> dot
+  TyFamNameMismatch fam_tc_name eqn_tc_name ->
+    hang (text "Mismatched type name in type family instance.")
+       2 (vcat [ text "Expected:" <+> ppr fam_tc_name
+               , text "  Actual:" <+> ppr eqn_tc_name ])
+  FamInstRHSOutOfScopeTyVars mb_dodgy tvs ->
+    hang (text "Out of scope type variable" <> plural tvs
+         <+> pprWithCommas (quotes . ppr) tvs
+         <+> text "in the RHS of a family instance.")
+       2 (text "All such variables must be bound on the LHS.")
+    $$ mk_extra
+    where
+    -- mk_extra: #7536: give a decent error message for
+    --         type T a = Int
+    --         type instance F (T a) = a
+    mk_extra = case mb_dodgy of
+      Nothing -> empty
+      Just (fam_tc, pats, dodgy_tvs) ->
+        ppWhen (any (`elemVarSetByKey` dodgy_tvs) (map nameUnique tvs)) $
+          hang (text "The real LHS (expanding synonyms) is:")
+             2 (pprTypeApp fam_tc (map expandTypeSynonyms pats))
+  FamInstLHSUnusedBoundTyVars tvs ->
+    hang (text "Type variable" <> plural tvs <+> pprQuotedList tvs
+          <+> isOrAre tvs <+> text "bound by a forall,")
+       2 (text "but not used in the family instance.")
+
+illegalFamilyInstanceHints :: IllegalFamilyInstanceReason -> [GhcHint]
+illegalFamilyInstanceHints = \case
+  InvalidAssoc rea -> invalidAssocHints rea
+  NotAFamilyTyCon {} -> noHints
+  NotAnOpenFamilyTyCon {} -> noHints
+  FamilyCategoryMismatch {} -> noHints
+  FamilyArityMismatch {} -> noHints
+  TyFamNameMismatch {} -> noHints
+  FamInstRHSOutOfScopeTyVars {} -> noHints
+  FamInstLHSUnusedBoundTyVars {} -> noHints
+
+illegalFamilyInstanceReason :: IllegalFamilyInstanceReason -> DiagnosticReason
+illegalFamilyInstanceReason = \case
+  InvalidAssoc rea -> invalidAssocReason rea
+  NotAFamilyTyCon {} -> ErrorWithoutFlag
+  NotAnOpenFamilyTyCon {} -> ErrorWithoutFlag
+  FamilyCategoryMismatch {} -> ErrorWithoutFlag
+  FamilyArityMismatch {} -> ErrorWithoutFlag
+  TyFamNameMismatch {} -> ErrorWithoutFlag
+  FamInstRHSOutOfScopeTyVars {} -> ErrorWithoutFlag
+  FamInstLHSUnusedBoundTyVars {} -> ErrorWithoutFlag
+
+pprInvalidAssoc :: InvalidAssoc -> SDoc
+pprInvalidAssoc = \case
+  InvalidAssocInstance rea -> pprInvalidAssocInstance rea
+  InvalidAssocDefault  rea -> pprInvalidAssocDefault  rea
+
+pprInvalidAssocInstance :: InvalidAssocInstance -> SDoc
+pprInvalidAssocInstance = \case
+  AssocInstanceMissing name ->
+    text "No explicit" <+> text "associated type"
+    <+> text "or default declaration for"
+    <+> quotes (ppr name)
+  AssocInstanceNotInAClass fam_tc ->
+    text "Associated type" <+> quotes (ppr fam_tc) <+>
+    text "must be inside a class instance"
+  AssocNotInThisClass cls fam_tc ->
+    hsep [ text "Class", quotes (ppr cls)
+         , text "does not have an associated type", quotes (ppr fam_tc) ]
+  AssocNoClassTyVar cls fam_tc ->
+    sep [ text "The associated type" <+> quotes (ppr fam_tc <+> hsep (map ppr (tyConTyVars fam_tc)))
+        , text "mentions none of the type or kind variables of the class" <+>
+                quotes (ppr cls <+> hsep (map ppr (classTyVars cls)))]
+  AssocTyVarsDontMatch vis fam_tc exp_tys act_tys ->
+    pprWithExplicitKindsWhen (isInvisibleForAllTyFlag vis) $
+    vcat [ text "Type indexes must match class instance head"
+         , text "Expected:" <+> pp exp_tys
+         , text "  Actual:" <+> pp act_tys ]
+    where
+      pp tys = pprIfaceTypeApp topPrec (toIfaceTyCon fam_tc) $
+               toIfaceTcArgs fam_tc tys
+
+pprInvalidAssocDefault :: InvalidAssocDefault -> SDoc
+pprInvalidAssocDefault = \case
+  AssocDefaultNotAssoc cls tc ->
+    hsep [ text "Class", quotes (ppr cls)
+         , text "does not have an associated type", quotes (ppr tc) ]
+  AssocMultipleDefaults name ->
+      text "More than one default declaration for" <+> quotes (ppr name)
+  AssocDefaultBadArgs fam_tc pat_tys bad_arg ->
+    let (pat_vis, main_msg) = case bad_arg of
+          AssocDefaultNonTyVarArg (pat_ty, pat_vis) ->
+            (pat_vis,
+             text "Illegal argument" <+> quotes (ppr pat_ty) <+> text "in:")
+          AssocDefaultDuplicateTyVars dups ->
+            let (pat_tv, pat_vis) = NE.head dups
+            in (pat_vis,
+                text "Illegal duplicate variable" <+> quotes (ppr pat_tv) <+> text "in:")
+    in pprWithExplicitKindsWhen (isInvisibleForAllTyFlag pat_vis) $
+         hang main_msg
+            2 (vcat [ppr_eqn, suggestion])
+    where
+      ppr_eqn :: SDoc
+      ppr_eqn =
+        quotes (text "type" <+> ppr (mkTyConApp fam_tc pat_tys)
+                <+> equals <+> text "...")
+
+      suggestion :: SDoc
+      suggestion = text "The arguments to" <+> quotes (ppr fam_tc)
+               <+> text "must all be distinct type variables."
+
+invalidAssocHints :: InvalidAssoc -> [GhcHint]
+invalidAssocHints = \case
+  InvalidAssocInstance rea -> invalidAssocInstanceHints rea
+  InvalidAssocDefault  rea -> invalidAssocDefaultHints  rea
+
+invalidAssocInstanceHints :: InvalidAssocInstance -> [GhcHint]
+invalidAssocInstanceHints = \case
+  AssocInstanceMissing {} -> noHints
+  AssocInstanceNotInAClass {} -> noHints
+  AssocNotInThisClass {} -> noHints
+  AssocNoClassTyVar {} -> noHints
+  AssocTyVarsDontMatch {} -> noHints
+
+invalidAssocDefaultHints :: InvalidAssocDefault -> [GhcHint]
+invalidAssocDefaultHints = \case
+  AssocDefaultNotAssoc {} -> noHints
+  AssocMultipleDefaults {} -> noHints
+  AssocDefaultBadArgs _ _ bad ->
+    assocDefaultBadArgHints bad
+
+assocDefaultBadArgHints :: AssocDefaultBadArgs -> [GhcHint]
+assocDefaultBadArgHints = \case
+  AssocDefaultNonTyVarArg {} -> noHints
+  AssocDefaultDuplicateTyVars {} -> noHints
+
+invalidAssocReason :: InvalidAssoc -> DiagnosticReason
+invalidAssocReason = \case
+  InvalidAssocInstance rea -> invalidAssocInstanceReason rea
+  InvalidAssocDefault  rea -> invalidAssocDefaultReason  rea
+
+invalidAssocInstanceReason :: InvalidAssocInstance -> DiagnosticReason
+invalidAssocInstanceReason = \case
+  AssocInstanceMissing {} -> WarningWithFlag (Opt_WarnMissingMethods)
+  AssocInstanceNotInAClass {} -> ErrorWithoutFlag
+  AssocNotInThisClass {} -> ErrorWithoutFlag
+  AssocNoClassTyVar {} -> ErrorWithoutFlag
+  AssocTyVarsDontMatch {} -> ErrorWithoutFlag
+
+invalidAssocDefaultReason :: InvalidAssocDefault -> DiagnosticReason
+invalidAssocDefaultReason = \case
+  AssocDefaultNotAssoc {} -> ErrorWithoutFlag
+  AssocMultipleDefaults {} -> ErrorWithoutFlag
+  AssocDefaultBadArgs _ _ rea ->
+    assocDefaultBadArgReason rea
+
+assocDefaultBadArgReason :: AssocDefaultBadArgs -> DiagnosticReason
+assocDefaultBadArgReason = \case
+  AssocDefaultNonTyVarArg {} -> ErrorWithoutFlag
+  AssocDefaultDuplicateTyVars {} -> ErrorWithoutFlag
+
 --------------------------------------------------------------------------------
 -- Template Haskell quotes and splices


--- a/compiler/GHC/Tc/Errors/Types.hs
+++ b/compiler/GHC/Tc/Errors/Types.hs
@@ -130,10 +130,15 @@ module GHC.Tc.Errors.Types (
  , SynAbstractDataError(..)
  , BootListMismatch(..), BootListMismatches

-    -- * Instance errors
+    -- * Class and family instance errors
  , IllegalInstanceReason(..)
+  , IllegalClassInstanceReason(..)
+  , IllegalInstanceHeadReason(..)
  , IllegalHasFieldInstance(..)
  , CoverageProblem(..), FailedCoverageCondition(..)
+  , IllegalFamilyInstanceReason(..)
+  , InvalidAssoc(..), InvalidAssocInstance(..)
+  , InvalidAssocDefault(..), AssocDefaultBadArgs(..)

    -- * Template Haskell errors
  , THError(..), THSyntaxError(..), THNameError(..)
@@ -196,7 +201,7 @@ import GHC.Core.InstEnv (LookupInstanceErrReason, ClsInst, DFunId)
 import GHC.Core.PatSyn (PatSyn)
 import GHC.Core.Predicate (EqRel, predTypeEqRel)
 import GHC.Core.TyCon (TyCon, Role, FamTyConFlav, AlgTyConRhs)
-import GHC.Core.Type (Kind, Type, ThetaType, PredType, ErrorMsgType)
+import GHC.Core.Type (Kind, Type, ThetaType, PredType, ErrorMsgType, ForAllTyFlag)
 import GHC.Driver.Backend (Backend)
 import GHC.Unit.State (UnitState)
 import GHC.Utils.Misc (filterOut)
@@ -225,11 +230,8 @@ data TcRnMessageOpts = TcRnMessageOpts { tcOptsShowContext :: !Bool -- ^ Whether
                                       , tcOptsIfaceOpts   :: !IfaceMessageOpts
                                       }

-
-{-
-Note [Migrating TcM Messages]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
+{- Note [Migrating TcM Messages]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 As part of #18516, we are slowly migrating the diagnostic messages emitted
 and reported in the TcM from SDoc to TcRnMessage. Historically, GHC emitted
 some diagnostics in 3 pieces, i.e. there were lots of error-reporting functions
@@ -258,7 +260,6 @@ diagnostic API inside Tc.Utils.Monad, enabling further refactorings.
 In the future, once the conversion will be complete and we will successfully eradicate
 any use of SDoc in the diagnostic reporting of GHC, we can surely revisit the usage and
 existence of these two types, which for now remain a "necessary evil".
-
 -}

 -- The majority of TcRn messages come with extra context about the error,
@@ -270,7 +271,6 @@ data ErrInfo = ErrInfo {
    -- ^ Extra supplementary info associated to the error.
  }

-
 -- | 'TcRnMessageDetailed' is an \"internal\" type (used only inside
 -- 'GHC.Tc.Utils.Monad' that wraps a 'TcRnMessage' while also providing
 -- any extra info needed to correctly pretty-print this diagnostic later on.
@@ -283,6 +283,11 @@ data TcRnMessageDetailed
 mkTcRnUnknownMessage :: (Diagnostic a, Typeable a, DiagnosticOpts a ~ NoDiagnosticOpts)
                     => a -> TcRnMessage
 mkTcRnUnknownMessage diag = TcRnUnknownMessage (mkSimpleUnknownDiagnostic diag)
+  -- Please don't use this function inside the GHC codebase;
+  -- it mainly exists for users of the GHC API, such as plugins.
+  --
+  -- If you need to emit a new error message in the typechecker,
+  -- you should add a new constructor to 'TcRnMessage' instead.

 -- | An error which might arise during typechecking/renaming.
 data TcRnMessage where
@@ -318,7 +323,7 @@ data TcRnMessage where
  {-| TcRnSolverReport is the constructor used to report unsolved constraints
      after constraint solving, as well as other errors such as hole fit errors.

-      See the documentation of the 'TcSolverReportMsg' datatype for an overview
+      See the documentation of t'TcSolverReportMsg' datatype for an overview
      of the different errors.
  -}
  TcRnSolverReport :: SolverReportWithCtxt
@@ -329,6 +334,30 @@ data TcRnMessage where
    -- so that we can compute the reason and hints, as opposed
    -- to having to pass them here.

+  {-| TcRnSolverDepthError is an error that occurs when the constraint solver
+      exceeds the maximum recursion depth.
+
+      Example:
+
+        class C a where { meth :: a }
+        instance Cls [a] => Cls a where { meth = head . meth }
+
+        t :: ()
+        t = meth
+
+      Test cases:
+        T7788
+        T8550
+        T9554
+        T15316A
+        T17267{∅,a,b,c,e}
+        T17458
+        ContextStack1
+        T22924b
+        TcCoercibleFail
+  -}
+  TcRnSolverDepthError :: !Type -> !SubGoalDepth -> TcRnMessage
+
  {-| TcRnRedundantConstraints is a warning that is emitted when a binding
      has a user-written type signature which contains superfluous constraints.

@@ -533,7 +562,6 @@ data TcRnMessage where
  -}
  TcRnInvalidWarningCategory :: !WarningCategory -> TcRnMessage

-
  {-| TcRnDuplicateWarningDecls is an error that occurs whenever
      a warning is declared twice.

@@ -680,7 +708,6 @@ data TcRnMessage where
        saks_fail003
        T15433a
  -}
-
  TcRnIllegalWildcardInType
    :: Maybe Name
        -- ^ the wildcard name, or 'Nothing' for an anonymous wildcard
@@ -998,44 +1025,6 @@ data TcRnMessage where
  -}
  TcRnTupleConstraintInst :: !Class -> TcRnMessage

-  {-| TcRnAbstractClassInst is an error that occurs whenever an instance
-      of an abstract class is specified.
-
-      Examples(s):
-        -- A.hs-boot
-        module A where
-        class C a
-
-        -- B.hs
-        module B where
-        import {-# SOURCE #-} A
-        instance C Int where
-
-        -- A.hs
-        module A where
-        import B
-        class C a where
-          f :: a
-
-        -- Main.hs
-        import A
-        main = print (f :: Int)
-
-      Test cases: typecheck/should_fail/T13068
-  -}
-  TcRnAbstractClassInst :: !Class -> TcRnMessage
-
-  {-| TcRnNoClassInstHead is an error that occurs whenever an instance
-      head is not headed by a class.
-
-      Examples(s):
-        instance c
-
-      Test cases: typecheck/rename/T5513
-                  typecheck/rename/T16385
-  -}
-  TcRnNoClassInstHead :: !Type -> TcRnMessage
-
  {-| TcRnUserTypeError is an error that occurs due to a user's custom type error,
      which can be triggered by adding a `TypeError` constraint in a type signature
      or typeclass instance.
@@ -1200,21 +1189,6 @@ data TcRnMessage where
  -}
  TcRnIllegalConstraintSynonymOfKind :: !Type -> TcRnMessage

-  {-| TcRnIllegalClassInst is an error that occurs whenever a class instance is specified
-      for a non-class.
-
-      This also includes derived instances. See the T23522 test case.
-
-      Examples(s):
-        type C1 a = (Show (a -> Bool))
-        instance C1 Int where
-
-      Test cases:
-        polykinds/T13267
-        deriving/should_fail/T23522
-  -}
-  TcRnIllegalClassInst :: !(TyConFlavour TyCon) -> TcRnMessage
-
  {-| TcRnOversaturatedVisibleKindArg is an error that occurs whenever an illegal oversaturated
      visible kind argument is specified.

@@ -1228,21 +1202,6 @@ data TcRnMessage where
  -}
  TcRnOversaturatedVisibleKindArg :: !Type -> TcRnMessage

-  {-| TcRnBadAssociatedType is an error that occurs whenever a class doesn't have an
-      associated type.
-
-      Examples(s):
-        $(do d <- instanceD (cxt []) (conT ''Eq `appT` conT ''Foo)
-                    [tySynInstD $ tySynEqn Nothing (conT ''Rep `appT` conT ''Foo) (conT ''Maybe)]
-             return [d])
-        ======>
-        instance Eq Foo where
-          type Rep Foo = Maybe
-
-      Test cases: th/T12387a
-  -}
-  TcRnBadAssociatedType :: {-Class-} !Name -> {-TyCon-} !Name -> TcRnMessage
-
  {-| TcRnForAllRankErr is an error that occurs whenever an illegal ranked type
      is specified.

@@ -1319,13 +1278,12 @@ data TcRnMessage where
                    -> !Arity -- ^ actual arity
                    -> TcRnMessage

-  {-| TcRnIllegalInstanceDecl is an error that arises from an invalid class
-      instance declaration.
+  {-| TcRnIllegalClassInstance is a collection of diagnostics that arise
+      from an invalid class or family instance declaration.

-      See 'IllegalInstanceReason'.
+      See t'IllegalInstanceReason'.
  -}
-  TcRnIllegalInstanceDecl :: !Class -> ![Type] -> IllegalInstanceReason
-                          -> TcRnMessage
+  TcRnIllegalInstance :: IllegalInstanceReason -> TcRnMessage

  {-| TcRnMonomorphicBindings is a warning (controlled by -Wmonomorphism-restriction)
      that arises when the monomorphism restriction applies to the given bindings.
@@ -1429,7 +1387,15 @@ data TcRnMessage where
  -}
  TcRnConflictingFamInstDecls :: NE.NonEmpty FamInst -> TcRnMessage

-  TcRnFamInstNotInjective :: InjectivityErrReason -> TyCon -> NE.NonEmpty CoAxBranch -> TcRnMessage
+  {-| TcRnFamInstNotInjective is a collection of errors that arise from
+      a type family equation violating the injectivity annotation.
+
+      See 'InjectivityErrReason'.
+  -}
+  TcRnFamInstNotInjective :: InjectivityErrReason -- ^ the violation
+                          -> TyCon -- ^ the family 'TyCon'
+                          -> NE.NonEmpty CoAxBranch -- ^ the family equations
+                          -> TcRnMessage

  {-| TcRnBangOnUnliftedType is a warning (controlled by -Wredundant-strictness-flags) that
      occurs when a strictness annotation is applied to an unlifted type.
@@ -1765,21 +1731,6 @@ data TcRnMessage where
                rename/should_fail/RnStaticPointersFail03
  -}
  TcRnStaticFormNotClosed :: Name -> NotClosedReason -> TcRnMessage
-  {-| TcRnSpecialClassInst is an error that occurs when a user
-      attempts to define an instance for a built-in typeclass such as
-      'Coercible', 'Typeable', or 'KnownNat', outside of a signature file.
-
-     Test cases: deriving/should_fail/T9687
-                 deriving/should_fail/T14916
-                 polykinds/T8132
-                 typecheck/should_fail/TcCoercibleFail2
-                 typecheck/should_fail/T12837
-                 typecheck/should_fail/T14390
-
-  -}
-  TcRnSpecialClassInst :: !Class
-                       -> !Bool -- ^ Whether the error is due to Safe Haskell being enabled
-                       -> TcRnMessage

  {-| TcRnUselessTypeable is a warning (controlled by -Wderiving-typeable) that
      occurs when trying to derive an instance of the 'Typeable' class. Deriving
@@ -1988,7 +1939,6 @@ data TcRnMessage where
  -}
  TcRnIllegalTypeOperatorDecl :: !RdrName -> TcRnMessage

-
  {-| TcRnGADTMonoLocalBinds is a warning controlled by -Wgadt-mono-local-binds
      that occurs when pattern matching on a GADT when -XMonoLocalBinds is off.

@@ -1997,6 +1947,7 @@ data TcRnMessage where
      Test cases: T20485, T20485a
  -}
  TcRnGADTMonoLocalBinds :: TcRnMessage
+
  {-| The TcRnNotInScope constructor is used for various not-in-scope errors.
      See 'NotInScopeError' for more details. -}
  TcRnNotInScope :: NotInScopeError  -- ^ what the problem is
@@ -2004,6 +1955,19 @@ data TcRnMessage where
                 -> [ImportError]    -- ^ import errors that are relevant
                 -> [GhcHint]        -- ^ hints, e.g. enable DataKinds to refer to a promoted data constructor
                 -> TcRnMessage
+
+  {-| TcRnTermNameInType is an error that occurs when a term-level identifier
+      is used in a type.
+
+      Example:
+
+        import qualified Prelude
+
+        bad :: Prelude.fst (Bool, Float)
+        bad = False
+
+      Test cases: T21605{c,d}
+  -}
  TcRnTermNameInType :: RdrName -> [GhcHint] -> TcRnMessage

  {-| TcRnUntickedPromotedThing is a warning (controlled with -Wunticked-promoted-constructors)
@@ -2607,7 +2571,7 @@ data TcRnMessage where
       meth = 0

    Test case:
-      testsuite/tests/typecheck/should_fail/MissingDefaultMethodBinding.hs
+      typecheck/should_fail/MissingDefaultMethodBinding.hs
  -}
  TcRnBadGenericMethod :: !Name   -- ^ 'Name' of the class
                       -> !Name   -- ^ Problematic method
@@ -2622,7 +2586,7 @@ data TcRnMessage where
       {-# MINIMAL #-} -- warning!

     Test case:
-       testsuite/tests/warnings/minimal/WarnMinimal.hs:
+       warnings/minimal/WarnMinimal.hs:
  -}
  TcRnWarningMinimalDefIncomplete :: ClassMinimalDef -> TcRnMessage

@@ -2646,8 +2610,8 @@ data TcRnMessage where
      a default method pragma is missing an accompanying binding.

    Test cases:
-      testsuite/tests/typecheck/should_fail/T5084.hs
-      testsuite/tests/typecheck/should_fail/T2354.hs
+      typecheck/should_fail/T5084.hs
+      typecheck/should_fail/T2354.hs
  -}
  TcRnDefaultMethodForPragmaLacksBinding
            :: Id             -- ^ method
@@ -2662,27 +2626,16 @@ data TcRnMessage where
            :: !Name
            -> TcRnMessage
  {-| TcRnBadMethodErr is an error that happens when one attempts to provide a method
-     in a class instance, when the class doesn't have a method by that name.
+      in a class instance, when the class doesn't have a method by that name.

     Test case:
-       testsuite/tests/th/T12387
+       th/T12387
  -}
  TcRnBadMethodErr
    :: { badMethodErrClassName  :: !Name
       , badMethodErrMethodName :: !Name
       } -> TcRnMessage
-  {-| TcRnNoExplicitAssocTypeOrDefaultDeclaration is an error that occurs
-      when a class instance does not provide an expected associated type
-      or default declaration.

-    Test cases:
-      testsuite/tests/deriving/should_compile/T14094
-      testsuite/tests/indexed-types/should_compile/Simple2
-      testsuite/tests/typecheck/should_compile/tc254
-  -}
-  TcRnNoExplicitAssocTypeOrDefaultDeclaration
-            :: Name
-            -> TcRnMessage
  {-| TcRnIllegalNewtype is an error that occurs when a newtype:

      * Does not have exactly one field, or
@@ -2693,18 +2646,18 @@ data TcRnMessage where
      * has strictness annotations.

    Test cases:
-      testsuite/tests/gadt/T14719
-      testsuite/tests/indexed-types/should_fail/T14033
-      testsuite/tests/indexed-types/should_fail/T2334A
-      testsuite/tests/linear/should_fail/LinearGADTNewtype
-      testsuite/tests/parser/should_fail/readFail008
-      testsuite/tests/polykinds/T11459
-      testsuite/tests/typecheck/should_fail/T15523
-      testsuite/tests/typecheck/should_fail/T15796
-      testsuite/tests/typecheck/should_fail/T17955
-      testsuite/tests/typecheck/should_fail/T18891a
-      testsuite/tests/typecheck/should_fail/T21447
-      testsuite/tests/typecheck/should_fail/tcfail156
+      gadt/T14719
+      indexed-types/should_fail/T14033
+      indexed-types/should_fail/T2334A
+      linear/should_fail/LinearGADTNewtype
+      parser/should_fail/readFail008
+      polykinds/T11459
+      typecheck/should_fail/T15523
+      typecheck/should_fail/T15796
+      typecheck/should_fail/T17955
+      typecheck/should_fail/T18891a
+      typecheck/should_fail/T21447
+      typecheck/should_fail/tcfail156
  -}
  TcRnIllegalNewtype
            :: DataCon
@@ -2718,7 +2671,7 @@ data TcRnMessage where
      See Note [Type data declarations]

     Test case:
-       testsuite/tests/type-data/should_fail/TDNoPragma
+       type-data/should_fail/TDNoPragma
  -}
  TcRnIllegalTypeData :: TcRnMessage

@@ -2729,11 +2682,11 @@ data TcRnMessage where
      See Note [Type data declarations]

     Test cases:
-       testsuite/tests/type-data/should_fail/TDDeriving
-       testsuite/tests/type-data/should_fail/TDRecordsGADT
-       testsuite/tests/type-data/should_fail/TDRecordsH98
-       testsuite/tests/type-data/should_fail/TDStrictnessGADT
-       testsuite/tests/type-data/should_fail/TDStrictnessH98
+       type-data/should_fail/TDDeriving
+       type-data/should_fail/TDRecordsGADT
+       type-data/should_fail/TDRecordsH98
+       type-data/should_fail/TDStrictnessGADT
+       type-data/should_fail/TDStrictnessH98
  -}
  TcRnTypeDataForbids :: !TypeDataForbids -> TcRnMessage

@@ -2746,35 +2699,35 @@ data TcRnMessage where
          instance C ()        -- | foo needs to be defined here

       Test cases:
-         testsuite/tests/typecheck/prog001/typecheck.prog001
-         testsuite/tests/typecheck/should_compile/tc126
-         testsuite/tests/typecheck/should_compile/T7903
-         testsuite/tests/typecheck/should_compile/tc116
-         testsuite/tests/typecheck/should_compile/tc175
-         testsuite/tests/typecheck/should_compile/HasKey
-         testsuite/tests/typecheck/should_compile/tc125
-         testsuite/tests/typecheck/should_compile/tc078
-         testsuite/tests/typecheck/should_compile/tc161
-         testsuite/tests/typecheck/should_fail/T5051
-         testsuite/tests/typecheck/should_compile/T21583
-         testsuite/tests/backpack/should_compile/bkp47
-         testsuite/tests/backpack/should_fail/bkpfail25
-         testsuite/tests/parser/should_compile/T2245
-         testsuite/tests/parser/should_compile/read014
-         testsuite/tests/indexed-types/should_compile/Class3
-         testsuite/tests/indexed-types/should_compile/Simple2
-         testsuite/tests/indexed-types/should_fail/T7862
-         testsuite/tests/deriving/should_compile/deriving-1935
-         testsuite/tests/deriving/should_compile/T9968a
-         testsuite/tests/deriving/should_compile/drv003
-         testsuite/tests/deriving/should_compile/T4966
-         testsuite/tests/deriving/should_compile/T14094
-         testsuite/tests/perf/compiler/T15304
-         testsuite/tests/warnings/minimal/WarnMinimal
-         testsuite/tests/simplCore/should_compile/simpl020
-         testsuite/tests/deSugar/should_compile/T14546d
-         testsuite/tests/ghci/scripts/T5820
-         testsuite/tests/ghci/scripts/ghci019
+         typecheck/prog001/typecheck.prog001
+         typecheck/should_compile/tc126
+         typecheck/should_compile/T7903
+         typecheck/should_compile/tc116
+         typecheck/should_compile/tc175
+         typecheck/should_compile/HasKey
+         typecheck/should_compile/tc125
+         typecheck/should_compile/tc078
+         typecheck/should_compile/tc161
+         typecheck/should_fail/T5051
+         typecheck/should_compile/T21583
+         backpack/should_compile/bkp47
+         backpack/should_fail/bkpfail25
+         parser/should_compile/T2245
+         parser/should_compile/read014
+         indexed-types/should_compile/Class3
+         indexed-types/should_compile/Simple2
+         indexed-types/should_fail/T7862
+         deriving/should_compile/deriving-1935
+         deriving/should_compile/T9968a
+         deriving/should_compile/drv003
+         deriving/should_compile/T4966
+         deriving/should_compile/T14094
+         perf/compiler/T15304
+         warnings/minimal/WarnMinimal
+         simplCore/should_compile/simpl020
+         deSugar/should_compile/T14546d
+         ghci/scripts/T5820
+         ghci/scripts/ghci019
  -}
  TcRnUnsatisfiedMinimalDef :: ClassMinimalDef -> TcRnMessage

@@ -2782,33 +2735,9 @@ data TcRnMessage where
       a class instance is given a type signature, but the user has not
       enabled the @InstanceSigs@ extension.

-       Test case:
-       testsuite/tests/module/mod45
+       Test case: module/mod45
  -}
  TcRnMisplacedInstSig :: Name -> (LHsSigType GhcRn) -> TcRnMessage
-  {-| 'TcRnIllegalFamilyInstance' is an error that occurs when an associated
-       type or data family is given a top-level instance.
-
-       Test case:
-       testsuite/tests/indexed-types/should_fail/T3092
-  -}
-  TcRnIllegalFamilyInstance :: TyCon -> TcRnMessage
-  {-| 'TcRnMissingClassAssoc' is an error that occurs when a class instance
-       for a class with an associated type or data family is missing a corresponding
-       family instance declaration.
-
-       Test case:
-       testsuite/tests/indexed-types/should_fail/SimpleFail7
-  -}
-  TcRnMissingClassAssoc :: TyCon -> TcRnMessage
-  {-| 'TcRnNotOpenFamily' is an error that is triggered by attempting to give
-       a top-level (open) type family instance for a closed type family.
-
-       Test cases:
-         testsuite/tests/indexed-types/should_fail/Overlap7
-         testsuite/tests/indexed-types/should_fail/Overlap3
-  -}
-  TcRnNotOpenFamily :: TyCon -> TcRnMessage
  {-| TcRnNoRebindableSyntaxRecordDot is an error triggered by an overloaded record update
      without RebindableSyntax enabled.

@@ -3153,20 +3082,6 @@ data TcRnMessage where
                           -> PredType -- ^ Wanted 'PredType'
                           -> TcRnMessage

-  {-| TcRnIllegalInstanceHeadDecl is an error triggered by malformed head of
-      type class instance
-
-      Examples:
-
-        instance 42
-
-        instance !Show D
-
-      Test cases: parser/should_fail/T3811c
-                  rename/should_fail/T18240a
-  -}
-  TcRnIllegalInstanceHeadDecl :: LHsType GhcRn -> TcRnMessage
-
  {-| TcRnUnexpectedStandaloneDerivingDecl is an error thrown when a user uses
      standalone deriving without enabling the StandaloneDeriving extension.

@@ -3219,20 +3134,6 @@ data TcRnMessage where
    -> HsExpr GhcRn -- Bad expression
    -> TcRnMessage

-  {-| TcRnBadAssocRhs is an error triggered by out-of-scope type variables
-      occurred in right-hand side of an associated type declaration
-
-      Example:
-
-        instance forall a. C Int where
-          data instance D Int = MkD1 a
-
-       cases: indexed-types/should_fail/T5515
-                  polykinds/T9574
-                  rename/should_fail/T18021
-  -}
-  TcRnBadAssocRhs :: [Name] -> TcRnMessage
-
  {-| TcRnDuplicateRoleAnnot is an error triggered by two or more role
      annotations for one type

@@ -3489,15 +3390,6 @@ data TcRnMessage where
  -}
  TcRnZonkerMessage :: ZonkerMessage -> TcRnMessage

-  {-| TcRnMultiAssocTyFamDefaults is an error indicating that multiple default
-    declarations were specified for an associated type family.
-
-    Test cases:
-      none
-  -}
-  TcRnMultiAssocTyFamDefaults :: !(IdP GhcRn) -- ^ Name of the associated type
-                              -> TcRnMessage
-
  {-| TcRnTyFamDepsDisabled is an error indicating that a type family injectivity
    annotation was used without enabling the extension TypeFamilyDependencies.

@@ -3560,6 +3452,26 @@ data TcRnMessage where
  TcRnTyFamsDisabled :: !TyFamsDisabledReason -- ^ The name of the family or instance
                     -> TcRnMessage

+  {-| TcRnBadTyConTelescope is an error caused by an ill-scoped 'TyCon' kind,
+     due to type variables being out of dependency order.
+
+     Example:
+
+      class C a (b :: Proxy a) (c :: Proxy b) where
+        type T c a
+
+     Test cases:
+       BadTelescope{∅,3,4}
+       T14066{f,g}
+       T14887
+       T15591{b,c}
+       T15743{c,d}
+       T15764
+       T23252
+
+  -}
+  TcRnBadTyConTelescope :: !TyCon -> TcRnMessage
+
  {-| TcRnTyFamResultDisabled is an error indicating that a result variable
    was used on a type family while the extension TypeFamilyDependencies was
    disabled.
@@ -3610,16 +3522,6 @@ data TcRnMessage where
                             -> !DisabledClassExtension -- ^ The extension
                             -> TcRnMessage

-  {-| TcRnAssocNoClassTyVar is an error indicating that no class parameters
-    are used in an associated type family.
-
-    Test cases:
-      T2888, T9167, T12867
-  -}
-  TcRnAssocNoClassTyVar :: !Class -- ^ The class
-                        -> !TyCon -- ^ The associated family
-                        -> TcRnMessage
-
  {-| TcRnDataConParentTypeMismatch is an error indicating that a data
    constructor was declared with a type that doesn't match its type
    constructor (i.e. a GADT result type and its data name).
@@ -3687,27 +3589,6 @@ data TcRnMessage where
  TcRnEmptyDataDeclsDisabled :: !Name -- ^ The data type name
                             -> TcRnMessage

-  {-| TcRnFamilyCategoryMismatch is an error indicating that a family instance
-    was declared for a family of a different kind, i.e. data vs type family.
-
-    Test cases:
-      T9896, SimpleFail3a
-  -}
-  TcRnFamilyCategoryMismatch :: !TyCon -- ^ The family tycon
-                             -> TcRnMessage
-
-  {-| TcRnFamilyArityMismatch is an error indicating that a family instance
-    was declared with a different number of arguments than the family.
-    See Note [Oversaturated type family equations] in "GHC.Tc.Validity".
-
-    Test cases:
-      TyFamArity1, TyFamArity2, T11136, Overlap4, AssocTyDef05, AssocTyDef06,
-      T14110
-  -}
-  TcRnFamilyArityMismatch :: !TyCon -- ^ The family tycon
-                          -> !Arity -- ^ The right number of parameters
-                          -> TcRnMessage
-
  {-| TcRnRoleMismatch is an error indicating that the role specified
    in an annotation differs from its inferred role.

@@ -3755,17 +3636,6 @@ data TcRnMessage where
  -}
  TcRnIncoherentRoles :: !TyCon -- ^ The class tycon
                      -> TcRnMessage
-
-  {-| TcRnIncoherentRoles is an error indicating that a type family equation
-    used a different name than the family.
-
-    Test cases:
-      Overlap5, T15362, T16002, T20260, T11623
-  -}
-  TcRnTyFamNameMismatch :: !Name -- ^ The family name
-                        -> !Name -- ^ The name used in the equation
-                        -> TcRnMessage
-
  {-| TcRnPrecedenceParsingError is an error caused by attempting to
      use operators with the same precedence in one infix expression.

@@ -4175,6 +4045,8 @@ data ZonkerMessage where

  deriving Generic

+----
+
 -- | Things forbidden in @type data@ declarations.
 -- See Note [Type data declarations]
 data TypeDataForbids
@@ -4506,6 +4378,245 @@ data SoleExtraConstraintWildcardAllowed
  = SoleExtraConstraintWildcardNotAllowed
  | SoleExtraConstraintWildcardAllowed

+-- | Why is a class instance head invalid?
+data IllegalInstanceHeadReason
+  -- | An instance for an abstract class from an hs-boot or Backpack
+  -- hsig file.
+  --
+  --  Example:
+  --
+  --    -- A.hs-boot
+  --    module A where
+  --    class C a
+  --
+  --    -- B.hs
+  --    module B where
+  --    import {-# SOURCE #-} A
+  --    instance C Int where
+  --
+  --    -- A.hs
+  --    module A where
+  --    import B
+  --    class C a where
+  --      f :: a
+  --
+  -- Test cases: typecheck/should_fail/T13068
+  = InstHeadAbstractClass !Class
+  -- | An instance whose head is not a class.
+  --
+  -- Examples(s):
+  --
+  --   instance c
+  --
+  --   instance 42
+  --
+  --   instance !Show D
+  --
+  --   type C1 a = (Show (a -> Bool))
+  --   instance C1 Int where
+  --
+  -- Test cases: typecheck/rename/T5513
+  --             typecheck/rename/T16385
+  --             parser/should_fail/T3811c
+  --             rename/should_fail/T18240a
+  --             polykinds/T13267
+  --             deriving/should_fail/T23522
+  | InstHeadNonClass
+    !(Maybe TyCon) -- ^ the 'TyCon' at the head of the instance head,
+                   -- or 'Nothing' if the instance head is not even headed
+                   -- by a 'TyCon'
+
+  -- | Instance head was headed by a type synonym.
+  --
+  -- Example:
+  --    type MyInt = Int
+  --    class C a where {..}
+  --    instance C MyInt where {..}
+  --
+  -- Test cases: drvfail015, mod42, TidyClassKinds, tcfail139
+  | InstHeadTySynArgs
+  -- | Instance head was not of the form @T a1 ... an@,
+  -- where @a1, ..., an@ are all type variables or literals.
+  --
+  -- Example:
+  --
+  --    instance Num [Int] where {..}
+  --
+  -- Test cases: mod41, mod42, tcfail044, tcfail047.
+  | InstHeadNonTyVarArgs
+  -- | Multi-param instance without -XMultiParamTypeClasses.
+  --
+  -- Example:
+  --
+  --  instance C a b where {..}
+  --
+  -- Test case: IllegalMultiParamInstance
+  | InstHeadMultiParam
+  deriving Generic
+
+
+-- | Why is a (type or data) family instance invalid?
+data IllegalFamilyInstanceReason
+  {-| A top-level family instance for a 'TyCon' that isn't a family 'TyCon'.
+
+    Example:
+
+      data D a = MkD
+      type instance D Int = Bool
+
+    Test case: indexed-types/should_fail/T3092
+  -}
+  = NotAFamilyTyCon
+      !TypeOrData -- ^ was this a 'type' or a 'data' instance?
+      !TyCon
+  {-| A top-level (open) type family instance for a closed type family.
+
+    Test cases:
+      indexed-types/should_fail/Overlap7
+      indexed-types/should_fail/Overlap3
+  -}
+  | NotAnOpenFamilyTyCon !TyCon
+
+  {-| A family instance was declared for a family of a different kind,
+      e.g. a data instance for a type family 'TyCon'.
+
+     Test cases:
+       T9896, SimpleFail3a
+  -}
+  | FamilyCategoryMismatch !TyCon -- ^ The family tycon
+
+
+  {-| A family instance was declared with a different number of arguments
+      than expected.
+      See Note [Oversaturated type family equations] in "GHC.Tc.Validity".
+
+    Test cases:
+      TyFamArity1, TyFamArity2, T11136, Overlap4, AssocTyDef05, AssocTyDef06,
+      T14110
+  -}
+  | FamilyArityMismatch !TyCon -- ^ The family tycon
+                        !Arity -- ^ The right number of parameters
+
+  {-| A closed type family equation used a different name than the parent family.
+
+    Example:
+
+      type family F a where
+        G Int = Bool
+
+    Test cases:
+      Overlap5, T15362, T16002, T20260, T11623
+  -}
+  | TyFamNameMismatch !Name -- ^ The family name
+                      !Name -- ^ The name used in the equation
+
+
+  -- | There are out-of-scope type variables in the right-hand side
+  -- of an associated type or data family instance.
+  --
+  -- Example:
+  --
+  --    instance forall a. C Int where
+  --      data instance D Int = MkD1 a
+  --
+  -- Test cases: indexed-types/should_fail/T5515, polykinds/T9574, rename/should_fail/T18021
+  | FamInstRHSOutOfScopeTyVars
+      !(Maybe (TyCon, [Type], TyVarSet))
+        -- ^ family 'TyCon', arguments, and set of "dodgy" type variables
+        -- See Note [Dodgy binding sites in type family instances]
+        -- in GHC.Tc.Validity
+      ![Name] -- ^ the out-of-scope type variables
+
+  | FamInstLHSUnusedBoundTyVars
+      ![Name] -- ^ the unused bound type variables
+
+  | InvalidAssoc !InvalidAssoc
+  deriving Generic
+
+data InvalidAssoc
+  -- | An invalid associated family instance.
+  --
+  -- See t'InvalidAssocInstance'.Builder
+  = InvalidAssocInstance !InvalidAssocInstance
+  -- | An invalid associated family default declaration.
+  --
+  -- See t'InvalidAssocDefault'.
+  | InvalidAssocDefault  !InvalidAssocDefault
+  deriving Generic
+
+-- | The reason that an associated family instance was invalid.
+data InvalidAssocInstance
+  -- | A class instance is missing its expected associated type/data instance.
+  --
+  -- Test cases: deriving/should_compile/T14094
+  --             indexed-types/should_compile/Simple2
+  --             typecheck/should_compile/tc254
+  = AssocInstanceMissing !Name
+
+  -- | A top-level instance for an associated family 'TyCon'.
+  --
+  -- Example:
+  --
+  --  class C a where { type T a }
+  --  instance T Int = Bool
+  --
+  -- Test case: indexed-types/should_fail/SimpleFail7
+  | AssocInstanceNotInAClass !TyCon
+
+  -- | An associated type instance is provided for a class that doesn't have
+  -- that associated type.
+  --
+  -- Examples(s):
+  --   $(do d <- instanceD (cxt []) (conT ''Eq `appT` conT ''Foo)
+  --               [tySynInstD $ tySynEqn Nothing (conT ''Rep `appT` conT ''Foo) (conT ''Maybe)]
+  --        return [d])
+  --   ======>
+  --   instance Eq Foo where
+  --     type Rep Foo = Maybe
+  --
+  -- Test cases: th/T12387a
+  | AssocNotInThisClass !Class !TyCon
+  -- | An associated family instance does not mention any of the parent 'Class'
+  -- 'TyVar's.
+  --
+  -- Test cases: T2888, T9167, T12867
+  | AssocNoClassTyVar !Class !TyCon
+
+  | AssocTyVarsDontMatch
+      !ForAllTyFlag
+      !TyCon  -- ^ family 'TyCon'
+      ![Type] -- ^ expected type arguments
+      ![Type] -- ^ actual type arguments
+  deriving Generic
+
+
+-- | The reason that an associated family default declaration was invalid.
+data InvalidAssocDefault
+    -- | An associated family default declaration for something that isn't
+    -- an associated family.
+  = AssocDefaultNotAssoc !Name -- ^ 'Class' 'Name'
+                         !Name -- ^ 'TyCon' 'Name'
+    -- | Multiple default declarations were given for an associated
+    -- family instance.
+    --
+    -- Test cases: none.
+  | AssocMultipleDefaults !Name
+    -- | Invalid arguments in an associated family instance.
+    --
+    -- See t'AssocDefaultBadArgs'.
+  | AssocDefaultBadArgs !TyCon ![Type] AssocDefaultBadArgs
+  deriving Generic
+
+-- | Invalid arguments in an associated family instance declaration.
+data AssocDefaultBadArgs
+  -- | An argument which isn't a type variable in an associated
+  -- family instance default declaration.
+  = AssocDefaultNonTyVarArg !(Type, ForAllTyFlag)
+  -- | Duplicate occurrence of a type variable in an associated
+  -- family instance default declaration.
+  | AssocDefaultDuplicateTyVars !(NE.NonEmpty (TyCoVar, ForAllTyFlag))
+  deriving Generic
+
 -- | A type representing whether or not the input type has associated data family instances.
 data HasAssociatedDataFamInsts
  = YesHasAdfs
@@ -5815,34 +5926,35 @@ data NonCanonical_Monad =

 -- | Why was an instance declaration rejected?
 data IllegalInstanceReason
-  -- | Instance head was headed by a type synonym.
-  --
-  -- Example:
-  --    type MyInt = Int
-  --    class C a where {..}
-  --    instance C MyInt where {..}
-  --
-  -- Test cases: drvfail015, mod42, TidyClassKinds, tcfail139
-  = IllegalInstanceHeadTypeSynonym
-  -- | Instance head was not of the form @T a1 ... an@,
-  -- where @a1, ..., an@ are all type variables or literals.
-  --
-  -- Example:
-  --
-  --    instance Num [Int] where {..}
-  --
-  -- Test cases: mod41, mod42, tcfail044, tcfail047.
-  | IllegalInstanceHeadNonTyVarArgs
-  -- | Multi-param instance without -XMultiParamTypeClasses.
-  --
-  -- Example:
-  --
-  --  instance C a b where {..}
+  = IllegalClassInstance
+      !TypedThing -- ^ the instance head type
+      !IllegalClassInstanceReason -- ^ the problem with the instance head
+  | IllegalFamilyInstance !IllegalFamilyInstanceReason
+  | IllegalFamilyApplicationInInstance
+      !Type   -- ^ the instance head type
+      !Bool   -- ^ is this an invisible argument?
+      !TyCon  -- ^ type family
+      ![Type] -- ^ type family argument
+  deriving Generic
+
+-- | Why was a class instance declaration rejected?
+data IllegalClassInstanceReason
+  -- | An illegal type at the head of the instance.
  --
-  -- Test case: IllegalMultiParamInstance
-  | IllegalMultiParamInstance
+  -- See t'IllegalInstanceHeadReason'.
+  = IllegalInstanceHead !IllegalInstanceHeadReason
  -- | An illegal HasField instance. See t'IllegalHasFieldInstance'.
  | IllegalHasFieldInstance !IllegalHasFieldInstance
+  -- | An illegal instance for a built-in typeclass such as
+  --   'Coercible', 'Typeable', or 'KnownNat', outside of a signature file.
+  --
+  --   Test cases: deriving/should_fail/T9687
+  --               deriving/should_fail/T14916
+  --               polykinds/T8132
+  --               typecheck/should_fail/TcCoercibleFail2
+  --               typecheck/should_fail/T12837
+  --               typecheck/should_fail/T14390
+  | IllegalSpecialClassInstance !Class !Bool -- ^ Whether the error is due to Safe Haskell being enabled
  -- | The instance failed the coverage condition, i.e. the functional
  -- dependencies were not respected.
  --
@@ -5853,7 +5965,7 @@ data IllegalInstanceReason
  --
  -- Test cases: T9106, T10570, T2247, T12803, tcfail170.
  | IllegalInstanceFailsCoverageCondition
-      !CoverageProblem
+      !Class !CoverageProblem
  deriving Generic

 -- | Why was a HasField instance declaration rejected?

--- a/compiler/GHC/Tc/Gen/HsType.hs
+++ b/compiler/GHC/Tc/Gen/HsType.hs
@@ -644,7 +644,11 @@ tcHsDeriv hs_ty
            case tyConClass_maybe tyCon of
              Just clas ->
                return (tvs, clas, tyConArgs, map scaledThing kind_args)
-              Nothing -> failWithTc $ TcRnIllegalClassInst (tyConFlavour tyCon)
+              Nothing -> failWithTc $ TcRnIllegalInstance
+                                    $ IllegalClassInstance
+                                        (TypeThing ty)
+                                    $ IllegalInstanceHead
+                                    $ InstHeadNonClass (Just tyCon)
          Nothing -> failWithTc $ TcRnIllegalDerivingItem hs_ty
    }

@@ -3548,7 +3552,7 @@ filterConstrainedCandidates
  -> TcM CandidatesQTvs
 -- filterConstrainedCandidates removes any candidates that are free in
 -- 'wanted'; instead, it promotes them.  This bit is very much like
-- decideMonoTyVars in GHC.Tc.Solver, but constraints are so much
+-- decidePromotedTyVars in GHC.Tc.Solver, but constraints are so much
 -- simpler in kinds, it is much easier here. (In particular, we never
 -- quantify over a constraint in a type.)
 filterConstrainedCandidates wanted dvs
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