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  1. 30 Jul, 2018 1 commit
    • Ryan Scott's avatar
      Fix #15385 by using addDictsDs in matchGuards · 9d388eb8
      Ryan Scott authored
      When coverage checking pattern-matches, we rely on the call
      sites in the desugarer to populate the local dictionaries and term
      evidence in scope using `addDictsDs` and `addTmCsDs`. But it turns
      out that only the call site for desugaring `case` expressions was
      actually doing this properly. In another part of the desugarer,
      `matchGuards` (which handles pattern guards), it did not update the
      local dictionaries in scope at all, leading to #15385.
      Fixing this is relatively straightforward: just augment the
      `BindStmt` case of `matchGuards` to use `addDictsDs` and `addTmCsDs`.
      Accomplishing this took a little bit of import/export tweaking:
      * We now need to export `collectEvVarsPat` from `HsPat.hs`.
      * To avoid an import cycle with `Check.hs`, I moved `isTrueLHsExpr`
        from `DsGRHSs.hs` to `DsUtils.hs`, which resides lower on the
        import chain.
      Test Plan: make test TEST=T15385
      Reviewers: simonpj, bgamari
      Reviewed By: simonpj
      Subscribers: rwbarton, thomie, carter
      GHC Trac Issues: #15385
      Differential Revision:
  2. 15 Jul, 2018 1 commit
    • Richard Eisenberg's avatar
      Reclassify some performance tests · 8a70ccbb
      Richard Eisenberg authored
      There were some performance tests not classified by
      compiler_num_stats_field, causing erroneous failures when
      testing a DEBUG compiler. This fixes that oversight,
      addressing #15374.
  3. 02 Mar, 2018 1 commit
    • Ryan Scott's avatar
      Fix the coverage checker's treatment of existential tyvars · a2d03c69
      Ryan Scott authored
      Previously, the pattern-match coverage checker was far too
      eager to freshen the names of existentially quantified type
      variables, which led to incorrect sets of type constraints that
      misled GHC into thinking that certain programs that involve nested
      GADT pattern matches were non-exhaustive (when in fact they were).
      Now, we generate extra equality constraints in the ConCon case of
      the coverage algorithm to ensure that these fresh tyvars align
      with existing existential tyvars. See
      `Note [Coverage checking and existential tyvars]` for the full story.
      Test Plan: make test TEST="T11984 T14098"
      Reviewers: gkaracha, bgamari, simonpj
      Reviewed By: simonpj
      Subscribers: simonpj, rwbarton, thomie, carter
      GHC Trac Issues: #11984, #14098
      Differential Revision:
  4. 05 Aug, 2017 1 commit
    • Ryan Scott's avatar
      Don't warn when empty casing on Type · a267580e
      Ryan Scott authored
      `Type` (a.k.a. `TYPE LiftedRep`) can be used at the type level thanks
      to `TypeInType`. However, expressions like
      f :: Type -> Int
      f x = case x of {}
      were falsely claiming that the empty case on the value of type `Type` was
      non-exhaustive. The reason is a bit silly: `TYPE` is technically not an empty
      datatype in GHC's eyes, since it's a builtin, primitive type. To convince the
      pattern coverage checker otherwise, this adds a special case for `TYPE`.
      Test Plan: make test TEST=T14086
      Reviewers: gkaracha, austin, bgamari, goldfire
      Reviewed By: goldfire
      Subscribers: goldfire, rwbarton, thomie
      GHC Trac Issues: #14086
      Differential Revision:
  5. 21 Apr, 2017 1 commit
  6. 04 Apr, 2017 1 commit
  7. 08 Feb, 2017 1 commit
    • Simon Peyton Jones's avatar
      Kill inaccessible-branch complaints in record update · 3cfef763
      Simon Peyton Jones authored
      Trac #12957 (the original case in the Description) showed a record
      update that yielded an "inaccessible code" warning. This should not
      happen; it's just some redundant code generated by the desugarer (later
      pruned away) and it's not the user's fault.
      This patch suppresses the warning.  See Check.hs
      Note [Inaccessible warnings for record updates]
  8. 06 Feb, 2017 1 commit
    • Matthew Pickering's avatar
      Don't return empty initial uncovered set for an unsat context · adb565aa
      Matthew Pickering authored
      Previously when the checker encountered an unsatisfiable term of type
      context it would return an empty initial uncovered set. This caused all
      pattern matches in the context to be reported as redudant.
      This is arguably correct behaviour as they will never be reached but it
      is better to recover and provide accurate warnings for these cases to
      avoid error cascades. It would perhaps be better to report an error to
      the user about an inacessible branch but this is certainly better than
      many confusing redundant match warnings.
      Reviewers: gkaracha, austin, bgamari
      Reviewed By: bgamari
      Subscribers: thomie
      Differential Revision:
  9. 02 Feb, 2017 1 commit
    • Georgios Karachalias's avatar
      Exhaustiveness check for EmptyCase (Trac #10746) · b1035321
      Georgios Karachalias authored
      Empty case expressions have strict semantics so the problem boils down
      to inhabitation checking for the type of the scrutinee. 3 main functions
      - pmTopNormaliseType_maybe for the normalisation of the scrutinee type
      - inhabitationCandidates for generating the possible patterns of the
        appropriate type
      - checkEmptyCase' to filter out the candidates that give rise to
        unsatisfiable constraints.
      See Note [Checking EmptyCase Expressions] in Check
      and Note [Type normalisation for EmptyCase] in FamInstEnv
      Test Plan: validate
      Reviewers: simonpj, goldfire, dfeuer, austin, bgamari
      Reviewed By: bgamari
      Subscribers: mpickering, thomie
      Differential Revision:
      GHC Trac Issues: #10746
  10. 26 Jan, 2017 1 commit
    • Matthew Pickering's avatar
      COMPLETE pragmas for enhanced pattern exhaustiveness checking · 1a3f1eeb
      Matthew Pickering authored
      This patch adds a new pragma so that users can specify `COMPLETE` sets of
      `ConLike`s in order to sate the pattern match checker.
      A function which matches on all the patterns in a complete grouping
      will not cause the exhaustiveness checker to emit warnings.
      pattern P :: ()
      pattern P = ()
      {-# COMPLETE P #-}
      foo P = ()
      This example would previously have caused the checker to warn that
      all cases were not matched even though matching on `P` is sufficient to
      make `foo` covering. With the addition of the pragma, the compiler
      will recognise that matching on `P` alone is enough and not emit
      any warnings.
      Reviewers: goldfire, gkaracha, alanz, austin, bgamari
      Reviewed By: alanz
      Subscribers: lelf, nomeata, gkaracha, thomie
      Differential Revision:
      GHC Trac Issues: #8779
  11. 17 Feb, 2016 1 commit
  12. 16 Feb, 2016 1 commit
  13. 04 Feb, 2016 1 commit
    • Georgios Karachalias's avatar
      Overhaul the Overhauled Pattern Match Checker · 28f951ed
      Georgios Karachalias authored
      Overhaul the Overhauled Pattern Match Checker
      * Changed the representation of Value Set Abstractions. Instead of
      using a prefix tree, we now use a list of Value Vector Abstractions.
      The set of constraints Delta for every Value Vector Abstraction is the
      oracle state so that we solve everything only once.
      * Instead of doing everything lazily, we prune at once (and in general
      everything is much stricter). Hence, an example written with pattern
      guards is checked in almost the same time as the equivalent with
      pattern matching.
      * Do not store the covered and the divergent sets at all. Since what we
      only need is a yes/no (does this clause cover anything? Does it force
      any thunk?) We just keep a boolean for each.
      * Removed flags `-Wtoo-many-guards` and `-ffull-guard-reasoning`.
      Replaced with `fmax-pmcheck-iterations=n`. Still debatable what should
      the default `n` be.
      * When a guard is for sure not going to contribute anything, we treat
      it as such: The oracle is not called and cases `CGuard`, `UGuard` and
      `DGuard` from the paper are not happening at all (the generation of a
      fresh variable, the unfolding of the pattern list etc.). his combined
      with the above seems to be enough to drop the memory increase for test
      T783 down to 18.7%.
      * Do not export function `dsPmWarn` (it is now called directly from
      within `checkSingle` and `checkMatches`).
      * Make `PmExprVar` hold a `Name` instead of an `Id`. The term oracle
      does not handle type information so using `Id` was a waste of
      * Added testcases T11195, T11303b (data families) and T11374
      The patch addresses at least the following:
      Trac #11195, #11276, #11303, #11374, #11162
      Test Plan: validate
      Reviewers: goldfire, bgamari, hvr, austin
      Subscribers: simonpj, thomie
      Differential Revision:
  14. 04 Jan, 2016 1 commit
  15. 31 Dec, 2015 1 commit
  16. 30 Dec, 2015 1 commit
  17. 29 Dec, 2015 1 commit
  18. 04 Dec, 2015 1 commit
  19. 03 Dec, 2015 1 commit
    • Georgios Karachalias's avatar
      Major Overhaul of Pattern Match Checking (Fixes #595) · 8a506104
      Georgios Karachalias authored
      This patch adresses several problems concerned with exhaustiveness and
      redundancy checking of pattern matching. The list of improvements includes:
      * Making the check type-aware (handles GADTs, Type Families, DataKinds, etc.).
        This fixes #4139, #3927, #8970 and other related tickets.
      * Making the check laziness-aware. Cases that are overlapped but affect
        evaluation are issued now with "Patterns have inaccessible right hand side".
        Additionally, "Patterns are overlapped" is now replaced by "Patterns are
      * Improved messages for literals. This addresses tickets #5724, #2204, etc.
      * Improved reasoning concerning cases where simple and overloaded
        patterns are matched (See #322).
      * Substantially improved reasoning for pattern guards. Addresses #3078.
      * OverloadedLists extension does not break exhaustiveness checking anymore
        (addresses #9951). Note that in general this cannot be handled but if we know
        that an argument has type '[a]', we treat it as a list since, the instance of
        'IsList' gives the identity for both 'fromList' and 'toList'. If the type is
        not clear or is not the list type, then the check cannot do much still. I am
        a bit concerned about OverlappingInstances though, since one may override the
        '[a]' instance with e.g. an '[Int]' instance that is not the identity.
      * Improved reasoning for nested pattern matching (partial solution). Now we
        propagate type and (some) term constraints deeper when checking, so we can
        detect more inconsistencies. For example, this is needed for #4139.
      I am still not satisfied with several things but I would like to address at
      least the following before the next release:
          Term constraints are too many and not printed for non-exhaustive matches
      (with the exception of literals). This sometimes results in two identical (in
      appearance) uncovered warnings. Unless we actually show their difference, I
      would like to have a single warning.