Do not install/register internal libraries when unnecessary.

This commit fails its tests, because dynamic executables
linked against internal libraries aren't handled correctly
yet.  I had to do more refactoring to handle this correctly,
so it's in a separate commit.

Some refactoring in this one for identifying public libraries
as opposed to internal ones.
Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Cabal/Distribution/PackageDescription.hs

@@ -43,6 +43,7 @@ module Distribution.PackageDescription (
         ModuleReexport(..),
         emptyLibrary,
         withLib,
+        hasPublicLib,
         hasLibs,
         libModules,
 
@@ -124,7 +125,6 @@ import Distribution.Text
 import Language.Haskell.Extension
 
 import Data.Data                  (Data)
-import Data.Foldable              (traverse_)
 import Data.List                  (nub, intercalate)
 import Data.Maybe                 (fromMaybe, maybeToList)
 import Data.Foldable as Fold      (Foldable(foldMap))
@@ -432,22 +432,21 @@ instance Semigroup Library where
 emptyLibrary :: Library
 emptyLibrary = mempty
 
--- |does this package have any libraries?
+-- | Does this package have a PUBLIC library?
+hasPublicLib :: PackageDescription -> Bool
+hasPublicLib p = any f (libraries p)
+    where f lib = buildable (libBuildInfo lib) &&
+                  libName lib == display (packageName (package p))
+
+-- | Does this package have any libraries?
 hasLibs :: PackageDescription -> Bool
 hasLibs p = any (buildable . libBuildInfo) (libraries p)
 
--- |'Maybe' version of 'hasLibs'
-maybeHasLibs :: PackageDescription -> [Library]
-maybeHasLibs p =
-   libraries p >>= \lib -> if buildable (libBuildInfo lib)
-                           then return lib
-                           else []
-
 -- |If the package description has a library section, call the given
 --  function with the library build info as argument.
 withLib :: PackageDescription -> (Library -> IO ()) -> IO ()
 withLib pkg_descr f =
-   traverse_ f (maybeHasLibs pkg_descr)
+   sequence_ [f lib | lib <- libraries pkg_descr, buildable (libBuildInfo lib)]
 
 -- | Get all the module names from the library (exposed and internal modules)
 -- which need to be compiled.  (This does not include reexports, which

Cabal/Distribution/Simple/GHC.hs

@@ -1121,17 +1121,20 @@ installLib    :: Verbosity
               -> Library
               -> ComponentLocalBuildInfo
               -> IO ()
-installLib verbosity lbi targetDir dynlibTargetDir _builtDir _pkg lib clbi = do
+installLib verbosity lbi targetDir dynlibTargetDir _builtDir pkg lib clbi = do
   -- copy .hi files over:
-  whenVanilla $ copyModuleFiles "hi"
-  whenProf    $ copyModuleFiles "p_hi"
-  whenShared  $ copyModuleFiles "dyn_hi"
+  whenRegistered $ do
+    whenVanilla $ copyModuleFiles "hi"
+    whenProf    $ copyModuleFiles "p_hi"
+    whenShared  $ copyModuleFiles "dyn_hi"
 
   -- copy the built library files over:
-  whenVanilla $ installOrdinary builtDir targetDir       vanillaLibName
-  whenProf    $ installOrdinary builtDir targetDir       profileLibName
-  whenGHCi    $ installOrdinary builtDir targetDir       ghciLibName
-  whenShared  $ installShared   builtDir dynlibTargetDir sharedLibName
+  whenRegistered $ do
+    whenVanilla $ installOrdinary builtDir targetDir       vanillaLibName
+    whenProf    $ installOrdinary builtDir targetDir       profileLibName
+    whenGHCi    $ installOrdinary builtDir targetDir       ghciLibName
+  whenRegisteredOrDynExecutable $ do
+    whenShared  $ installShared   builtDir dynlibTargetDir sharedLibName
 
   where
     builtDir = libBuildDir lbi clbi
@@ -1169,6 +1172,17 @@ installLib verbosity lbi targetDir dynlibTargetDir _builtDir _pkg lib clbi = do
     whenGHCi    = when (hasLib && withGHCiLib    lbi)
     whenShared  = when (hasLib && withSharedLib  lbi)
 
+    -- Some files (e.g. interface files) are completely unnecessary when
+    -- we are not actually going to register the library.  A library is
+    -- not registered if there is no "public library", e.g. in the case
+    -- that we have an internal library and executables, but no public
+    -- library.
+    whenRegistered = when (hasPublicLib pkg)
+
+    -- However, we must always install dynamic libraries when linking
+    -- dynamic executables, because we'll try to load them!
+    whenRegisteredOrDynExecutable = when (hasPublicLib pkg || (hasExes pkg && withDynExe lbi))
+
 -- -----------------------------------------------------------------------------
 -- Registering
 

Cabal/Distribution/Simple/Register.hs

@@ -82,7 +82,13 @@ import qualified Data.ByteString.Lazy.Char8 as BS.Char8
 register :: PackageDescription -> LocalBuildInfo
          -> RegisterFlags -- ^Install in the user's database?; verbose
          -> IO ()
-register pkg lbi regFlags = withLib pkg (registerOne pkg lbi regFlags)
+register pkg lbi regFlags =
+    -- We do NOT register libraries outside of the inplace database
+    -- if there is no public library, since no one else can use it
+    -- usefully (they're not public.)  If we start supporting scoped
+    -- packages, we'll have to relax this.
+    when (hasPublicLib pkg) $
+        withLib pkg (registerOne pkg lbi regFlags)
 
 registerOne :: PackageDescription -> LocalBuildInfo -> RegisterFlags
             -> Library

cabal-install/Distribution/Client/ProjectPlanning.hs

@@ -1105,7 +1105,7 @@ elaborateInstallPlan platform compiler progdb
                                 then BuildInplaceOnly else BuildAndInstall
         pkgBuildPackageDBStack    = buildAndRegisterDbs
         pkgRegisterPackageDBStack = buildAndRegisterDbs
-        pkgRequiresRegistration   = isJust (Cabal.condLibrary gdesc)
+        pkgRequiresRegistration   = PD.hasPublicLib (PD.packageDescription gdesc)
 
         pkgSetupScriptStyle       = packageSetupScriptStylePostSolver
                                       pkgsImplicitSetupDeps pkg pkgDescription