Add libname install-dirs variable, use it by default. Fixes #2437.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Cabal/Distribution/Simple/InstallDirs.hs

@@ -57,7 +57,7 @@ import System.FilePath ((</>), isPathSeparator, pathSeparator)
 import System.FilePath (dropDrive)
 
 import Distribution.Package
-         ( PackageIdentifier, PackageKey, packageName, packageVersion )
+         ( PackageIdentifier, PackageKey, packageName, packageVersion, packageKeyLibraryName )
 import Distribution.System
          ( OS(..), buildOS, Platform(..) )
 import Distribution.Compiler
@@ -183,7 +183,7 @@ appendSubdirs append dirs = dirs {
 -- users to be able to configure @--libdir=\/usr\/lib64@ for example but
 -- because by default we want to support installing multiple versions of
 -- packages and building the same package for multiple compilers we append the
--- libsubdir to get: @\/usr\/lib64\/$pkgkey\/$compiler@.
+-- libsubdir to get: @\/usr\/lib64\/$libname\/$compiler@.
 --
 -- An additional complication is the need to support relocatable packages on
 -- systems which support such things, like Windows.
@@ -216,10 +216,10 @@ defaultInstallDirs comp userInstall _hasLibs = do
            JHC    -> "$compiler"
            LHC    -> "$compiler"
            UHC    -> "$pkgid"
-           _other -> "$abi" </> "$pkgkey",
+           _other -> "$abi" </> "$libname",
       dynlibdir    = "$libdir",
       libexecdir   = case buildOS of
-        Windows   -> "$prefix" </> "$pkgkey"
+        Windows   -> "$prefix" </> "$libname"
         _other    -> "$prefix" </> "libexec",
       includedir   = "$libdir" </> "$libsubdir" </> "include",
       datadir      = case buildOS of
@@ -373,6 +373,7 @@ data PathTemplateVariable =
      | PkgVerVar     -- ^ The @$version@ package version path variable
      | PkgIdVar      -- ^ The @$pkgid@ package Id path variable, eg @foo-1.0@
      | PkgKeyVar     -- ^ The @$pkgkey@ package key path variable
+     | LibNameVar    -- ^ The @$libname@ expanded package key path variable
      | CompilerVar   -- ^ The compiler name and version, eg @ghc-6.6.1@
      | OSVar         -- ^ The operating system name, eg @windows@ or @linux@
      | ArchVar       -- ^ The CPU architecture name, eg @i386@ or @x86_64@
@@ -430,6 +431,7 @@ packageTemplateEnv pkgId pkg_key =
   [(PkgNameVar,  PathTemplate [Ordinary $ display (packageName pkgId)])
   ,(PkgVerVar,   PathTemplate [Ordinary $ display (packageVersion pkgId)])
   ,(PkgKeyVar,   PathTemplate [Ordinary $ display pkg_key])
+  ,(LibNameVar,  PathTemplate [Ordinary $ packageKeyLibraryName pkgId pkg_key])
   ,(PkgIdVar,    PathTemplate [Ordinary $ display pkgId])
   ]
 
@@ -479,6 +481,7 @@ installDirsTemplateEnv dirs =
 instance Show PathTemplateVariable where
   show PrefixVar     = "prefix"
   show PkgKeyVar     = "pkgkey"
+  show LibNameVar     = "libname"
   show BindirVar     = "bindir"
   show LibdirVar     = "libdir"
   show LibsubdirVar  = "libsubdir"
@@ -516,6 +519,7 @@ instance Read PathTemplateVariable where
                  ,("htmldir",    HtmldirVar)
                  ,("pkgid",      PkgIdVar)
                  ,("pkgkey",     PkgKeyVar)
+                 ,("libname",    LibNameVar)
                  ,("pkg",        PkgNameVar)
                  ,("version",    PkgVerVar)
                  ,("compiler",   CompilerVar)