Have ghc-pkg use an old-style package key when it's not provided.

Summary:
When this occurs, it means that the user is using an old version of Cabal.
In that case, don't barf out: just go ahead and install it as an old-style
package key.  The user won't be able to link multiple versions together,
but that should not be a problem because their Cabal can't handle it anyway.

What happens if old-style are mixed up with new-style?  Well, currently
with Cabal, it's indistinguishable.  However, if at some later point we
add private dependencies, libraries compiled with old style linker names
are incompatible with each other.  We'll cross that road when we come
to it.

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

Test Plan: validate

Reviewers: tibbe, hvr, austin

Subscribers: simonmar, relrod, ezyang, carter

Differential Revision: https://phabricator.haskell.org/D154

1 files changed, 9 insertions, 1 deletions

diff --git a/utils/ghc-pkg/Main.hs b/utils/ghc-pkg/Main.hs
index 970ab67083..c88b814a71 100644
--- a/utils/ghc-pkg/Main.hs
+++ b/utils/ghc-pkg/Main.hs
@@ -916,7 +916,7 @@ parsePackageInfo
         -> IO (InstalledPackageInfo, [ValidateWarning])
 parsePackageInfo str =
   case parseInstalledPackageInfo str of
-    ParseOk warnings ok -> return (ok, ws)
+    ParseOk warnings ok -> return (mungePackageInfo ok, ws)
       where
         ws = [ msg | PWarning msg <- warnings
                    , not ("Unrecognized field pkgroot" `isPrefixOf` msg) ]
@@ -924,6 +924,14 @@ parsePackageInfo str =
                            (Nothing, s) -> die s
                            (Just l, s) -> die (show l ++ ": " ++ s)
 
+mungePackageInfo :: InstalledPackageInfo -> InstalledPackageInfo
+mungePackageInfo ipi = ipi { packageKey = packageKey' }
+  where
+    packageKey'
+      | OldPackageKey (PackageIdentifier (PackageName "") _) <- packageKey ipi
+          = OldPackageKey (sourcePackageId ipi)
+      | otherwise = packageKey ipi
+
 -- | Takes the "reexported-modules" field of an InstalledPackageInfo
 -- and resolves the references so they point to the original exporter
 -- of a module (i.e. the module is in exposed-modules, not