From: simonpj@microsoft.com <unknown>
Date: Thu, 20 Dec 2007 16:43:07 +0000 (+0000)
Subject: Fix nasty recompilation bug in MkIface.computeChangedOccs
X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=commitdiff_plain;h=c4ea1371c0683bbd6e6c78d73435de369bb6c468

Fix nasty recompilation bug in MkIface.computeChangedOccs

	MERGE to 6.8 branch

In computeChangedOccs we look up the old version of a Name.
But a WiredIn Name doesn't have an old version, because WiredIn things
don't appear in interface files at all.

Result: ghc-6.9: panic! (the 'impossible' happened)
  (GHC version 6.9 for x86_64-unknown-linux):
	lookupVers1 base:GHC.Prim chr#{v}

This fixes the problem.  The patch should merge easily onto the branch.
---

diff --git a/compiler/iface/MkIface.lhs b/compiler/iface/MkIface.lhs
index f972a91..1521069 100644
--- a/compiler/iface/MkIface.lhs
+++ b/compiler/iface/MkIface.lhs
@@ -708,6 +708,8 @@ computeChangedOccs ver_fn this_module old_usages eq_info
     -- return True if an external name has changed
     name_changed :: Name -> Bool
     name_changed nm
+	| isWiredInName nm	-- Wired-in things don't get into interface
+	= False			-- files and hence don't get into the ver_fn
         | Just ents <- lookupUFM usg_modmap (moduleName mod),
           Just v    <- lookupUFM ents parent_occ
         = v < new_version