From fdf6c02f72fbcbad9982bf78473916c40dcaa5ec Mon Sep 17 00:00:00 2001
From: "simonpj@microsoft.com" <unknown>
Date: Wed, 10 Jan 2007 12:43:27 +0000
Subject: [PATCH] Sort rules and instances lexicographically in interface
 files

We should sort rules and instances lexicographically, not by Unique,
in interface files, else we get unnecessary "rules changed" and hence
unnecessary recompilation.

This bug has been there since the interface-file upheaval that put Names
into IfaceSyn.
---
 compiler/basicTypes/OccName.lhs |    5 +++--
 compiler/iface/MkIface.lhs      |   18 +++++++++++++-----
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/compiler/basicTypes/OccName.lhs b/compiler/basicTypes/OccName.lhs
index 48aa6db..0810d73 100644
--- a/compiler/basicTypes/OccName.lhs
+++ b/compiler/basicTypes/OccName.lhs
@@ -176,8 +176,9 @@ instance Eq OccName where
     (OccName sp1 s1) == (OccName sp2 s2) = s1 == s2 && sp1 == sp2
 
 instance Ord OccName where
-    compare (OccName sp1 s1) (OccName sp2 s2) = (s1  `compare` s2) `thenCmp`
-						(sp1 `compare` sp2)
+	-- Compares lexicographically, *not* by Unique of the string
+    compare (OccName sp1 s1) (OccName sp2 s2) 
+	= (s1  `compare` s2) `thenCmp` (sp1 `compare` sp2)
 \end{code}
 
 
diff --git a/compiler/iface/MkIface.lhs b/compiler/iface/MkIface.lhs
index 7518111..0fc3972 100644
--- a/compiler/iface/MkIface.lhs
+++ b/compiler/iface/MkIface.lhs
@@ -188,7 +188,6 @@ import TyCon
 import DataCon
 import Type
 import TcType
-import TysPrim
 import InstEnv
 import FamInstEnv
 import TcRnMonad
@@ -276,9 +275,13 @@ mkIface hsc_env maybe_old_iface
 			mi_deps     = deps,
 			mi_usages   = usages,
 			mi_exports  = mkIfaceExports exports,
+	
+			-- Sort these lexicographically, so that
+			-- the result is stable across compilations
 			mi_insts    = sortLe le_inst iface_insts,
 			mi_fam_insts= sortLe le_fam_inst iface_fam_insts,
 			mi_rules    = sortLe le_rule iface_rules,
+
 			mi_fixities = fixities,
 			mi_deprecs  = deprecs,
 			mi_globals  = Just rdr_env,
@@ -314,13 +317,18 @@ mkIface hsc_env maybe_old_iface
 
 	; return (new_iface, no_change_at_all) }
   where
-     r1 `le_rule`     r2      = ifRuleName        r1 <= ifRuleName        r2
-     i1 `le_inst`     i2      = ifDFun            i1 <= ifDFun            i2
-     i1 `le_fam_inst` i2      = ifFamInstTyConOcc i1 <= ifFamInstTyConOcc i2
+     r1 `le_rule`     r2 = ifRuleName      r1    <=    ifRuleName      r2
+     i1 `le_inst`     i2 = ifDFun          i1 `le_occ` ifDFun          i2  
+     i1 `le_fam_inst` i2 = ifFamInstTcName i1 `le_occ` ifFamInstTcName i2
+
+     le_occ :: Name -> Name -> Bool
+	-- Compare lexicographically by OccName, *not* by unique, because 
+	-- the latter is not stable across compilations
+     le_occ n1 n2 = nameOccName n1 <= nameOccName n2
 
      dflags = hsc_dflags hsc_env
      deliberatelyOmitted x = panic ("Deliberately omitted: " ++ x)
-     ifFamInstTyConOcc = nameOccName . ifaceTyConName . ifFamInstTyCon
+     ifFamInstTcName = ifaceTyConName . ifFamInstTyCon
 
 					      
 -----------------------------
-- 
1.7.10.4