If I add a "return 0" after the comment but before the call to Visit here

// All of the Visit implementations for the various potential friend
// declarations have to be carefully written to work for friend
// objects, with the most important detail being that the target
// decl should almost certainly not be placed in Owner.
Decl *NewND = Visit(ND);

in TemplateDeclInstantiator::VisitFriendDecl(), the problem goes away. +rjmccall who added the comment – maybe it's obvious to him what needs to be done here.

Further down the stack, removing this block

if (isFriend) {
if (Qualifier) {
CXXScopeSpec SS;
SS.setScopeRep(Qualifier);
SS.setRange(D->getQualifierRange());
DC = SemaRef.computeDeclContext(SS);

  if (DC && SemaRef.RequireCompleteDeclContext(SS, DC))
    return 0;
} else {
  DC = SemaRef.FindInstantiatedContext(D->getLocation(),
                                       D->getDeclContext(),
                                       TemplateArgs);
}
if (!DC) return 0;

}

from TemplateDeclInstantiator::VisitCXXMethodDecl() helps.

Proposed patch (will add a test case):

Index: lib/Sema/SemaTemplateInstantiateDecl.cpp

--- lib/Sema/SemaTemplateInstantiateDecl.cpp (revision 121783)
+++ lib/Sema/SemaTemplateInstantiateDecl.cpp (working copy)
@@ -1437,7 +1436,7 @@
? cast(FunctionTemplate)
: Method);
if (isFriend)

•  Record->makeDeclVisibleInContext(DeclToAdd);
  

•  Owner->makeDeclVisibleInContext(DeclToAdd);
  
  else
  Owner->addDecl(DeclToAdd);
  }

Probably better proposed patch:

@@ -1436,9 +1435,7 @@
NamedDecl *DeclToAdd = (TemplateParams
? cast(FunctionTemplate)
: Method);

• if (isFriend)

•  Record->makeDeclVisibleInContext(DeclToAdd);
  
• else

• if (!isFriend)
  Owner->addDecl(DeclToAdd);
  }

Patch attempt at http://lists.cs.uiuc.edu/pipermail/cfe-dev/2010-December/012590.html

I fixed this in a totally different way in r121833.

Our builders are happy again – thanks!