Modules: Search for a visible definition of the decl context when computing visibility of a default template parameter

The code is/was already correct for the case where a parameter is a
parameter of its enclosing lexical DeclContext (functions and classes).
But for other templates (alias and variable templates) they don't create
their own scope to be members of - in those cases, they parameter should
be considered visible if any definition of the lexical decl context is
visible.

[this should cleanup the failure on the libstdc++ modules buildbot]
[this doesn't actually fix the variable template case for a
secondary/compounding reason (its lexical decl context is incorrectly
considered to be the translation unit)]

Test covers all 4 kinds of templates with default args, including a
regression test for the still broken variable template case.

Reviewers: rsmith

Differential Revision: https://reviews.llvm.org/D60892

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@358795 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 15 insertions, 2 deletions

diff --git a/lib/Sema/SemaLookup.cpp b/lib/Sema/SemaLookup.cpp
index 874e561130..c26fbac406 100644
--- a/lib/Sema/SemaLookup.cpp
+++ b/lib/Sema/SemaLookup.cpp
@@ -1543,8 +1543,21 @@ bool LookupResult::isVisibleSlow(Sema &SemaRef, NamedDecl *D) {
     // and in C we must not because each declaration of a function gets its own
     // set of declarations for tags in prototype scope.
     bool VisibleWithinParent;
-    if (D->isTemplateParameter() || isa<ParmVarDecl>(D) ||
-        (isa<FunctionDecl>(DC) && !SemaRef.getLangOpts().CPlusPlus))
+    if (D->isTemplateParameter()) {
+      bool SearchDefinitions = true;
+      if (const auto *DCD = dyn_cast<Decl>(DC)) {
+        if (const auto *TD = DCD->getDescribedTemplate()) {
+          TemplateParameterList *TPL = TD->getTemplateParameters();
+          auto Index = getDepthAndIndex(D).second;
+          SearchDefinitions = Index >= TPL->size() || TPL->getParam(Index) != D;
+        }
+      }
+      if (SearchDefinitions)
+        VisibleWithinParent = SemaRef.hasVisibleDefinition(cast<NamedDecl>(DC));
+      else
+        VisibleWithinParent = isVisible(SemaRef, cast<NamedDecl>(DC));
+    } else if (isa<ParmVarDecl>(D) ||
+               (isa<FunctionDecl>(DC) && !SemaRef.getLangOpts().CPlusPlus))
       VisibleWithinParent = isVisible(SemaRef, cast<NamedDecl>(DC));
     else if (D->isModulePrivate()) {
       // A module-private declaration is only visible if an enclosing lexical