Fix regression introduced by r279164: only pass definitions as the PatternDef
to DiagnoseUninstantiableTemplate, teach hasVisibleDefinition to correctly
determine whether a function definition is visible, and mark both the function
and the template as visible when merging function template definitions to
provide hasVisibleDefinition with the relevant information.

The change to always pass the right declaration as the PatternDef to
DiagnoseUninstantiableTemplate also caused those checks to happen before other
diagnostics in InstantiateFunctionDefinition, giving worse diagnostics for the
same situations, so I sunk the relevant diagnostics into
DiagnoseUninstantiableTemplate. Those parts of this patch are based on changes
in reviews.llvm.org/D23492 by Vassil Vassilev.


This reinstates r279486, reverted in r279500, with a fix to
DiagnoseUninstantiableTemplate to only mark uninstantiable explicit
instantiation declarations as invalid if we actually diagnosed them. (When we
trigger an explicit instantiation of a class member from an explicit
instantiation declaration for the class, it's OK if there is no corresponding
definition and we certainly don't want to mark the member invalid in that
case.) This previously caused a build failure during bootstrap.

llvm-svn: 279557
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 3f4a0f6..75d7f70 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -3554,23 +3554,38 @@
   const FunctionDecl *PatternDecl = Function->getTemplateInstantiationPattern();
   assert(PatternDecl && "instantiating a non-template");
 
-  Stmt *Pattern = PatternDecl->getBody(PatternDecl);
-  assert(PatternDecl && "template definition is not a template");
-  if (!Pattern) {
-    // Try to find a defaulted definition
-    PatternDecl->isDefined(PatternDecl);
-  }
-  assert(PatternDecl && "template definition is not a template");
+  const FunctionDecl *PatternDef = PatternDecl->getDefinition();
+  Stmt *Pattern = PatternDef->getBody(PatternDef);
+  if (PatternDef)
+    PatternDecl = PatternDef;
 
   // FIXME: We need to track the instantiation stack in order to know which
   // definitions should be visible within this instantiation.
   if (DiagnoseUninstantiableTemplate(PointOfInstantiation, Function,
                                 Function->getInstantiatedFromMemberFunction(),
-                                     PatternDecl, PatternDecl, TSK,
-                                     /*Complain*/DefinitionRequired))
-     return;
+                                     PatternDecl, PatternDef, TSK,
+                                     /*Complain*/DefinitionRequired)) {
+    if (DefinitionRequired)
+      Function->setInvalidDecl();
+    else if (TSK == TSK_ExplicitInstantiationDefinition) {
+      // Try again at the end of the translation unit (at which point a
+      // definition will be required).
+      assert(!Recursive);
+      PendingInstantiations.push_back(
+        std::make_pair(Function, PointOfInstantiation));
+    } else if (TSK == TSK_ImplicitInstantiation) {
+      if (AtEndOfTU && !getDiagnostics().hasErrorOccurred()) {
+        Diag(PointOfInstantiation, diag::warn_func_template_missing)
+          << Function;
+        Diag(PatternDecl->getLocation(), diag::note_forward_template_decl);
+        if (getLangOpts().CPlusPlus11)
+          Diag(PointOfInstantiation, diag::note_inst_declaration_hint)
+            << Function;
+      }
+    }
 
-
+    return;
+  }
 
   // Postpone late parsed template instantiations.
   if (PatternDecl->isLateTemplateParsed() &&
@@ -3604,40 +3619,9 @@
     Pattern = PatternDecl->getBody(PatternDecl);
   }
 
-  // FIXME: Check if we could sink these diagnostics in
-  // DiagnoseUninstantiableTemplate.
-  if (!Pattern && !PatternDecl->isDefaulted()) {
-    if (DefinitionRequired) {
-      if (Function->getPrimaryTemplate())
-        Diag(PointOfInstantiation,
-             diag::err_explicit_instantiation_undefined_func_template)
-          << Function->getPrimaryTemplate();
-      else
-        Diag(PointOfInstantiation,
-             diag::err_explicit_instantiation_undefined_member)
-          << 1 << Function->getDeclName() << Function->getDeclContext();
-
-      if (PatternDecl)
-        Diag(PatternDecl->getLocation(),
-             diag::note_explicit_instantiation_here);
-      Function->setInvalidDecl();
-    } else if (TSK == TSK_ExplicitInstantiationDefinition) {
-      assert(!Recursive);
-      PendingInstantiations.push_back(
-        std::make_pair(Function, PointOfInstantiation));
-    } else if (TSK == TSK_ImplicitInstantiation) {
-      if (AtEndOfTU && !getDiagnostics().hasErrorOccurred()) {
-        Diag(PointOfInstantiation, diag::warn_func_template_missing)
-          << Function;
-        Diag(PatternDecl->getLocation(), diag::note_forward_template_decl);
-        if (getLangOpts().CPlusPlus11)
-          Diag(PointOfInstantiation, diag::note_inst_declaration_hint)
-            << Function;
-      }
-    }
-
-    return;
-  }
+  // Note, we should never try to instantiate a deleted function template.
+  assert((Pattern || PatternDecl->isDefaulted()) &&
+         "unexpected kind of function template definition");
 
   // C++1y [temp.explicit]p10:
   //   Except for inline functions, declarations with types deduced from their