clang-cl: Don't warn for unused private fields when encountering a late parsed template member

[• ehsan]

Summary

This fixes PR21235.

[hans]

lib/Sema/Sema.cpp

548 ↗

(On Diff #14698)

Is the issue that the template has been defined, but we haven't parsed and semantically analysed it because it's late-parsed?

This gets called from ActOnEndOfTranslationUnit, so shouldn't the delayed template parsing already have taken place?

[• ehsan]

lib/Sema/Sema.cpp

548 ↗

(On Diff #14698)

Yes the template is not defined by we haven't done semantic analysis (and parsing!) on it yet. It looks like by ActOnEndOfTranslationUnit the semantic analysis still wouldn't happen unless if we see a call to that function (or presumably other things such as its address being taken etc.) IOW if the test case includes an instantiation of the template member, the warning doesn't appear.

[hans]

lib/Sema/Sema.cpp

548 ↗

(On Diff #14698)

Oh that makes sense. If we don't instantiate it, we don't parse it.

This patch seems correct to me, but please add a comment about this check.

[• ehsan]

Closed by commit rL219551 (authored by @ehsan).

cfe/trunk/lib/Sema/Sema.cpp

if (!RD->isCompleteDefinition())
     return false;
   bool Complete = true;
   for (DeclContext::decl_iterator I = RD->decls_begin(),
                                   E = RD->decls_end();
        I != E && Complete; ++I) {
     if (const CXXMethodDecl *M = dyn_cast<CXXMethodDecl>(*I))
       Complete = M->isDefined() || (M->isPure() && !isa<CXXDestructorDecl>(M));
     else if (const FunctionTemplateDecl *F = dyn_cast<FunctionTemplateDecl>(*I))
-      Complete = F->getTemplatedDecl()->isDefined();
+      // If the template function is marked as late template parsed at this point,
+      // it has not been instantiated and therefore we have not performed semantic
+      // analysis on it yet, so we cannot know if the type can be considered
+      // complete.
+      Complete = !F->getTemplatedDecl()->isLateTemplateParsed() &&
+                  F->getTemplatedDecl()->isDefined();
     else if (const CXXRecordDecl *R = dyn_cast<CXXRecordDecl>(*I)) {
       if (R->isInjectedClassName())
         continue;
       if (R->hasDefinition())
         Complete = MethodsAndNestedClassesComplete(R->getDefinition(),
                                                    MNCComplete);
       else
         Complete = false;

cfe/trunk/test/SemaCXX/warn-unused-private-field-delayed-template.cpp

+// RUN: %clang_cc1 -fsyntax-only -fdelayed-template-parsing -Wunused-private-field -Wused-but-marked-unused -Wno-uninitialized -verify -std=c++11 %s
+// expected-no-diagnostics
+
+class EverythingMayBeUsed {
+  int x;
+public:
+  template <class T>
+  void f() {
+    x = 0;
+  }
+};