Reland "Warn about unused static file scope function template declarations."

This patch reinstates r299930, reverted in r299956, as a separate diagnostic
option (-Wunused-template). 

llvm-svn: 302518

2 files changed, 31 insertions, 10 deletions

diff --git a/clang/lib/Sema/Sema.cpp b/clang/lib/Sema/Sema.cpp
index 2f493fa5fbe..ca1d27e9505 100644
--- a/clang/lib/Sema/Sema.cpp
+++ b/clang/lib/Sema/Sema.cpp
@@ -477,6 +477,13 @@ static bool ShouldRemoveFromUnused(Sema *SemaRef, const DeclaratorDecl *D) {
     return true;
 
   if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
+    // If this is a function template and none of its specializations is used,
+    // we should warn.
+    if (FunctionTemplateDecl *Template = FD->getDescribedFunctionTemplate())
+      for (const auto *Spec : Template->specializations())
+        if (ShouldRemoveFromUnused(SemaRef, Spec))
+          return true;
+
     // UnusedFileScopedDecls stores the first declaration.
     // The declaration may have become definition so check again.
     const FunctionDecl *DeclToCheck;
@@ -500,6 +507,13 @@ static bool ShouldRemoveFromUnused(Sema *SemaRef, const DeclaratorDecl *D) {
         VD->isUsableInConstantExpressions(SemaRef->Context))
       return true;
 
+    if (VarTemplateDecl *Template = VD->getDescribedVarTemplate())
+      // If this is a variable template and none of its specializations is used,
+      // we should warn.
+      for (const auto *Spec : Template->specializations())
+        if (ShouldRemoveFromUnused(SemaRef, Spec))
+          return true;
+
     // UnusedFileScopedDecls stores the first declaration.
     // The declaration may have become definition so check again.
     const VarDecl *DeclToCheck = VD->getDefinition();
@@ -905,10 +919,14 @@ void Sema::ActOnEndOfTranslationUnit() {
                    << /*function*/0 << DiagD->getDeclName();
           }
         } else {
-          Diag(DiagD->getLocation(),
-               isa<CXXMethodDecl>(DiagD) ? diag::warn_unused_member_function
-                                         : diag::warn_unused_function)
-                << DiagD->getDeclName();
+          if (FD->getDescribedFunctionTemplate())
+            Diag(DiagD->getLocation(), diag::warn_unused_template)
+              << /*function*/0 << DiagD->getDeclName();
+          else
+            Diag(DiagD->getLocation(),
+                 isa<CXXMethodDecl>(DiagD) ? diag::warn_unused_member_function
+                                           : diag::warn_unused_function)
+              << DiagD->getDeclName();
         }
       } else {
         const VarDecl *DiagD = cast<VarDecl>(*I)->getDefinition();
@@ -924,7 +942,11 @@ void Sema::ActOnEndOfTranslationUnit() {
             Diag(DiagD->getLocation(), diag::warn_unused_const_variable)
                 << DiagD->getDeclName();
         } else {
-          Diag(DiagD->getLocation(), diag::warn_unused_variable)
+          if (DiagD->getDescribedVarTemplate())
+            Diag(DiagD->getLocation(), diag::warn_unused_template)
+              << /*variable*/1 << DiagD->getDeclName();
+          else
+            Diag(DiagD->getLocation(), diag::warn_unused_variable)
               << DiagD->getDeclName();
         }
       }
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 2612023f59d..2d15c75f48f 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -8923,6 +8923,7 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
     if (FunctionTemplate) {
       if (NewFD->isInvalidDecl())
         FunctionTemplate->setInvalidDecl();
+      MarkUnusedFileScopedDecl(NewFD);
       return FunctionTemplate;
     }
   }
@@ -11023,8 +11024,7 @@ static bool hasDependentAlignment(VarDecl *VD) {
 
 /// FinalizeDeclaration - called by ParseDeclarationAfterDeclarator to perform
 /// any semantic actions necessary after any initializer has been attached.
-void
-Sema::FinalizeDeclaration(Decl *ThisDecl) {
+void Sema::FinalizeDeclaration(Decl *ThisDecl) {
   // Note that we are no longer parsing the initializer for this declaration.
   ParsingInitForAutoVars.erase(ThisDecl);
 
@@ -11189,9 +11189,8 @@ Sema::FinalizeDeclaration(Decl *ThisDecl) {
   if (DC->getRedeclContext()->isFileContext() && VD->isExternallyVisible())
     AddPushedVisibilityAttribute(VD);
 
-  // FIXME: Warn on unused templates.
-  if (VD->isFileVarDecl() && !VD->getDescribedVarTemplate() &&
-      !isa<VarTemplatePartialSpecializationDecl>(VD))
+  // FIXME: Warn on unused var template partial specializations.
+  if (VD->isFileVarDecl() && !isa<VarTemplatePartialSpecializationDecl>(VD))
     MarkUnusedFileScopedDecl(VD);
 
   // Now we have parsed the initializer and can update the table of magic