Split -Wunused-variable warning.

With r190382, -Wunused-variable warns about unused const variables when
appropriate. For codebases that use -Werror, this poses a problem as
existing unused const variables need to be cleaned up first. To make the
transistion easier, this patch splits -Wunused-variable by pulling out
an additional -Wunused-const-variable (by default activated along with
-Wunused-variable).

llvm-svn: 190508

clang/include/clang/Basic/DiagnosticGroups.td

@@ -336,7 +336,9 @@ def UnusedLabel : DiagGroup<"unused-label">;
 def UnusedParameter : DiagGroup<"unused-parameter">;
 def UnusedResult : DiagGroup<"unused-result">;
 def UnusedValue : DiagGroup<"unused-value", [UnusedComparison, UnusedResult]>;
-def UnusedVariable : DiagGroup<"unused-variable">;
+def UnusedConstVariable : DiagGroup<"unused-const-variable">;
+def UnusedVariable : DiagGroup<"unused-variable",
+                               [UnusedConstVariable]>;
 def UsedButMarkedUnused : DiagGroup<"used-but-marked-unused">;
 def UserDefinedLiterals : DiagGroup<"user-defined-literals">;
 def ReadOnlySetterAttrs : DiagGroup<"readonly-setter-attrs">;

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -155,6 +155,8 @@ def warn_unused_parameter : Warning<"unused parameter %0">,
   InGroup<UnusedParameter>, DefaultIgnore;
 def warn_unused_variable : Warning<"unused variable %0">,
   InGroup<UnusedVariable>, DefaultIgnore;
+def warn_unused_const_variable : Warning<"unused variable %0">,
+  InGroup<UnusedConstVariable>, DefaultIgnore;
 def warn_unused_exception_param : Warning<"unused exception parameter %0">,
   InGroup<UnusedExceptionParameter>, DefaultIgnore;
 def warn_decl_in_param_list : Warning<

clang/lib/Sema/Sema.cpp

@@ -758,6 +758,9 @@ void Sema::ActOnEndOfTranslationUnit() {
         if (DiagD->isReferenced()) {
           Diag(DiagD->getLocation(), diag::warn_unneeded_internal_decl)
                 << /*variable*/1 << DiagD->getDeclName();
+        } else if (DiagD->getType().isConstQualified()) {
+          Diag(DiagD->getLocation(), diag::warn_unused_const_variable)
+              << DiagD->getDeclName();
         } else {
           Diag(DiagD->getLocation(), diag::warn_unused_variable)
               << DiagD->getDeclName();

clang/test/SemaCXX/no-warn-unused-const-variables.cpp

@@ -0,0 +1,6 @@
+// RUN: %clang_cc1 -fsyntax-only -Wunused-variable -Wno-unused-const-variable -verify %s
+
+namespace {
+  int i = 0; // expected-warning {{unused variable 'i'}}
+  const int j = 0;;
+}