Don't look into incomplete types when trying to warn about unused

variables. Fixes PR6948.

llvm-svn: 102436

clang/lib/Sema/SemaDecl.cpp

@@ -543,6 +543,11 @@ static bool ShouldDiagnoseUnusedDecl(const NamedDecl *D) {
         return false;
     }
 
+    // If we failed to complete the type for some reason, don't
+    // diagnose the variable.
+    if (Ty->isIncompleteType())
+      return false;
+
     if (const TagType *TT = Ty->getAs<TagType>()) {
       const TagDecl *Tag = TT->getDecl();
       if (Tag->hasAttr<UnusedAttr>())

clang/test/SemaCXX/warn-unused-variables.cpp

@@ -51,3 +51,11 @@ void test_dependent_init(T *p) {
   X0<int> i(p);
   (void)i;
 }
+
+namespace PR6948 {
+  template<typename T> class X;
+  
+  void f() {
+    X<char> str (read_from_file()); // expected-error{{use of undeclared identifier 'read_from_file'}}
+  }
+}