PR8455: Handle an attribute between a goto label and a variable declaration per

the GNU documentation: the attribute only appertains to the label if it is
followed by a semicolon. Based on a patch by Aaron Ballman!

llvm-svn: 194869

clang/lib/Parse/ParseStmt.cpp

@@ -516,11 +516,40 @@ StmtResult Parser::ParseLabeledStatement(ParsedAttributesWithRange &attrs) {
   // identifier ':' statement
   SourceLocation ColonLoc = ConsumeToken();
 
-  // Read label attributes, if present. attrs will contain both C++11 and GNU
-  // attributes (if present) after this point.
-  MaybeParseGNUAttributes(attrs);
+  // Read label attributes, if present.
+  StmtResult SubStmt;
+  if (Tok.is(tok::kw___attribute)) {
+    ParsedAttributesWithRange TempAttrs(AttrFactory);
+    ParseGNUAttributes(TempAttrs);
 
-  StmtResult SubStmt(ParseStatement());
+    // In C++, GNU attributes only apply to the label if they are followed by a
+    // semicolon, to disambiguate label attributes from attributes on a labeled
+    // declaration.
+    //
+    // This doesn't quite match what GCC does; if the attribute list is empty
+    // and followed by a semicolon, GCC will reject (it appears to parse the
+    // attributes as part of a statement in that case). That looks like a bug.
+    if (!getLangOpts().CPlusPlus || Tok.is(tok::semi))
+      attrs.takeAllFrom(TempAttrs);
+    else if (isDeclarationStatement()) {
+      StmtVector Stmts;
+      // FIXME: We should do this whether or not we have a declaration
+      // statement, but that doesn't work correctly (because ProhibitAttributes
+      // can't handle GNU attributes), so only call it in the one case where
+      // GNU attributes are allowed.
+      SubStmt = ParseStatementOrDeclarationAfterAttributes(
+          Stmts, /*OnlyStmts*/ true, 0, TempAttrs);
+      if (!TempAttrs.empty() && !SubStmt.isInvalid())
+        SubStmt = Actions.ProcessStmtAttributes(
+            SubStmt.get(), TempAttrs.getList(), TempAttrs.Range);
+    } else {
+      Diag(Tok, diag::err_expected_semi_after) << "__attribute__";
+    }
+  }
+
+  // If we've not parsed a statement yet, parse one now.
+  if (!SubStmt.isInvalid() && !SubStmt.isUsable())
+    SubStmt = ParseStatement();
 
   // Broken substmt shouldn't prevent the label from being added to the AST.
   if (SubStmt.isInvalid())
@@ -557,7 +586,7 @@ StmtResult Parser::ParseCaseStatement(bool MissingCase, ExprResult Expr) {
   // out of stack space in our recursive descent parser.  As a special case,
   // flatten this recursion into an iterative loop.  This is complex and gross,
   // but all the grossness is constrained to ParseCaseStatement (and some
-  // wierdness in the actions), so this is just local grossness :).
+  // weirdness in the actions), so this is just local grossness :).
 
   // TopLevelCase - This is the highest level we have parsed.  'case 1' in the
   // example above.

clang/test/Misc/ast-dump-attr.cpp

@@ -95,3 +95,19 @@ void *TestVariadicUnsigned1(int) __attribute__((alloc_size(1)));
 void *TestVariadicUnsigned2(int, int) __attribute__((alloc_size(1,2)));
 // CHECK: FunctionDecl{{.*}}TestVariadicUnsigned2
 // CHECK:   AllocSizeAttr{{.*}} 0 1
+
+void TestLabel() {
+L: __attribute__((unused)) int i;
+// CHECK: LabelStmt{{.*}}'L'
+// CHECK: VarDecl{{.*}}i 'int'
+// CHECK-NEXT: UnusedAttr{{.*}}
+
+M: __attribute(()) int j;
+// CHECK: LabelStmt {{.*}} 'M'
+// CHECK-NEXT: DeclStmt
+// CHECK-NEXT: VarDecl {{.*}} j 'int'
+
+N: __attribute(()) ;
+// CHECK: LabelStmt {{.*}} 'N'
+// CHECK-NEXT: NullStmt
+}

clang/test/Sema/warn-unused-label.c

@@ -9,3 +9,7 @@ void f() {
   goto d;
   return;
 }
+
+void PR8455() {
+  L: __attribute__((unused)) return; // ok, no semicolon required
+}

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

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsyntax-only -Wunused-variable -verify %s
+// RUN: %clang_cc1 -fsyntax-only -Wunused-variable -Wunused-label -verify %s
 template<typename T> void f() {
   T t;
   t = 17;
@@ -128,3 +128,26 @@ namespace ctor_with_cleanups {
 }
 
 #include "Inputs/warn-unused-variables.h"
+
+namespace PR8455 {
+  void f() {
+    A: // expected-warning {{unused label 'A'}}
+      __attribute__((unused)) int i; // attribute applies to variable
+    B: // attribute applies to label
+      __attribute__((unused)); int j; // expected-warning {{unused variable 'j'}}
+  }
+
+  void g() {
+    C: // unused label 'C' will not appear here because an error occurs
+      __attribute__((unused))
+      #pragma weak unused_local_static  // expected-error {{expected ';' after __attribute__}}
+      ;
+  }
+
+  void h() {
+    D: // expected-warning {{unused label 'D'}}
+      #pragma weak unused_local_static
+      __attribute__((unused))  // expected-warning {{declaration does not declare anything}}
+      ;
+  }
+}