[PATCH] Don't crash on [[clang::fallthrough]] on Decls.

[Nico Weber]

Hi aaron.ballman,

Fixes PR23089

http://reviews.llvm.org/D8750

Files:
  include/clang/Basic/Attr.td
  include/clang/Basic/DiagnosticSemaKinds.td
  include/clang/Sema/AttributeList.h
  test/SemaCXX/switch-implicit-fallthrough.cpp

Index: include/clang/Basic/Attr.td
===================================================================
--- include/clang/Basic/Attr.td
+++ include/clang/Basic/Attr.td
@@ -106,6 +106,8 @@
 def GlobalVar : SubsetSubject<Var,
                              [{S->hasGlobalStorage()}]>;
 
+def NotAllowedOnDecls : SubsetSubject<Var, [{false}]>;
+
 // FIXME: this hack is needed because DeclNodes.td defines the base Decl node
 // type to be a class, not a definition. This makes it impossible to create an
 // attribute subject which accepts a Decl. Normally, this is not a problem,
@@ -690,7 +692,8 @@
 
 def FallThrough : Attr {
   let Spellings = [CXX11<"clang", "fallthrough">];
-//  let Subjects = [NullStmt];
+  let Subjects = SubjectList<[NotAllowedOnDecls], ErrorDiag,
+                             "ExpectedEmptyStatement">;
   let Documentation = [FallthroughDocs];
 }
 
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -2264,7 +2264,7 @@
   "Objective-C instance methods|init methods of interface or class extension declarations|"
   "variables, functions and classes|Objective-C protocols|"
   "functions and global variables|structs, unions, and typedefs|structs and typedefs|"
-  "interface or protocol declarations|kernel functions}1">,
+  "interface or protocol declarations|kernel functions|empty statements}1">,
   InGroup<IgnoredAttributes>;
 def err_attribute_wrong_decl_type : Error<warn_attribute_wrong_decl_type.Text>;
 def warn_type_attribute_wrong_type : Warning<
Index: include/clang/Sema/AttributeList.h
===================================================================
--- include/clang/Sema/AttributeList.h
+++ include/clang/Sema/AttributeList.h
@@ -846,7 +846,8 @@
   ExpectedStructOrUnionOrTypedef,
   ExpectedStructOrTypedef,
   ExpectedObjectiveCInterfaceOrProtocol,
-  ExpectedKernelFunction
+  ExpectedKernelFunction,
+  ExpectedEmptyStatement
 };
 
 }  // end namespace clang
Index: test/SemaCXX/switch-implicit-fallthrough.cpp
===================================================================
--- test/SemaCXX/switch-implicit-fallthrough.cpp
+++ test/SemaCXX/switch-implicit-fallthrough.cpp
@@ -1,6 +1,5 @@
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 -Wimplicit-fallthrough %s
 
-
 int fallthrough(int n) {
   switch (n / 10) {
       if (n - 1) {
@@ -300,3 +299,8 @@
   }
   return n;
 }
+
+[[clang::fallthrough]] int a; // expected-error {{'fallthrough' attribute only applies to empty statements}}
+[[clang::fallthrough]] int f(); // expected-error {{'fallthrough' attribute only applies to empty statements}}
+void g([[clang::fallthrough]] int p); // expected-error {{'fallthrough' attribute only applies to empty statements}}
+struct [[clang::fallthrough]] S; // expected-error {{'fallthrough' attribute only applies to empty statements}}

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