Add diagnostic for for-range-declaration being specificed with thread_local

[shafik]

Summary

Currently we have a diagnostic that catches the other storage class specifies for the range based for loop declaration but we miss the thread_local case. This changes adds a diagnostic for that case as well.

[shafik]

The problem with this approach is given:

for (static thread_local int a : A()) {}

it just issues one diagnostic and it points to static but I am not sure what the right approach to handling this case is.

[• Quuxplusone]

Spoilsport. ;)
LGTM, fwiw.

[• Quuxplusone]

clang/lib/Sema/SemaDecl.cpp

12783

Incidentally, why is this case here to begin with? Loop variables can totally be register. (But I guess it's moot at this point; clearly no Clang user is depending on this to work, and register is gone from C++20.)

[aaron.ballman]

LGTM!

In D92671#2434154, @shafik wrote:

The problem with this approach is given:

for (static thread_local int a : A()) {}

it just issues one diagnostic and it points to static but I am not sure what the right approach to handling this case is.

I think that's reasonable behavior for this corner case.

clang/lib/Sema/SemaDecl.cpp

12783

See [stmt.ranged]p2 -- it's explicitly disallowed. FWIW, loop variables in C++ can also be static (https://godbolt.org/z/rM15Yz). ;-)

clang/include/clang/Basic/DiagnosticSemaKinds.td

 def note_it_delegates_to : Note<"it delegates to">;
 def note_which_delegates_to : Note<"which delegates to">;
 
 // C++11 range-based for loop
 def err_for_range_decl_must_be_var : Error<
   "for range declaration must declare a variable">;
 def err_for_range_storage_class : Error<
   "loop variable %0 may not be declared %select{'extern'|'static'|"
-  "'__private_extern__'|'auto'|'register'|'constexpr'}1">;
+  "'__private_extern__'|'auto'|'register'|'constexpr'|'thread_local'}1">;
 def err_type_defined_in_for_range : Error<
   "types may not be defined in a for range declaration">;
 def err_for_range_deduction_failure : Error<
   "cannot use type %0 as a range">;
 def err_for_range_incomplete_type : Error<
   "cannot use incomplete type %0 as a range">;
 def err_for_range_iter_deduction_failure : Error<
   "cannot use type %0 as an iterator">;

clang/lib/Sema/SemaDecl.cpp

void Sema::ActOnCXXForRangeDecl(Decl *D) {
   case SC_PrivateExtern:
     Error = 2;
     break;
   case SC_Auto:
     Error = 3;
     break;
   case SC_Register:
     Error = 4;
     break;
   }
+
+  // for-range-declaration cannot be given a storage class specifier con't.
+  switch (VD->getTSCSpec()) {
+  case TSCS_thread_local:
+    Error = 6;
+    break;
+  case TSCS___thread:
+  case TSCS__Thread_local:
+  case TSCS_unspecified:
+    break;
+  }
+
   if (Error != -1) {
     Diag(VD->getOuterLocStart(), diag::err_for_range_storage_class)
         << VD << Error;
     D->setInvalidDecl();
   }
 }
 
 StmtResult

clang/test/CXX/stmt.stmt/stmt.iter/stmt.ranged/p1.cpp

 #endif
     ;
 
   for (void f() : "error") // expected-error {{for range declaration must declare a variable}}
     ;
 
   for (extern int a : A()) {} // expected-error {{loop variable 'a' may not be declared 'extern'}}
   for (static int a : A()) {} // expected-error {{loop variable 'a' may not be declared 'static'}}
+  for (thread_local int a : A()) {} // expected-error {{loop variable 'a' may not be declared 'thread_local'}}
   for (register int a : A()) {} // expected-error {{loop variable 'a' may not be declared 'register'}} expected-warning 0-1{{register}} expected-error 0-1{{register}}
   for (constexpr int a : X::C()) {} // OK per CWG issue #1204.
 
   for (auto u : X::NoBeginADL()) { // expected-error {{invalid range expression of type 'X::NoBeginADL'; no viable 'begin' function available}}
   }
   for (auto u : X::NoEndADL()) { // expected-error {{invalid range expression of type 'X::NoEndADL'; no viable 'end' function available}}
   }