[Clang] Use ExtWarn for static local variable in extern inline function (fixes #39524)

clang/docs/ReleaseNotes.rst

@@ -404,6 +404,10 @@ Improvements to Clang's diagnostics
 - Clang now emits a diagnostic in case `vector_size` or `ext_vector_type`
   attributes are used with a negative size (#GH165463).
 
+- The warning about static local variables declared inside `inline` 
+  functions is now correctly converted to an error if `-pedantic-errors` is 
+  passed (#GH39524).
+
 Improvements to Clang's time-trace
 ----------------------------------
 

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -6339,7 +6339,7 @@ def warn_c2y_compat_internal_in_extern_inline : Warning<
   "using static %select{function|variable}0 %1 in an inline function with "
   "external linkage is incompatible with standards before C2y">,
   InGroup<CPre2yCompat>, DefaultIgnore;
-def warn_static_local_in_extern_inline : Warning<
+def warn_static_local_in_extern_inline : ExtWarn<
   "non-constant static local variable in inline function may be different "
   "in different files">, InGroup<StaticLocalInInline>;
 def note_convert_inline_to_static : Note<

clang/test/Sema/inline-static-var.c

@@ -0,0 +1,6 @@
+// RUN: %clang_cc1 -std=c11 -pedantic-errors -verify %s
+
+inline void f(void) { // expected-note {{use 'static' to give inline function 'f' internal linkage}}
+  static int x; // expected-error {{non-constant static local variable in inline function may be different in different files}}
+}
+