[C2y] Allow static local variables in inline functions with external …

clang/include/clang/Basic/DiagnosticGroups.td

@@ -1401,7 +1401,7 @@ def C23 : DiagGroup<"c23-extensions", [VariadicMacroArgumentsOmitted]>;
 def : DiagGroup<"c2x-extensions", [C23]>;
 
 // A warning group for warnings about using C2y features as extensions.
-def C2y : DiagGroup<"c2y-extensions", [StaticInInline]>;
+def C2y : DiagGroup<"c2y-extensions", [StaticInInline, StaticLocalInInline]>;
 
 // Previously supported warning group which is no longer pertinent as binary
 // literals are a C++14 and C23 extension now instead of a GNU extension.

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -6339,9 +6339,13 @@ 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<
-  "non-constant static local variable in inline function may be different "
-  "in different files">, InGroup<StaticLocalInInline>;
+def ext_static_local_in_extern_inline : ExtWarn<
+  "non-constant static local variable in an inline function with "
+  "external linkage is a C2y extension">, InGroup<StaticLocalInInline>;
+def warn_c2y_compat_static_local_in_extern_inline : Warning<
+  "non-constant static local variable in an inline function with "
+  "external linkage is incompatible with standards before C2y">,
+  InGroup<CPre2yCompat>, DefaultIgnore;
 def note_convert_inline_to_static : Note<
   "use 'static' to give inline function %0 internal linkage">;
 

clang/lib/Sema/SemaDecl.cpp

@@ -8111,6 +8111,11 @@ NamedDecl *Sema::ActOnVariableDeclarator(
   //   An inline definition of a function with external linkage shall
   //   not contain a definition of a modifiable object with static or
   //   thread storage duration...
+  //
+  // WG14 N3622 which removed the constraint entirely in C2y. It is left
+  // enabled in earlier language modes because this is a constraint in those
+  // language modes. But in C2y mode, we still want to issue the "incompatible
+  // with previous standards" diagnostic, too.
   // We only apply this when the function is required to be defined
   // elsewhere, i.e. when the function is not 'extern inline'.  Note
   // that a local variable with thread storage duration still has to
@@ -8120,8 +8125,13 @@ NamedDecl *Sema::ActOnVariableDeclarator(
       !NewVD->getType().isConstQualified()) {
     FunctionDecl *CurFD = getCurFunctionDecl();
     if (CurFD && isFunctionDefinitionDiscarded(*this, CurFD)) {
-      Diag(D.getDeclSpec().getStorageClassSpecLoc(),
-           diag::warn_static_local_in_extern_inline);
+      unsigned DiagID;
+      if (getLangOpts().C2y)
+        DiagID = diag::warn_c2y_compat_static_local_in_extern_inline;
+      else
+        DiagID = diag::ext_static_local_in_extern_inline;
+
+      Diag(D.getDeclSpec().getStorageClassSpecLoc(), DiagID);
       MaybeSuggestAddingStaticToDecl(CurFD);
     }
   }

clang/test/C/C2y/n3622_1.c

@@ -0,0 +1,25 @@
+// RUN: %clang_cc1 -verify=good -pedantic -Wall -std=c2y %s
+// RUN: %clang_cc1 -verify=compat,expected -pedantic -Wall -Wpre-c2y-compat -std=c2y %s
+// RUN: %clang_cc1 -verify=ped,expected -pedantic -Wall -std=c23 %s
+// RUN: %clang_cc1 -verify=ped,expected -pedantic -Wall -std=c17 %s
+// good-no-diagnostics
+
+/* WG14 N3622: Clang 22
+ * Allow static local variables in extern inline functions
+ *
+ * This verifies that a constraint from previous standards is no longer
+ * triggered in C2y mode. The constraint is regarding static local
+ * variables in inline functions with external linkage.
+ */
+
+inline void func1(void) {   // expected-note {{use 'static' to give inline function 'func1' internal linkage}}
+    static int x = 0;   /* ped-warning {{non-constant static local variable in an inline function with external linkage is a C2y extension}}
+                      compat-warning {{non-constant static local variable in an inline function with external linkage is incompatible with standards before C2y}}
+                    */
+    (void)x;
+}
+
+inline void func2(void) {
+    static const int x = 0;
+    (void)x;
+}

clang/test/Sema/inline.c

@@ -73,9 +73,9 @@ inline int useStaticAgain (void) { // expected-note 2 {{use 'static' to give inl
 
 #pragma clang diagnostic pop
 
-inline void defineStaticVar(void) { // expected-note {{use 'static' to give inline function 'defineStaticVar' internal linkage}}
+inline void defineStaticVar(void) { // ok (no -pedantic)
   static const int x = 0; // ok
-  static int y = 0; // expected-warning {{non-constant static local variable in inline function may be different in different files}}
+  static int y = 0; // ok (no -pedantic)
 }
 
 extern inline void defineStaticVarInExtern(void) {