[clang] [Clang] Use ExtWarn for static local variable in extern inline function (fixes #39524) (PR #166332)

[V S Susi Krishna via cfe-commits]

https://github.com/Susikrishna updated https://github.com/llvm/llvm-project/pull/166332

>From 16414b96e0ca5ee44b0332bc387ecbd0046eacd4 Mon Sep 17 00:00:00 2001
From: Susikrishna <krishnasusi323 at gmail.com>
Date: Tue, 4 Nov 2025 12:49:38 +0530
Subject: [PATCH 1/3] [Clang] Use ExtWarn for static local variable in extern
 inline function (fixes #39524)

---
 clang/include/clang/Basic/DiagnosticSemaKinds.td | 8 +++++---
 clang/test/Sema/inline-static-var.c              | 7 +++++++
 2 files changed, 12 insertions(+), 3 deletions(-)
 create mode 100644 clang/test/Sema/inline-static-var.c

diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 4e369be0bbb92..80272e24eced8 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -6337,9 +6337,11 @@ 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 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<
   "use 'static' to give inline function %0 internal linkage">;
 
diff --git a/clang/test/Sema/inline-static-var.c b/clang/test/Sema/inline-static-var.c
new file mode 100644
index 0000000000000..f622a7f22e02c
--- /dev/null
+++ b/clang/test/Sema/inline-static-var.c
@@ -0,0 +1,7 @@
+// RUN: %clang_cc1 -std=c11 -Wno-unused-variable -Wno-deprecated-non-prototype -Wno-inline -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}}
+}
+
+int main(void) { return 0; }

>From ee314e1af7b74a02c31f38493262025912bc1d8e Mon Sep 17 00:00:00 2001
From: V S Susi Krishna <142647179+Susikrishna at users.noreply.github.com>
Date: Wed, 5 Nov 2025 21:42:38 +0530
Subject: [PATCH 2/3] Update clang/test/Sema/inline-static-var.c

Co-authored-by: Sirraide <aeternalmail at gmail.com>
---
 clang/test/Sema/inline-static-var.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/clang/test/Sema/inline-static-var.c b/clang/test/Sema/inline-static-var.c
index f622a7f22e02c..641f952ac6da7 100644
--- a/clang/test/Sema/inline-static-var.c
+++ b/clang/test/Sema/inline-static-var.c
@@ -4,4 +4,3 @@ inline void f(void) { // expected-note {{use 'static' to give inline function 'f
   static int x; // expected-error {{non-constant static local variable in inline function may be different in different files}}
 }
 
-int main(void) { return 0; }

>From b4abe8eab1fc27e584da327c581260a93596f1d7 Mon Sep 17 00:00:00 2001
From: Susikrishna <krishnasusi323 at gmail.com>
Date: Wed, 5 Nov 2025 22:23:48 +0530
Subject: [PATCH 3/3] Update release notes and diagnostics for static local
 variables in extern inline functions

---
 clang/docs/ReleaseNotes.rst                      | 4 ++++
 clang/include/clang/Basic/DiagnosticSemaKinds.td | 8 +++-----
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 3f57ddc92d5e8..f4d1d379e5608 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -402,6 +402,10 @@ 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).
 
+- Clang now emits an extension warning (`ExtWarn`) instead of a regular warning
+  for static local variables declared inside `extern inline` functions
+  (#GH39524).
+
 Improvements to Clang's time-trace
 ----------------------------------
 
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 629a2b9493c66..7f10a0cd0a770 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -6339,11 +6339,9 @@ 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
-    : ExtWarn<"non-constant static local variable in inline function may be "
-              "different "
-              "in different files">,
-      InGroup<StaticLocalInInline>;
+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<
   "use 'static' to give inline function %0 internal linkage">;