[clang] 0f28cf4 - Correct the __has_c_attribute value for maybe_unused

[Aaron Ballman via cfe-commits]

Author: Aaron Ballman
Date: 2022-09-13T09:33:20-04:00
New Revision: 0f28cf416d00a0fa0cb6cf572dd7ebbc19529190

URL: https://github.com/llvm/llvm-project/commit/0f28cf416d00a0fa0cb6cf572dd7ebbc19529190
DIFF: https://github.com/llvm/llvm-project/commit/0f28cf416d00a0fa0cb6cf572dd7ebbc19529190.diff

LOG: Correct the __has_c_attribute value for maybe_unused

The original proposal was adopted in Apr 2019, but was subsequently
updated by WG14 N2662 in June 2021. We already supported the attribute
on a label and it behaved as expected, but we had not bumped the
feature test value.

Added: 
    

Modified: 
    clang/docs/ReleaseNotes.rst
    clang/include/clang/Basic/Attr.td
    clang/test/Preprocessor/has_c_attribute.c
    clang/test/Sema/c2x-maybe_unused.c
    clang/www/c_status.html

Removed: 
    


################################################################################
diff  --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index d0d44cbc5ebcd..9bc96f4dc1e96 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -210,6 +210,9 @@ C Language Changes in Clang
 
 C2x Feature Support
 -------------------
+- Implemented `WG14 N2662 <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2662.pdf>`_,
+  so the [[maybe_unused]] attribute may be applied to a label to silence an
+  ``-Wunused-label`` warning.
 
 C++ Language Changes in Clang
 -----------------------------

diff  --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
index 6b9f0aab6c91d..48c7791ebe330 100644
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -2893,7 +2893,7 @@ def ObjCRequiresPropertyDefs : InheritableAttr {
 
 def Unused : InheritableAttr {
   let Spellings = [CXX11<"", "maybe_unused", 201603>, GCC<"unused">,
-                   C2x<"", "maybe_unused", 201904>];
+                   C2x<"", "maybe_unused", 202106>];
   let Subjects = SubjectList<[Var, ObjCIvar, Type, Enum, EnumConstant, Label,
                               Field, ObjCMethod, FunctionLike]>;
   let Documentation = [WarnMaybeUnusedDocs];

diff  --git a/clang/test/Preprocessor/has_c_attribute.c b/clang/test/Preprocessor/has_c_attribute.c
index 972bb0fe04e4f..401daa72b85b1 100644
--- a/clang/test/Preprocessor/has_c_attribute.c
+++ b/clang/test/Preprocessor/has_c_attribute.c
@@ -24,7 +24,7 @@ C2x(clang::annotate)
 // CHECK: deprecated: 201904L
 C2x(deprecated)
 
-// CHECK: maybe_unused: 201904L
+// CHECK: maybe_unused: 202106L
 C2x(maybe_unused)
 
 // CHECK: __gnu__::warn_unused_result: 202003L

diff  --git a/clang/test/Sema/c2x-maybe_unused.c b/clang/test/Sema/c2x-maybe_unused.c
index 82b9634fc9f39..f531521227d7f 100644
--- a/clang/test/Sema/c2x-maybe_unused.c
+++ b/clang/test/Sema/c2x-maybe_unused.c
@@ -1,5 +1,8 @@
 // RUN: %clang_cc1 -fsyntax-only -Wunused -std=c2x -verify %s
 
+// This is the latest version of maybe_unused that we support.
+_Static_assert(__has_c_attribute(maybe_unused) == 202106L);
+
 struct [[maybe_unused]] S1 { // ok
   int a [[maybe_unused]];
 };
@@ -33,3 +36,10 @@ void f2(void);
 void f2(void) {
 }
 
+void label(void) {
+  [[maybe_unused]] label:
+  ;
+
+  other_label: // expected-warning {{unused label 'other_label'}}
+  ;
+}

diff  --git a/clang/www/c_status.html b/clang/www/c_status.html
index 7d97a6bc1f13f..381a05d07eda6 100644
--- a/clang/www/c_status.html
+++ b/clang/www/c_status.html
@@ -851,7 +851,7 @@ <h2 id="c2x">C2x implementation status</h2>
     <tr>
       <td>[[maybe_unused]] for labels</td>
       <td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2662.pdf">N2662</a></td>
-      <td class="none" align="center">No</td>
+      <td class="unreleased" align="center">Clang 16</td>
     </tr>
     <tr>
       <td>Zeros compare equal</td>