[[clang::always_destroy]] attribute silences warn-exit-time-destructor (#86486)

This attribute tells the compiler that the variable must have its exit-time
destructor run, so it makes sense that it would silence the warning telling
users that an exit-time destructor is required.

Fixes #68686

Author: ycdtosa

clang/docs/ReleaseNotes.rst

@@ -295,6 +295,10 @@ Improvements to Clang's diagnostics
 - Clang now correctly diagnoses no arguments to a variadic macro parameter as a C23/C++20 extension.
   Fixes #GH84495.
 
+- Clang no longer emits a ``-Wexit-time destructors`` warning on static variables explicitly
+  annotated with the ``clang::always_destroy`` attribute.
+  Fixes #GH68686, #GH86486
+
 Improvements to Clang's time-trace
 ----------------------------------
 

clang/include/clang/Basic/AttrDocs.td

@@ -6069,6 +6069,9 @@ def AlwaysDestroyDocs : Documentation {
 The ``always_destroy`` attribute specifies that a variable with static or thread
 storage duration should have its exit-time destructor run. This attribute is the
 default unless clang was invoked with -fno-c++-static-destructors.
+
+If a variable is explicitly declared with this attribute, Clang will silence
+otherwise applicable ``-Wexit-time-destructors`` warnings.
   }];
 }
 

clang/lib/Sema/SemaDeclCXX.cpp

@@ -16202,7 +16202,8 @@ void Sema::FinalizeVarWithDestructor(VarDecl *VD, const RecordType *Record) {
 
   // Emit warning for non-trivial dtor in global scope (a real global,
   // class-static, function-static).
-  Diag(VD->getLocation(), diag::warn_exit_time_destructor);
+  if (!VD->hasAttr<AlwaysDestroyAttr>())
+    Diag(VD->getLocation(), diag::warn_exit_time_destructor);
 
   // TODO: this should be re-enabled for static locals by !CXAAtExit
   if (!VD->isStaticLocal())

clang/test/SemaCXX/warn-exit-time-destructors.cpp

@@ -51,6 +51,15 @@ struct A { ~A(); };
 }
 
 namespace test5 {
+  struct A { ~A(); };
+  [[clang::always_destroy]] A a; // no warning
+
+  void func() {
+    [[clang::always_destroy]] static A a; // no warning
+  }
+}
+
+namespace test6 {
 #if __cplusplus >= 202002L
 #define CPP20_CONSTEXPR constexpr
 #else
@@ -68,3 +77,4 @@ namespace test5 {
   T t; // expected-warning {{exit-time destructor}}
 #undef CPP20_CONSTEXPR
 }
+