[clang] [Clang] Do not allow `[[clang::lifetimebound]]` on explicit object member functions (PR #96113)

[Mital Ashok via cfe-commits]

https://github.com/MitalAshok updated https://github.com/llvm/llvm-project/pull/96113

>From 453fea9fee85aef61c449761f24b0accecf03d29 Mon Sep 17 00:00:00 2001
From: Mital Ashok <mital at mitalashok.co.uk>
Date: Wed, 19 Jun 2024 21:03:34 +0100
Subject: [PATCH 1/2] [Clang] Do not allow `[[clang::lifetimebound]]` on
 explicit object member functions

---
 clang/include/clang/Basic/DiagnosticSemaKinds.td |  5 +++--
 clang/lib/Sema/SemaDecl.cpp                      | 11 +++++++++--
 clang/test/SemaCXX/attr-lifetimebound.cpp        |  3 ++-
 3 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 8a92973236ddbd..94be9c874afe97 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -10066,8 +10066,9 @@ def warn_null_ret : Warning<
   InGroup<NonNull>;
 
 def err_lifetimebound_no_object_param : Error<
-  "'lifetimebound' attribute cannot be applied; %select{static |non-}0member "
-  "function has no implicit object parameter">;
+  "'lifetimebound' attribute cannot be applied; "
+  "%select{non-|static |explicit object }0"
+  "member function has no implicit object parameter">;
 def err_lifetimebound_ctor_dtor : Error<
   "'lifetimebound' attribute cannot be applied to a "
   "%select{constructor|destructor}0">;
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index d19a16cf2ba150..61a465ca55c5c7 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -6938,9 +6938,16 @@ static void checkAttributesAfterMerging(Sema &S, NamedDecl &ND) {
       // by applying it to the function type.
       if (const auto *A = ATL.getAttrAs<LifetimeBoundAttr>()) {
         const auto *MD = dyn_cast<CXXMethodDecl>(FD);
-        if (!MD || MD->isStatic()) {
+        int NoImplicitObjectError = -1;
+        if (!MD)
+          NoImplicitObjectError = 0;
+        else if (MD->isStatic())
+          NoImplicitObjectError = 1;
+        else if (MD->isExplicitObjectMemberFunction())
+          NoImplicitObjectError = 2;
+        if (NoImplicitObjectError != -1) {
           S.Diag(A->getLocation(), diag::err_lifetimebound_no_object_param)
-              << !MD << A->getRange();
+              << NoImplicitObjectError << A->getRange();
         } else if (isa<CXXConstructorDecl>(MD) || isa<CXXDestructorDecl>(MD)) {
           S.Diag(A->getLocation(), diag::err_lifetimebound_ctor_dtor)
               << isa<CXXDestructorDecl>(MD) << A->getRange();
diff --git a/clang/test/SemaCXX/attr-lifetimebound.cpp b/clang/test/SemaCXX/attr-lifetimebound.cpp
index 7db0a4d64d2596..f4ca840cb276f9 100644
--- a/clang/test/SemaCXX/attr-lifetimebound.cpp
+++ b/clang/test/SemaCXX/attr-lifetimebound.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -std=c++2a -verify %s
+// RUN: %clang_cc1 -std=c++23 -verify %s
 
 namespace usage_invalid {
   // FIXME: Should we diagnose a void return type?
@@ -9,6 +9,7 @@ namespace usage_invalid {
     A() [[clang::lifetimebound]]; // expected-error {{cannot be applied to a constructor}}
     ~A() [[clang::lifetimebound]]; // expected-error {{cannot be applied to a destructor}}
     static int *static_class_member() [[clang::lifetimebound]]; // expected-error {{static member function has no implicit object parameter}}
+    int *explicit_object(this A&) [[clang::lifetimebound]]; // expected-error {{explicit object member function has no implicit object parameter}}
     int not_function [[clang::lifetimebound]]; // expected-error {{only applies to parameters and implicit object parameters}}
     int [[clang::lifetimebound]] also_not_function; // expected-error {{cannot be applied to types}}
   };

>From a8295b7e294fbf13006d182a0f8ee02a7921370e Mon Sep 17 00:00:00 2001
From: Mital Ashok <mital at mitalashok.co.uk>
Date: Sun, 18 Aug 2024 09:29:10 +0100
Subject: [PATCH 2/2] Add release note

---
 clang/docs/ReleaseNotes.rst | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index ffdd063ec99037..556d1ceae7a4e9 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -189,6 +189,9 @@ Attribute Changes in Clang
 - The ``hybrid_patchable`` attribute is now supported on ARM64EC targets. It can be used to specify
   that a function requires an additional x86-64 thunk, which may be patched at runtime.
 
+- ``[[clang::lifetimebound]]`` is now explicitly disallowed on explicit object member functions
+  where they were previously silently ignored.
+
 Improvements to Clang's diagnostics
 -----------------------------------