[clang] [clang] Handle consteval constructors with default initialization. (PR #144970)

[Eli Friedman via cfe-commits]

https://github.com/efriedma-quic created https://github.com/llvm/llvm-project/pull/144970

This is a simple extension of 443377a9d1a8d4a69a317a1a892184c59dd0aec6 to also handle the implicit expressions created by default initialization.  This usually doesn't matter, but it's relevant if the constructor stores "this" as a member.

Fixes #135281 .

>From ef713152a6fb5d2321330d8fbaa77970e8666b13 Mon Sep 17 00:00:00 2001
From: Eli Friedman <efriedma at quicinc.com>
Date: Thu, 19 Jun 2025 18:29:49 -0700
Subject: [PATCH] [clang] Handle consteval constructors with default
 initialization.

This is a simple extension of 443377a9d1a8d4a69a317a1a892184c59dd0aec6
to also handle the implicit expressions created by default
initialization.  This usually doesn't matter, but it's relevant if the
constructor stores "this" as a member.

Fixes #135281 .
---
 clang/lib/Sema/SemaDecl.cpp                    |  6 ++++++
 .../test/SemaCXX/cxx2b-consteval-propagate.cpp | 18 ++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index bbd63372c168b..e10dc65897b8a 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -14423,6 +14423,9 @@ void Sema::ActOnUninitializedDecl(Decl *RealDecl) {
         Var->getType().getAddressSpace() == LangAS::hlsl_input)
       return;
 
+    if (getLangOpts().CPlusPlus)
+      ActOnCXXEnterDeclInitializer(nullptr, Var);
+
     // C++03 [dcl.init]p9:
     //   If no initializer is specified for an object, and the
     //   object is of (possibly cv-qualified) non-POD class type (or
@@ -14458,6 +14461,9 @@ void Sema::ActOnUninitializedDecl(Decl *RealDecl) {
     }
 
     CheckCompleteVariableDeclaration(Var);
+
+    if (getLangOpts().CPlusPlus)
+      ActOnCXXExitDeclInitializer(nullptr, Var);
   }
 }
 
diff --git a/clang/test/SemaCXX/cxx2b-consteval-propagate.cpp b/clang/test/SemaCXX/cxx2b-consteval-propagate.cpp
index dd5063cb29c5b..aa5d79af589ca 100644
--- a/clang/test/SemaCXX/cxx2b-consteval-propagate.cpp
+++ b/clang/test/SemaCXX/cxx2b-consteval-propagate.cpp
@@ -576,3 +576,21 @@ int f() {
   //expected-note at -2 {{read of non-const variable 'a' is not allowed in a constant expression}}
 }
 }
+
+#if __cplusplus >= 202302L
+namespace GH135281 {
+  struct B {
+    const void* p;
+    consteval B() : p{this} {}
+  };
+  B b;
+  B b2{};
+  B &&b3{};
+  void f() {
+    static B b4;
+    B b5; // expected-error {{call to consteval function 'GH135281::B::B' is not a constant expression}} \
+          // expected-note {{pointer to temporary is not a constant expression}} \
+          // expected-note {{temporary created here}}
+  }
+}
+#endif