[clang] fix explicit incomplete enum (PR #184210)

[via cfe-commits]

https://github.com/Serosh-commits updated https://github.com/llvm/llvm-project/pull/184210

>From d6eeca0f7e30ff37d051004b598e31c01f435125 Mon Sep 17 00:00:00 2001
From: Serosh-commits <janmejayapanda400 at gmail.com>
Date: Thu, 5 Mar 2026 02:24:01 +0530
Subject: [PATCH] fix explicit incomplete enum

---
 clang/docs/ReleaseNotes.rst     | 1 +
 clang/lib/Sema/SemaOverload.cpp | 3 +++
 clang/test/SemaCXX/gh183887.cpp | 8 ++++++++
 3 files changed, 12 insertions(+)
 create mode 100644 clang/test/SemaCXX/gh183887.cpp

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 18ce0f919daa9..82b80e2b287c5 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -334,6 +334,7 @@ Bug Fixes to C++ Support
 - Fixed a bug where captured variables in non-mutable lambdas were incorrectly treated as mutable 
   when used inside decltype in the return type. (#GH180460)
 - Fixed a crash when evaluating uninitialized GCC vector/ext_vector_type vectors in ``constexpr``. (#GH180044)
+- Fixed a crash when `explicit(bool)` is used with an incomplete enumeration. (#GH183887)
 - Fixed a crash on ``typeid`` of incomplete local types during template instantiation. (#GH63242), (#GH176397)
 
 - Fix initialization of GRO when GRO-return type mismatches, as part of CWG2563. (#GH98744)
diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index e5c4c59e9ffbb..432f85a554d1c 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -6464,6 +6464,9 @@ static ExprResult BuildConvertedConstantExpression(Sema &S, Expr *From,
   if (checkPlaceholderForOverload(S, From))
     return ExprError();
 
+  if (From->containsErrors())
+    return S.ImpCastExprToType(From, T, CK_NoOp);
+
   // C++1z [expr.const]p3:
   //  A converted constant expression of type T is an expression,
   //  implicitly converted to type T, where the converted
diff --git a/clang/test/SemaCXX/gh183887.cpp b/clang/test/SemaCXX/gh183887.cpp
new file mode 100644
index 0000000000000..d89b2d5068ea0
--- /dev/null
+++ b/clang/test/SemaCXX/gh183887.cpp
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify %s
+
+namespace GH183887 {
+enum E1 explicit(E1()); // expected-error {{ISO C++ forbids forward references to 'enum' types}} \
+                        // expected-error {{invalid use of incomplete type 'E1'}} \
+                        // expected-error {{'explicit' can only appear on non-static member functions}} \
+                        // expected-note {{forward declaration of 'GH183887::E1'}}
+}