[clang] [clang] Prevent nested RecoveryExpr in BuildConvertedConstantExpression (PR #207072)

[Hrólf Kraki via cfe-commits]

https://github.com/Serosh-commits updated https://github.com/llvm/llvm-project/pull/207072

>From 1e46141a50fac27787966018522f09f32d22a082 Mon Sep 17 00:00:00 2001
From: Serosh-commits <janmejayapanda400 at gmail.com>
Date: Wed, 1 Jul 2026 22:51:09 +0530
Subject: [PATCH 1/2] [clang] Prevent nested RecoveryExpr in
 BuildConvertedConstantExpression

---
 clang/lib/Sema/SemaOverload.cpp | 2 ++
 clang/test/SemaCXX/gh186656.cpp | 7 +++++++
 clang/test/SemaCXX/gh202117.cpp | 6 ++++++
 3 files changed, 15 insertions(+)
 create mode 100644 clang/test/SemaCXX/gh186656.cpp
 create mode 100644 clang/test/SemaCXX/gh202117.cpp

diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index 11e771bc240f1..f088425e139cf 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -6469,6 +6469,8 @@ static ExprResult BuildConvertedConstantExpression(Sema &S, Expr *From,
     return ExprError();
 
   if (From->containsErrors()) {
+    if (isa<RecoveryExpr>(From))
+      return From;
     // The expression already has errors, so the correct cast kind can't be
     // determined. Use RecoveryExpr to keep the expected type T and mark the
     // result as invalid, preventing further cascading errors.
diff --git a/clang/test/SemaCXX/gh186656.cpp b/clang/test/SemaCXX/gh186656.cpp
new file mode 100644
index 0000000000000..227489833da1b
--- /dev/null
+++ b/clang/test/SemaCXX/gh186656.cpp
@@ -0,0 +1,7 @@
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify %s
+
+template <template <int> typename> struct S;
+template <int, int = (foo<void, void>())> struct T; // expected-error {{use of undeclared identifier 'foo'}}
+template <typename...> struct U;
+
+using V = U<S<T>>;
diff --git a/clang/test/SemaCXX/gh202117.cpp b/clang/test/SemaCXX/gh202117.cpp
new file mode 100644
index 0000000000000..7fd0fddf598a7
--- /dev/null
+++ b/clang/test/SemaCXX/gh202117.cpp
@@ -0,0 +1,6 @@
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify %s
+
+template<template<decltype(foo())> typename T> struct S {}; // expected-error {{use of undeclared identifier 'foo'}}
+template<int*> struct P;
+
+S<P> s;

>From e1f9d89f7455568a248d33454f41ec11a2d03418 Mon Sep 17 00:00:00 2001
From: Serosh-commits <janmejayapanda400 at gmail.com>
Date: Fri, 10 Jul 2026 19:29:41 +0530
Subject: [PATCH 2/2] [clang] Avoid redundant RecoveryExpr for typed invalid
 CCE

---
 clang/lib/Sema/SemaOverload.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index 6fc5428b48769..eafda32198f11 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -6499,8 +6499,9 @@ static ExprResult BuildConvertedConstantExpression(Sema &S, Expr *From,
     return ExprError();
 
   if (From->containsErrors()) {
-    if (isa<RecoveryExpr>(From))
+    if (S.Context.hasSameType(From->getType(), T))
       return From;
+
     // The expression already has errors, so the correct cast kind can't be
     // determined. Use RecoveryExpr to keep the expected type T and mark the
     // result as invalid, preventing further cascading errors.