[clang] [Concepts] Add Decls from the outer scope of the current lambda for conversion function constraints (PR #83420)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 updated https://github.com/llvm/llvm-project/pull/83420

>From 072d2aa8b758d61e0459bd626fbea881c3e1596c Mon Sep 17 00:00:00 2001
From: Younan Zhang <zyn7109 at gmail.com>
Date: Thu, 29 Feb 2024 19:47:01 +0800
Subject: [PATCH] [Concepts] Consider outer scope Decls for conversion function
 constraints

This fixes the case shown by https://github.com/llvm/llvm-project/issues/64808#issuecomment-1929129271.

Similar to https://github.com/llvm/llvm-project/commit/f9caa12328b265b77221fe7a310d4504673d814a,
we have some calls to constraint checking for a lambda's conversion
function while determining the conversion sequence.

This patch addresses the problem where the requires-expression within
such a lambda references to a Decl outside of the lambda by adding
these Decls to the current instantiation scope.

I'm abusing the flag 'ForOverloadResolution' of CheckFunctionConstraints,
which is actually meant to consider the Decls from parent DeclContexts.
---
 clang/docs/ReleaseNotes.rst          |  3 +++
 clang/lib/Sema/SemaOverload.cpp      |  3 ++-
 clang/test/SemaTemplate/concepts.cpp | 29 ++++++++++++++++++++++++++++
 3 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index bac166e6c35627..53f8395b6de69d 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -275,6 +275,9 @@ Bug Fixes to C++ Support
   (`#82258 <https://github.com/llvm/llvm-project/issues/82258>`_)
 - Correctly immediate-escalate lambda conversion functions.
   (`#82258 <https://github.com/llvm/llvm-project/issues/82258>`_)
+- Fixed a crash while checking constraints of a trailing requires-expression of a lambda, that the
+  expression references to an entity declared outside of the lambda. This is a reduction from
+  (`#64808 <https://github.com/llvm/llvm-project/issues/64808>`_).
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index f7645422348b65..40c7d0e17890d0 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -7976,7 +7976,8 @@ void Sema::AddConversionCandidate(
 
   if (Conversion->getTrailingRequiresClause()) {
     ConstraintSatisfaction Satisfaction;
-    if (CheckFunctionConstraints(Conversion, Satisfaction) ||
+    if (CheckFunctionConstraints(Conversion, Satisfaction, /*UsageLoc=*/{},
+                                 /*ShouldAddDeclsFromParentScope=*/true) ||
         !Satisfaction.IsSatisfied) {
       Candidate.Viable = false;
       Candidate.FailureKind = ovl_fail_constraints_not_satisfied;
diff --git a/clang/test/SemaTemplate/concepts.cpp b/clang/test/SemaTemplate/concepts.cpp
index bac209a28da912..b7ea0d003a52d7 100644
--- a/clang/test/SemaTemplate/concepts.cpp
+++ b/clang/test/SemaTemplate/concepts.cpp
@@ -1085,3 +1085,32 @@ template void Struct<void>::bar<>();
 template int Struct<void>::field<1, 2>;
 
 }
+
+namespace GH64808 {
+
+template <class T> struct basic_sender {
+  T func;
+  basic_sender(T) : func(T()) {}
+};
+
+auto a = basic_sender{[](auto... __captures) {
+  return []() // #note-a-1
+    requires((__captures, ...), false) // #note-a-2
+  {};
+}()};
+
+auto b = basic_sender{[](auto... __captures) {
+  return []()
+    requires([](int, double) { return true; }(decltype(__captures)()...))
+  {};
+}(1, 2.33)};
+
+void foo() {
+  a.func();
+  // expected-error at -1{{no matching function for call}}
+  // expected-note@#note-a-1{{constraints not satisfied}}
+  // expected-note@#note-a-2{{evaluated to false}}
+  b.func();
+}
+
+} // namespace GH64808