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

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Younan Zhang (zyn0217)

<details>
<summary>Changes</summary>

This fixes the case shown by https://github.com/llvm/llvm-project/issues/64808#issuecomment-1929131611.

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.

---
Full diff: https://github.com/llvm/llvm-project/pull/83420.diff


3 Files Affected:

- (modified) clang/docs/ReleaseNotes.rst (+3) 
- (modified) clang/lib/Sema/SemaOverload.cpp (+2-1) 
- (modified) clang/test/SemaTemplate/concepts.cpp (+29) 


``````````diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 7e16b9f0c67dbd..10f7e7129e97ac 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -290,6 +290,9 @@ Bug Fixes to C++ Support
   lookup searches the bases of an incomplete class.
 - Fix a crash when an unresolved overload set is encountered on the RHS of a ``.*`` operator.
   (`#53815 <https://github.com/llvm/llvm-project/issues/53815>`_)
+- 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 7d38043890ca20..f6a2cfa60892f9 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

``````````

</details>


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