[clang] [Clang] Recover GLTemplateParameterList for generic lambdas in RebuildLambdaScopeInfo (PR #118176)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 updated https://github.com/llvm/llvm-project/pull/118176

>From 6d55d79dc7a67a94be0f72b15f8da90813ebb9fd Mon Sep 17 00:00:00 2001
From: Younan Zhang <zyn7109 at gmail.com>
Date: Sat, 30 Nov 2024 23:23:47 +0800
Subject: [PATCH 1/2] [Clang] Recover GLTemplateParameterList for generic
 lambdas in RebuildLambdaScopeInfo

---
 clang/docs/ReleaseNotes.rst                   |  2 ++
 clang/lib/Sema/SemaDecl.cpp                   | 21 ++++++++++++++++---
 .../SemaCXX/lambda-capture-type-deduction.cpp | 16 ++++++++++++++
 3 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 8bd06fadfdc984..e8e8a8cff76e45 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -714,6 +714,8 @@ Bug Fixes to C++ Support
   assumption if they also occur inside of a dependent lambda. (#GH114787)
 - Clang now uses valid deduced type locations when diagnosing functions with trailing return type
   missing placeholder return type. (#GH78694)
+- Fixed an incorrect lambda scope of generic lambdas that caused Clang to crash when computing potential lambda
+  captures at the end of a full expression. (#GH115931)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 74b0e5ad23bd48..75389d6ba7bfd8 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -15504,10 +15504,25 @@ LambdaScopeInfo *Sema::RebuildLambdaScopeInfo(CXXMethodDecl *CallOperator) {
   LSI->CallOperator = CallOperator;
   LSI->Lambda = LambdaClass;
   LSI->ReturnType = CallOperator->getReturnType();
-  // This function in calls in situation where the context of the call operator
-  // is not entered, so we set AfterParameterList to false, so that
+  // When this function is called in situation where the context of the call
+  // operator is not entered, we set AfterParameterList to false, so that
   // `tryCaptureVariable` finds explicit captures in the appropriate context.
-  LSI->AfterParameterList = false;
+  //
+  // There is also at least a situation as in FinishTemplateArgumentDeduction(),
+  // where we would set the CurContext to the lambda operator before
+  // substituting into it. In this case the flag needs to be true such that
+  // tryCaptureVariable can correctly handle potential captures thereof.
+  LSI->AfterParameterList = CurContext == CallOperator;
+  // GLTemplateParameterList is necessary for getCurGenericLambda() which is
+  // used at the point of dealing with potential captures.
+  //
+  // We don't use LambdaClass->isGenericLambda() because this value doesn't
+  // flip for instantiated generic lambdas, where no FunctionTemplateDecls are
+  // associated. (Technically, we could recover that list from their
+  // instantiation patterns, but for now, the GLTemplateParameterList seems
+  // unnecessary in these cases.)
+  if (FunctionTemplateDecl *FTD = CallOperator->getDescribedFunctionTemplate())
+    LSI->GLTemplateParameterList = FTD->getTemplateParameters();
   const LambdaCaptureDefault LCD = LambdaClass->getLambdaCaptureDefault();
 
   if (LCD == LCD_None)
diff --git a/clang/test/SemaCXX/lambda-capture-type-deduction.cpp b/clang/test/SemaCXX/lambda-capture-type-deduction.cpp
index a86f3018989927..234cb6806f041a 100644
--- a/clang/test/SemaCXX/lambda-capture-type-deduction.cpp
+++ b/clang/test/SemaCXX/lambda-capture-type-deduction.cpp
@@ -298,6 +298,22 @@ void __trans_tmp_1() {
 
 }
 
+namespace GH115931 {
+
+struct Range {};
+
+template <Range>
+struct LengthPercentage {};
+
+void reflectSum() {
+  Range resultR;
+  [&] (auto) -> LengthPercentage<resultR> { 
+    return {};
+  }(0);
+}
+
+} // namespace GH115931
+
 namespace GH47400 {
 
 struct Foo {};

>From 1370880d15472d8f587b730c37ed6d51ad539dce Mon Sep 17 00:00:00 2001
From: Younan Zhang <zyn7109 at gmail.com>
Date: Tue, 3 Dec 2024 09:41:19 +0800
Subject: [PATCH 2/2] Address feedback

---
 clang/lib/Sema/SemaDecl.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 10a933077b5111..c4bb73b2924bc9 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -15522,12 +15522,12 @@ LambdaScopeInfo *Sema::RebuildLambdaScopeInfo(CXXMethodDecl *CallOperator) {
   // When this function is called in situation where the context of the call
   // operator is not entered, we set AfterParameterList to false, so that
   // `tryCaptureVariable` finds explicit captures in the appropriate context.
-  //
   // There is also at least a situation as in FinishTemplateArgumentDeduction(),
   // where we would set the CurContext to the lambda operator before
   // substituting into it. In this case the flag needs to be true such that
   // tryCaptureVariable can correctly handle potential captures thereof.
   LSI->AfterParameterList = CurContext == CallOperator;
+
   // GLTemplateParameterList is necessary for getCurGenericLambda() which is
   // used at the point of dealing with potential captures.
   //