[clang] 9ea993f - [Clang] Recover GLTemplateParameterList for generic lambdas in RebuildLambdaScopeInfo (#118176)

[via cfe-commits]

Author: Younan Zhang
Date: 2024-12-03T10:10:17+08:00
New Revision: 9ea993f975b045679907a0789d6fd4d7180593a0

URL: https://github.com/llvm/llvm-project/commit/9ea993f975b045679907a0789d6fd4d7180593a0
DIFF: https://github.com/llvm/llvm-project/commit/9ea993f975b045679907a0789d6fd4d7180593a0.diff

LOG: [Clang] Recover GLTemplateParameterList for generic lambdas in RebuildLambdaScopeInfo (#118176)

The NTTP argument appearing inside a trailing return type of a generic
lambda would have us check for potential lambda captures, where the
function needs GLTemplateParameterList of the current LSI to tell
whether the lambda is generic.

The lambda scope in this context is rebuilt by the
LambdaScopeForCallOperatorInstantiationRAII when substituting the lambda
operator during template argument deduction. Thus, I think the template
parameter list should be preserved in the rebuilding process, as it
seems otherwise innocuous to me.

Fixes #115931

Added: 
    

Modified: 
    clang/docs/ReleaseNotes.rst
    clang/lib/Sema/SemaDecl.cpp
    clang/test/SemaCXX/lambda-capture-type-deduction.cpp

Removed: 
    


################################################################################
diff  --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 20bd27ad52f577..01c7899e36c932 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -764,6 +764,8 @@ Bug Fixes to C++ Support
 - Fixed an assertion failure caused by using ``consteval`` in condition in consumed analyses. (#GH117385)
 - Fix a crash caused by incorrect argument position in merging deduced template arguments. (#GH113659)
 - Fixed an assertion failure caused by mangled names with invalid identifiers. (#GH112205)
+- 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 ba574307055c6b..c4bb73b2924bc9 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -15519,10 +15519,25 @@ 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 {};