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llvm · Jul 6, 2024 · 85730ed · 85730ed
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diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
@@ -929,6 +929,7 @@ Bug Fixes to C++ Support
 - Fix a crash caused by improper use of ``__array_extent``. (#GH80474)
 - Fixed several bugs in capturing variables within unevaluated contexts. (#GH63845), (#GH67260), (#GH69307),
   (#GH88081), (#GH89496), (#GH90669) and (#GH91633).
+- Fixed a crash in constraint instantiation under nested lambdas with dependent parameters.
 - Fixed handling of brace ellison when building deduction guides. (#GH64625), (#GH83368).
 - Clang now instantiates local constexpr functions eagerly for constant evaluators. (#GH35052), (#GH94849)
 - Fixed a failed assertion when attempting to convert an integer representing the difference

diff --git a/clang/lib/Sema/SemaLambda.cpp b/clang/lib/Sema/SemaLambda.cpp
@@ -2390,21 +2390,26 @@ Sema::LambdaScopeForCallOperatorInstantiationRAII::
 
   llvm::SmallVector<std::pair<FunctionDecl *, FunctionDecl *>, 4>
       ParentInstantiations;
-  std::pair<FunctionDecl *, FunctionDecl *> Current = {FDPattern, FD};
   while (true) {
-    Current.first = dyn_cast<FunctionDecl>(
-        getLambdaAwareParentOfDeclContext(Current.first));
-    Current.second = dyn_cast<FunctionDecl>(
-        getLambdaAwareParentOfDeclContext(Current.second));
+    FDPattern =
+        dyn_cast<FunctionDecl>(getLambdaAwareParentOfDeclContext(FDPattern));
+    FD = dyn_cast<FunctionDecl>(getLambdaAwareParentOfDeclContext(FD));
 
-    if (!Current.first || !Current.second)
+    if (!FDPattern || !FD)
       break;
 
-    ParentInstantiations.push_back(Current);
+    ParentInstantiations.emplace_back(FDPattern, FD);
   }
 
-  for (const auto &[Pattern, Inst] : llvm::reverse(ParentInstantiations)) {
-    SemaRef.addInstantiatedParametersToScope(Inst, Pattern, Scope, MLTAL);
-    SemaRef.addInstantiatedLocalVarsToScope(Inst, Pattern, Scope);
+  // Add instantiated parameters and local vars to scopes, starting from the
+  // outermost lambda to the innermost lambda. This ordering ensures that
+  // parameters in inner lambdas can correctly depend on those defined
+  // in outer lambdas, e.g. auto L = [](auto... x) {
+  //   return [](decltype(x)... y) { }; // `y` depends on `x`
+  // };
+
+  for (const auto &[FDPattern, FD] : llvm::reverse(ParentInstantiations)) {
+    SemaRef.addInstantiatedParametersToScope(FD, FDPattern, Scope, MLTAL);
+    SemaRef.addInstantiatedLocalVarsToScope(FD, FDPattern, Scope);
   }
 }