[Clang] Fix the order of addInstantiatedParameters in LambdaScopeForCallOperatorInstantiationRAII

[LYP951018]

Currently, addInstantiatedParameters is called from the innermost lambda outward. However, when the function parameters of an inner lambda depend on the function parameters of an outer lambda, it can lead to a crash due to the inability to find a mapping for the instantiated decl.

This PR corrects this behavior by calling addInstantiatedParameters from the outside in.

repro code: https://godbolt.org/z/KbsxWesW6

namespace dependent_param_concept {
template <typename... Ts> void sink(Ts...) {}
void dependent_param() {
  auto L = [](auto... x) {
    return [](decltype(x)... y) { // `y` depends on `x`
      return [](int z)
        requires requires { sink(y..., z); }
      {};
    };
  };
  L(0, 1)(1, 2)(1);
}
} // namespace dependent_param_concept

This PR is a prerequisite for implmenting #61426

[llvmbot]

@llvm/pr-subscribers-clang

Author: Yupei Liu (LYP951018)

Changes

Currently, addInstantiatedParameters is called from the innermost lambda outward. However, when the function parameters of an inner lambda depend on the function parameters of an outer lambda, it can lead to a crash due to the inability to find a mapping for the instantiated decl.

This PR corrects this behavior by calling addInstantiatedParameters from the outside in.

repro code: https://godbolt.org/z/KbsxWesW6

namespace dependent_param_concept {
template <typename... Ts> void sink(Ts...) {}
void dependent_param() {
  auto L = [](auto... x) {
    return [](decltype(x)... y) { // `y` depends on `x`
      return [](int z)
        requires requires { sink(y..., z); }
      {};
    };
  };
  L(0, 1)(1, 2)(1);
}
} // namespace dependent_param_concept

---

Full diff: https://github.com/llvm/llvm-project/pull/97215.diff

2 Files Affected:

• (modified) clang/lib/Sema/SemaLambda.cpp (+23-14)
• (modified) clang/test/SemaTemplate/concepts-lambda.cpp (+14)

diff --git a/clang/lib/Sema/SemaLambda.cpp b/clang/lib/Sema/SemaLambda.cpp
index e9476a0c93c5d..b6344f53861f4 100644
--- a/clang/lib/Sema/SemaLambda.cpp
+++ b/clang/lib/Sema/SemaLambda.cpp
@@ -2379,23 +2379,32 @@ Sema::LambdaScopeForCallOperatorInstantiationRAII::
 
   SemaRef.RebuildLambdaScopeInfo(cast<CXXMethodDecl>(FD));
 
-  FunctionDecl *Pattern = getPatternFunctionDecl(FD);
-  if (Pattern) {
-    SemaRef.addInstantiatedCapturesToScope(FD, Pattern, Scope, MLTAL);
+  FunctionDecl *FDPattern = getPatternFunctionDecl(FD);
+  if (!FDPattern)
+    return;
 
-    FunctionDecl *ParentFD = FD;
-    while (ShouldAddDeclsFromParentScope) {
+  SemaRef.addInstantiatedCapturesToScope(FD, FDPattern, Scope, MLTAL);
 
-      ParentFD =
-          dyn_cast<FunctionDecl>(getLambdaAwareParentOfDeclContext(ParentFD));
-      Pattern =
-          dyn_cast<FunctionDecl>(getLambdaAwareParentOfDeclContext(Pattern));
+  if (!ShouldAddDeclsFromParentScope)
+    return;
 
-      if (!FD || !Pattern)
-        break;
+  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));
 
-      SemaRef.addInstantiatedParametersToScope(ParentFD, Pattern, Scope, MLTAL);
-      SemaRef.addInstantiatedLocalVarsToScope(ParentFD, Pattern, Scope);
-    }
+    if (!Current.first || !Current.second)
+      break;
+
+    ParentInstantiations.push_back(Current);
+  }
+
+  for (const auto &[Pattern, Inst] : llvm::reverse(ParentInstantiations)) {
+    SemaRef.addInstantiatedParametersToScope(Inst, Pattern, Scope, MLTAL);
+    SemaRef.addInstantiatedLocalVarsToScope(Inst, Pattern, Scope);
   }
 }
diff --git a/clang/test/SemaTemplate/concepts-lambda.cpp b/clang/test/SemaTemplate/concepts-lambda.cpp
index 280be71284f97..252ef08549a48 100644
--- a/clang/test/SemaTemplate/concepts-lambda.cpp
+++ b/clang/test/SemaTemplate/concepts-lambda.cpp
@@ -237,3 +237,17 @@ concept D = []<C T = int>() { return true; }();
 D auto x = 0;
 
 } // namespace GH93821
+
+namespace dependent_param_concept {
+template <typename... Ts> void sink(Ts...) {}
+void dependent_param() {
+  auto L = [](auto... x) {
+    return [](decltype(x)... y) {
+      return [](int z)
+        requires requires { sink(y..., z); }
+      {};
+    };
+  };
+  L(0, 1)(1, 2)(1);
+}
+} // namespace dependent_param_concept

[LYP951018]

Sorry for disturbing... I'm trying to get the CI working. I can't figure out why buildkite/github-pull-requests failed...

[zyn0217]

Thanks! I think the approach makes sense. Just some nits from me
@cor3ntin do you have any other comments? I think you can do the last approval. :)

[zyn0217]

nit: Can you revert unrelated changes?

[LYP951018]

I would prefer to keep the current change. Firstly, this change is minimal and won’t significantly impact the review workload for this PR. Secondly, it reduces one level of indentation, which slightly improves readability. ;)

[zyn0217]

Oh, I forgot it: this also needs a release note.

[mizvekov]

LGTM

[LYP951018]

Thanks for the review ;)