1 files changed, 17 insertions, 3 deletions
diff --git a/lib/Sema/SemaLambda.cpp b/lib/Sema/SemaLambda.cpp
index 803b253e45..aa60ce113d 100644
--- a/lib/Sema/SemaLambda.cpp
+++ b/lib/Sema/SemaLambda.cpp
@@ -493,7 +493,9 @@ void Sema::finishLambdaExplicitCaptures(LambdaScopeInfo *LSI) {
   LSI->finishedExplicitCaptures();
 }
 
-void Sema::addLambdaParameters(CXXMethodDecl *CallOperator, Scope *CurScope) {
+void Sema::addLambdaParameters(
+    ArrayRef<LambdaIntroducer::LambdaCapture> Captures,
+    CXXMethodDecl *CallOperator, Scope *CurScope) {
   // Introduce our parameters into the function scope
   for (unsigned p = 0, NumParams = CallOperator->getNumParams();
        p < NumParams; ++p) {
@@ -501,7 +503,19 @@ void Sema::addLambdaParameters(CXXMethodDecl *CallOperator, Scope *CurScope) {
 
     // If this has an identifier, add it to the scope stack.
     if (CurScope && Param->getIdentifier()) {
-      CheckShadow(CurScope, Param);
+      bool Error = false;
+      // Resolution of CWG 2211 in C++17 renders shadowing ill-formed, but we
+      // retroactively apply it.
+      for (const auto &Capture : Captures) {
+        if (Capture.Id == Param->getIdentifier()) {
+          Error = true;
+          Diag(Param->getLocation(), diag::err_parameter_shadow_capture);
+          Diag(Capture.Loc, diag::note_var_explicitly_captured_here)
+              << Capture.Id << true;
+        }
+      }
+      if (!Error)
+        CheckShadow(CurScope, Param);
 
       PushOnScopeChains(Param, CurScope);
     }
@@ -1142,7 +1156,7 @@ void Sema::ActOnStartOfLambdaDefinition(LambdaIntroducer &Intro,
   LSI->ContainsUnexpandedParameterPack = ContainsUnexpandedParameterPack;
 
   // Add lambda parameters into scope.
-  addLambdaParameters(Method, CurScope);
+  addLambdaParameters(Intro.Captures, Method, CurScope);
 
   // Enter a new evaluation context to insulate the lambda from any
   // cleanups from the enclosing full-expression.