Sema: Diagnose duplicate capture list entires when parser lookup is off

Another spot where we have to check for redeclaration manually now.
As before, we can use the existing mechanism though.

Author: slavapestov

lib/Sema/CSGen.cpp

@@ -3440,6 +3440,8 @@ namespace {
 
       // Generate constraints for each of the entries in the capture list.
       if (auto captureList = dyn_cast<CaptureListExpr>(expr)) {
+        TypeChecker::diagnoseDuplicateCaptureVars(captureList);
+
         auto &CS = CG.getConstraintSystem();
         for (const auto &capture : captureList->getCaptureList()) {
           SolutionApplicationTarget target(capture.Init);

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -1334,6 +1334,14 @@ void TypeChecker::diagnoseDuplicateBoundVars(Pattern *pattern) {
   diagnoseDuplicateDecls(boundVars);
 }
 
+void TypeChecker::diagnoseDuplicateCaptureVars(CaptureListExpr *expr) {
+  SmallVector<VarDecl *, 2> captureListVars;
+  for (auto &capture : expr->getCaptureList())
+    captureListVars.push_back(capture.Var);
+
+  diagnoseDuplicateDecls(captureListVars);
+}
+
 namespace {
 class DeclChecker : public DeclVisitor<DeclChecker> {
 public:

lib/Sema/TypeChecker.h

@@ -502,6 +502,8 @@ void checkParameterList(ParameterList *params);
 
 void diagnoseDuplicateBoundVars(Pattern *pattern);
 
+void diagnoseDuplicateCaptureVars(CaptureListExpr *expr);
+
 Type checkReferenceOwnershipAttr(VarDecl *D, Type interfaceType,
                                  ReferenceOwnershipAttr *attr);