[ConstraintSystem] Retrieve contextual from a solution for ambiguities

In ambiguity scenarios solutions are not applied back to the constraint
system, so it might not always have contextual type information when it
was recorded e.g. for a multi-statement closure.

Resolves: rdar://97396399

Author: xedin

include/swift/Sema/ConstraintSystem.h

@@ -1489,6 +1489,15 @@ class Solution {
   /// types where possible.
   Type resolveInterfaceType(Type type) const;
 
+  Type getContextualType(ASTNode anchor) const {
+    for (const auto &entry : contextualTypes) {
+      if (entry.first == anchor) {
+        return simplifyType(entry.second.getType());
+      }
+    }
+    return Type();
+  }
+
   /// For a given locator describing a function argument conversion, or a
   /// constraint within an argument conversion, returns information about the
   /// application of the argument to its parameter. If the locator is not

lib/Sema/ConstraintSystem.cpp

@@ -4257,9 +4257,12 @@ static bool diagnoseAmbiguityWithContextualType(
 
   auto anchor = locator->getAnchor();
   auto name = result->choices.front().getName();
+  auto contextualTy = solution.getContextualType(anchor);
+
+  assert(contextualTy);
+
   DE.diagnose(getLoc(anchor), diag::no_candidates_match_result_type,
-              name.getBaseName().userFacingName(),
-              cs.getContextualType(anchor, /*forConstraint=*/false));
+              name.getBaseName().userFacingName(), contextualTy);
 
   for (const auto &solution : solutions) {
     auto overload = solution.getOverloadChoice(calleeLocator);
@@ -4272,10 +4275,9 @@ static bool diagnoseAmbiguityWithContextualType(
 
       if (isExpr<ApplyExpr>(anchor) || isExpr<SubscriptExpr>(anchor)) {
         auto fnType = type->castTo<FunctionType>();
-        DE.diagnose(
-            loc, diag::cannot_convert_candidate_result_to_contextual_type,
-            decl->getName(), fnType->getResult(),
-            cs.getContextualType(anchor, /*forConstraint=*/false));
+        DE.diagnose(loc,
+                    diag::cannot_convert_candidate_result_to_contextual_type,
+                    decl->getName(), fnType->getResult(), contextualTy);
       } else {
         DE.diagnose(loc, diag::found_candidate_type, type);
       }