[ConstraintSystem] Detect and diagnose contextual mismatches in key path components

Author: xedin

lib/Sema/CSDiagnostics.cpp

@@ -1888,7 +1888,16 @@ bool ContextualFailure::diagnoseAsError() {
   if (diagnoseConversionToNil())
     return true;
 
-  assert(!path.empty());
+  if (path.empty()) {
+    if (auto *KPE = dyn_cast<KeyPathExpr>(anchor)) {
+      emitDiagnostic(KPE->getLoc(),
+                     diag::expr_smart_keypath_value_covert_to_contextual_type,
+                     getFromType(), getToType());
+      return true;
+    }
+
+    return false;
+  }
 
   if (diagnoseMissingFunctionCall())
     return true;

lib/Sema/CSSimplify.cpp

@@ -2523,6 +2523,10 @@ bool ConstraintSystem::repairFailures(
       auto *fnType = lhs->getAs<FunctionType>();
       if (fnType && fnType->getResult()->isEqual(rhs))
         return true;
+
+      conversionsOrFixes.push_back(IgnoreContextualType::create(
+          *this, lhs, rhs, getConstraintLocator(locator)));
+      return true;
     }
 
     if (auto *AE = dyn_cast<AssignExpr>(anchor)) {