Merge pull request #26577 from xedin/improve-force-downcast-diags

[Diagnostics] Make force downcast fix contextual and move it to `repa…

lib/Sema/CSSimplify.cpp

@@ -2186,6 +2186,58 @@ static ConstraintFix *fixPropertyWrapperFailure(
   return nullptr;
 }
 
+static bool canBridgeThroughCast(ConstraintSystem &cs, Type fromType,
+                                 Type toType) {
+  // If we have a value of type AnyObject that we're trying to convert to
+  // a class, force a downcast.
+  // FIXME: Also allow types bridged through Objective-C classes.
+  if (fromType->isAnyObject() && toType->getClassOrBoundGenericClass())
+    return true;
+
+  auto &TC = cs.getTypeChecker();
+  auto bridged = TC.getDynamicBridgedThroughObjCClass(cs.DC, fromType, toType);
+  if (!bridged)
+    return false;
+
+  // Note: don't perform this recovery for NSNumber;
+  if (auto classType = bridged->getAs<ClassType>()) {
+    SmallString<16> scratch;
+    if (classType->getDecl()->isObjC() &&
+        classType->getDecl()->getObjCRuntimeName(scratch) == "NSNumber")
+      return false;
+  }
+
+  return true;
+}
+
+static bool
+repairViaBridgingCast(ConstraintSystem &cs, Type fromType, Type toType,
+                      SmallVectorImpl<RestrictionOrFix> &conversionsOrFixes,
+                      ConstraintLocatorBuilder locator) {
+  auto objectType1 = fromType->getOptionalObjectType();
+  auto objectType2 = toType->getOptionalObjectType();
+
+  if (objectType1 && !objectType2) {
+    auto *anchor = locator.trySimplifyToExpr();
+    if (!anchor)
+      return false;
+
+    if (auto *overload = cs.findSelectedOverloadFor(anchor)) {
+      auto *decl = overload->Choice.getDeclOrNull();
+      if (decl &&
+          decl->getAttrs().hasAttribute<ImplicitlyUnwrappedOptionalAttr>())
+        fromType = objectType1;
+    }
+  }
+
+  if (!canBridgeThroughCast(cs, fromType, toType))
+    return false;
+
+  conversionsOrFixes.push_back(ForceDowncast::create(
+      cs, fromType, toType, cs.getConstraintLocator(locator)));
+  return true;
+}
+
 /// Attempt to repair typing failures and record fixes if needed.
 /// \return true if at least some of the failures has been repaired
 /// successfully, which allows type matcher to continue.
@@ -2301,6 +2353,9 @@ bool ConstraintSystem::repairFailures(
 
       if (repairByAnyToAnyObjectCast(lhs, rhs))
         return true;
+
+      if (repairViaBridgingCast(*this, lhs, rhs, conversionsOrFixes, locator))
+        return true;
     }
 
     return false;
@@ -2321,7 +2376,10 @@ bool ConstraintSystem::repairFailures(
   case ConstraintLocator::ApplyArgToParam: {
     auto loc = getConstraintLocator(locator);
     if (repairByInsertingExplicitCall(lhs, rhs))
-      return true;
+      break;
+
+    if (repairViaBridgingCast(*this, lhs, rhs, conversionsOrFixes, locator))
+      break;
 
     if (lhs->getOptionalObjectType() && !rhs->getOptionalObjectType()) {
       conversionsOrFixes.push_back(
@@ -2444,10 +2502,13 @@ bool ConstraintSystem::repairFailures(
     }
 
     if (repairByInsertingExplicitCall(lhs, rhs))
-      return true;
+      break;
 
     if (repairByAnyToAnyObjectCast(lhs, rhs))
-      return true;
+      break;
+
+    if (repairViaBridgingCast(*this, lhs, rhs, conversionsOrFixes, locator))
+      break;
 
     // If both types are key path, the only differences
     // between them are mutability and/or root, value type mismatch.
@@ -3317,32 +3378,6 @@ ConstraintSystem::matchTypes(Type type1, Type type2, ConstraintKind kind,
       }
     }
 
-    // If we have a value of type AnyObject that we're trying to convert to
-    // a class, force a downcast.
-    // FIXME: Also allow types bridged through Objective-C classes.
-    if (objectType1->isAnyObject() &&
-        type2->getClassOrBoundGenericClass()) {
-      conversionsOrFixes.push_back(
-          ForceDowncast::create(*this, type2, getConstraintLocator(locator)));
-    }
-
-    // If we could perform a bridging cast, try it.
-    if (auto bridged =
-            TC.getDynamicBridgedThroughObjCClass(DC, objectType1, type2)) {
-      // Note: don't perform this recovery for NSNumber;
-      bool useFix = true;
-      if (auto classType = bridged->getAs<ClassType>()) {
-        SmallString<16> scratch;
-        if (classType->getDecl()->isObjC() &&
-            classType->getDecl()->getObjCRuntimeName(scratch) == "NSNumber")
-          useFix = false;
-      }
-
-      if (useFix)
-        conversionsOrFixes.push_back(
-            ForceDowncast::create(*this, type2, getConstraintLocator(locator)));
-    }
-
     if (!type1->is<LValueType>() && type2->is<InOutType>()) {
       // If we have a concrete type that's an rvalue, "fix" it.
       conversionsOrFixes.push_back(