[Migrator] Refactor fixit filter from JSONFixitWriter to common code

This filter is used for both applying fix-its during the normal
migration flow and by the -emit-fixits-path output for a normal
-typecheck frontend invocation, for example.

rdar://problem/30926261

lib/FrontendTool/FrontendTool.cpp

@@ -46,6 +46,7 @@
 #include "swift/Frontend/SerializedDiagnosticConsumer.h"
 #include "swift/Immediate/Immediate.h"
 #include "swift/Option/Options.h"
+#include "swift/Migrator/FixitFilter.h"
 #include "swift/Migrator/Migrator.h"
 #include "swift/PrintAsObjC/PrintAsObjC.h"
 #include "swift/Serialization/SerializationOptions.h"
@@ -209,7 +210,8 @@ namespace {
 
 /// If there is an error with fixits it writes the fixits as edits in json
 /// format.
-class JSONFixitWriter : public DiagnosticConsumer {
+class JSONFixitWriter
+  : public DiagnosticConsumer, public migrator::FixitFilter {
   std::unique_ptr<llvm::raw_ostream> OSPtr;
   bool FixitAll;
   std::vector<SingleEdit> AllEdits;
@@ -229,89 +231,12 @@ private:
                         StringRef FormatString,
                         ArrayRef<DiagnosticArgument> FormatArgs,
                         const DiagnosticInfo &Info) override {
-    if (!shouldFix(Kind, Info))
+    if (!(FixitAll || shouldTakeFixit(Kind, Info)))
       return;
     for (const auto &Fix : Info.FixIts) {
       AllEdits.push_back({SM, Fix.getRange(), Fix.getText()});
     }
   }
-
-  bool shouldFix(DiagnosticKind Kind, const DiagnosticInfo &Info) {
-    if (FixitAll)
-      return true;
-
-    // Do not add a semi or comma as it is wrong in most cases during migration
-    if (Info.ID == diag::statement_same_line_without_semi.ID ||
-        Info.ID == diag::declaration_same_line_without_semi.ID ||
-        Info.ID == diag::expected_separator.ID)
-      return false;
-    // The following interact badly with the swift migrator, they are undoing
-    // migration of arguments to preserve the no-label for first argument.
-    if (Info.ID == diag::witness_argument_name_mismatch.ID ||
-      Info.ID == diag::missing_argument_labels.ID ||
-      Info.ID == diag::override_argument_name_mismatch.ID)
-      return false;
-    // This also interacts badly with the swift migrator, it unnecessary adds
-    // @objc(selector) attributes triggered by the mismatched label changes.
-    if (Info.ID == diag::objc_witness_selector_mismatch.ID ||
-        Info.ID == diag::witness_non_objc.ID)
-      return false;
-    // This interacts badly with the migrator. For such code:
-    //   func test(p: Int, _: String) {}
-    //   test(0, "")
-    // the compiler bizarrely suggests to change order of arguments in the call
-    // site.
-    if (Info.ID == diag::argument_out_of_order_unnamed_unnamed.ID)
-      return false;
-    // The following interact badly with the swift migrator by removing @IB*
-    // attributes when there is some unrelated type issue.
-    if (Info.ID == diag::invalid_iboutlet.ID ||
-        Info.ID == diag::iboutlet_nonobjc_class.ID ||
-        Info.ID == diag::iboutlet_nonobjc_protocol.ID ||
-        Info.ID == diag::iboutlet_nonobject_type.ID ||
-        Info.ID == diag::iboutlet_only_mutable.ID ||
-        Info.ID == diag::invalid_ibdesignable_extension.ID ||
-        Info.ID == diag::invalid_ibinspectable.ID ||
-        Info.ID == diag::invalid_ibaction_decl.ID)
-      return false;
-    // Adding type(of:) interacts poorly with the swift migrator by
-    // invalidating some inits with type errors.
-    if (Info.ID == diag::init_not_instance_member.ID)
-      return false;
-    // Renaming enum cases interacts poorly with the swift migrator by
-    // reverting changes made by the migrator.
-    if (Info.ID == diag::could_not_find_enum_case.ID)
-      return false;
-
-    if (Kind == DiagnosticKind::Error)
-      return true;
-
-    // Fixits from warnings/notes that should be applied.
-    if (Info.ID == diag::forced_downcast_coercion.ID ||
-        Info.ID == diag::forced_downcast_noop.ID ||
-        Info.ID == diag::variable_never_mutated.ID ||
-        Info.ID == diag::function_type_no_parens.ID ||
-        Info.ID == diag::convert_let_to_var.ID ||
-        Info.ID == diag::parameter_extraneous_double_up.ID ||
-        Info.ID == diag::attr_decl_attr_now_on_type.ID ||
-        Info.ID == diag::noescape_parameter.ID ||
-        Info.ID == diag::noescape_autoclosure.ID ||
-        Info.ID == diag::where_inside_brackets.ID ||
-        Info.ID == diag::selector_construction_suggest.ID ||
-        Info.ID == diag::selector_literal_deprecated_suggest.ID ||
-        Info.ID == diag::attr_noescape_deprecated.ID ||
-        Info.ID == diag::attr_autoclosure_escaping_deprecated.ID ||
-        Info.ID == diag::attr_warn_unused_result_removed.ID ||
-        Info.ID == diag::any_as_anyobject_fixit.ID ||
-        Info.ID == diag::deprecated_protocol_composition.ID ||
-        Info.ID == diag::deprecated_protocol_composition_single.ID ||
-        Info.ID == diag::deprecated_any_composition.ID ||
-        Info.ID == diag::deprecated_operator_body.ID ||
-        Info.ID == diag::unbound_generic_parameter_explicit_fix.ID)
-      return true;
-
-    return false;
-  }
 };
 
 } // anonymous namespace