[messages] Remove hacks that allowed for non-existent file.

Removes the following hacks:

- The `allowNonExistent` parameter from `_loadCfeStyleMessages`.

- The `!file.existsSync()` check from `messages_suite.dart`.

These were temporary hacks to allow code generation (and presubmits,
respectively) to succeed during the transition period before
`pkg/_fe_analyzer_shared/messages.yaml` was introduced.

Now that `pkg/_fe_analyzer_shared/messages.yaml` is present, the hacks
are no longer needed.

Change-Id: I6a6a69642565a8278a94b61912308bfdcbd04d50
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/448661
Commit-Queue: Paul Berry <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>

Author: stereotype441

pkg/analyzer_utilities/lib/messages.dart

@@ -23,11 +23,7 @@ const Map<String, String> severityEnumNames = <String, String>{
 /// Decoded messages from the `_fe_analyzer_shared` package's `messages.yaml`
 /// file.
 final Map<String, CfeStyleErrorCodeInfo> feAnalyzerSharedMessages =
-    _loadCfeStyleMessages(
-      feAnalyzerSharedPkgPath,
-      allowNonExistent: true,
-      isShared: true,
-    );
+    _loadCfeStyleMessages(feAnalyzerSharedPkgPath, isShared: true);
 
 /// The path to the `fe_analyzer_shared` package.
 final String feAnalyzerSharedPkgPath = normalize(
@@ -107,19 +103,11 @@ Map<String, CfeStyleErrorCodeInfo> decodeCfeStyleMessagesYaml(
 }
 
 /// Loads messages in CFE style `messages.yaml` format.
-///
-/// If [allowNonExistent] is `true`, and the `messages.yaml` file does not
-/// exist, an empty map is returned. This is a temporary measure to allow for an
-/// easier transition when the file `pkg/_fe_analyzer_shared/messages.yaml` is
-/// created.
-// TODO(paulberry): remove [allowNonExistent] once it's no longer needed.
 Map<String, CfeStyleErrorCodeInfo> _loadCfeStyleMessages(
   String packagePath, {
-  bool allowNonExistent = false,
   required bool isShared,
 }) {
   var path = join(packagePath, 'messages.yaml');
-  if (allowNonExistent && !File(path).existsSync()) return {};
   Object? messagesYaml = loadYaml(
     File(path).readAsStringSync(),
     sourceUrl: Uri.file(path),

pkg/front_end/test/messages_suite.dart

@@ -179,10 +179,6 @@ class MessageTestSuite extends ChainContext {
     List<MessageTestDescription> result = [];
     Uri uri = root.resolve("messages.yaml");
     File file = new File.fromUri(uri);
-    // Allow for the possibility that the file might not exist yet.
-    // TODO(paulberry): remove this hack once
-    // `pkg/_fe_analyzer_shared/messages.yaml` exists
-    if (!file.existsSync()) return const [];
     String fileContent = file.readAsStringSync();
     YamlMap messages = loadYamlNode(fileContent, sourceUrl: uri) as YamlMap;
     for (String name in messages.keys) {