[front_end] Rework diagnostic code generation.

This change reworks the logic for generating the files
`pkg/_fe_analyzer_shared/lib/src/messages/codes_generated.dart` and
`pkg/front_end/lib/src/codes/cfe_codes_generated.dart`.

The following changes are made:

- The generated code is changed so that each `withArgumentsOld`
  function forwards to a corresponding `withArguments` function, which
  accepts named arguments rather than positional ones. In later CLs
  these new `withArguments` functions will be made available to call
  directly from CFE code.

- The code in the `withArguments` functions uses a uniform naming
  convention, where the parameter names match the parameter names
  specified in the error message templates, and the variables holding
  the result of string conversions are named by appending `_0` to the
  parameter names.*

  *In principle, variables suffixed with `_1`, `_2`, etc. might be
  generated in the circumstance where a single parameter gets
  converted to strings in multiple ways. But this doesn't happen in
  practice.

- The code in the `withArguments` functions converts arguments to
  strings in a uniform way, by calling either top level functions in
  `pkg/_fe_analyzer_shared/lib/src/messages/conversions.dart` or
  methods on the `TypeLabeler` class.

- The code generation logic in
  `pkg/front_end/tool/generate_messages_lib.dart` has been refactored
  considerably, with an eye toward allowing it to be further
  generalized in the future. In particular, in follow-up CLs I plan to
  allow each error message to define the precise set of placeholders
  it will use, and their types, as is done in the analyzer's
  `messages.yaml` file.

There is no change to functionality.

Change-Id: I6a6a69644e3bd3a5871bc4d156865f2ac499e8a6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/447823
Reviewed-by: Johnni Winther <[email protected]>
Commit-Queue: Paul Berry <[email protected]>

Author: stereotype441

pkg/_fe_analyzer_shared/lib/src/messages/codes.dart

@@ -14,6 +14,9 @@ import 'severity.dart' show CfeSeverity;
 
 import '../util/relativize.dart' as util show isWindows, relativizeUri;
 
+import 'conversions.dart' as conversions;
+import 'codes.dart' as conversions show relativizeUri;
+
 part 'codes_generated.dart';
 
 const int noLength = 1;

pkg/_fe_analyzer_shared/lib/src/messages/codes_generated.dart

@@ -0,0 +1,51 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:_fe_analyzer_shared/src/messages/codes.dart';
+import 'package:_fe_analyzer_shared/src/scanner/scanner.dart';
+
+String codePointToUnicode(int codePoint) {
+  // Write unicode value using at least four (but otherwise no more than
+  // necessary) hex digits, using uppercase letters.
+  // http://www.unicode.org/versions/Unicode10.0.0/appA.pdf
+  return "U+${codePoint.toRadixString(16).toUpperCase().padLeft(4, '0')}";
+}
+
+String formatNumber(
+  num num, {
+  int? fractionDigits,
+  int padWidth = 0,
+  bool padWithZeros = false,
+}) {
+  String s = fractionDigits == null
+      ? '$num'
+      : num.toStringAsFixed(fractionDigits);
+  return s.padLeft(padWidth, padWithZeros ? '0' : ' ');
+}
+
+String nameOrUnnamed(String name) => name.isEmpty ? '(unnamed)' : name;
+
+String stringOrEmpty(String string) => string.isEmpty ? '(empty)' : string;
+
+String tokenToLexeme(Token token) => token.lexeme;
+
+String validateAndDemangleName(String name) {
+  if (name.isEmpty) throw 'No name provided';
+  return demangleMixinApplicationName(name);
+}
+
+String validateAndItemizeNames(List<String> names) {
+  if (names.isEmpty) throw 'No names provided';
+  return itemizeNames(names);
+}
+
+String validateCharacter(String character) {
+  if (character.runes.length != 1) throw "Not a character '${character}'";
+  return character;
+}
+
+String validateString(String string) {
+  if (string.isEmpty) throw 'No string provided';
+  return string;
+}

pkg/_fe_analyzer_shared/lib/src/messages/conversions.dart

@@ -6,6 +6,8 @@ import 'package:_fe_analyzer_shared/src/messages/codes.dart';
 import 'package:_fe_analyzer_shared/src/messages/severity.dart';
 import 'package:kernel/ast.dart' show Constant, DartType;
 
+import 'package:_fe_analyzer_shared/src/messages/conversions.dart'
+    as conversions;
 import 'type_labeler.dart';
 
 export 'package:_fe_analyzer_shared/src/messages/codes.dart';