[parser] Add first iteration of a parser benchmark

Modelled after the scanner_benchmark.

In jit mode it's currently at around 14 tokens/ms for
pkg/front_end/lib/src/type_inference/inference_visitor.dart
and 20 tokens/ms for pkg/analyzer/lib/src/dart/ast/ast.dart.

In aot mode it's currently at around 18 tokens/ms for
pkg/front_end/lib/src/type_inference/inference_visitor.dart
and 25 tokens/ms for pkg/analyzer/lib/src/dart/ast/ast.dart.

Change-Id: Ib080b68b99ddbddc16321237afb0d0d83fccdd11
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/439720
Reviewed-by: Chloe Stefantsova <[email protected]>
Commit-Queue: Jens Johansen <[email protected]>

Author: jensjoha

pkg/_fe_analyzer_shared/test/parser_benchmark.dart

@@ -0,0 +1,120 @@
+// 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 'dart:io';
+import 'dart:typed_data';
+
+import 'package:_fe_analyzer_shared/src/messages/codes.dart';
+import 'package:_fe_analyzer_shared/src/parser/forwarding_listener.dart';
+import 'package:_fe_analyzer_shared/src/parser/listener.dart';
+import 'package:_fe_analyzer_shared/src/parser/parser_impl.dart';
+import 'package:_fe_analyzer_shared/src/parser/stack_listener.dart';
+import 'package:_fe_analyzer_shared/src/scanner/scanner.dart';
+
+void main(List<String> args) {
+  if (args.length != 1) {
+    throw "Expected 1 argument: <dart file>.";
+  }
+  File f = new File(args.single);
+  if (!f.existsSync()) {
+    throw "File $f doesn't exist.";
+  }
+  Uint8List contentBytes = f.readAsBytesSync();
+  ScannerResult scanResult = scan(
+    contentBytes,
+    configuration: new ScannerConfiguration(enableTripleShift: true),
+    includeComments: true,
+  );
+
+  const int iterations = 1000;
+
+  int countTokens = 0;
+  {
+    Token t = scanResult.tokens;
+    while (!t.isEof) {
+      countTokens++;
+      t = t.next!;
+    }
+  }
+
+  // TODO: Should we make 1000 copies of the tokens?
+  // Or maybe scan 1000 times?
+  /*
+  List<Token> tokenStarts = [];
+  tokenStarts.add(scanResult.tokens);
+  while (tokenStarts.length < iterations) {
+    tokenStarts.add(
+      scan(
+        contentBytes,
+        configuration: new ScannerConfiguration(enableTripleShift: true),
+        includeComments: true,
+      ).tokens,
+    );
+  }
+  */
+
+  Listener listener = new NullListener();
+  if (f.path == "42") {
+    // Let's not let it optimize too many things away or do weird optimizations
+    // that it can't do in practise.
+    listener = new FooListener(f.uri);
+  }
+
+  int numErrors = 0;
+  Stopwatch stopwatch = new Stopwatch()..start();
+  int lengthProcessed = countTokens;
+
+  for (int i = 0; i < iterations; i++) {
+    Parser parser = new Parser(listener, allowPatterns: true);
+    Token after = parser.parseUnit(scanResult.tokens);
+    if (!after.isEof) {
+      throw "parsed returned before eof?!?";
+    }
+    if (listener is NullListener && listener.hasErrors) {
+      numErrors++;
+    }
+  }
+
+  stopwatch.stop();
+  print(
+    "Parsed $lengthProcessed tokens $iterations times "
+    "in ${stopwatch.elapsed}",
+  );
+  print("Found errors $numErrors times");
+  double lengthPerMicrosecond =
+      (lengthProcessed * iterations) / stopwatch.elapsedMicroseconds;
+  print("That's $lengthPerMicrosecond tokens per microsecond");
+  print("");
+}
+
+class FooListener extends StackListener {
+  List<Message> problems = [];
+
+  @override
+  final Uri uri;
+
+  FooListener(this.uri);
+
+  @override
+  void addProblem(
+    Message message,
+    int charOffset,
+    int length, {
+    bool wasHandled = false,
+    List<LocatedMessage>? context,
+  }) {
+    if (charOffset == 42) {
+      throw "$message $charOffset $length $wasHandled $context";
+    }
+    problems.add(message);
+  }
+
+  @override
+  Never internalProblem(Message message, int charOffset, Uri uri) {
+    throw UnimplementedError();
+  }
+
+  @override
+  bool get isDartLibrary => false;
+}