82 lines
3.1 KiB
Dart
82 lines
3.1 KiB
Dart
// Copyright 2014 The Flutter Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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import 'package:file/file.dart';
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import 'package:package_config/package_config.dart';
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final RegExp _languageVersion = RegExp(r'\/\/\s*@dart\s*=\s*([0-9])\.([0-9]+)');
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final RegExp _declarationEnd = RegExp('(import)|(library)|(part)');
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const String _blockCommentStart = '/*';
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const String _blockCommentEnd = '*/';
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/// The first language version where null safety was available by default.
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final LanguageVersion nullSafeVersion = LanguageVersion(2, 12);
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/// Attempts to read the language version of a dart [file].
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///
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/// If this is not present, falls back to the language version defined in
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/// [package]. If [package] is not provided and there is no
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/// language version header, returns 2.12. This does not specifically check
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/// for language declarations other than library, part, or import.
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///
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/// The specification for the language version tag is defined at:
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/// https://github.com/dart-lang/language/blob/master/accepted/future-releases/language-versioning/feature-specification.md#individual-library-language-version-override
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LanguageVersion determineLanguageVersion(File file, Package package) {
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int blockCommentDepth = 0;
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for (final String line in file.readAsLinesSync()) {
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final String trimmedLine = line.trim();
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if (trimmedLine.isEmpty) {
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continue;
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}
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// Check for the start or end of a block comment. Within a block
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// comment, all language version declarations are ignored. Block
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// comments can be nested, and the start or end may occur on
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// the same line. This does not handle the case of invalid
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// block comment combinations like `*/ /*` since that will cause
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// a compilation error anyway.
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bool sawBlockComment = false;
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final int startMatches = _blockCommentStart.allMatches(trimmedLine).length;
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final int endMatches = _blockCommentEnd.allMatches(trimmedLine).length;
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if (startMatches > 0) {
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blockCommentDepth += startMatches;
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sawBlockComment = true;
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}
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if (endMatches > 0) {
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blockCommentDepth -= endMatches;
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sawBlockComment = true;
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}
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if (blockCommentDepth != 0 || sawBlockComment) {
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continue;
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}
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// Check for a match with the language version.
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final Match match = _languageVersion.matchAsPrefix(trimmedLine);
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if (match != null) {
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final String rawMajor = match.group(1);
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final String rawMinor = match.group(2);
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try {
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final int major = int.parse(rawMajor);
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final int minor = int.parse(rawMinor);
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return LanguageVersion(major, minor);
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} on FormatException {
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// Language comment was invalid in a way that the regexp did not
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// anticipate.
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break;
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}
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}
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// Check for a declaration which ends the search for a language
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// version.
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if (_declarationEnd.matchAsPrefix(trimmedLine) != null) {
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break;
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}
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}
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// If the language version cannot be found, use the package version.
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if (package != null) {
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return package.languageVersion;
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}
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// Default to 2.12
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return nullSafeVersion;
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}
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