tools/verify_docs/bin/verify_docs.dart - sdk.git - Git at Google

 // Copyright (c) 2021, 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.

 // Read the ../README.md file for the recognized syntax.

 import 'dart:collection';
 import 'dart:io';

 import 'package:analyzer/dart/analysis/analysis_context_collection.dart';
 import 'package:analyzer/dart/analysis/features.dart';
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/dart/analysis/utilities.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/diagnostic/diagnostic.dart';
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/file_system/overlay_file_system.dart';
 import 'package:analyzer/file_system/physical_file_system.dart';
 import 'package:analyzer/source/line_info.dart';
 import 'package:analyzer/src/error/codes.dart';
 import 'package:analyzer/src/util/comment.dart';
 import 'package:path/path.dart' as path;

 final libDir = Directory(path.join('sdk', 'lib'));
 void main(List<String> args) async {
   if (!libDir.existsSync()) {
     print('Please run this tool from the root of the sdk repository.');
     exit(1);
   }

   print('Validating the dartdoc code samples from the dart: libraries.');
   print('');
   print('To run this tool, run `dart tools/verify_docs/bin/verify_docs.dart`.');
   print('');
   print('For documentation about how to author dart: code samples,'
       ' see tools/verify_docs/README.md.');
   print('');

   final coreLibraries = args.isEmpty
       ? libDir.listSync().whereType<Directory>().toList()
       : args.map(parseArg).toList();
   coreLibraries.sort((a, b) => a.path.compareTo(b.path));

   // Skip some dart: libraries.
   const skipLibraries = {
     'html',
     'indexed_db',
     'svg',
     'vmservice',
     'web_audio',
     'web_gl',
     'web_sql'
   };
   coreLibraries.removeWhere(
     (lib) => skipLibraries.contains(path.basename(lib.path)),
   );

   var hadErrors = false;
   for (final dir in coreLibraries) {
     hadErrors |= !(await validateLibrary(dir));
   }

   exitCode = hadErrors ? 1 : 0;
 }

 Future<bool> validateLibrary(Directory dir) async {
   final libName = path.basename(dir.path);

   final analysisHelper = AnalysisHelper(libName);

   print('## dart:$libName');
   print('');

   var validDocs = true;

   for (final file in dir
       .listSync(recursive: true)
       .whereType<File>()
       .where((file) => file.path.endsWith('.dart'))) {
     validDocs &= await verifyFile(analysisHelper, libName, file, dir);
   }

   return validDocs;
 }

 Future<bool> verifyFile(
   AnalysisHelper analysisHelper,
   String coreLibName,
   File file,
   Directory parent,
 ) async {
   final text = file.readAsStringSync();
   var parseResult = parseString(
     content: text,
     featureSet: FeatureSet.latestLanguageVersion(),
     path: file.path,
     throwIfDiagnostics: false,
   );

   // Throw if there are syntactic errors.
   var syntacticErrors = parseResult.errors.where((error) {
     return error.errorCode.type == ErrorType.SYNTACTIC_ERROR;
   }).toList();
   if (syntacticErrors.isNotEmpty) {
     throw Exception(syntacticErrors);
   }

   final sampleAssumptions = findFileAssumptions(text);

   var visitor = ValidateCommentCodeSamplesVisitor(
     analysisHelper,
     coreLibName,
     file.path,
     parseResult.lineInfo,
     sampleAssumptions,
   );
   await visitor.process(parseResult);
   return !visitor.hadErrors;
 }

 /// Visit a compilation unit and validate the code samples found in dartdoc
 /// comments.
 class ValidateCommentCodeSamplesVisitor extends GeneralizingAstVisitor {
   final AnalysisHelper analysisHelper;
   final String coreLibName;
   final String filePath;
   final LineInfo lineInfo;
   final String? sampleAssumptions;

   final List<CodeSample> samples = [];
   bool hadErrors = false;

   ValidateCommentCodeSamplesVisitor(
     this.analysisHelper,
     this.coreLibName,
     this.filePath,
     this.lineInfo,
     this.sampleAssumptions,
   );

   Future process(ParseStringResult parseResult) async {
     // collect code samples
     visitCompilationUnit(parseResult.unit);

     // analyze them
     for (CodeSample sample in samples) {
       await validateCodeSample(sample);
     }
   }

   @override
   void visitAnnotatedNode(AnnotatedNode node) {
     _handleDocumentableNode(node);
     super.visitAnnotatedNode(node);
   }

   void _handleDocumentableNode(AnnotatedNode node) {
     final docComment = node.documentationComment;
     if (docComment == null || !docComment.isDocumentation) {
       return;
     }

     const sampleStart = '```dart';
     const sampleEnd = '```';

     final text = getCommentNodeRawText(docComment)!;
     final commentOffset = docComment.offset;
     final commentLineStart = lineInfo.getLocation(commentOffset).lineNumber;
     if (!text.contains(sampleStart)) {
       return;
     }

     var offset = text.indexOf(sampleStart);
     while (offset != -1) {
       // Collect template directives, like "```dart import:async".
       final codeFenceSuffix = text
           .substring(offset + sampleStart.length, text.indexOf('\n', offset))
           .trim();

       offset = text.indexOf('\n', offset) + 1;
       final end = text.indexOf(sampleEnd, offset);

       var snippet = text.substring(offset, end);
       snippet = snippet.substring(0, snippet.lastIndexOf('\n'));

       List<String> lines = snippet.split('\n');
       var startLineNumber = commentLineStart +
           text.substring(0, offset - 1).split('\n').length -
           1;
       if (codeFenceSuffix == "continued") {
         if (samples.isEmpty) {
           throw "Continued code block without previous code";
         }
         samples.last = samples.last.append(lines, startLineNumber);
       } else {
         final directives = Set.unmodifiable(codeFenceSuffix.split(' '));
         samples.add(
           CodeSample(
             [for (var e in lines) '  ${cleanDocLine(e)}'],
             coreLibName: coreLibName,
             directives: directives,
             lineStartOffset: startLineNumber,
           ),
         );
       }

       offset = text.indexOf(sampleStart, offset);
     }
   }

   // RegExp detecting various top-level declarations or `main(`.
   //
   // If the top-level declaration is `library` or `import`,
   // then match 1 (`libdecl`) will be non-null.
   // This is a sign that no auto-imports should be added.
   //
   // If an import declaration is included in the sample, no
   // assumed-declarations are added.
   // Use the `import:foo` template to import other `dart:` libraries
   // instead of writing them explicitly to.
   //
   // Captures:
   // 1/libdecl: Non-null if mathcing a `library` declaration.
   // 2: Internal use, quote around import URI.
   // 3/importuri: Import URI.
   final _toplevelDeclarationRE = RegExp(r'^\s*(?:'
       r'library\b(?<libdecl>)|'
       r'''import (['"])(?<importuri>.*?)\2|'''
       r'class\b|mixin\b|enum\b|extension\b|typedef\b|.*\bmain\('
       r')');

   validateCodeSample(CodeSample sample) async {
     final lines = sample.lines;

     // The default imports includes the library itself
     // and any import directives.
     Set<String> autoImports = sample.imports;

     // One of 'none', 'top, 'main', or 'expression'.
     String template;

     bool hasImport = false;

     final templateDirective = sample.templateDirective;
     if (templateDirective != null) {
       template = templateDirective;
     } else {
       // Scan lines for top-level declarations.
       bool hasTopDeclaration = false;
       bool hasLibraryDeclaration = false;
       for (var line in lines) {
         var topDeclaration = _toplevelDeclarationRE.firstMatch(line);
         if (topDeclaration != null) {
           hasTopDeclaration = true;
           hasLibraryDeclaration |=
               (topDeclaration.namedGroup("libdecl") != null);
           var importDecl = topDeclaration.namedGroup("importuri");
           if (importDecl != null) {
             hasImport = true;
             if (importDecl.startsWith('dart:')) {
               // Remove explicit imports from automatic imports
               // to avoid duplicate import warnings.
               autoImports.remove(importDecl.substring('dart:'.length));
             }
           }
         }
       }
       if (hasLibraryDeclaration) {
         template = 'none';
       } else if (hasTopDeclaration) {
         template = 'top';
       } else if (lines.length == 1 && !lines.first.contains(';')) {
         // If single line with no `;`, assume expression.
         template = 'expression';
       } else {
         // Otherwise default to `main`.
         template = 'main';
       }
     }

     var buffer = StringBuffer();

     if (template != 'none') {
       for (var library in autoImports) {
         buffer.writeln("import 'dart:$library';");
       }
       if (!hasImport) {
         buffer.write(sampleAssumptions ?? '');
       }
     }
     if (template == 'none' || template == 'top') {
       buffer.writeAllLines(lines);
     } else if (template == 'main') {
       buffer
         ..writeln('void main() async {')
         ..writeAllLines(lines)
         ..writeln('}');
     } else if (template == 'expression') {
       assert(lines.isNotEmpty);
       buffer
         ..writeln('void main() async =>')
         ..writeAllLines(lines.take(lines.length - 1))
         ..writeln("${lines.last.trimRight()};");
     } else {
       throw 'unexpected template directive: $template';
     }

     final text = buffer.toString();

     final result = await analysisHelper.resolveFile(text);

     if (result is ResolvedUnitResult) {
       var errors = SplayTreeSet<AnalysisError>.from(
         result.errors,
         (a, b) {
           var value = a.offset.compareTo(b.offset);
           if (value == 0) {
             value = a.message.compareTo(b.message);
           }
           return value;
         },
       );

       // Filter out unused imports, since we speculatively add imports to some
       // samples.
       errors.removeWhere(
         (e) => e.errorCode == HintCode.UNUSED_IMPORT,
       );

       // Also, don't worry about 'unused_local_variable' and related; this may
       // be intentional in samples.
       errors.removeWhere(
         (e) =>
             e.errorCode == HintCode.UNUSED_LOCAL_VARIABLE ||
             e.errorCode == HintCode.UNUSED_ELEMENT,
       );

       // Remove warnings about deprecated member use from the same library.
       errors.removeWhere(
         (e) =>
             e.errorCode == HintCode.DEPRECATED_MEMBER_USE_FROM_SAME_PACKAGE ||
             e.errorCode ==
                 HintCode.DEPRECATED_MEMBER_USE_FROM_SAME_PACKAGE_WITH_MESSAGE,
       );

       // Handle edge case around dart:_http
       errors.removeWhere((e) {
         if (e.message.contains("'dart:_http'")) {
           return e.errorCode == HintCode.UNNECESSARY_IMPORT ||
               e.errorCode == CompileTimeErrorCode.IMPORT_INTERNAL_LIBRARY;
         }
         return false;
       });

       if (errors.isNotEmpty) {
         print('$filePath:${sample.lineStartOffset}: ${errors.length} errors');

         hadErrors = true;

         for (final error in errors) {
           final location = result.lineInfo.getLocation(error.offset);
           print(
             '  ${_severity(error.severity)}: ${error.message} '
             '[$location] (${error.errorCode.name.toLowerCase()})',
           );
         }
         print('');

         // Print out the code sample.
         print(sample.lines
             .map((line) =>
                 '  >${line.length >= 5 ? line.substring(5) : line.trimLeft()}')
             .join('\n'));
         print('');
       }
     } else {
       throw 'unexpected result type: $result';
     }

     return;
   }
 }

 String cleanDocLine(String line) {
   var copy = line.trimLeft();
   if (copy.startsWith('///')) {
     copy = copy.substring(3);
   } else if (copy.startsWith('*')) {
     copy = copy.substring(1);
   }
   return copy.padLeft(line.length, ' ');
 }

 class CodeSample {
   /// Currently valid template names.
   static const validTemplates = ['none', 'top', 'main', 'expression'];

   final String coreLibName;
   final Set<String> directives;
   final List<String> lines;
   final int lineStartOffset;

   CodeSample(
     this.lines, {
     required this.coreLibName,
     this.directives = const {},
     required this.lineStartOffset,
   });

   String get text => lines.join('\n');

   bool get hasTemplateDirective => templateDirective != null;

   /// The specified template, or `null` if no template is specified.
   ///
   /// A specified template must be of [validTemplates].
   String? get templateDirective {
     const prefix = 'template:';

     for (var directive in directives) {
       if (directive.startsWith(prefix)) {
         var result = directive.substring(prefix.length);
         if (!validTemplates.contains(result)) {
           throw "Invalid template name: $result";
         }
         return result;
       }
     }
     return null;
   }

   /// The implicit or explicitly requested imports.
   Set<String> get imports => {
         if (coreLibName != 'internal' && coreLibName != 'core') coreLibName,
         for (var directive in directives)
           if (directive.startsWith('import:'))
             directive.substring('import:'.length)
       };

   /// Creates a new code sample by appending [lines] to this sample.
   ///
   /// The new sample only differs from this sample in that it has
   /// more lines appended, first `this.lines`, then a gap of `  //` lines
   /// and then [lines].
   CodeSample append(List<String> lines, int lineStartOffset) {
     var gapSize = lineStartOffset - (this.lineStartOffset + this.lines.length);
     return CodeSample(
         [...this.lines, for (var i = 0; i < gapSize; i++) "  //", ...lines],
         coreLibName: coreLibName,
         directives: directives,
         lineStartOffset: this.lineStartOffset);
   }
 }

 /// Find and return any '// Examples can assume:' sample text.
 String? findFileAssumptions(String text) {
   var inAssumptions = false;
   var assumptions = <String>[];

   for (final line in text.split('\n')) {
     if (line == '// Examples can assume:') {
       inAssumptions = true;
     } else if (line.trim().isEmpty && inAssumptions) {
       inAssumptions = false;
     } else if (inAssumptions) {
       assumptions.add(line.substring('// '.length));
     }
   }

   return '${assumptions.join('\n')}\n';
 }

 String _severity(Severity severity) {
   switch (severity) {
     case Severity.info:
       return 'info';
     case Severity.warning:
       return 'warning';
     case Severity.error:
       return 'error';
   }
 }

 class AnalysisHelper {
   final String libraryName;
   final resourceProvider =
       OverlayResourceProvider(PhysicalResourceProvider.INSTANCE);
   final pathRoot = Platform.isWindows ? r'c:\' : '/';
   late AnalysisContextCollection collection;
   int index = 0;

   AnalysisHelper(this.libraryName) {
     resourceProvider.pathContext;

     collection = AnalysisContextCollection(
       includedPaths: ['$pathRoot$libraryName'],
       resourceProvider: resourceProvider,
     );
   }

   Future<SomeResolvedUnitResult> resolveFile(String contents) async {
     final samplePath =
         '$pathRoot$libraryName${resourceProvider.pathContext.separator}'
         'sample_${index++}.dart';
     resourceProvider.setOverlay(
       samplePath,
       content: contents,
       modificationStamp: 0,
     );

     var analysisContext = collection.contextFor(samplePath);
     var analysisSession = analysisContext.currentSession;
     return await analysisSession.getResolvedUnit(samplePath);
   }
 }

 // Helper function to make things easier to read.
 extension on StringBuffer {
   /// Write every line, right-trimmed, of [lines] with a newline after.
   void writeAllLines(Iterable<String> lines) {
     for (var line in lines) {
       writeln(line.trimRight());
     }
   }
 }

 /// Interprets [arg] as directory containing a platform library.
 ///
 /// If [arg] is `dart:foo`, the directory is the default directory for
 /// the `dart:foo` library source.
 /// Otherwise, if [arg] is a directory (relative to the current directory)
 /// which exists, that is the result.
 /// Otherwise, if [arg] is the name of a platform library,
 /// like `foo` where `dart:foo` is a platform library,
 /// the result is the default directory for that library's source.
 /// Otherwise it's treated as a directory relative to the current directory,
 /// which doesn't exist (but that's what the error will refer to).
 Directory parseArg(String arg) {
   if (arg.startsWith('dart:')) {
     return Directory(path.join(libDir.path, arg.substring('dart:'.length)));
   }
   var dir = Directory(arg);
   if (dir.existsSync()) return dir;
   var relDir = Directory(path.join(libDir.path, arg));
   if (relDir.existsSync()) return relDir;
   return dir;
 }
	// Copyright (c) 2021, 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.

	// Read the ../README.md file for the recognized syntax.

	import 'dart:collection';
	import 'dart:io';

	import 'package:analyzer/dart/analysis/analysis_context_collection.dart';
	import 'package:analyzer/dart/analysis/features.dart';
	import 'package:analyzer/dart/analysis/results.dart';
	import 'package:analyzer/dart/analysis/utilities.dart';
	import 'package:analyzer/dart/ast/ast.dart';
	import 'package:analyzer/dart/ast/visitor.dart';
	import 'package:analyzer/diagnostic/diagnostic.dart';
	import 'package:analyzer/error/error.dart';
	import 'package:analyzer/file_system/overlay_file_system.dart';
	import 'package:analyzer/file_system/physical_file_system.dart';
	import 'package:analyzer/source/line_info.dart';
	import 'package:analyzer/src/error/codes.dart';
	import 'package:analyzer/src/util/comment.dart';
	import 'package:path/path.dart' as path;

	final libDir = Directory(path.join('sdk', 'lib'));
	void main(List<String> args) async {
	if (!libDir.existsSync()) {
	print('Please run this tool from the root of the sdk repository.');
	exit(1);
	}

	print('Validating the dartdoc code samples from the dart: libraries.');
	print('');
	print('To run this tool, run `dart tools/verify_docs/bin/verify_docs.dart`.');
	print('');
	print('For documentation about how to author dart: code samples,'
	' see tools/verify_docs/README.md.');
	print('');

	final coreLibraries = args.isEmpty
	? libDir.listSync().whereType<Directory>().toList()
	: args.map(parseArg).toList();
	coreLibraries.sort((a, b) => a.path.compareTo(b.path));

	// Skip some dart: libraries.
	const skipLibraries = {
	'html',
	'indexed_db',
	'svg',
	'vmservice',
	'web_audio',
	'web_gl',
	'web_sql'
	};
	coreLibraries.removeWhere(
	(lib) => skipLibraries.contains(path.basename(lib.path)),
	);

	var hadErrors = false;
	for (final dir in coreLibraries) {
	hadErrors \|= !(await validateLibrary(dir));
	}

	exitCode = hadErrors ? 1 : 0;
	}

	Future<bool> validateLibrary(Directory dir) async {
	final libName = path.basename(dir.path);

	final analysisHelper = AnalysisHelper(libName);

	print('## dart:$libName');
	print('');

	var validDocs = true;

	for (final file in dir
	.listSync(recursive: true)
	.whereType<File>()
	.where((file) => file.path.endsWith('.dart'))) {
	validDocs &= await verifyFile(analysisHelper, libName, file, dir);
	}

	return validDocs;
	}

	Future<bool> verifyFile(
	AnalysisHelper analysisHelper,
	String coreLibName,
	File file,
	Directory parent,
	) async {
	final text = file.readAsStringSync();
	var parseResult = parseString(
	content: text,
	featureSet: FeatureSet.latestLanguageVersion(),
	path: file.path,
	throwIfDiagnostics: false,
	);

	// Throw if there are syntactic errors.
	var syntacticErrors = parseResult.errors.where((error) {
	return error.errorCode.type == ErrorType.SYNTACTIC_ERROR;
	}).toList();
	if (syntacticErrors.isNotEmpty) {
	throw Exception(syntacticErrors);
	}

	final sampleAssumptions = findFileAssumptions(text);

	var visitor = ValidateCommentCodeSamplesVisitor(
	analysisHelper,
	coreLibName,
	file.path,
	parseResult.lineInfo,
	sampleAssumptions,
	);
	await visitor.process(parseResult);
	return !visitor.hadErrors;
	}

	/// Visit a compilation unit and validate the code samples found in dartdoc
	/// comments.
	class ValidateCommentCodeSamplesVisitor extends GeneralizingAstVisitor {
	final AnalysisHelper analysisHelper;
	final String coreLibName;
	final String filePath;
	final LineInfo lineInfo;
	final String? sampleAssumptions;

	final List<CodeSample> samples = [];
	bool hadErrors = false;

	ValidateCommentCodeSamplesVisitor(
	this.analysisHelper,
	this.coreLibName,
	this.filePath,
	this.lineInfo,
	this.sampleAssumptions,
	);

	Future process(ParseStringResult parseResult) async {
	// collect code samples
	visitCompilationUnit(parseResult.unit);

	// analyze them
	for (CodeSample sample in samples) {
	await validateCodeSample(sample);
	}
	}

	@override
	void visitAnnotatedNode(AnnotatedNode node) {
	_handleDocumentableNode(node);
	super.visitAnnotatedNode(node);
	}

	void _handleDocumentableNode(AnnotatedNode node) {
	final docComment = node.documentationComment;
	if (docComment == null \|\| !docComment.isDocumentation) {
	return;
	}

	const sampleStart = '```dart';
	const sampleEnd = '```';

	final text = getCommentNodeRawText(docComment)!;
	final commentOffset = docComment.offset;
	final commentLineStart = lineInfo.getLocation(commentOffset).lineNumber;
	if (!text.contains(sampleStart)) {
	return;
	}

	var offset = text.indexOf(sampleStart);
	while (offset != -1) {
	// Collect template directives, like "```dart import:async".
	final codeFenceSuffix = text
	.substring(offset + sampleStart.length, text.indexOf('\n', offset))
	.trim();

	offset = text.indexOf('\n', offset) + 1;
	final end = text.indexOf(sampleEnd, offset);

	var snippet = text.substring(offset, end);
	snippet = snippet.substring(0, snippet.lastIndexOf('\n'));

	List<String> lines = snippet.split('\n');
	var startLineNumber = commentLineStart +
	text.substring(0, offset - 1).split('\n').length -
	1;
	if (codeFenceSuffix == "continued") {
	if (samples.isEmpty) {
	throw "Continued code block without previous code";
	}
	samples.last = samples.last.append(lines, startLineNumber);
	} else {
	final directives = Set.unmodifiable(codeFenceSuffix.split(' '));
	samples.add(
	CodeSample(
	[for (var e in lines) ' ${cleanDocLine(e)}'],
	coreLibName: coreLibName,
	directives: directives,
	lineStartOffset: startLineNumber,
	),
	);
	}

	offset = text.indexOf(sampleStart, offset);
	}
	}

	// RegExp detecting various top-level declarations or `main(`.
	//
	// If the top-level declaration is `library` or `import`,
	// then match 1 (`libdecl`) will be non-null.
	// This is a sign that no auto-imports should be added.
	//
	// If an import declaration is included in the sample, no
	// assumed-declarations are added.
	// Use the `import:foo` template to import other `dart:` libraries
	// instead of writing them explicitly to.
	//
	// Captures:
	// 1/libdecl: Non-null if mathcing a `library` declaration.
	// 2: Internal use, quote around import URI.
	// 3/importuri: Import URI.
	final _toplevelDeclarationRE = RegExp(r'^\s*(?:'
	r'library\b(?<libdecl>)\|'
	r'''import (['"])(?<importuri>.*?)\2\|'''
	r'class\b\|mixin\b\|enum\b\|extension\b\|typedef\b\|.*\bmain\('
	r')');

	validateCodeSample(CodeSample sample) async {
	final lines = sample.lines;

	// The default imports includes the library itself
	// and any import directives.
	Set<String> autoImports = sample.imports;

	// One of 'none', 'top, 'main', or 'expression'.
	String template;

	bool hasImport = false;

	final templateDirective = sample.templateDirective;
	if (templateDirective != null) {
	template = templateDirective;
	} else {
	// Scan lines for top-level declarations.
	bool hasTopDeclaration = false;
	bool hasLibraryDeclaration = false;
	for (var line in lines) {
	var topDeclaration = _toplevelDeclarationRE.firstMatch(line);
	if (topDeclaration != null) {
	hasTopDeclaration = true;
	hasLibraryDeclaration \|=
	(topDeclaration.namedGroup("libdecl") != null);
	var importDecl = topDeclaration.namedGroup("importuri");
	if (importDecl != null) {
	hasImport = true;
	if (importDecl.startsWith('dart:')) {
	// Remove explicit imports from automatic imports
	// to avoid duplicate import warnings.
	autoImports.remove(importDecl.substring('dart:'.length));
	}
	}
	}
	}
	if (hasLibraryDeclaration) {
	template = 'none';
	} else if (hasTopDeclaration) {
	template = 'top';
	} else if (lines.length == 1 && !lines.first.contains(';')) {
	// If single line with no `;`, assume expression.
	template = 'expression';
	} else {
	// Otherwise default to `main`.
	template = 'main';
	}
	}

	var buffer = StringBuffer();

	if (template != 'none') {
	for (var library in autoImports) {
	buffer.writeln("import 'dart:$library';");
	}
	if (!hasImport) {
	buffer.write(sampleAssumptions ?? '');
	}
	}
	if (template == 'none' \|\| template == 'top') {
	buffer.writeAllLines(lines);
	} else if (template == 'main') {
	buffer
	..writeln('void main() async {')
	..writeAllLines(lines)
	..writeln('}');
	} else if (template == 'expression') {
	assert(lines.isNotEmpty);
	buffer
	..writeln('void main() async =>')
	..writeAllLines(lines.take(lines.length - 1))
	..writeln("${lines.last.trimRight()};");
	} else {
	throw 'unexpected template directive: $template';
	}

	final text = buffer.toString();

	final result = await analysisHelper.resolveFile(text);

	if (result is ResolvedUnitResult) {
	var errors = SplayTreeSet<AnalysisError>.from(
	result.errors,
	(a, b) {
	var value = a.offset.compareTo(b.offset);
	if (value == 0) {
	value = a.message.compareTo(b.message);
	}
	return value;
	},
	);

	// Filter out unused imports, since we speculatively add imports to some
	// samples.
	errors.removeWhere(
	(e) => e.errorCode == HintCode.UNUSED_IMPORT,
	);

	// Also, don't worry about 'unused_local_variable' and related; this may
	// be intentional in samples.
	errors.removeWhere(
	(e) =>
	e.errorCode == HintCode.UNUSED_LOCAL_VARIABLE \|\|
	e.errorCode == HintCode.UNUSED_ELEMENT,
	);

	// Remove warnings about deprecated member use from the same library.
	errors.removeWhere(
	(e) =>
	e.errorCode == HintCode.DEPRECATED_MEMBER_USE_FROM_SAME_PACKAGE \|\|
	e.errorCode ==
	HintCode.DEPRECATED_MEMBER_USE_FROM_SAME_PACKAGE_WITH_MESSAGE,
	);

	// Handle edge case around dart:_http
	errors.removeWhere((e) {
	if (e.message.contains("'dart:_http'")) {
	return e.errorCode == HintCode.UNNECESSARY_IMPORT \|\|
	e.errorCode == CompileTimeErrorCode.IMPORT_INTERNAL_LIBRARY;
	}
	return false;
	});

	if (errors.isNotEmpty) {
	print('$filePath:${sample.lineStartOffset}: ${errors.length} errors');

	hadErrors = true;

	for (final error in errors) {
	final location = result.lineInfo.getLocation(error.offset);
	print(
	' ${_severity(error.severity)}: ${error.message} '
	'[$location] (${error.errorCode.name.toLowerCase()})',
	);
	}
	print('');

	// Print out the code sample.
	print(sample.lines
	.map((line) =>
	' >${line.length >= 5 ? line.substring(5) : line.trimLeft()}')
	.join('\n'));
	print('');
	}
	} else {
	throw 'unexpected result type: $result';
	}

	return;
	}
	}

	String cleanDocLine(String line) {
	var copy = line.trimLeft();
	if (copy.startsWith('///')) {
	copy = copy.substring(3);
	} else if (copy.startsWith('*')) {
	copy = copy.substring(1);
	}
	return copy.padLeft(line.length, ' ');
	}

	class CodeSample {
	/// Currently valid template names.
	static const validTemplates = ['none', 'top', 'main', 'expression'];

	final String coreLibName;
	final Set<String> directives;
	final List<String> lines;
	final int lineStartOffset;

	CodeSample(
	this.lines, {
	required this.coreLibName,
	this.directives = const {},
	required this.lineStartOffset,
	});

	String get text => lines.join('\n');

	bool get hasTemplateDirective => templateDirective != null;

	/// The specified template, or `null` if no template is specified.
	///
	/// A specified template must be of [validTemplates].
	String? get templateDirective {
	const prefix = 'template:';

	for (var directive in directives) {
	if (directive.startsWith(prefix)) {
	var result = directive.substring(prefix.length);
	if (!validTemplates.contains(result)) {
	throw "Invalid template name: $result";
	}
	return result;
	}
	}
	return null;
	}

	/// The implicit or explicitly requested imports.
	Set<String> get imports => {
	if (coreLibName != 'internal' && coreLibName != 'core') coreLibName,
	for (var directive in directives)
	if (directive.startsWith('import:'))
	directive.substring('import:'.length)
	};

	/// Creates a new code sample by appending [lines] to this sample.
	///
	/// The new sample only differs from this sample in that it has
	/// more lines appended, first `this.lines`, then a gap of ` //` lines
	/// and then [lines].
	CodeSample append(List<String> lines, int lineStartOffset) {
	var gapSize = lineStartOffset - (this.lineStartOffset + this.lines.length);
	return CodeSample(
	[...this.lines, for (var i = 0; i < gapSize; i++) " //", ...lines],
	coreLibName: coreLibName,
	directives: directives,
	lineStartOffset: this.lineStartOffset);
	}
	}

	/// Find and return any '// Examples can assume:' sample text.
	String? findFileAssumptions(String text) {
	var inAssumptions = false;
	var assumptions = <String>[];

	for (final line in text.split('\n')) {
	if (line == '// Examples can assume:') {
	inAssumptions = true;
	} else if (line.trim().isEmpty && inAssumptions) {
	inAssumptions = false;
	} else if (inAssumptions) {
	assumptions.add(line.substring('// '.length));
	}
	}

	return '${assumptions.join('\n')}\n';
	}

	String _severity(Severity severity) {
	switch (severity) {
	case Severity.info:
	return 'info';
	case Severity.warning:
	return 'warning';
	case Severity.error:
	return 'error';
	}
	}

	class AnalysisHelper {
	final String libraryName;
	final resourceProvider =
	OverlayResourceProvider(PhysicalResourceProvider.INSTANCE);
	final pathRoot = Platform.isWindows ? r'c:\' : '/';
	late AnalysisContextCollection collection;
	int index = 0;

	AnalysisHelper(this.libraryName) {
	resourceProvider.pathContext;

	collection = AnalysisContextCollection(
	includedPaths: ['$pathRoot$libraryName'],
	resourceProvider: resourceProvider,
	);
	}

	Future<SomeResolvedUnitResult> resolveFile(String contents) async {
	final samplePath =
	'$pathRoot$libraryName${resourceProvider.pathContext.separator}'
	'sample_${index++}.dart';
	resourceProvider.setOverlay(
	samplePath,
	content: contents,
	modificationStamp: 0,
	);

	var analysisContext = collection.contextFor(samplePath);
	var analysisSession = analysisContext.currentSession;
	return await analysisSession.getResolvedUnit(samplePath);
	}
	}

	// Helper function to make things easier to read.
	extension on StringBuffer {
	/// Write every line, right-trimmed, of [lines] with a newline after.
	void writeAllLines(Iterable<String> lines) {
	for (var line in lines) {
	writeln(line.trimRight());
	}
	}
	}

	/// Interprets [arg] as directory containing a platform library.
	///
	/// If [arg] is `dart:foo`, the directory is the default directory for
	/// the `dart:foo` library source.
	/// Otherwise, if [arg] is a directory (relative to the current directory)
	/// which exists, that is the result.
	/// Otherwise, if [arg] is the name of a platform library,
	/// like `foo` where `dart:foo` is a platform library,
	/// the result is the default directory for that library's source.
	/// Otherwise it's treated as a directory relative to the current directory,
	/// which doesn't exist (but that's what the error will refer to).
	Directory parseArg(String arg) {
	if (arg.startsWith('dart:')) {
	return Directory(path.join(libDir.path, arg.substring('dart:'.length)));
	}
	var dir = Directory(arg);
	if (dir.existsSync()) return dir;
	var relDir = Directory(path.join(libDir.path, arg));
	if (relDir.existsSync()) return relDir;
	return dir;
	}