lib/src/packages_file.dart - pub - Git at Google

 // Copyright (c) 2012, 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.

 // ignore_for_file: prefer_single_quotes

 // This code is copied from an older version of package:package_config - and
 // kept here until we completely abandon the old .packages file.
 // See: https://github.com/dart-lang/package_config/blob/04b9abec2627dfaf9b7ec39c31a3b03f06ed9be7/lib/packages_file.dart

 /// Parses a `.packages` file into a map from package name to base URI.
 ///
 /// The [source] is the byte content of a `.packages` file, assumed to be
 /// UTF-8 encoded. In practice, all significant parts of the file must be ASCII,
 /// so Latin-1 or Windows-1252 encoding will also work fine.
 ///
 /// If the file content is available as a string, its [String.codeUnits] can
 /// be used as the `source` argument of this function.
 ///
 /// The [baseLocation] is used as a base URI to resolve all relative
 /// URI references against.
 /// If the content was read from a file, `baseLocation` should be the
 /// location of that file.
 ///
 /// If [allowDefaultPackage] is set to true, an entry with an empty package name
 /// is accepted. This entry does not correspond to a package, but instead
 /// represents a *default package* which non-package libraries may be considered
 /// part of in some cases. The value of that entry must be a valid package name.
 ///
 /// Returns a simple mapping from package name to package location.
 /// If default package is allowed, the map maps the empty string to the default package's name.
 Map<String, Uri> parse(List<int> source, Uri baseLocation,
     {bool allowDefaultPackage = false}) {
   var index = 0;
   var result = <String, Uri>{};
   while (index < source.length) {
     var isComment = false;
     var start = index;
     var separatorIndex = -1;
     var end = source.length;
     var char = source[index++];
     if (char == $cr || char == $lf) {
       continue;
     }
     if (char == $colon) {
       if (!allowDefaultPackage) {
         throw FormatException("Missing package name", source, index - 1);
       }
       separatorIndex = index - 1;
     }
     isComment = char == $hash;
     while (index < source.length) {
       char = source[index++];
       if (char == $colon && separatorIndex < 0) {
         separatorIndex = index - 1;
       } else if (char == $cr || char == $lf) {
         end = index - 1;
         break;
       }
     }
     if (isComment) continue;
     if (separatorIndex < 0) {
       throw FormatException("No ':' on line", source, index - 1);
     }
     var packageName = String.fromCharCodes(source, start, separatorIndex);
     if (packageName.isEmpty
         ? !allowDefaultPackage
         : !isValidPackageName(packageName)) {
       throw FormatException("Not a valid package name", packageName, 0);
     }
     var packageValue = String.fromCharCodes(source, separatorIndex + 1, end);
     Uri packageLocation;
     if (packageName.isEmpty) {
       if (!isValidPackageName(packageValue)) {
         throw FormatException(
             "Default package entry value is not a valid package name");
       }
       packageLocation = Uri(path: packageValue);
     } else {
       packageLocation = baseLocation.resolve(packageValue);
       if (!packageLocation.path.endsWith('/')) {
         packageLocation =
             packageLocation.replace(path: packageLocation.path + "/");
       }
     }
     if (result.containsKey(packageName)) {
       if (packageName.isEmpty) {
         throw FormatException(
             "More than one default package entry", source, start);
       }
       throw FormatException("Same package name occured twice", source, start);
     }
     result[packageName] = packageLocation;
   }
   return result;
 }

 /// Writes the mapping to a [StringSink].
 ///
 /// If [comment] is provided, the output will contain this comment
 /// with `# ` in front of each line.
 /// Lines are defined as ending in line feed (`'\n'`). If the final
 /// line of the comment doesn't end in a line feed, one will be added.
 ///
 /// If [baseUri] is provided, package locations will be made relative
 /// to the base URI, if possible, before writing.
 ///
 /// If [allowDefaultPackage] is `true`, the [packageMapping] may contain an
 /// empty string mapping to the _default package name_.
 ///
 /// All the keys of [packageMapping] must be valid package names,
 /// and the values must be URIs that do not have the `package:` scheme.
 void write(StringSink output, Map<String, Uri> packageMapping,
     {Uri baseUri, String comment, bool allowDefaultPackage = false}) {
   ArgumentError.checkNotNull(allowDefaultPackage, 'allowDefaultPackage');

   if (baseUri != null && !baseUri.isAbsolute) {
     throw ArgumentError.value(baseUri, "baseUri", "Must be absolute");
   }

   if (comment != null) {
     var lines = comment.split('\n');
     if (lines.last.isEmpty) lines.removeLast();
     for (var commentLine in lines) {
       output.write('# ');
       output.writeln(commentLine);
     }
   } else {
     output.write("# generated by package:package_config at ");
     output.write(DateTime.now());
     output.writeln();
   }

   packageMapping.forEach((String packageName, Uri uri) {
     // If [packageName] is empty then [uri] is the _default package name_.
     if (allowDefaultPackage && packageName.isEmpty) {
       final defaultPackageName = uri.toString();
       if (!isValidPackageName(defaultPackageName)) {
         throw ArgumentError.value(
           defaultPackageName,
           'defaultPackageName',
           '"$defaultPackageName" is not a valid package name',
         );
       }
       output.write(':');
       output.write(defaultPackageName);
       output.writeln();
       return;
     }
     // Validate packageName.
     if (!isValidPackageName(packageName)) {
       throw ArgumentError('"$packageName" is not a valid package name');
     }
     if (uri.scheme == "package") {
       throw ArgumentError.value(
           "Package location must not be a package: URI", uri.toString());
     }
     output.write(packageName);
     output.write(':');
     // If baseUri provided, make uri relative.
     if (baseUri != null) {
       uri = _relativize(uri, baseUri);
     }
     if (!uri.path.endsWith('/')) {
       uri = uri.replace(path: uri.path + '/');
     }
     output.write(uri);
     output.writeln();
   });
 }

 // All ASCII characters that are valid in a package name, with space
 // for all the invalid ones (including space).
 const String _validPackageNameCharacters =
     r"                                 !  $ &'()*+,-. 0123456789 ; =  "
     r"@ABCDEFGHIJKLMNOPQRSTUVWXYZ    _ abcdefghijklmnopqrstuvwxyz   ~ ";

 /// Tests whether something is a valid Dart package name.
 bool isValidPackageName(String string) {
   return checkPackageName(string) < 0;
 }

 /// Check if a string is a valid package name.
 ///
 /// Valid package names contain only characters in [_validPackageNameCharacters]
 /// and must contain at least one non-'.' character.
 ///
 /// Returns `-1` if the string is valid.
 /// Otherwise returns the index of the first invalid character,
 /// or `string.length` if the string contains no non-'.' character.
 int checkPackageName(String string) {
   // Becomes non-zero if any non-'.' character is encountered.
   var nonDot = 0;
   for (var i = 0; i < string.length; i++) {
     var c = string.codeUnitAt(i);
     if (c > 0x7f || _validPackageNameCharacters.codeUnitAt(c) <= $space) {
       return i;
     }
     nonDot += c ^ $dot;
   }
   if (nonDot == 0) return string.length;
   return -1;
 }

 /// Validate that a [Uri] is a valid `package:` URI.
 ///
 /// Used to validate user input.
 ///
 /// Returns the package name extracted from the package URI,
 /// which is the path segment between `package:` and the first `/`.
 String checkValidPackageUri(Uri packageUri, String name) {
   if (packageUri.scheme != "package") {
     throw PackageConfigArgumentError(packageUri, name, "Not a package: URI");
   }
   if (packageUri.hasAuthority) {
     throw PackageConfigArgumentError(
         packageUri, name, "Package URIs must not have a host part");
   }
   if (packageUri.hasQuery) {
     // A query makes no sense if resolved to a file: URI.
     throw PackageConfigArgumentError(
         packageUri, name, "Package URIs must not have a query part");
   }
   if (packageUri.hasFragment) {
     // We could leave the fragment after the URL when resolving,
     // but it would be odd if "package:foo/foo.dart#1" and
     // "package:foo/foo.dart#2" were considered different libraries.
     // Keep the syntax open in case we ever get multiple libraries in one file.
     throw PackageConfigArgumentError(
         packageUri, name, "Package URIs must not have a fragment part");
   }
   if (packageUri.path.startsWith('/')) {
     throw PackageConfigArgumentError(
         packageUri, name, "Package URIs must not start with a '/'");
   }
   var firstSlash = packageUri.path.indexOf('/');
   if (firstSlash == -1) {
     throw PackageConfigArgumentError(packageUri, name,
         "Package URIs must start with the package name followed by a '/'");
   }
   var packageName = packageUri.path.substring(0, firstSlash);
   var badIndex = checkPackageName(packageName);
   if (badIndex >= 0) {
     if (packageName.isEmpty) {
       throw PackageConfigArgumentError(
           packageUri, name, "Package names mus be non-empty");
     }
     if (badIndex == packageName.length) {
       throw PackageConfigArgumentError(packageUri, name,
           "Package names must contain at least one non-'.' character");
     }
     assert(badIndex < packageName.length);
     var badCharCode = packageName.codeUnitAt(badIndex);
     var badChar = "U+" + badCharCode.toRadixString(16).padLeft(4, '0');
     if (badCharCode >= 0x20 && badCharCode <= 0x7e) {
       // Printable character.
       badChar = "'${packageName[badIndex]}' ($badChar)";
     }
     throw PackageConfigArgumentError(
         packageUri, name, "Package names must not contain $badChar");
   }
   return packageName;
 }

 /// Checks whether URI is just an absolute directory.
 ///
 /// * It must have a scheme.
 /// * It must not have a query or fragment.
 /// * The path must end with `/`.
 bool isAbsoluteDirectoryUri(Uri uri) {
   if (uri.hasQuery) return false;
   if (uri.hasFragment) return false;
   if (!uri.hasScheme) return false;
   var path = uri.path;
   if (!path.endsWith("/")) return false;
   return true;
 }

 /// Whether the former URI is a prefix of the latter.
 bool isUriPrefix(Uri prefix, Uri path) {
   assert(!prefix.hasFragment);
   assert(!prefix.hasQuery);
   assert(!path.hasQuery);
   assert(!path.hasFragment);
   assert(prefix.path.endsWith('/'));
   return path.toString().startsWith(prefix.toString());
 }

 /// Finds the first non-JSON-whitespace character in a file.
 ///
 /// Used to heuristically detect whether a file is a JSON file or an .ini file.
 int firstNonWhitespaceChar(List<int> bytes) {
   for (var i = 0; i < bytes.length; i++) {
     var char = bytes[i];
     if (char != 0x20 && char != 0x09 && char != 0x0a && char != 0x0d) {
       return char;
     }
   }
   return -1;
 }

 /// Attempts to return a relative path-only URI for [uri].
 ///
 /// First removes any query or fragment part from [uri].
 ///
 /// If [uri] is already relative (has no scheme), it's returned as-is.
 /// If that is not desired, the caller can pass `baseUri.resolveUri(uri)`
 /// as the [uri] instead.
 ///
 /// If the [uri] has a scheme or authority part which differs from
 /// the [baseUri], or if there is no overlap in the paths of the
 /// two URIs at all, the [uri] is returned as-is.
 ///
 /// Otherwise the result is a path-only URI which satsifies
 /// `baseUri.resolveUri(result) == uri`,
 ///
 /// The `baseUri` must be absolute.
 Uri relativizeUri(Uri uri, Uri /*?*/ baseUri) {
   if (baseUri == null) return uri;
   assert(baseUri.isAbsolute);
   if (uri.hasQuery || uri.hasFragment) {
     uri = Uri(
         scheme: uri.scheme,
         userInfo: uri.hasAuthority ? uri.userInfo : null,
         host: uri.hasAuthority ? uri.host : null,
         port: uri.hasAuthority ? uri.port : null,
         path: uri.path);
   }

   // Already relative. We assume the caller knows what they are doing.
   if (!uri.isAbsolute) return uri;

   if (baseUri.scheme != uri.scheme) {
     return uri;
   }

   // If authority differs, we could remove the scheme, but it's not worth it.
   if (uri.hasAuthority != baseUri.hasAuthority) return uri;
   if (uri.hasAuthority) {
     if (uri.userInfo != baseUri.userInfo ||
         uri.host.toLowerCase() != baseUri.host.toLowerCase() ||
         uri.port != baseUri.port) {
       return uri;
     }
   }

   baseUri = baseUri.normalizePath();
   var base = [...baseUri.pathSegments];
   if (base.isNotEmpty) base.removeLast();
   uri = uri.normalizePath();
   var target = [...uri.pathSegments];
   if (target.isNotEmpty && target.last.isEmpty) target.removeLast();
   var index = 0;
   while (index < base.length && index < target.length) {
     if (base[index] != target[index]) {
       break;
     }
     index++;
   }
   if (index == base.length) {
     if (index == target.length) {
       return Uri(path: "./");
     }
     return Uri(path: target.skip(index).join('/'));
   } else if (index > 0) {
     var buffer = StringBuffer();
     for (var n = base.length - index; n > 0; --n) {
       buffer.write("../");
     }
     buffer.writeAll(target.skip(index), "/");
     return Uri(path: buffer.toString());
   } else {
     return uri;
   }
 }

 /// Attempts to return a relative URI for [uri].
 ///
 /// The result URI satisfies `baseUri.resolveUri(result) == uri`,
 /// but may be relative.
 /// The `baseUri` must be absolute.
 Uri _relativize(Uri uri, Uri baseUri) {
   assert(baseUri.isAbsolute);
   if (uri.hasQuery || uri.hasFragment) {
     uri = Uri(
         scheme: uri.scheme,
         userInfo: uri.hasAuthority ? uri.userInfo : null,
         host: uri.hasAuthority ? uri.host : null,
         port: uri.hasAuthority ? uri.port : null,
         path: uri.path);
   }

   // Already relative. We assume the caller knows what they are doing.
   if (!uri.isAbsolute) return uri;

   if (baseUri.scheme != uri.scheme) {
     return uri;
   }

   // If authority differs, we could remove the scheme, but it's not worth it.
   if (uri.hasAuthority != baseUri.hasAuthority) return uri;
   if (uri.hasAuthority) {
     if (uri.userInfo != baseUri.userInfo ||
         uri.host.toLowerCase() != baseUri.host.toLowerCase() ||
         uri.port != baseUri.port) {
       return uri;
     }
   }

   baseUri = baseUri.normalizePath();
   var base = baseUri.pathSegments.toList();
   if (base.isNotEmpty) {
     base = List<String>.from(base)..removeLast();
   }
   uri = uri.normalizePath();
   var target = uri.pathSegments.toList();
   if (target.isNotEmpty && target.last.isEmpty) target.removeLast();
   var index = 0;
   while (index < base.length && index < target.length) {
     if (base[index] != target[index]) {
       break;
     }
     index++;
   }
   if (index == base.length) {
     if (index == target.length) {
       return Uri(path: "./");
     }
     return Uri(path: target.skip(index).join('/'));
   } else if (index > 0) {
     return Uri(
         path: '../' * (base.length - index) + target.skip(index).join('/'));
   } else {
     return uri;
   }
 }

 // Character constants used by this package.
 /// "Line feed" control character.
 const int $lf = 0x0a;

 /// "Carriage return" control character.
 const int $cr = 0x0d;

 /// Space character.
 const int $space = 0x20;

 /// Character `#`.
 const int $hash = 0x23;

 /// Character `.`.
 const int $dot = 0x2e;

 /// Character `:`.
 const int $colon = 0x3a;

 /// Character `?`.
 const int $question = 0x3f;

 /// Character `{`.
 const int $lbrace = 0x7b;

 /// General superclass of most errors and exceptions thrown by this package.
 ///
 /// Only covers errors thrown while parsing package configuration files.
 /// Programming errors and I/O exceptions are not covered.
 abstract class PackageConfigError {
   PackageConfigError._();
 }

 class PackageConfigArgumentError extends ArgumentError
     implements PackageConfigError {
   PackageConfigArgumentError(Object /*?*/ value, String name, String message)
       : super.value(value, name, message);

   PackageConfigArgumentError.from(ArgumentError error)
       : super.value(error.invalidValue, error.name, error.message);
 }

 class PackageConfigFormatException extends FormatException
     implements PackageConfigError {
   PackageConfigFormatException(String message, Object /*?*/ source,
       [int /*?*/ offset])
       : super(message, source, offset);

   PackageConfigFormatException.from(FormatException exception)
       : super(exception.message, exception.source, exception.offset);
 }
	// Copyright (c) 2012, 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.

	// ignore_for_file: prefer_single_quotes

	// This code is copied from an older version of package:package_config - and
	// kept here until we completely abandon the old .packages file.
	// See: https://github.com/dart-lang/package_config/blob/04b9abec2627dfaf9b7ec39c31a3b03f06ed9be7/lib/packages_file.dart

	/// Parses a `.packages` file into a map from package name to base URI.
	///
	/// The [source] is the byte content of a `.packages` file, assumed to be
	/// UTF-8 encoded. In practice, all significant parts of the file must be ASCII,
	/// so Latin-1 or Windows-1252 encoding will also work fine.
	///
	/// If the file content is available as a string, its [String.codeUnits] can
	/// be used as the `source` argument of this function.
	///
	/// The [baseLocation] is used as a base URI to resolve all relative
	/// URI references against.
	/// If the content was read from a file, `baseLocation` should be the
	/// location of that file.
	///
	/// If [allowDefaultPackage] is set to true, an entry with an empty package name
	/// is accepted. This entry does not correspond to a package, but instead
	/// represents a default package which non-package libraries may be considered
	/// part of in some cases. The value of that entry must be a valid package name.
	///
	/// Returns a simple mapping from package name to package location.
	/// If default package is allowed, the map maps the empty string to the default package's name.
	Map<String, Uri> parse(List<int> source, Uri baseLocation,
	{bool allowDefaultPackage = false}) {
	var index = 0;
	var result = <String, Uri>{};
	while (index < source.length) {
	var isComment = false;
	var start = index;
	var separatorIndex = -1;
	var end = source.length;
	var char = source[index++];
	if (char == $cr \|\| char == $lf) {
	continue;
	}
	if (char == $colon) {
	if (!allowDefaultPackage) {
	throw FormatException("Missing package name", source, index - 1);
	}
	separatorIndex = index - 1;
	}
	isComment = char == $hash;
	while (index < source.length) {
	char = source[index++];
	if (char == $colon && separatorIndex < 0) {
	separatorIndex = index - 1;
	} else if (char == $cr \|\| char == $lf) {
	end = index - 1;
	break;
	}
	}
	if (isComment) continue;
	if (separatorIndex < 0) {
	throw FormatException("No ':' on line", source, index - 1);
	}
	var packageName = String.fromCharCodes(source, start, separatorIndex);
	if (packageName.isEmpty
	? !allowDefaultPackage
	: !isValidPackageName(packageName)) {
	throw FormatException("Not a valid package name", packageName, 0);
	}
	var packageValue = String.fromCharCodes(source, separatorIndex + 1, end);
	Uri packageLocation;
	if (packageName.isEmpty) {
	if (!isValidPackageName(packageValue)) {
	throw FormatException(
	"Default package entry value is not a valid package name");
	}
	packageLocation = Uri(path: packageValue);
	} else {
	packageLocation = baseLocation.resolve(packageValue);
	if (!packageLocation.path.endsWith('/')) {
	packageLocation =
	packageLocation.replace(path: packageLocation.path + "/");
	}
	}
	if (result.containsKey(packageName)) {
	if (packageName.isEmpty) {
	throw FormatException(
	"More than one default package entry", source, start);
	}
	throw FormatException("Same package name occured twice", source, start);
	}
	result[packageName] = packageLocation;
	}
	return result;
	}

	/// Writes the mapping to a [StringSink].
	///
	/// If [comment] is provided, the output will contain this comment
	/// with `# ` in front of each line.
	/// Lines are defined as ending in line feed (`'\n'`). If the final
	/// line of the comment doesn't end in a line feed, one will be added.
	///
	/// If [baseUri] is provided, package locations will be made relative
	/// to the base URI, if possible, before writing.
	///
	/// If [allowDefaultPackage] is `true`, the [packageMapping] may contain an
	/// empty string mapping to the _default package name_.
	///
	/// All the keys of [packageMapping] must be valid package names,
	/// and the values must be URIs that do not have the `package:` scheme.
	void write(StringSink output, Map<String, Uri> packageMapping,
	{Uri baseUri, String comment, bool allowDefaultPackage = false}) {
	ArgumentError.checkNotNull(allowDefaultPackage, 'allowDefaultPackage');

	if (baseUri != null && !baseUri.isAbsolute) {
	throw ArgumentError.value(baseUri, "baseUri", "Must be absolute");
	}

	if (comment != null) {
	var lines = comment.split('\n');
	if (lines.last.isEmpty) lines.removeLast();
	for (var commentLine in lines) {
	output.write('# ');
	output.writeln(commentLine);
	}
	} else {
	output.write("# generated by package:package_config at ");
	output.write(DateTime.now());
	output.writeln();
	}

	packageMapping.forEach((String packageName, Uri uri) {
	// If [packageName] is empty then [uri] is the _default package name_.
	if (allowDefaultPackage && packageName.isEmpty) {
	final defaultPackageName = uri.toString();
	if (!isValidPackageName(defaultPackageName)) {
	throw ArgumentError.value(
	defaultPackageName,
	'defaultPackageName',
	'"$defaultPackageName" is not a valid package name',
	);
	}
	output.write(':');
	output.write(defaultPackageName);
	output.writeln();
	return;
	}
	// Validate packageName.
	if (!isValidPackageName(packageName)) {
	throw ArgumentError('"$packageName" is not a valid package name');
	}
	if (uri.scheme == "package") {
	throw ArgumentError.value(
	"Package location must not be a package: URI", uri.toString());
	}
	output.write(packageName);
	output.write(':');
	// If baseUri provided, make uri relative.
	if (baseUri != null) {
	uri = _relativize(uri, baseUri);
	}
	if (!uri.path.endsWith('/')) {
	uri = uri.replace(path: uri.path + '/');
	}
	output.write(uri);
	output.writeln();
	});
	}

	// All ASCII characters that are valid in a package name, with space
	// for all the invalid ones (including space).
	const String _validPackageNameCharacters =
	r" ! $ &'()*+,-. 0123456789 ; = "
	r"@ABCDEFGHIJKLMNOPQRSTUVWXYZ _ abcdefghijklmnopqrstuvwxyz ~ ";

	/// Tests whether something is a valid Dart package name.
	bool isValidPackageName(String string) {
	return checkPackageName(string) < 0;
	}

	/// Check if a string is a valid package name.
	///
	/// Valid package names contain only characters in [_validPackageNameCharacters]
	/// and must contain at least one non-'.' character.
	///
	/// Returns `-1` if the string is valid.
	/// Otherwise returns the index of the first invalid character,
	/// or `string.length` if the string contains no non-'.' character.
	int checkPackageName(String string) {
	// Becomes non-zero if any non-'.' character is encountered.
	var nonDot = 0;
	for (var i = 0; i < string.length; i++) {
	var c = string.codeUnitAt(i);
	if (c > 0x7f \|\| _validPackageNameCharacters.codeUnitAt(c) <= $space) {
	return i;
	}
	nonDot += c ^ $dot;
	}
	if (nonDot == 0) return string.length;
	return -1;
	}

	/// Validate that a [Uri] is a valid `package:` URI.
	///
	/// Used to validate user input.
	///
	/// Returns the package name extracted from the package URI,
	/// which is the path segment between `package:` and the first `/`.
	String checkValidPackageUri(Uri packageUri, String name) {
	if (packageUri.scheme != "package") {
	throw PackageConfigArgumentError(packageUri, name, "Not a package: URI");
	}
	if (packageUri.hasAuthority) {
	throw PackageConfigArgumentError(
	packageUri, name, "Package URIs must not have a host part");
	}
	if (packageUri.hasQuery) {
	// A query makes no sense if resolved to a file: URI.
	throw PackageConfigArgumentError(
	packageUri, name, "Package URIs must not have a query part");
	}
	if (packageUri.hasFragment) {
	// We could leave the fragment after the URL when resolving,
	// but it would be odd if "package:foo/foo.dart#1" and
	// "package:foo/foo.dart#2" were considered different libraries.
	// Keep the syntax open in case we ever get multiple libraries in one file.
	throw PackageConfigArgumentError(
	packageUri, name, "Package URIs must not have a fragment part");
	}
	if (packageUri.path.startsWith('/')) {
	throw PackageConfigArgumentError(
	packageUri, name, "Package URIs must not start with a '/'");
	}
	var firstSlash = packageUri.path.indexOf('/');
	if (firstSlash == -1) {
	throw PackageConfigArgumentError(packageUri, name,
	"Package URIs must start with the package name followed by a '/'");
	}
	var packageName = packageUri.path.substring(0, firstSlash);
	var badIndex = checkPackageName(packageName);
	if (badIndex >= 0) {
	if (packageName.isEmpty) {
	throw PackageConfigArgumentError(
	packageUri, name, "Package names mus be non-empty");
	}
	if (badIndex == packageName.length) {
	throw PackageConfigArgumentError(packageUri, name,
	"Package names must contain at least one non-'.' character");
	}
	assert(badIndex < packageName.length);
	var badCharCode = packageName.codeUnitAt(badIndex);
	var badChar = "U+" + badCharCode.toRadixString(16).padLeft(4, '0');
	if (badCharCode >= 0x20 && badCharCode <= 0x7e) {
	// Printable character.
	badChar = "'${packageName[badIndex]}' ($badChar)";
	}
	throw PackageConfigArgumentError(
	packageUri, name, "Package names must not contain $badChar");
	}
	return packageName;
	}

	/// Checks whether URI is just an absolute directory.
	///
	/// * It must have a scheme.
	/// * It must not have a query or fragment.
	/// * The path must end with `/`.
	bool isAbsoluteDirectoryUri(Uri uri) {
	if (uri.hasQuery) return false;
	if (uri.hasFragment) return false;
	if (!uri.hasScheme) return false;
	var path = uri.path;
	if (!path.endsWith("/")) return false;
	return true;
	}

	/// Whether the former URI is a prefix of the latter.
	bool isUriPrefix(Uri prefix, Uri path) {
	assert(!prefix.hasFragment);
	assert(!prefix.hasQuery);
	assert(!path.hasQuery);
	assert(!path.hasFragment);
	assert(prefix.path.endsWith('/'));
	return path.toString().startsWith(prefix.toString());
	}

	/// Finds the first non-JSON-whitespace character in a file.
	///
	/// Used to heuristically detect whether a file is a JSON file or an .ini file.
	int firstNonWhitespaceChar(List<int> bytes) {
	for (var i = 0; i < bytes.length; i++) {
	var char = bytes[i];
	if (char != 0x20 && char != 0x09 && char != 0x0a && char != 0x0d) {
	return char;
	}
	}
	return -1;
	}

	/// Attempts to return a relative path-only URI for [uri].
	///
	/// First removes any query or fragment part from [uri].
	///
	/// If [uri] is already relative (has no scheme), it's returned as-is.
	/// If that is not desired, the caller can pass `baseUri.resolveUri(uri)`
	/// as the [uri] instead.
	///
	/// If the [uri] has a scheme or authority part which differs from
	/// the [baseUri], or if there is no overlap in the paths of the
	/// two URIs at all, the [uri] is returned as-is.
	///
	/// Otherwise the result is a path-only URI which satsifies
	/// `baseUri.resolveUri(result) == uri`,
	///
	/// The `baseUri` must be absolute.
	Uri relativizeUri(Uri uri, Uri /?/ baseUri) {
	if (baseUri == null) return uri;
	assert(baseUri.isAbsolute);
	if (uri.hasQuery \|\| uri.hasFragment) {
	uri = Uri(
	scheme: uri.scheme,
	userInfo: uri.hasAuthority ? uri.userInfo : null,
	host: uri.hasAuthority ? uri.host : null,
	port: uri.hasAuthority ? uri.port : null,
	path: uri.path);
	}

	// Already relative. We assume the caller knows what they are doing.
	if (!uri.isAbsolute) return uri;

	if (baseUri.scheme != uri.scheme) {
	return uri;
	}

	// If authority differs, we could remove the scheme, but it's not worth it.
	if (uri.hasAuthority != baseUri.hasAuthority) return uri;
	if (uri.hasAuthority) {
	if (uri.userInfo != baseUri.userInfo \|\|
	uri.host.toLowerCase() != baseUri.host.toLowerCase() \|\|
	uri.port != baseUri.port) {
	return uri;
	}
	}

	baseUri = baseUri.normalizePath();
	var base = [...baseUri.pathSegments];
	if (base.isNotEmpty) base.removeLast();
	uri = uri.normalizePath();
	var target = [...uri.pathSegments];
	if (target.isNotEmpty && target.last.isEmpty) target.removeLast();
	var index = 0;
	while (index < base.length && index < target.length) {
	if (base[index] != target[index]) {
	break;
	}
	index++;
	}
	if (index == base.length) {
	if (index == target.length) {
	return Uri(path: "./");
	}
	return Uri(path: target.skip(index).join('/'));
	} else if (index > 0) {
	var buffer = StringBuffer();
	for (var n = base.length - index; n > 0; --n) {
	buffer.write("../");
	}
	buffer.writeAll(target.skip(index), "/");
	return Uri(path: buffer.toString());
	} else {
	return uri;
	}
	}

	/// Attempts to return a relative URI for [uri].
	///
	/// The result URI satisfies `baseUri.resolveUri(result) == uri`,
	/// but may be relative.
	/// The `baseUri` must be absolute.
	Uri _relativize(Uri uri, Uri baseUri) {
	assert(baseUri.isAbsolute);
	if (uri.hasQuery \|\| uri.hasFragment) {
	uri = Uri(
	scheme: uri.scheme,
	userInfo: uri.hasAuthority ? uri.userInfo : null,
	host: uri.hasAuthority ? uri.host : null,
	port: uri.hasAuthority ? uri.port : null,
	path: uri.path);
	}

	// Already relative. We assume the caller knows what they are doing.
	if (!uri.isAbsolute) return uri;

	if (baseUri.scheme != uri.scheme) {
	return uri;
	}

	// If authority differs, we could remove the scheme, but it's not worth it.
	if (uri.hasAuthority != baseUri.hasAuthority) return uri;
	if (uri.hasAuthority) {
	if (uri.userInfo != baseUri.userInfo \|\|
	uri.host.toLowerCase() != baseUri.host.toLowerCase() \|\|
	uri.port != baseUri.port) {
	return uri;
	}
	}

	baseUri = baseUri.normalizePath();
	var base = baseUri.pathSegments.toList();
	if (base.isNotEmpty) {
	base = List<String>.from(base)..removeLast();
	}
	uri = uri.normalizePath();
	var target = uri.pathSegments.toList();
	if (target.isNotEmpty && target.last.isEmpty) target.removeLast();
	var index = 0;
	while (index < base.length && index < target.length) {
	if (base[index] != target[index]) {
	break;
	}
	index++;
	}
	if (index == base.length) {
	if (index == target.length) {
	return Uri(path: "./");
	}
	return Uri(path: target.skip(index).join('/'));
	} else if (index > 0) {
	return Uri(
	path: '../' * (base.length - index) + target.skip(index).join('/'));
	} else {
	return uri;
	}
	}

	// Character constants used by this package.
	/// "Line feed" control character.
	const int $lf = 0x0a;

	/// "Carriage return" control character.
	const int $cr = 0x0d;

	/// Space character.
	const int $space = 0x20;

	/// Character `#`.
	const int $hash = 0x23;

	/// Character `.`.
	const int $dot = 0x2e;

	/// Character `:`.
	const int $colon = 0x3a;

	/// Character `?`.
	const int $question = 0x3f;

	/// Character `{`.
	const int $lbrace = 0x7b;

	/// General superclass of most errors and exceptions thrown by this package.
	///
	/// Only covers errors thrown while parsing package configuration files.
	/// Programming errors and I/O exceptions are not covered.
	abstract class PackageConfigError {
	PackageConfigError._();
	}

	class PackageConfigArgumentError extends ArgumentError
	implements PackageConfigError {
	PackageConfigArgumentError(Object /?/ value, String name, String message)
	: super.value(value, name, message);

	PackageConfigArgumentError.from(ArgumentError error)
	: super.value(error.invalidValue, error.name, error.message);
	}

	class PackageConfigFormatException extends FormatException
	implements PackageConfigError {
	PackageConfigFormatException(String message, Object /?/ source,
	[int /?/ offset])
	: super(message, source, offset);

	PackageConfigFormatException.from(FormatException exception)
	: super(exception.message, exception.source, exception.offset);
	}