Harvest from pub. Mostly a straight copy, except:

lib/src/version.dart

+// Copyright (c) 2014, 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.
+
+library pub_semver.src.version;
+
+import 'dart:math';
+
+import 'package:collection/equality.dart';
+
+import 'patterns.dart';
+import 'version_constraint.dart';
+import 'version_range.dart';
+
+/// The equality operator to use for comparing version components.
+final _equality = const IterableEquality();
+
+/// A parsed semantic version number.
+class Version implements Comparable<Version>, VersionConstraint {
+  /// No released version: i.e. "0.0.0".
+  static Version get none => new Version(0, 0, 0);
+
+  /// Compares [a] and [b] to see which takes priority over the other.
+  ///
+  /// Returns `1` if [a] takes priority over [b] and `-1` if vice versa. If
+  /// [a] and [b] are equivalent, returns `0`.
+  ///
+  /// Unlike [compareTo], which *orders* versions, this determines which
+  /// version a user is likely to prefer. In particular, it prioritizes
+  /// pre-release versions lower than stable versions, regardless of their
+  /// version numbers. Pub uses this when determining which version to prefer
+  /// when a number of versions are allowed. In that case, it will always
+  /// choose a stable version when possible.
+  ///
+  /// When used to sort a list, orders in ascending priority so that the
+  /// highest priority version is *last* in the result.
+  static int prioritize(Version a, Version b) {
+    // Sort all prerelease versions after all normal versions. This way
+    // the solver will prefer stable packages over unstable ones.
+    if (a.isPreRelease && !b.isPreRelease) return -1;
+    if (!a.isPreRelease && b.isPreRelease) return 1;
+
+    return a.compareTo(b);
+  }
+
+  /// Like [proiritize], but lower version numbers are considered greater than
+  /// higher version numbers.
+  ///
+  /// This still considers prerelease versions to be lower than non-prerelease
+  /// versions. Pub uses this when downgrading -- it chooses the lowest version
+  /// but still excludes pre-release versions when possible.
+  static int antiprioritize(Version a, Version b) {
+    if (a.isPreRelease && !b.isPreRelease) return -1;
+    if (!a.isPreRelease && b.isPreRelease) return 1;
+
+    return b.compareTo(a);
+  }
+
+  /// The major version number: "1" in "1.2.3".
+  final int major;
+
+  /// The minor version number: "2" in "1.2.3".
+  final int minor;
+
+  /// The patch version number: "3" in "1.2.3".
+  final int patch;
+
+  /// The pre-release identifier: "foo" in "1.2.3-foo".
+  ///
+  /// This is split into a list of components, each of which may be either a
+  /// string or a non-negative integer. It may also be empty, indicating that
+  /// this version has no pre-release identifier.
+  final List preRelease;
+
+  /// The build identifier: "foo" in "1.2.3+foo".
+  ///
+  /// This is split into a list of components, each of which may be either a
+  /// string or a non-negative integer. It may also be empty, indicating that
+  /// this version has no build identifier.
+  final List build;
+
+  /// The original string representation of the version number.
+  ///
+  /// This preserves textual artifacts like leading zeros that may be left out
+  /// of the parsed version.
+  final String _text;
+
+  Version._(this.major, this.minor, this.patch, String preRelease, String build,
+            this._text)
+      : preRelease = preRelease == null ? [] : _splitParts(preRelease),
+        build = build == null ? [] : _splitParts(build) {
+    if (major < 0) throw new ArgumentError(
+        'Major version must be non-negative.');
+    if (minor < 0) throw new ArgumentError(
+        'Minor version must be non-negative.');
+    if (patch < 0) throw new ArgumentError(
+        'Patch version must be non-negative.');
+  }
+
+  /// Creates a new [Version] object.
+  factory Version(int major, int minor, int patch, {String pre, String build}) {
+    var text = "$major.$minor.$patch";
+    if (pre != null) text += "-$pre";
+    if (build != null) text += "+$build";
+
+    return new Version._(major, minor, patch, pre, build, text);
+  }
+
+  /// Creates a new [Version] by parsing [text].
+  factory Version.parse(String text) {
+    final match = COMPLETE_VERSION.firstMatch(text);
+    if (match == null) {
+      throw new FormatException('Could not parse "$text".');
+    }
+
+    try {
+      int major = int.parse(match[1]);
+      int minor = int.parse(match[2]);
+      int patch = int.parse(match[3]);
+
+      String preRelease = match[5];
+      String build = match[8];
+
+      return new Version._(major, minor, patch, preRelease, build, text);
+    } on FormatException catch (ex) {
+      throw new FormatException('Could not parse "$text".');
+    }
+  }
+
+  /// Returns the primary version out of a list of candidates.
+  ///
+  /// This is the highest-numbered stable (non-prerelease) version. If there
+  /// are no stable versions, it's just the highest-numbered version.
+  static Version primary(List<Version> versions) {
+    var primary;
+    for (var version in versions) {
+      if (primary == null || (!version.isPreRelease && primary.isPreRelease) ||
+          (version.isPreRelease == primary.isPreRelease && version > primary)) {
+        primary = version;
+      }
+    }
+    return primary;
+  }
+
+  /// Splits a string of dot-delimited identifiers into their component parts.
+  ///
+  /// Identifiers that are numeric are converted to numbers.
+  static List _splitParts(String text) {
+    return text.split('.').map((part) {
+      try {
+        return int.parse(part);
+      } on FormatException catch (ex) {
+        // Not a number.
+        return part;
+      }
+    }).toList();
+  }
+
+  bool operator ==(other) {
+    if (other is! Version) return false;
+    return major == other.major && minor == other.minor &&
+        patch == other.patch &&
+        _equality.equals(preRelease, other.preRelease) &&
+        _equality.equals(build, other.build);
+  }
+
+  int get hashCode => major ^ minor ^ patch ^ _equality.hash(preRelease) ^
+      _equality.hash(build);
+
+  bool operator <(Version other) => compareTo(other) < 0;
+  bool operator >(Version other) => compareTo(other) > 0;
+  bool operator <=(Version other) => compareTo(other) <= 0;
+  bool operator >=(Version other) => compareTo(other) >= 0;
+
+  bool get isAny => false;
+  bool get isEmpty => false;
+
+  /// Whether or not this is a pre-release version.
+  bool get isPreRelease => preRelease.isNotEmpty;
+
+  /// Gets the next major version number that follows this one.
+  ///
+  /// If this version is a pre-release of a major version release (i.e. the
+  /// minor and patch versions are zero), then it just strips the pre-release
+  /// suffix. Otherwise, it increments the major version and resets the minor
+  /// and patch.
+  Version get nextMajor {
+    if (isPreRelease && minor == 0 && patch == 0) {
+      return new Version(major, minor, patch);
+    }
+
+    return new Version(major + 1, 0, 0);
+  }
+
+  /// Gets the next minor version number that follows this one.
+  ///
+  /// If this version is a pre-release of a minor version release (i.e. the
+  /// patch version is zero), then it just strips the pre-release suffix.
+  /// Otherwise, it increments the minor version and resets the patch.
+  Version get nextMinor {
+    if (isPreRelease && patch == 0) {
+      return new Version(major, minor, patch);
+    }
+
+    return new Version(major, minor + 1, 0);
+  }
+
+  /// Gets the next patch version number that follows this one.
+  ///
+  /// If this version is a pre-release, then it just strips the pre-release
+  /// suffix. Otherwise, it increments the patch version.
+  Version get nextPatch {
+    if (isPreRelease) {
+      return new Version(major, minor, patch);
+    }
+
+    return new Version(major, minor, patch + 1);
+  }
+
+  /// Tests if [other] matches this version exactly.
+  bool allows(Version other) => this == other;
+
+  VersionConstraint intersect(VersionConstraint other) {
+    if (other.isEmpty) return other;
+
+    // Intersect a version and a range.
+    if (other is VersionRange) return other.intersect(this);
+
+    // Intersecting two versions only works if they are the same.
+    if (other is Version) {
+      return this == other ? this : VersionConstraint.empty;
+    }
+
+    throw new ArgumentError(
+        'Unknown VersionConstraint type $other.');
+  }
+
+  int compareTo(Version other) {
+    if (major != other.major) return major.compareTo(other.major);
+    if (minor != other.minor) return minor.compareTo(other.minor);
+    if (patch != other.patch) return patch.compareTo(other.patch);
+
+    // Pre-releases always come before no pre-release string.
+    if (!isPreRelease && other.isPreRelease) return 1;
+    if (!other.isPreRelease && isPreRelease) return -1;
+
+    var comparison = _compareLists(preRelease, other.preRelease);
+    if (comparison != 0) return comparison;
+
+    // Builds always come after no build string.
+    if (build.isEmpty && other.build.isNotEmpty) return -1;
+    if (other.build.isEmpty && build.isNotEmpty) return 1;
+    return _compareLists(build, other.build);
+  }
+
+  String toString() => _text;
+
+  /// Compares a dot-separated component of two versions.
+  ///
+  /// This is used for the pre-release and build version parts. This follows
+  /// Rule 12 of the Semantic Versioning spec (v2.0.0-rc.1).
+  int _compareLists(List a, List b) {
+    for (var i = 0; i < max(a.length, b.length); i++) {
+      var aPart = (i < a.length) ? a[i] : null;
+      var bPart = (i < b.length) ? b[i] : null;
+
+      if (aPart == bPart) continue;
+
+      // Missing parts come before present ones.
+      if (aPart == null) return -1;
+      if (bPart == null) return 1;
+
+      if (aPart is num) {
+        if (bPart is num) {
+          // Compare two numbers.
+          return aPart.compareTo(bPart);
+        } else {
+          // Numbers come before strings.
+          return -1;
+        }
+      } else {
+        if (bPart is num) {
+          // Strings come after numbers.
+          return 1;
+        } else {
+          // Compare two strings.
+          return aPart.compareTo(bPart);
+        }
+      }
+    }
+
+    // The lists are entirely equal.
+    return 0;
+  }
+}