Harvest from pub. Mostly a straight copy, except:

lib/src/version_range.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_range;
+
+import 'version.dart';
+import 'version_constraint.dart';
+
+/// Constrains versions to a fall within a given range.
+///
+/// If there is a minimum, then this only allows versions that are at that
+/// minimum or greater. If there is a maximum, then only versions less than
+/// that are allowed. In other words, this allows `>= min, < max`.
+class VersionRange implements VersionConstraint {
+  final Version min;
+  final Version max;
+  final bool includeMin;
+  final bool includeMax;

[nweiz, 2014/09/25 22:52:02]

Document these, especially what it means for [min] and [max] to be null.

[Bob Nystrom, 2014/09/26 19:41:07]

Done.

+
+  VersionRange({this.min, this.max,

[nweiz, 2014/09/25 22:52:02]

Document this.

[Bob Nystrom, 2014/09/26 19:41:07]

Done.

+      this.includeMin: false, this.includeMax: false}) {
+    if (min != null && max != null && min > max) {

[nweiz, 2014/09/25 22:52:02]

Nit: short-circuit to save a line.

[Bob Nystrom, 2014/09/26 19:41:07]

I would in most cases, but I think this is a bit easier to read this way, and
the extra line and indentation are minimal.

+      throw new ArgumentError(
+          'Minimum version ("$min") must be less than maximum ("$max").');
+    }
+  }
+
+  bool operator ==(other) {
+    if (other is! VersionRange) return false;
+
+    return min == other.min &&
+           max == other.max &&
+           includeMin == other.includeMin &&
+           includeMax == other.includeMax;
+  }
+
+  bool get isEmpty => false;
+
+  bool get isAny => min == null && max == null;
+
+  /// Tests if [other] matches falls within this version range.

[nweiz, 2014/09/25 22:52:02]

-"matches"

[Bob Nystrom, 2014/09/26 19:41:07]

Done.

+  bool allows(Version other) {
+    if (min != null) {
+      if (other < min) return false;
+      if (!includeMin && other == min) return false;
+    }
+
+    if (max != null) {
+      if (other > max) return false;
+      if (!includeMax && other == max) return false;
+
+      // If the max isn't itself a pre-release, don't allow any pre-release
+      // versions of the max.
+      //
+      // See: https://www.npmjs.org/doc/misc/semver.html
+      if (!includeMax &&
+          !max.isPreRelease && other.isPreRelease &&
+          other.major == max.major && other.minor == max.minor &&
+          other.patch == max.patch) {
+        return false;
+      }
+    }
+
+    return true;
+  }
+
+  VersionConstraint intersect(VersionConstraint other) {
+    if (other.isEmpty) return other;
+
+    // A range and a Version just yields the version if it's in the range.
+    if (other is Version) {
+      return allows(other) ? other : VersionConstraint.empty;
+    }
+
+    if (other is VersionRange) {
+      // Intersect the two ranges.
+      var intersectMin = min;
+      var intersectIncludeMin = includeMin;
+      var intersectMax = max;
+      var intersectIncludeMax = includeMax;
+
+      if (other.min == null) {
+        // Do nothing.
+      } else if (intersectMin == null || intersectMin < other.min) {
+        intersectMin = other.min;
+        intersectIncludeMin = other.includeMin;
+      } else if (intersectMin == other.min && !other.includeMin) {
+        // The edges are the same, but one is exclusive, make it exclusive.
+        intersectIncludeMin = false;
+      }
+
+      if (other.max == null) {
+        // Do nothing.
+      } else if (intersectMax == null || intersectMax > other.max) {
+        intersectMax = other.max;
+        intersectIncludeMax = other.includeMax;
+      } else if (intersectMax == other.max && !other.includeMax) {
+        // The edges are the same, but one is exclusive, make it exclusive.
+        intersectIncludeMax = false;
+      }
+
+      if (intersectMin == null && intersectMax == null) {
+        // Open range.
+        return new VersionRange();
+      }
+
+      // If the range is just a single version.
+      if (intersectMin == intersectMax) {
+        // If both ends are inclusive, allow that version.
+        if (intersectIncludeMin && intersectIncludeMax) return intersectMin;
+
+        // Otherwise, no versions.
+        return VersionConstraint.empty;
+      }
+
+      if (intersectMin != null && intersectMax != null &&
+          intersectMin > intersectMax) {
+        // Non-overlapping ranges, so empty.
+        return VersionConstraint.empty;
+      }
+
+      // If we got here, there is an actual range.
+      return new VersionRange(min: intersectMin, max: intersectMax,
+          includeMin: intersectIncludeMin, includeMax: intersectIncludeMax);
+    }
+
+    throw new ArgumentError(
+        'Unknown VersionConstraint type $other.');
+  }
+
+  String toString() {
+    var buffer = new StringBuffer();
+
+    if (min != null) {
+      buffer.write(includeMin ? '>=' : '>');
+      buffer.write(min);
+    }
+
+    if (max != null) {
+      if (min != null) buffer.write(' ');
+      buffer.write(includeMax ? '<=' : '<');
+      buffer.write(max);
+    }
+
+    if (min == null && max == null) buffer.write('any');
+    return buffer.toString();
+  }
+}