Use a lockfile to persist Pub's installed version constellation.

utils/pub/git_source.dart

 // 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.
 
 #library('git_source');
 
 #import('io.dart');
 #import('package.dart');
 #import('source.dart');
 #import('source_registry.dart');
@@ skipping 36 matching lines @@
       return ensureDir(join(systemCacheRoot, 'cache'));
     }).chain((_) => _ensureRepoCache(id))
       .chain((_) => _revisionCachePath(id))
       .chain((path) {
       revisionCachePath = path;
       return exists(revisionCachePath);
     }).chain((exists) {
       if (exists) return new Future.immediate(null);
       return _clone(_repoCachePath(id), revisionCachePath);
     }).chain((_) {
-      var ref = _getRef(id);
-      if (ref == null) return new Future.immediate(null);
+      var ref = _getEffectiveRef(id);
+      if (ref == 'HEAD') return new Future.immediate(null);
       return _checkOut(revisionCachePath, ref);
     }).chain((_) => Package.load(revisionCachePath, systemCache.sources));
   }
 
   /**
    * The package name of a Git repo is the name of the directory into which
    * it'll be cloned.
    */
   String packageName(description) =>
     basename(_getUrl(description)).replaceFirst(const RegExp("\.git\$"), "");
 
   /**
    * Ensures [description] is a Git URL.
    */
-  void validateDescription(description) {
+  void validateDescription(description, [bool fromLockFile = false]) {
     // A single string is assumed to be a Git URL.
     if (description is String) return;
     if (description is! Map || !description.containsKey('url')) {
       throw new FormatException("The description must be a Git URL or a map "
           "with a 'url' key.");
     }
     description = new Map.from(description);
     description.remove('url');
     description.remove('ref');
+    if (fromLockFile) description.remove('resolved-ref');
 
     if (!description.isEmpty()) {
       var plural = description.length > 1;
-      var keys = Strings.join(description.keys, ', ');
+      var keys = Strings.join(description.getKeys(), ', ');
       throw new FormatException("Invalid key${plural ? 's' : ''}: $keys.");
     }
   }
 
   /**
    * Two Git descriptions are equal if both their URLs and their refs are equal.
    */
   bool descriptionsEqual(description1, description2) {
     // TODO(nweiz): Do we really want to throw an error if you have two
     // dependencies on some repo, one of which specifies a ref and one of which
     // doesn't? If not, how do we handle that case in the version solver?
     return _getUrl(description1) == _getUrl(description2) &&
       _getRef(description1) == _getRef(description2);
   }
 
   /**
+   * Attaches a specific commit to [id] to disambiguate it.
+   */
+  Future<PackageId> resolveId(PackageId id) {
+    return _revisionAt(id).transform((revision) {
+      var description = {'url': _getUrl(id), 'ref': _getRef(id)};
+      description['resolved-ref'] = revision;
+      return new PackageId(this, id.version, description);
+    });
+  }
+
+  /**
    * Ensure that the canonical clone of the repository referred to by [id] (the
    * one in `<system cache>/git/cache`) exists and is up-to-date. Returns a
    * future that completes once this is finished and throws an exception if it
    * fails.
    */
   Future _ensureRepoCache(PackageId id) {
     var path = _repoCachePath(id);
     return exists(path).chain((exists) {
       if (!exists) return _clone(_getUrl(id), path);
 
       return runProcess("git", ["pull", "--force"], workingDir: path,
           pipeStdout: true, pipeStderr: true).transform((result) {
         if (!result.success) throw 'Git failed.';
         return null;
       });
     });
   }
 
   /**
-   * Returns a future that completes to the revision hash of the repository for
-   * [id] at [ref], which can be any Git ref.
+   * Returns a future that completes to the revision hash of [id].
    */
-  Future<String> _revisionAt(PackageId id, String ref) {
-    return runProcess("git", ["rev-parse", ref],
+  Future<String> _revisionAt(PackageId id) {
+    return runProcess("git", ["rev-parse", _getEffectiveRef(id)],
         workingDir: _repoCachePath(id), pipeStderr: true).transform((result) {
       if (!result.success) throw 'Git failed.';
       return result.stdout[0];
     });
   }
 
   /**
-   * Returns the path to the revision-specific cache of [id] at [ref], which can
-   * be any Git ref.
+   * Returns the path to the revision-specific cache of [id].
    */
   Future<String> _revisionCachePath(PackageId id) {
-    var ref = _getRef(id);
-    if (ref == null) ref = 'HEAD';
-    return _revisionAt(id, ref).transform((rev) {
+    return _revisionAt(id).transform((rev) {
       var revisionCacheName = '${id.name}-$rev';
       return join(systemCacheRoot, revisionCacheName);
     });
   }
 
   /**
    * Clones the repo at the URI [from] to the path [to] on the local filesystem.
    */
   Future _clone(String from, String to) {
     return runProcess("git", ["clone", from, to], pipeStdout: true,
@@ skipping 28 matching lines @@
    *
    * [description] may be a description or a [PackageId].
    */
   String _getUrl(description) {
     description = _getDescription(description);
     if (description is String) return description;
     return description['url'];
   }
 
   /**
-   * Returns the commit ref for [id], or null if none is given.
+   * Returns the commit ref that should be checked out for [description].
+   *
+   * This differs from [_getRef] in that it doesn't just return the ref in
+   * [description]. It will return a sensible default if that ref doesn't exist,
+   * and it will respect the "resolved-ref" parameter set by [resolveId].
    *
    * [description] may be a description or a [PackageId].
    */
+  String _getEffectiveRef(description) {
+    description = _getDescription(description);
+    if (description is Map && description.containsKey('resolved-ref')) {
+      return description['resolved-ref'];
+    }
+
+    var ref = _getRef(description);
+    return ref == null ? 'HEAD' : ref;
+  }
+
+  /**
+   * Returns the commit ref for [description], or null if none is given.
+   *
+   * [description] may be a description or a [PackageId].
+   */
   String _getRef(description) {
     description = _getDescription(description);
     if (description is String) return null;
     return description['ref'];
   }
 
   /**
    * Returns [description] if it's a description, or [PackageId.description] if
    * it's a [PackageId].
    */
   _getDescription(description) {
     if (description is PackageId) return description.description;
     return description;
   }
 }