mirror.rb in braid-1.1.0

- old
+ new

@@ -1,8 +1,11 @@
 module Braid
   class Mirror
-    ATTRIBUTES = %w(url branch revision tag path)
+    # Since Braid 1.1.0, the attributes are written to .braids.json in this
+    # canonical order.  For now, the order is chosen to match what Braid 1.0.22
+    # produced for newly added mirrors.
+    ATTRIBUTES = %w(url branch path tag revision)
 
     class UnknownType < BraidError
       def message
         "unknown type: #{super}"
       end
@@ -20,24 +23,59 @@
 
     include Operations::VersionControl
 
     attr_reader :path, :attributes
 
-    def initialize(path, attributes = {})
+    def initialize(path, attributes = {}, breaking_change_cb = DUMMY_BREAKING_CHANGE_CB)
       @path       = path.sub(/\/$/, '')
-      @attributes = attributes
+      @attributes = attributes.dup
+
+      # Not that it's terribly important to check for such an old feature.  This
+      # is mainly to demonstrate the RemoveMirrorDueToBreakingChange mechanism
+      # in case we want to use it for something else in the future.
+      if !@attributes['type'].nil? && @attributes['type'] != 'git'
+        breaking_change_cb.call <<-DESC
+- Mirror '#{path}' is of a Subversion repository, which is no
+  longer supported.  The mirror will be removed from your configuration, leaving
+  the data in the tree.
+DESC
+        raise Config::RemoveMirrorDueToBreakingChange
+      end
+      @attributes.delete('type')
+
+      # Migrate revision locks from Braid < 1.0.18.  We no longer store the
+      # original branch or tag (the user has to specify it again when
+      # unlocking); we simply represent a locked revision by the absence of a
+      # branch or tag.
+      if @attributes['lock']
+        @attributes.delete('lock')
+        @attributes['branch'] = nil
+        @attributes['tag'] = nil
+      end
+
+      # Removal of support for full-history mirrors from Braid < 1.0.17 is a
+      # breaking change for users who wanted to use the imported history in some
+      # way.
+      if !@attributes['squashed'].nil? && @attributes['squashed'] != true
+        breaking_change_cb.call <<-DESC
+- Mirror '#{path}' is full-history, which is no longer supported.
+  It will be changed to squashed.  Upstream history already imported will remain
+  in your project's history and will have no effect on Braid.
+DESC
+      end
+      @attributes.delete('squashed')
     end
 
     def self.new_from_options(url, options = {})
       url    = url.sub(/\/$/, '')
 
       raise NoTagAndBranch if options['tag'] && options['branch']
 
       tag = options['tag']
       branch = options['branch'] || (tag.nil? ? 'master' : nil)
 
-      path = (options['path'] || extract_path_from_url(url)).sub(/\/$/, '')
+      path = (options['path'] || extract_path_from_url(url, options['remote_path'])).sub(/\/$/, '')
       raise PathRequired unless path
 
       remote_path = options['remote_path']
 
       attributes = {'url' => url, 'branch' => branch, 'path' => remote_path, 'tag' => tag}
@@ -57,19 +95,72 @@
       # `test z$(git merge-base A B) = z$(git rev-parse --verify A)`
       commit = git.rev_parse(commit)
       !!base_revision && git.merge_base(commit, base_revision) == commit
     end
 
-    def versioned_path(revision)
-      "#{revision}:#{self.remote_path}"
+    def upstream_item_for_revision(revision)
+      git.get_tree_item(revision, self.remote_path)
     end
 
+    # Return the arguments that should be passed to "git diff" to diff this
+    # mirror (including uncommitted changes by default), incorporating the given
+    # user-specified arguments.  Having the caller run "git diff" is convenient
+    # for now but violates encapsulation a little; we may have to reorganize the
+    # code in order to add features.
+    def diff_args(user_args = [])
+      upstream_item = upstream_item_for_revision(base_revision)
+
+      # We do not need to spend the time to copy the content outside the
+      # mirror from HEAD because --relative will exclude it anyway.  Rename
+      # detection seems to apply only to the files included in the diff, so we
+      # shouldn't have another bug like
+      # https://github.com/cristibalan/braid/issues/41.
+      base_tree = git.make_tree_with_item(nil, path, upstream_item)
+
+      # Note: --relative does a naive prefix comparison.  If we set (for
+      # example) `--relative=a/b`, that will match an unrelated file or
+      # directory name `a/bb`.  If the mirror is a directory, we can avoid this
+      # by adding a trailing slash to the prefix.
+      #
+      # If the mirror is a file, the only way we can avoid matching a path like
+      # `a/bb` is to pass a path argument to limit the diff.  This means if the
+      # user passes additional path arguments, we won't get the behavior we
+      # expect, which is the intersection of the user-specified paths with the
+      # mirror.  However, it's probably unreasonable for a user to pass path
+      # arguments when diffing a single-file mirror, so we ignore the issue.
+      #
+      # Note: This code doesn't handle various cases in which a directory at the
+      # root of a mirror turns into a file or vice versa.  If that happens,
+      # hopefully the user takes corrective action manually.
+      if upstream_item.is_a?(git.BlobWithMode)
+        # For a single-file mirror, we use the upstream basename for the
+        # upstream side of the diff and the downstream basename for the
+        # downstream side, like what `git diff` does when given two blobs as
+        # arguments.  Use --relative to strip away the entire downstream path
+        # before we add the basenames.
+        return [
+          '--relative=' + path,
+          '--src-prefix=a/' + File.basename(remote_path),
+          '--dst-prefix=b/' + File.basename(path),
+          base_tree,
+          # user_args may contain options, which must come before paths.
+          *user_args,
+          path
+        ]
+      else
+        return [
+          '--relative=' + path + '/',
+          base_tree,
+          *user_args
+        ]
+      end
+    end
+
+    # Precondition: the remote for this mirror is set up.
     def diff
       fetch_base_revision_if_missing
-      remote_hash = git.rev_parse(versioned_path(base_revision))
-      local_hash  = git.tree_hash(path)
-      remote_hash != local_hash ? git.diff_tree(remote_hash, local_hash) : ''
+      git.diff(diff_args)
     end
 
     # Re-fetching the remote after deleting and re-adding it may be slow even if
     # all objects are still present in the repository
     # (https://github.com/cristibalan/braid/issues/71).  Mitigate this for
@@ -77,11 +168,11 @@
     # if the base revision is already present in the repository.
     def fetch_base_revision_if_missing
       begin
         # Without ^{commit}, this will happily pass back an object hash even if
         # the object isn't present.  See the git-rev-parse(1) man page.
-        git.rev_parse(base_revision + "^{commit}")
+        git.rev_parse(base_revision + '^{commit}')
       rescue Operations::UnknownRevision
         fetch
       end
     end
 
@@ -128,10 +219,15 @@
       "#{branch || tag || 'revision'}/braid/#{path}"
     end
 
     private
 
+    DUMMY_BREAKING_CHANGE_CB = lambda { |desc|
+      raise InternalError, 'Instantiated a mirror using an unsupported ' +
+        'feature outside of configuration loading.'
+    }
+
     def method_missing(name, *args)
       if ATTRIBUTES.find { |attribute| name.to_s =~ /^(#{attribute})(=)?$/ }
         if $2
           attributes[$1] = args[0]
         else
@@ -157,10 +253,14 @@
         end
       end
       hash
     end
 
-    def self.extract_path_from_url(url)
+    def self.extract_path_from_url(url, remote_path)
+      if remote_path
+        return File.basename(remote_path)
+      end
+
       return nil unless url
       name = File.basename(url)
 
       if File.extname(name) == '.git'
         # strip .git