Merge branch 'ds/commit-graph'

Precompute and store information necessary for ancestry traversal
in a separate file to optimize graph walking.

* ds/commit-graph:
  commit-graph: implement "--append" option
  commit-graph: build graph from starting commits
  commit-graph: read only from specific pack-indexes
  commit: integrate commit graph with commit parsing
  commit-graph: close under reachability
  commit-graph: add core.commitGraph setting
  commit-graph: implement git commit-graph read
  commit-graph: implement git-commit-graph write
  commit-graph: implement write_commit_graph()
  commit-graph: create git-commit-graph builtin
  graph: add commit graph design document
  commit-graph: add format document
  csum-file: refactor finalize_hashfile() method
  csum-file: rename hashclose() to finalize_hashfile()

1 files changed, 94 insertions, 0 deletions

diff --git a/Documentation/git-commit-graph.txt b/Documentation/git-commit-graph.txt
new file mode 100644
index 0000000000..4c97b555cc
--- /dev/null
+++ b/Documentation/git-commit-graph.txt
@@ -0,0 +1,94 @@
+git-commit-graph(1)
+===================
+
+NAME
+----
+git-commit-graph - Write and verify Git commit graph files
+
+
+SYNOPSIS
+--------
+[verse]
+'git commit-graph read' [--object-dir <dir>]
+'git commit-graph write' <options> [--object-dir <dir>]
+
+
+DESCRIPTION
+-----------
+
+Manage the serialized commit graph file.
+
+
+OPTIONS
+-------
+--object-dir::
+	Use given directory for the location of packfiles and commit graph
+	file. This parameter exists to specify the location of an alternate
+	that only has the objects directory, not a full .git directory. The
+	commit graph file is expected to be at <dir>/info/commit-graph and
+	the packfiles are expected to be in <dir>/pack.
+
+
+COMMANDS
+--------
+'write'::
+
+Write a commit graph file based on the commits found in packfiles.
++
+With the `--stdin-packs` option, generate the new commit graph by
+walking objects only in the specified pack-indexes. (Cannot be combined
+with --stdin-commits.)
++
+With the `--stdin-commits` option, generate the new commit graph by
+walking commits starting at the commits specified in stdin as a list
+of OIDs in hex, one OID per line. (Cannot be combined with
+--stdin-packs.)
++
+With the `--append` option, include all commits that are present in the
+existing commit-graph file.
+
+'read'::
+
+Read a graph file given by the commit-graph file and output basic
+details about the graph file. Used for debugging purposes.
+
+
+EXAMPLES
+--------
+
+* Write a commit graph file for the packed commits in your local .git folder.
++
+------------------------------------------------
+$ git commit-graph write
+------------------------------------------------
+
+* Write a graph file, extending the current graph file using commits
+* in <pack-index>.
++
+------------------------------------------------
+$ echo <pack-index> | git commit-graph write --stdin-packs
+------------------------------------------------
+
+* Write a graph file containing all reachable commits.
++
+------------------------------------------------
+$ git show-ref -s | git commit-graph write --stdin-commits
+------------------------------------------------
+
+* Write a graph file containing all commits in the current
+* commit-graph file along with those reachable from HEAD.
++
+------------------------------------------------
+$ git rev-parse HEAD | git commit-graph write --stdin-commits --append
+------------------------------------------------
+
+* Read basic information from the commit-graph file.
++
+------------------------------------------------
+$ git commit-graph read
+------------------------------------------------
+
+
+GIT
+---
+Part of the linkgit:git[1] suite