Re: standalone library/tool to query commit-graph?

From: Derrick Stolee <stolee@gmail.com>
Date: May 23, 2019, 23:48 UTC
Message-ID: <f05405d7-c78d-a0e4-75a1-d623f977400a@gmail.com>
In-Reply-To: <20190523222031.GC951@szeder.dev>

On 5/23/2019 6:20 PM, SZEDER Gábor wrote:

Show 32 quoted lines

> On Thu, May 23, 2019 at 11:54:22PM +0200, Ævar Arnfjörð Bjarmason wrote:
>>
>> On Thu, May 23 2019, Jakub Narebski wrote:
>>
>>> Derrick Stolee <stolee@gmail.com> writes:
>>>> On 5/22/2019 2:49 PM, Karl Ostmo wrote:
>>>
>>>>> After producing the file ".git/objects/info/commit-graph" with the
>>>>> command "git commit-graph write", is there a way to answer queries
>>>>> like "git merge-base --is-ancestor" without having a .git directory?
>>>>> E.g. is there a library that will operate on the "commit-graph" file
>>>>> all by itself?
>>>>
>>>> You could certainly build such a tool, assuming your merge-base parameters are
>>>> full-length commit ids. If you try to start at ref names, you'll need the .git
>>>> directory.
>>>>
>>>> I would not expect such a tool to ever exist in the Git codebase. Instead, you
>>>> would need a new project, say "graph-analyzer --graph=<path> --is-ancestor <id1> <id2>"
>>>
>>> It would be nice if such tool could convert commit-graph into other
>>> commonly used augmented graph storage formats, like GEXF (Graph Exchange
>>> XML Format), GraphML, GML (Graph Modelling Language), Pajek format or
>>> Graphviz .dot format.
>>
>> Wouldn't that make more sense as a hypothetical output format for "log
>> --graph" rather than something you'd want to emit from the commit-graph?
>> Presumably you'd want to export in such a format to see the shape of the
>> repo, and since the commit graph doesn't include any commits outside of
>> packs you'd miss any loose commits.
> 
> No, the commit-graph includes loose commits as well.

Depends on how you build the commit-graph.

	git commit-graph write
	git commit-graph write --stdin-packs

These options build based on commits in packs (and closes under reachability).

	git commit-graph write --reachable
	git commit-graph write --stdin-commits

These options build based on a set of starting commits. Either the refs (--reachable) or the input commit ids (--stdin-commits).

But I do like the flexibility of `git log --graph` as you could export the graph after reparenting (with options like `--simplify-merges -- <path>`). You also would not include commits from random topic branches you have sitting around.

-Stolee