Re: [PATCH v4 1/1] commit-graph.c: no lazy fetch in lookup_commit_in_graph()

> The commit-graph is used to opportunistically optimize accesses to
> certain pieces of information on commit objects, and
> lookup_commit_in_graph() tries to say "no" when the requested commit
> does not locally exist by returning NULL, in which case the caller
> can ask for (which may result in on-demand fetching from a promisor
> remote) and parse the commit object itself.
> 
> However, it uses a wrong helper, repo_has_object_file(), to do so.
> This helper not only checks if an object is mmediately available in
> the local object store, but also tries to fetch from a promisor remote.
> But the fetch machinery calls lookup_commit_in_graph(), thus causing an
> infinite loop.
> 
> We should make lookup_commit_in_graph() expect that a commit given to it
> can be legitimately missing from the local object store, by using the
> has_object_file() helper instead.
> 
> Signed-off-by: Han Xin <hanxin.hx@bytedance.com>
> ---
>  commit-graph.c                             |  2 +-
>  t/t5330-no-lazy-fetch-with-commit-graph.sh | 70 ++++++++++++++++++++++
>  2 files changed, 71 insertions(+), 1 deletion(-)
>  create mode 100755 t/t5330-no-lazy-fetch-with-commit-graph.sh
> 
> diff --git a/commit-graph.c b/commit-graph.c
> index 92d4503336..2b04ef072d 100644
> --- a/commit-graph.c
> +++ b/commit-graph.c
> @@ -898,7 +898,7 @@ struct commit *lookup_commit_in_graph(struct repository *repo, const struct obje
>                 return NULL;
>         if (!search_commit_pos_in_graph(id, repo->objects->commit_graph, &pos))
>                 return NULL;
> -       if (!repo_has_object_file(repo, id))
> +       if (!has_object(repo, id, 0))
>                 return NULL;
>  
>         commit = lookup_commit(repo, id);
> diff --git a/t/t5330-no-lazy-fetch-with-commit-graph.sh b/t/t5330-no-lazy-fetch-with-commit-graph.sh
> new file mode 100755
> index 0000000000..be33334229
> --- /dev/null
> +++ b/t/t5330-no-lazy-fetch-with-commit-graph.sh
> @@ -0,0 +1,70 @@
> +#!/bin/sh
> +
> +test_description='test for no lazy fetch with the commit-graph'
> +
> +. ./test-lib.sh
> +
> +run_with_limited_processses () {
> +       # bash and ksh use "ulimit -u", dash uses "ulimit -p"
> +       if test -n "$BASH_VERSION"
> +       then
> +               ulimit_max_process="-u"
> +       elif test -n "$KSH_VERSION"
> +       then
> +               ulimit_max_process="-u"
> +       fi
> +       (ulimit ${ulimit_max_process-"-p"} 512 && "$@")
> +}

> +
> +test_lazy_prereq ULIMIT_PROCESSES '
> +       run_with_limited_processses true
> +'
> +
> +if ! test_have_prereq ULIMIT_PROCESSES
> +then
> +       skip_all='skipping tests for no lazy fetch with the commit-graph, ulimit processes not available'
> +       test_done
> +fi
> +
> +test_expect_success 'setup: prepare a repository with a commit' '
> +       git init with-commit &&
> +       test_commit -C with-commit the-commit &&
> +       oid=$(git -C with-commit rev-parse HEAD)
> +'
> +
> +test_expect_success 'setup: prepare a repository with commit-graph contains the commit' '
> +       git init with-commit-graph &&
> +       echo "$(pwd)/with-commit/.git/objects" \
> +               >with-commit-graph/.git/objects/info/alternates &&
> +       # create a ref that points to the commit in alternates
> +       git -C with-commit-graph update-ref refs/ref_to_the_commit "$oid" &&
> +       # prepare some other objects to commit-graph
> +       test_commit -C with-commit-graph something &&
> +       git -c gc.writeCommitGraph=true -C with-commit-graph gc &&
> +       test_path_is_file with-commit-graph/.git/objects/info/commit-graph
> +'
> +
> +test_expect_success 'setup: change the alternates to what without the commit' '
> +       git init --bare without-commit &&
> +       git -C with-commit-graph cat-file -e $oid &&
> +       echo "$(pwd)/without-commit/objects" \
> +               >with-commit-graph/.git/objects/info/alternates &&
> +       test_must_fail git -C with-commit-graph cat-file -e $oid
> +'
> +
> +test_expect_success 'fetch any commit from promisor with the usage of the commit graph' '
> +       # setup promisor and prepare any commit to fetch
> +       git -C with-commit-graph remote add origin "$(pwd)/with-commit" &&
> +       git -C with-commit-graph config remote.origin.promisor true &&
> +       git -C with-commit-graph config remote.origin.partialclonefilter blob:none &&
> +       test_commit -C with-commit any-commit &&
> +       anycommit=$(git -C with-commit rev-parse HEAD) &&
> +
> +       run_with_limited_processses env GIT_TRACE="$(pwd)/trace.txt" \
> +               git -C with-commit-graph fetch origin $anycommit 2>err &&

> +       ! grep "fatal: promisor-remote: unable to fork off fetch subprocess" err &&
> +       grep "git fetch origin" trace.txt >actual &&
> +       test_line_count = 1 actual
> +'
> +
> +test_done
> -- 
> 2.36.1
> 
>