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>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/commit-graph.c b/commit-graph.c
index 2b528187316e28eb114b575727dc26101aa9296a..2dd9bcc7ea36b013a9b646aaccbb6df503d481fd 100644 (file)
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -907,7 +907,7 @@ 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 (executable)
index 0000000..be33334
--- /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