Re: [PATCH v2 02/10] merge: check config before loading commits

[Junio C Hamano <gitster@pobox.com>]

Derrick Stolee <dstolee@microsoft.com> writes:

> diff --git a/builtin/merge.c b/builtin/merge.c
> index ee050a47f3..20897f8223 100644
> --- a/builtin/merge.c
> +++ b/builtin/merge.c
> @@ -1183,13 +1183,14 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
>  	branch = branch_to_free = resolve_refdup("HEAD", 0, &head_oid, NULL);
>  	if (branch)
>  		skip_prefix(branch, "refs/heads/", &branch);
> +	init_diff_ui_defaults();
> +	git_config(git_merge_config, NULL);
> +
>  	if (!branch || is_null_oid(&head_oid))
>  		head_commit = NULL;
>  	else
>  		head_commit = lookup_commit_or_die(&head_oid, "HEAD");
>  
> -	init_diff_ui_defaults();
> -	git_config(git_merge_config, NULL);

Wow, that's tricky.  git_merge_config() wants to know which "branch"
we are on, and this place is as early as we can move the call to
without breaking things.  Is this to allow parse_object() called
in lookup_commit_reference_gently() to know if we can rely on the
data cached in the commit-graph data?

> Move the config load to be between the initialization of 'branch'
> and the commit lookup. Also add a test to t5318-commit-graph.sh
> that exercises this code path to prevent a regression.

It is not clear to me how a successful merge of commits/8
demonstrates that reading the config earlier than before is
regression free.

> diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
> index a380419b65..77d85aefe7 100755
> --- a/t/t5318-commit-graph.sh
> +++ b/t/t5318-commit-graph.sh
> @@ -221,4 +221,13 @@ test_expect_success 'write graph in bare repo' '
>  graph_git_behavior 'bare repo with graph, commit 8 vs merge 1' bare commits/8 merge/1
>  graph_git_behavior 'bare repo with graph, commit 8 vs merge 2' bare commits/8 merge/2
>  
> +test_expect_success 'perform fast-forward merge in full repo' '
> +	cd "$TRASH_DIRECTORY/full" &&
> +	git checkout -b merge-5-to-8 commits/5 &&
> +	git merge commits/8 &&
> +	git show-ref -s merge-5-to-8 >output &&
> +	git show-ref -s commits/8 >expect &&
> +	test_cmp expect output
> +'
> +
>  test_done