Re: [PATCH v4 2/4] fetch: add --prefetch option

[Tom Saeger <tom.saeger@oracle.com>]

On Fri, Apr 16, 2021 at 12:49:57PM +0000, Derrick Stolee via GitGitGadget wrote:
> From: Derrick Stolee <dstolee@microsoft.com>
> 
> The --prefetch option will be used by the 'prefetch' maintenance task
> instead of sending refspecs explicitly across the command-line. The
> intention is to modify the refspec to place all results in
> refs/prefetch/ instead of anywhere else.
> 
> Create helper method filter_prefetch_refspec() to modify a given refspec
> to fit the rules expected of the prefetch task:
> 
>  * Negative refspecs are preserved.
>  * Refspecs without a destination are removed.
>  * Refspecs whose source starts with "refs/tags/" are removed.
>  * Other refspecs are placed within "refs/prefetch/".
> 
> Finally, we add the 'force' option to ensure that prefetch refs are
> replaced as necessary.
> 
> There are some interesting cases that are worth testing.
> 
> An earlier version of this change dropped the "i--" from the loop that
> deletes a refspec item and shifts the remaining entries down. This
> allowed some refspecs to not be modified. The subtle part about the
> first --prefetch test is that the "refs/tags/*" refspec appears directly
> before the "refs/heads/bogus/*" refspec. Without that "i--", this
> ordering would remove the "refs/tags/*" refspec and leave the last one
> unmodified, placing the result in "refs/heads/*".
> 
> It is possible to have an empty refspec. This is typically the case for
> remotes other than the origin, where users want to fetch a specific tag
> or branch. To correctly test this case, we need to further remove the
> upstream remote for the local branch. Thus, we are testing a refspec
> that will be deleted, leaving nothing to fetch.
> 
> Helped-by: Tom Saeger <tom.saeger@oracle.com>
> Helped-by: Ramsay Jones <ramsay@ramsayjones.plus.com>
> Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
> ---
>  Documentation/fetch-options.txt   |  5 +++
>  builtin/fetch.c                   | 59 ++++++++++++++++++++++++++++++-
>  t/t5582-fetch-negative-refspec.sh | 43 ++++++++++++++++++++++
>  3 files changed, 106 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/fetch-options.txt b/Documentation/fetch-options.txt
> index 07783deee309..9e7b4e189ce0 100644
> --- a/Documentation/fetch-options.txt
> +++ b/Documentation/fetch-options.txt
> @@ -110,6 +110,11 @@ ifndef::git-pull[]
>  	setting `fetch.writeCommitGraph`.
>  endif::git-pull[]
>  
> +--prefetch::
> +	Modify the configured refspec to place all refs into the
> +	`refs/prefetch/` namespace. See the `prefetch` task in
> +	linkgit:git-maintenance[1].
> +
>  -p::
>  --prune::
>  	Before fetching, remove any remote-tracking references that no
> diff --git a/builtin/fetch.c b/builtin/fetch.c
> index 0b90de87c7a2..97c4fe6e6d66 100644
> --- a/builtin/fetch.c
> +++ b/builtin/fetch.c
> @@ -48,6 +48,7 @@ enum {
>  static int fetch_prune_config = -1; /* unspecified */
>  static int fetch_show_forced_updates = 1;
>  static uint64_t forced_updates_ms = 0;
> +static int prefetch = 0;
>  static int prune = -1; /* unspecified */
>  #define PRUNE_BY_DEFAULT 0 /* do we prune by default? */
>  
> @@ -158,6 +159,8 @@ static struct option builtin_fetch_options[] = {
>  		    N_("do not fetch all tags (--no-tags)"), TAGS_UNSET),
>  	OPT_INTEGER('j', "jobs", &max_jobs,
>  		    N_("number of submodules fetched in parallel")),
> +	OPT_BOOL(0, "prefetch", &prefetch,
> +		 N_("modify the refspec to place all refs within refs/prefetch/")),
>  	OPT_BOOL('p', "prune", &prune,
>  		 N_("prune remote-tracking branches no longer on remote")),
>  	OPT_BOOL('P', "prune-tags", &prune_tags,
> @@ -436,6 +439,56 @@ static void find_non_local_tags(const struct ref *refs,
>  	oidset_clear(&fetch_oids);
>  }
>  
> +static void filter_prefetch_refspec(struct refspec *rs)
> +{
> +	int i;
> +
> +	if (!prefetch)
> +		return;
> +
> +	for (i = 0; i < rs->nr; i++) {
> +		struct strbuf new_dst = STRBUF_INIT;
> +		char *old_dst;
> +		const char *sub = NULL;
> +
> +		if (rs->items[i].negative)
> +			continue;
> +		if (!rs->items[i].dst ||
> +		    (rs->items[i].src &&
> +		     !strncmp(rs->items[i].src, "refs/tags/", 10))) {
> +			int j;
> +
> +			free(rs->items[i].src);
> +			free(rs->items[i].dst);
> +
> +			for (j = i + 1; j < rs->nr; j++) {
> +				rs->items[j - 1] = rs->items[j];
> +				rs->raw[j - 1] = rs->raw[j];
> +			}
> +			rs->nr--;
> +			i--;
> +			continue;
> +		}
> +
> +		old_dst = rs->items[i].dst;
> +		strbuf_addstr(&new_dst, "refs/prefetch/");
> +
> +		/*
> +		 * If old_dst starts with "refs/", then place
> +		 * sub after that prefix. Otherwise, start at
> +		 * the beginning of the string.
> +		 */
> +		if (!skip_prefix(old_dst, "refs/", &sub))
> +			sub = old_dst;
> +		strbuf_addstr(&new_dst, sub);
> +
> +		rs->items[i].dst = strbuf_detach(&new_dst, NULL);
> +		rs->items[i].force = 1;
> +
> +		free(old_dst);
> +	}
> +}
> +
>  static struct ref *get_ref_map(struct remote *remote,
>  			       const struct ref *remote_refs,
>  			       struct refspec *rs,
> @@ -452,6 +505,10 @@ static struct ref *get_ref_map(struct remote *remote,
>  	struct hashmap existing_refs;
>  	int existing_refs_populated = 0;
>  
> +	filter_prefetch_refspec(rs);
> +	if (remote)
> +		filter_prefetch_refspec(&remote->fetch);
> +
>  	if (rs->nr) {
>  		struct refspec *fetch_refspec;
>  
> @@ -520,7 +577,7 @@ static struct ref *get_ref_map(struct remote *remote,
>  			if (has_merge &&
>  			    !strcmp(branch->remote_name, remote->name))
>  				add_merge_config(&ref_map, remote_refs, branch, &tail);
> -		} else {
> +		} else if (!prefetch) {

That works for me.

>  			ref_map = get_remote_ref(remote_refs, "HEAD");
>  			if (!ref_map)
>  				die(_("Couldn't find remote ref HEAD"));
> diff --git a/t/t5582-fetch-negative-refspec.sh b/t/t5582-fetch-negative-refspec.sh
> index f34509727702..e5d2e79ad382 100755
> --- a/t/t5582-fetch-negative-refspec.sh
> +++ b/t/t5582-fetch-negative-refspec.sh
> @@ -240,4 +240,47 @@ test_expect_success "push with matching +: and negative refspec" '
>  	git -C two push -v one
>  '
>  
> +test_expect_success '--prefetch correctly modifies refspecs' '
> +	git -C one config --unset-all remote.origin.fetch &&
> +	git -C one config --add remote.origin.fetch ^refs/heads/bogus/ignore &&
> +	git -C one config --add remote.origin.fetch "refs/tags/*:refs/tags/*" &&
> +	git -C one config --add remote.origin.fetch "refs/heads/bogus/*:bogus/*" &&
> +
> +	git tag -a -m never never-fetch-tag HEAD &&
> +
> +	git branch bogus/fetched HEAD~1 &&
> +	git branch bogus/ignore HEAD &&
> +
> +	git -C one fetch --prefetch --no-tags &&
> +	test_must_fail git -C one rev-parse never-fetch-tag &&
> +	git -C one rev-parse refs/prefetch/bogus/fetched &&
> +	test_must_fail git -C one rev-parse refs/prefetch/bogus/ignore &&
> +
> +	# correctly handle when refspec set becomes empty
> +	# after removing the refs/tags/* refspec.
> +	git -C one config --unset-all remote.origin.fetch &&
> +	git -C one config --add remote.origin.fetch "refs/tags/*:refs/tags/*" &&
> +
> +	git -C one fetch --prefetch --no-tags &&
> +	test_must_fail git -C one rev-parse never-fetch-tag &&
> +
> +	# The refspec for refs that are not fully qualified
> +	# are filtered multiple times.
> +	git -C one rev-parse refs/prefetch/bogus/fetched &&
> +	test_must_fail git -C one rev-parse refs/prefetch/bogus/ignore
> +'
> +
> +test_expect_success '--prefetch succeeds when refspec becomes empty' '

technically this will get skipped based only on "skipfetchall" right?

The remote could have an empty-set of refspecs or multiple
valid refspecs post filter_prefetch_refspec, but the remote gets skipped altogether.

perhaps '--prefetch succeeds when remote.skipfetchall is true' '

anyway this is looking pretty solid

Reviewed-by: Tom Saeger <tom.saeger@oracle.com>

> +	git checkout bogus/fetched &&
> +	test_commit extra &&
> +
> +	git -C one config --unset-all remote.origin.fetch &&
> +	git -C one config --unset branch.main.remote &&
> +	git -C one config remote.origin.fetch "+refs/tags/extra" &&
> +	git -C one config remote.origin.skipfetchall true &&
> +	git -C one config remote.origin.tagopt "--no-tags" &&
> +
> +	git -C one fetch --prefetch
> +'
> +
>  test_done
> -- 
> gitgitgadget
>