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

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

On Fri, Apr 16, 2021 at 12:52:21PM -0500, Tom Saeger wrote:
> 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' '

Forget what I said here.   Now seeing this is using 'git fetch --prefetch'
directly and not using `mainenance --task=prefetch`

> 
> 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
> >