fetch: add a --prune-tags option and fetch.pruneTags config

Add a --prune-tags option to git-fetch, along with fetch.pruneTags
config option and a -P shorthand (-p is --prune). This allows for
doing any of:

    git fetch -p -P
    git fetch --prune --prune-tags
    git fetch -p -P origin
    git fetch --prune --prune-tags origin

Or simply:

    git config fetch.prune true &&
    git config fetch.pruneTags true &&
    git fetch

Instead of the much more verbose:

    git fetch --prune origin 'refs/tags/*:refs/tags/*' '+refs/heads/*:refs/remotes/origin/*'

Before this feature it was painful to support the use-case of pulling
from a repo which is having both its branches *and* tags deleted
regularly, and have our local references to reflect upstream.

At work we create deployment tags in the repo for each rollout, and
there's *lots* of those, so they're archived within weeks for
performance reasons.

Without this change it's hard to centrally configure such repos in
/etc/gitconfig (on servers that are only used for working with
them). You need to set fetch.prune=true globally, and then for each
repo:

    git -C {} config --replace-all remote.origin.fetch "refs/tags/*:refs/tags/*" "^\+*refs/tags/\*:refs/tags/\*$"

Now I can simply set fetch.pruneTags=true in /etc/gitconfig as well,
and users running "git pull" will automatically get the pruning
semantics I want.

Even though "git remote" has corresponding "prune" and "update
--prune" subcommands I'm intentionally not adding a corresponding
prune-tags or "update --prune --prune-tags" mode to that command.

It's advertised (as noted in my recent "git remote doc: correct
dangerous lies about what prune does") as only modifying remote
tracking references, whereas any --prune-tags option is always going
to modify what from the user's perspective is a local copy of the tag,
since there's no such thing as a remote tracking tag.

Ideally add_prune_tags_to_fetch_refspec() would be something that
would use ALLOC_GROW() to grow the 'fetch` member of the 'remote'
struct. Instead I'm realloc-ing remote->fetch and adding the
tag_refspec to the end.

The reason is that parse_{fetch,push}_refspec which allocate the
refspec (ultimately remote->fetch) struct are called many places that
don't have access to a 'remote' struct. It would be hard to change all
their callsites to be amenable to carry around the bookkeeping
variables required for dynamic allocation.

All the other callers of the API first incrementally construct the
string version of the refspec in remote->fetch_refspec via
add_fetch_refspec(), before finally calling parse_fetch_refspec() via
some variation of remote_get().

It's less of a pain to deal with the one special case that needs to
modify already constructed refspecs than to chase down and change all
the other callsites. The API I'm adding is intentionally not
generalized because if we add more of these we'd probably want to
re-visit how this is done.

See my "Re: [BUG] git remote prune removes local tags, depending on
fetch config" (87po6ahx87.fsf@evledraar.gmail.com;
https://public-inbox.org/git/87po6ahx87.fsf@evledraar.gmail.com/) for
more background info.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 70 insertions, 0 deletions

diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
index 1713111006..227dd70b7b 100755
--- a/t/t5510-fetch.sh
+++ b/t/t5510-fetch.sh
@@ -589,6 +589,15 @@ test_configured_prune_type () {
 			new_cmdline=$(printf "%s" "$cmdline" | perl -pe 's[origin(?!/)]["'"$remote_url"'"]g')
 		fi
 
+		if test "$fetch_prune_tags" = 'true' ||
+		   test "$remote_origin_prune_tags" = 'true'
+		then
+			if ! printf '%s' "$cmdline\n" | grep -q refs/remotes/origin/
+			then
+				new_cmdline="$new_cmdline refs/tags/*:refs/tags/*"
+			fi
+		fi
+
 		cmdline="$new_cmdline"
 	fi
 
@@ -702,6 +711,67 @@ test_configured_prune true  true  unset unset kept   pruned \
 test_configured_prune true  true  unset unset pruned pruned \
 	"--prune origin refs/tags/*:refs/tags/* +refs/heads/*:refs/remotes/origin/*"
 
+# --prune-tags on its own does nothing, needs --prune as well, same
+# for for fetch.pruneTags without fetch.prune
+test_configured_prune unset unset unset unset kept kept     "--prune-tags"
+test_configured_prune unset unset true unset  kept kept     ""
+test_configured_prune unset unset unset true  kept kept     ""
+
+# These will prune the tags
+test_configured_prune unset unset unset unset pruned pruned "--prune --prune-tags"
+test_configured_prune true  unset true  unset pruned pruned ""
+test_configured_prune unset true  unset true  pruned pruned ""
+
+# remote.<name>.pruneTags overrides fetch.pruneTags, just like
+# remote.<name>.prune overrides fetch.prune if set.
+test_configured_prune true  unset true unset pruned pruned  ""
+test_configured_prune false true  false true  pruned pruned ""
+test_configured_prune true  false true  false kept   kept   ""
+
+# When --prune-tags is supplied it's ignored if an explicit refspec is
+# given, same for the configuration options.
+test_configured_prune unset unset unset unset pruned kept \
+	"--prune --prune-tags origin +refs/heads/*:refs/remotes/origin/*"
+test_configured_prune unset unset true  unset pruned kept \
+	"--prune origin +refs/heads/*:refs/remotes/origin/*"
+test_configured_prune unset unset unset true pruned  kept \
+	"--prune origin +refs/heads/*:refs/remotes/origin/*"
+
+# Pruning that also takes place if a file:// url replaces a named
+# remote, with the exception of --prune-tags on the command-line
+# (arbitrary limitation).
+#
+# However, because there's no implicit
+# +refs/heads/*:refs/remotes/origin/* refspec and supplying it on the
+# command-line negates --prune-tags, the branches will not be pruned.
+test_configured_prune_type unset unset unset unset kept   kept   "origin --prune-tags" "name"
+test_configured_prune_type unset unset unset unset kept   kept   "origin --prune-tags" "link"
+test_configured_prune_type unset unset unset unset pruned pruned "origin --prune --prune-tags" "name"
+test_configured_prune_type unset unset unset unset kept   kept   "origin --prune --prune-tags" "link"
+test_configured_prune_type unset unset unset unset pruned pruned "--prune --prune-tags origin" "name"
+test_configured_prune_type unset unset unset unset kept   kept   "--prune --prune-tags origin" "link"
+test_configured_prune_type unset unset true  unset pruned pruned "--prune origin" "name"
+test_configured_prune_type unset unset true  unset kept   pruned "--prune origin" "link"
+test_configured_prune_type unset unset unset true  pruned pruned "--prune origin" "name"
+test_configured_prune_type unset unset unset true  kept   pruned "--prune origin" "link"
+test_configured_prune_type true  unset true  unset pruned pruned "origin" "name"
+test_configured_prune_type true  unset true  unset kept   pruned "origin" "link"
+test_configured_prune_type unset  true true  unset pruned pruned "origin" "name"
+test_configured_prune_type unset  true true  unset kept   pruned "origin" "link"
+test_configured_prune_type unset  true unset true  pruned pruned "origin" "name"
+test_configured_prune_type unset  true unset true  kept   pruned "origin" "link"
+
+# Interaction between --prune-tags and no "fetch" config in the remote
+# at all.
+test_expect_success 'remove remote.origin.fetch "one"' '
+	(
+		cd one &&
+		git config --unset-all remote.origin.fetch
+	)
+'
+test_configured_prune_type unset unset unset unset kept pruned "origin --prune --prune-tags" "name"
+test_configured_prune_type unset unset unset unset kept kept   "origin --prune --prune-tags" "link"
+
 test_expect_success 'all boundary commits are excluded' '
 	test_commit base &&
 	test_commit oneside &&