[PATCH 11/15] fetch --prune: prune only based on explicit refspecs

[Michael Haggerty <mhagger@alum.mit.edu>]

The old behavior of "fetch --prune" was to prune whatever was being
fetched.  In particular, "fetch --prune --tags" caused tags not only
to be fetched, but also to be pruned.  This is inappropriate because
there is only one tags namespace that is shared among the local
repository and all remotes.  Therefore, if the user defines a local
tag and then runs "git fetch --prune --tags", then the local tag is
deleted.  Moreover, "--prune" and "--tags" can also be configured via
fetch.prune / remote.<name>.prune and remote.<name>.tagopt, making it
even less obvious that an invocation of "git fetch" could result in
tag lossage.

Since the command "git remote update" invokes "git fetch", it had the
same problem.

The command "git remote prune", on the other hand, disregarded the
setting of remote.<name>.tagopt, and so its behavior was inconsistent
with that of the other commands.

So the old behavior made it too easy to lose tags.  To fix this
problem, change "fetch --prune" to prune references based only on
refspecs specified explicitly by the user, either on the command line
or via remote.<name>.fetch.  Thus, tags are no longer made subject to
pruning by the --tags option or the remote.<name>.tagopt setting.

However, tags *are* still subject to pruning if they are fetched as
part of a refspec, and that is good.  For example:

* On the command line,

      git fetch --prune 'refs/tags/*:refs/tags/*'

  causes tags, and only tags, to be fetched and pruned, and is
  therefore a simple way for the user to get the equivalent of the old
  behavior of "--prune --tag".

* For a remote that was configured with the "--mirror" option, the
  configuration is set to include

      [remote "name"]
              fetch = +refs/*:refs/*

  , which causes tags to be subject to pruning along with all other
  references.  This is the behavior that will typically be desired for
  a mirror.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
---
 Documentation/config.txt        |  2 +-
 Documentation/fetch-options.txt | 15 ++++++++++++---
 builtin/fetch.c                 | 39 +++++++++------------------------------
 t/t5510-fetch.sh                | 10 +++++-----
 4 files changed, 27 insertions(+), 39 deletions(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index d4d93c9..83c1700 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -2086,7 +2086,7 @@ remote.<name>.vcs::
 remote.<name>.prune::
 	When set to true, fetching from this remote by default will also
 	remove any remote-tracking branches which no longer exist on the
-	remote (as if the `--prune` option was give on the command line).
+	remote (as if the `--prune` option was given on the command line).
 	Overrides `fetch.prune` settings, if any.
 
 remotes.<group>::
diff --git a/Documentation/fetch-options.txt b/Documentation/fetch-options.txt
index 0e6d2ac..5d12219 100644
--- a/Documentation/fetch-options.txt
+++ b/Documentation/fetch-options.txt
@@ -41,8 +41,14 @@ ifndef::git-pull[]
 
 -p::
 --prune::
-	After fetching, remove any remote-tracking branches which
-	no longer exist	on the remote.
+	After fetching, remove any remote-tracking branches that
+	no longer exist	on the remote.  Tags are not subject to
+	pruning in the usual case that they are fetched because of the
+	--tags option or remote.<name>.tagopt.  However, if tags are
+	fetched due to an explicit refspec (either on the command line
+	or in the remote configuration, for example if the remote was
+	cloned with the --mirror option), then they are also subject
+	to pruning.
 endif::git-pull[]
 
 ifdef::git-pull[]
@@ -63,7 +69,10 @@ ifndef::git-pull[]
 --tags::
 	This is a short-hand requesting that all tags be fetched from
 	the remote in addition to whatever else is being fetched.  It
-	is similar to using the refspec `refs/tags/*:refs/tags/*`.
+	is similar to using the refspec `refs/tags/*:refs/tags/*`,
+	except that it doesn't subject tags to pruning, regardless of
+	a --prune option or the configuration settings of fetch.prune
+	or remote.<name>.prune.
 
 --recurse-submodules[=yes|on-demand|no]::
 	This option controls if and under what conditions new commits of
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 7edb1ea..47b63a7 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -829,38 +829,17 @@ static int do_fetch(struct transport *transport,
 		goto cleanup;
 	}
 	if (prune) {
-		struct refspec *prune_refspecs;
-		int prune_refspec_count;
-
+		/*
+		 * We only prune based on refspecs specified
+		 * explicitly (via command line or configuration); we
+		 * don't care whether --tags was specified.
+		 */
 		if (ref_count) {
-			prune_refspecs = refs;
-			prune_refspec_count = ref_count;
-		} else {
-			prune_refspecs = transport->remote->fetch;
-			prune_refspec_count = transport->remote->fetch_refspec_nr;
-		}
-
-		if (tags == TAGS_SET) {
-			/*
-			 * --tags was specified.  Pretend that the user also
-			 * gave us the canonical tags refspec
-			 */
-			const char *tags_str = "refs/tags/*:refs/tags/*";
-			struct refspec *tags_refspec, *refspec;
-
-			/* Copy the refspec and add the tags to it */
-			refspec = xcalloc(prune_refspec_count + 1, sizeof(*refspec));
-			tags_refspec = parse_fetch_refspec(1, &tags_str);
-			memcpy(refspec, prune_refspecs, prune_refspec_count * sizeof(*refspec));
-			memcpy(&refspec[prune_refspec_count], tags_refspec, sizeof(*refspec));
-
-			prune_refs(refspec, prune_refspec_count + 1, ref_map);
-
-			/* The rest of the strings belong to fetch_one */
-			free_refspec(1, tags_refspec);
-			free(refspec);
+			prune_refs(refs, ref_count, ref_map);
 		} else {
-			prune_refs(prune_refspecs, prune_refspec_count, ref_map);
+			prune_refs(transport->remote->fetch,
+				   transport->remote->fetch_refspec_nr,
+				   ref_map);
 		}
 	}
 	free_refs(ref_map);
diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
index 02e5901..5d4581d 100755
--- a/t/t5510-fetch.sh
+++ b/t/t5510-fetch.sh
@@ -113,7 +113,7 @@ test_expect_success 'fetch --prune with a namespace keeps other namespaces' '
 	git rev-parse origin/master
 '
 
-test_expect_success 'fetch --prune --tags prunes tags and branches' '
+test_expect_success 'fetch --prune --tags prunes branches but not tags' '
 	cd "$D" &&
 	git clone . prune-tags &&
 	cd prune-tags &&
@@ -125,10 +125,10 @@ test_expect_success 'fetch --prune --tags prunes tags and branches' '
 	git fetch --prune --tags origin &&
 	git rev-parse origin/master &&
 	test_must_fail git rev-parse origin/fake-remote &&
-	test_must_fail git rev-parse sometag
+	git rev-parse sometag
 '
 
-test_expect_success 'fetch --prune --tags with branch does not delete other remote-tracking branches' '
+test_expect_success 'fetch --prune --tags with branch does not prune other things' '
 	cd "$D" &&
 	git clone . prune-tags-branch &&
 	cd prune-tags-branch &&
@@ -137,7 +137,7 @@ test_expect_success 'fetch --prune --tags with branch does not delete other remo
 
 	git fetch --prune --tags origin master &&
 	git rev-parse origin/extrabranch &&
-	test_must_fail git rev-parse sometag
+	git rev-parse sometag
 '
 
 test_expect_success 'fetch --prune --tags with refspec prunes based on refspec' '
@@ -151,7 +151,7 @@ test_expect_success 'fetch --prune --tags with refspec prunes based on refspec'
 	git fetch --prune --tags origin refs/heads/foo/*:refs/remotes/origin/foo/* &&
 	test_must_fail git rev-parse refs/remotes/origin/foo/otherbranch &&
 	git rev-parse origin/extrabranch &&
-	test_must_fail git rev-parse sometag
+	git rev-parse sometag
 '
 
 test_expect_success 'fetch tags when there is no tags' '
-- 
1.8.4