merge: allow fast-forward when merging a tracked tag
Long time ago at fab47d05 ("merge: force edit and no-ff mode when merging a tag object", 2011-11-07), "git merge" was made to always create a merge commit when merging a tag, even when the side branch being merged is a descendant of the current branch. This default is good for merges made by upstream maintainers to integrate work signed by downstream contributors, but will leave pointless no-ff merges when downstream contributors pull a newer release tag to make their long-running topic branches catch up with the upstream. When there is no local work left on the topic, such a merge should simply fast-forward to the commit pointed at by the release tag. Update the default (again) for "git merge" that merges a tag object to (1) --no-ff (i.e. create a merge commit even when side branch fast forwards) if the tag being merged is not at its expected place in refs/tags/ hierarchy and (2) --ff (i.e. allow fast-forward update when able) otherwise. Signed-off-by: Junio C Hamano <gitster@pobox.com>
Junio C Hamano committed
Feb 14, 2018 at 10:18 UTC
adcc94a0aa7055be4133ebda8b25f4af63285c6d
4 files changed
+79
-7
Documentation/merge-options.txt
+2
-1
@@ -35,7 +35,8 @@ set to `no` at the beginning of them.
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--no-ff::
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Create a merge commit even when the merge resolves as a
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fast-forward. This is the default behaviour when merging an
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- annotated (and possibly signed) tag.
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+ annotated (and possibly signed) tag that is not stored in
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+ its natural place in 'refs/tags/' hierarchy.
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--ff-only::
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Refuse to merge and exit with a non-zero status unless the
builtin/merge.c
+39
-4
@@ -33,6 +33,7 @@
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#include "sequencer.h"
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#include "string-list.h"
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#include "packfile.h"
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+#include "tag.h"
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#define DEFAULT_TWOHEAD (1<<0)
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#define DEFAULT_OCTOPUS (1<<1)
@@ -1125,6 +1126,43 @@ static struct commit_list *collect_parents(struct commit *head_commit,
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return remoteheads;
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}
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+static int merging_a_throwaway_tag(struct commit *commit)
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+{
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+ char *tag_ref;
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+ struct object_id oid;
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+ int is_throwaway_tag = 0;
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+
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+ /* Are we merging a tag? */
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+ if (!merge_remote_util(commit) ||
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+ !merge_remote_util(commit)->obj ||
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+ merge_remote_util(commit)->obj->type != OBJ_TAG)
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+ return is_throwaway_tag;
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+
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+ /*
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+ * Now we know we are merging a tag object. Are we downstream
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+ * and following the tags from upstream? If so, we must have
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+ * the tag object pointed at by "refs/tags/$T" where $T is the
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+ * tagname recorded in the tag object. We want to allow such
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+ * a "just to catch up" merge to fast-forward.
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+ *
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+ * Otherwise, we are playing an integrator's role, making a
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+ * merge with a throw-away tag from a contributor with
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+ * something like "git pull $contributor $signed_tag".
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+ * We want to forbid such a merge from fast-forwarding
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+ * by default; otherwise we would not keep the signature
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+ * anywhere.
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+ */
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+ tag_ref = xstrfmt("refs/tags/%s",
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+ ((struct tag *)merge_remote_util(commit)->obj)->tag);
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+ if (!read_ref(tag_ref, &oid) &&
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+ !oidcmp(&oid, &merge_remote_util(commit)->obj->oid))
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+ is_throwaway_tag = 0;
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+ else
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+ is_throwaway_tag = 1;
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+ free(tag_ref);
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+ return is_throwaway_tag;
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+}
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+
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int cmd_merge(int argc, const char **argv, const char *prefix)
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{
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struct object_id result_tree, stash, head_oid;
@@ -1322,10 +1360,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
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oid_to_hex(&commit->object.oid));
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setenv(buf.buf, merge_remote_util(commit)->name, 1);
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strbuf_reset(&buf);
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- if (fast_forward != FF_ONLY &&
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- merge_remote_util(commit) &&
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- merge_remote_util(commit)->obj &&
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- merge_remote_util(commit)->obj->type == OBJ_TAG)
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+ if (fast_forward != FF_ONLY && merging_a_throwaway_tag(commit))
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fast_forward = FF_NO;
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}
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t/t6200-fmt-merge-msg.sh
+1
-1
@@ -512,7 +512,7 @@ test_expect_success 'merge-msg with "merging" an annotated tag' '
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test_when_finished "git reset --hard" &&
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annote=$(git rev-parse annote) &&
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- git merge --no-commit $annote &&
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+ git merge --no-commit --no-ff $annote &&
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{
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cat <<-EOF
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Merge tag '\''$annote'\''
t/t7600-merge.sh
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-1
@@ -700,6 +700,42 @@ test_expect_success 'merge --no-ff --edit' '
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test_cmp expected actual
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'
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+test_expect_success 'merge annotated/signed tag w/o tracking' '
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+ test_when_finished "rm -rf dst; git tag -d anno1" &&
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+ git tag -a -m "anno c1" anno1 c1 &&
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+ git init dst &&
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+ git rev-parse c1 >dst/expect &&
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+ (
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+ # c0 fast-forwards to c1 but because this repository
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+ # is not a "downstream" whose refs/tags follows along
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+ # tag from the "upstream", this pull defaults to --no-ff
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+ cd dst &&
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+ git pull .. c0 &&
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+ git pull .. anno1 &&
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+ git rev-parse HEAD^2 >actual &&
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+ test_cmp expect actual
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+ )
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+'
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+
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+test_expect_success 'merge annotated/signed tag w/ tracking' '
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+ test_when_finished "rm -rf dst; git tag -d anno1" &&
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+ git tag -a -m "anno c1" anno1 c1 &&
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+ git init dst &&
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+ git rev-parse c1 >dst/expect &&
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+ (
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+ # c0 fast-forwards to c1 and because this repository
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+ # is a "downstream" whose refs/tags follows along
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+ # tag from the "upstream", this pull defaults to --ff
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+ cd dst &&
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+ git remote add origin .. &&
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+ git pull origin c0 &&
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+ git fetch origin &&
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+ git merge anno1 &&
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+ git rev-parse HEAD >actual &&
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+ test_cmp expect actual
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+ )
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+'
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+
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test_expect_success GPG 'merge --ff-only tag' '
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git reset --hard c0 &&
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git commit --allow-empty -m "A newer commit" &&
@@ -718,7 +754,7 @@ test_expect_success GPG 'merge --no-edit tag should skip editor' '
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git tag -f -s -m "A newer commit" signed &&
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git reset --hard c0 &&
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- EDITOR=false git merge --no-edit signed &&
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+ EDITOR=false git merge --no-edit --no-ff signed &&
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git rev-parse signed^0 >expect &&
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git rev-parse HEAD^2 >actual &&
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test_cmp expect actual