From adcc94a0aa7055be4133ebda8b25f4af63285c6d Mon Sep 17 00:00:00 2001 From: Junio C Hamano Date: Wed, 14 Feb 2018 10:18:55 -0800 Subject: [PATCH] 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 --- Documentation/merge-options.txt | 3 ++- builtin/merge.c | 43 ++++++++++++++++++++++++++++++--- t/t6200-fmt-merge-msg.sh | 2 +- t/t7600-merge.sh | 38 ++++++++++++++++++++++++++++- 4 files changed, 79 insertions(+), 7 deletions(-) diff --git a/Documentation/merge-options.txt b/Documentation/merge-options.txt index 3888c3ff85..63a3fc0954 100644 --- a/Documentation/merge-options.txt +++ b/Documentation/merge-options.txt @@ -35,7 +35,8 @@ set to `no` at the beginning of them. --no-ff:: Create a merge commit even when the merge resolves as a fast-forward. This is the default behaviour when merging an - annotated (and possibly signed) tag. + annotated (and possibly signed) tag that is not stored in + its natural place in 'refs/tags/' hierarchy. --ff-only:: Refuse to merge and exit with a non-zero status unless the diff --git a/builtin/merge.c b/builtin/merge.c index 30264cfd7c..532522a854 100644 --- a/builtin/merge.c +++ b/builtin/merge.c @@ -33,6 +33,7 @@ #include "sequencer.h" #include "string-list.h" #include "packfile.h" +#include "tag.h" #define DEFAULT_TWOHEAD (1<<0) #define DEFAULT_OCTOPUS (1<<1) @@ -1125,6 +1126,43 @@ static struct commit_list *collect_parents(struct commit *head_commit, return remoteheads; } +static int merging_a_throwaway_tag(struct commit *commit) +{ + char *tag_ref; + struct object_id oid; + int is_throwaway_tag = 0; + + /* Are we merging a tag? */ + if (!merge_remote_util(commit) || + !merge_remote_util(commit)->obj || + merge_remote_util(commit)->obj->type != OBJ_TAG) + return is_throwaway_tag; + + /* + * Now we know we are merging a tag object. Are we downstream + * and following the tags from upstream? If so, we must have + * the tag object pointed at by "refs/tags/$T" where $T is the + * tagname recorded in the tag object. We want to allow such + * a "just to catch up" merge to fast-forward. + * + * Otherwise, we are playing an integrator's role, making a + * merge with a throw-away tag from a contributor with + * something like "git pull $contributor $signed_tag". + * We want to forbid such a merge from fast-forwarding + * by default; otherwise we would not keep the signature + * anywhere. + */ + tag_ref = xstrfmt("refs/tags/%s", + ((struct tag *)merge_remote_util(commit)->obj)->tag); + if (!read_ref(tag_ref, &oid) && + !oidcmp(&oid, &merge_remote_util(commit)->obj->oid)) + is_throwaway_tag = 0; + else + is_throwaway_tag = 1; + free(tag_ref); + return is_throwaway_tag; +} + int cmd_merge(int argc, const char **argv, const char *prefix) { struct object_id result_tree, stash, head_oid; @@ -1322,10 +1360,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix) oid_to_hex(&commit->object.oid)); setenv(buf.buf, merge_remote_util(commit)->name, 1); strbuf_reset(&buf); - if (fast_forward != FF_ONLY && - merge_remote_util(commit) && - merge_remote_util(commit)->obj && - merge_remote_util(commit)->obj->type == OBJ_TAG) + if (fast_forward != FF_ONLY && merging_a_throwaway_tag(commit)) fast_forward = FF_NO; } diff --git a/t/t6200-fmt-merge-msg.sh b/t/t6200-fmt-merge-msg.sh index 2e2fb0e957..a54a52aaa4 100755 --- a/t/t6200-fmt-merge-msg.sh +++ b/t/t6200-fmt-merge-msg.sh @@ -512,7 +512,7 @@ test_expect_success 'merge-msg with "merging" an annotated tag' ' test_when_finished "git reset --hard" && annote=$(git rev-parse annote) && - git merge --no-commit $annote && + git merge --no-commit --no-ff $annote && { cat <<-EOF Merge tag '\''$annote'\'' diff --git a/t/t7600-merge.sh b/t/t7600-merge.sh index dfde6a675a..6736d8d131 100755 --- a/t/t7600-merge.sh +++ b/t/t7600-merge.sh @@ -700,6 +700,42 @@ test_expect_success 'merge --no-ff --edit' ' test_cmp expected actual ' +test_expect_success 'merge annotated/signed tag w/o tracking' ' + test_when_finished "rm -rf dst; git tag -d anno1" && + git tag -a -m "anno c1" anno1 c1 && + git init dst && + git rev-parse c1 >dst/expect && + ( + # c0 fast-forwards to c1 but because this repository + # is not a "downstream" whose refs/tags follows along + # tag from the "upstream", this pull defaults to --no-ff + cd dst && + git pull .. c0 && + git pull .. anno1 && + git rev-parse HEAD^2 >actual && + test_cmp expect actual + ) +' + +test_expect_success 'merge annotated/signed tag w/ tracking' ' + test_when_finished "rm -rf dst; git tag -d anno1" && + git tag -a -m "anno c1" anno1 c1 && + git init dst && + git rev-parse c1 >dst/expect && + ( + # c0 fast-forwards to c1 and because this repository + # is a "downstream" whose refs/tags follows along + # tag from the "upstream", this pull defaults to --ff + cd dst && + git remote add origin .. && + git pull origin c0 && + git fetch origin && + git merge anno1 && + git rev-parse HEAD >actual && + test_cmp expect actual + ) +' + test_expect_success GPG 'merge --ff-only tag' ' git reset --hard c0 && git commit --allow-empty -m "A newer commit" && @@ -718,7 +754,7 @@ test_expect_success GPG 'merge --no-edit tag should skip editor' ' git tag -f -s -m "A newer commit" signed && git reset --hard c0 && - EDITOR=false git merge --no-edit signed && + EDITOR=false git merge --no-edit --no-ff signed && git rev-parse signed^0 >expect && git rev-parse HEAD^2 >actual && test_cmp expect actual