merge: handle FETCH_HEAD internally

The collect_parents() function now is responsible for

 1. parsing the commits given on the command line into a list of
    commits to be merged;

 2. filtering these parents into independent ones; and

 3. optionally calling fmt_merge_msg() via prepare_merge_message()
    to prepare an auto-generated merge log message, using fake
    contents that FETCH_HEAD would have had if these commits were
    fetched from the current repository with "git pull . $args..."

Make "git merge FETCH_HEAD" to be the same as the traditional

    git merge "$(git fmt-merge-msg <.git/FETCH_HEAD)" $commits

invocation of the command in "git pull", where $commits are the ones
that appear in FETCH_HEAD that are not marked as not-for-merge, by
making it do a bit more, specifically:

 - noticing "FETCH_HEAD" is the only "commit" on the command line
   and picking the commits that are not marked as not-for-merge as
   the list of commits to be merged (substitute for step #1 above);

 - letting the resulting list fed to step #2 above;

 - doing the step #3 above, using the contents of the FETCH_HEAD
   instead of fake contents crafted from the list of commits parsed
   in the step #1 above.

Note that this changes the semantics.  "git merge FETCH_HEAD" has
always behaved as if the first commit in the FETCH_HEAD file were
directly specified on the command line, creating a two-way merge
whose auto-generated merge log said "merge commit xyz".  With this
change, if the previous fetch was to grab multiple branches (e.g.
"git fetch $there topic-a topic-b"), the new world order is to
create an octopus, behaving as if "git pull $there topic-a topic-b"
were run.  This is a deliberate change to make that happen, and
can be seen in the changes to t3033 tests.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 5 insertions, 5 deletions

diff --git a/t/t3033-merge-toplevel.sh b/t/t3033-merge-toplevel.sh
index 9d92d3c1a..46aadc410 100755
--- a/t/t3033-merge-toplevel.sh
+++ b/t/t3033-merge-toplevel.sh
@@ -77,7 +77,7 @@ test_expect_success 'merge octopus, non-fast-forward' '
 
 # The same set with FETCH_HEAD
 
-test_expect_failure 'merge FETCH_HEAD octopus into void' '
+test_expect_success 'merge FETCH_HEAD octopus into void' '
 	t3033_reset &&
 	git checkout --orphan test &&
 	git rm -fr . &&
@@ -88,7 +88,7 @@ test_expect_failure 'merge FETCH_HEAD octopus into void' '
 	test_must_fail git rev-parse HEAD
 '
 
-test_expect_failure 'merge FETCH_HEAD octopus fast-forward (ff)' '
+test_expect_success 'merge FETCH_HEAD octopus fast-forward (ff)' '
 	t3033_reset &&
 	git reset --hard one &&
 	git fetch . left right &&
@@ -100,7 +100,7 @@ test_expect_failure 'merge FETCH_HEAD octopus fast-forward (ff)' '
 	test_cmp expect actual
 '
 
-test_expect_failure 'merge FETCH_HEAD octopus non-fast-forward (ff)' '
+test_expect_success 'merge FETCH_HEAD octopus non-fast-forward (ff)' '
 	t3033_reset &&
 	git reset --hard one &&
 	git fetch . left right &&
@@ -112,7 +112,7 @@ test_expect_failure 'merge FETCH_HEAD octopus non-fast-forward (ff)' '
 	test_cmp expect actual
 '
 
-test_expect_failure 'merge FETCH_HEAD octopus fast-forward (does not ff)' '
+test_expect_success 'merge FETCH_HEAD octopus fast-forward (does not ff)' '
 	t3033_reset &&
 	git fetch . left right &&
 	git merge FETCH_HEAD &&
@@ -123,7 +123,7 @@ test_expect_failure 'merge FETCH_HEAD octopus fast-forward (does not ff)' '
 	test_cmp expect actual
 '
 
-test_expect_failure 'merge FETCH_HEAD octopus non-fast-forward' '
+test_expect_success 'merge FETCH_HEAD octopus non-fast-forward' '
 	t3033_reset &&
 	git fetch . left right &&
 	git merge --no-ff FETCH_HEAD &&