[v3,04/24] merge-recursive: provide a better label for diff3 common ancestor
diff mbox series

Message ID 20190815214053.16594-5-newren@gmail.com
State New
Headers show
Series
  • Clean up merge API
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Commit Message

Elijah Newren Aug. 15, 2019, 9:40 p.m. UTC
In commit 7ca56aa07619 ("merge-recursive: add a label for ancestor",
2010-03-20), a label was added for the '||||||' line to make it have
the more informative heading '|||||| merged common ancestors', with
the statement:

    It would be nicer to use a more informative label.  Perhaps someone
    will provide one some day.

This chosen label was perfectly reasonable when recursiveness kicks in,
i.e. when there are multiple merge bases.  (I can't think of a better
label in such cases.)  But it is actually somewhat misleading when there
is a unique merge base or no merge base.  Change this based on the
number of merge bases:
    >=2: "merged common ancestors"
    1:   <abbreviated commit hash>
    0:   "<empty tree>"

Tests have also been added to check that we get the right ancestor name
for each of the three cases.

Also, since merge_recursive() and merge_trees() have polar opposite
pre-conditions for opt->ancestor, document merge_recursive()'s
pre-condition with an assertion.  (An assertion was added to
merge_trees() already a few commits ago.)  The differences in
pre-conditions stem from two factors: (1) merge_trees() does not recurse
and thus does not have multiple sub-merges to worry about -- each of
which would require a different value for opt->ancestor, (2)
merge_trees() is only passed trees rather than commits and thus cannot
internally guess as good of a label.  Thus, while external callers of
merge_trees() are required to provide a non-NULL opt->ancestor,
merge_recursive() expects to set this value itself.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 merge-recursive.c                 |  21 +++-
 t/t6036-recursive-corner-cases.sh |   8 +-
 t/t6047-diff3-conflict-markers.sh | 189 ++++++++++++++++++++++++++++++
 3 files changed, 214 insertions(+), 4 deletions(-)
 create mode 100755 t/t6047-diff3-conflict-markers.sh

Comments

Junio C Hamano Aug. 16, 2019, 9:33 p.m. UTC | #1
Elijah Newren <newren@gmail.com> writes:

> @@ -3507,6 +3507,11 @@ int merge_recursive(struct merge_options *opt,
>  	struct commit *merged_common_ancestors;
>  	struct tree *mrtree;
>  	int clean;
> +	int num_merge_bases;
> +	struct strbuf merge_base_abbrev = STRBUF_INIT;
> +
> +	if (!opt->call_depth)
> +		assert(opt->ancestor == NULL);

Hmph.  Do we have anything to say on this field when call_depth is
not zero?  Is it OK for opt->ancestor to be sometimes NULL and non
NULL some other times?

> @@ -3528,6 +3533,7 @@ int merge_recursive(struct merge_options *opt,
>  			output_commit_title(opt, iter->item);
>  	}
>  
> +	num_merge_bases = commit_list_count(ca);

Criss-cross merge with very large number of merge bases is rare, so
it is OK to count them all, even though we only care about "is it
zero, is it one, or is it two or more?"

I suspect this does not have to count, though, if we really wanted
to avoid counting.

>  	merged_common_ancestors = pop_commit(&ca);
>  	if (merged_common_ancestors == NULL) {
>  		/* if there is no common ancestor, use an empty tree */

Here is the case where we can already decide the ancestor name for
the later merge_trees() should be "empty tree".

And if merged_common_ancestors is not NULL, ca may have run out (in
which case, we only have a single merge base), or ca still has
another merge base (in which case, we have two or more).  So, if you
add
		ancestor_name = "empty tree";
	} else if (ca) {
		ancestor_name = "merged common ancestors";
	} else {
		ancestor_name = abbrev_name(merged_common_ancestors);
	}

to that if() statement above, that should be sufficient, no?

opt is used for inner merge in the for() loop, so you would probably
need another "char *" variable without contaminating opt->ancestor_name
at this point, and then assign the value in the temporary to the
opt->ancestor field where the original always assigned "merged
common ancestors".

> @@ -3568,10 +3574,23 @@ int merge_recursive(struct merge_options *opt,
>  	if (!opt->call_depth)
>  		repo_read_index(opt->repo);
>  
> -	opt->ancestor = "merged common ancestors";
> +	switch (num_merge_bases) {
> +	case 0:
> +		opt->ancestor = "<empty tree>";

Also, I do not see a reason why you want angle bra-ket pair around
"empty tree".  You are already using "merged common ancestors"
literal phrase without any special marker syntax.

Thanks.
Elijah Newren Aug. 16, 2019, 10:39 p.m. UTC | #2
On Fri, Aug 16, 2019 at 2:33 PM Junio C Hamano <gitster@pobox.com> wrote:
>
> Elijah Newren <newren@gmail.com> writes:
>
> > @@ -3507,6 +3507,11 @@ int merge_recursive(struct merge_options *opt,
> >       struct commit *merged_common_ancestors;
> >       struct tree *mrtree;
> >       int clean;
> > +     int num_merge_bases;
> > +     struct strbuf merge_base_abbrev = STRBUF_INIT;
> > +
> > +     if (!opt->call_depth)
> > +             assert(opt->ancestor == NULL);
>
> Hmph.  Do we have anything to say on this field when call_depth is
> not zero?  Is it OK for opt->ancestor to be sometimes NULL and non
> NULL some other times?

I was specifically trying to add a check for external callers of
merge_recursive() to make sure they called it correctly.  Since
merge_recursive() sets opt->ancestor before calling itself
recursively, I had to hide the assertion behind an if-check, namely on
call_depth.

We could add an assertion that opt->ancestor != NULL when
opt->call_depth > 0, but it seemed odd to document pre-conditions for
how merge_recursive() calls itself.  Anyway, this code block actually
becomes a bit cleaner later in the series when I create  separate
merge_recursive() and merge_recursive_internal() functions, as the
assertion can just go into merge_recursive() and not be protected by
the opt->call_depth check.

> > @@ -3528,6 +3533,7 @@ int merge_recursive(struct merge_options *opt,
> >                       output_commit_title(opt, iter->item);
> >       }
> >
> > +     num_merge_bases = commit_list_count(ca);
>
> Criss-cross merge with very large number of merge bases is rare, so
> it is OK to count them all, even though we only care about "is it
> zero, is it one, or is it two or more?"
>
> I suspect this does not have to count, though, if we really wanted
> to avoid counting.
>
> >       merged_common_ancestors = pop_commit(&ca);
> >       if (merged_common_ancestors == NULL) {
> >               /* if there is no common ancestor, use an empty tree */
>
> Here is the case where we can already decide the ancestor name for
> the later merge_trees() should be "empty tree".
>
> And if merged_common_ancestors is not NULL, ca may have run out (in
> which case, we only have a single merge base), or ca still has
> another merge base (in which case, we have two or more).  So, if you
> add
>                 ancestor_name = "empty tree";
>         } else if (ca) {
>                 ancestor_name = "merged common ancestors";
>         } else {
>                 ancestor_name = abbrev_name(merged_common_ancestors);
>         }
>
> to that if() statement above, that should be sufficient, no?
>
> opt is used for inner merge in the for() loop, so you would probably
> need another "char *" variable without contaminating opt->ancestor_name
> at this point, and then assign the value in the temporary to the
> opt->ancestor field where the original always assigned "merged
> common ancestors".

Sure, I can make these changes.

> > @@ -3568,10 +3574,23 @@ int merge_recursive(struct merge_options *opt,
> >       if (!opt->call_depth)
> >               repo_read_index(opt->repo);
> >
> > -     opt->ancestor = "merged common ancestors";
> > +     switch (num_merge_bases) {
> > +     case 0:
> > +             opt->ancestor = "<empty tree>";
>
> Also, I do not see a reason why you want angle bra-ket pair around
> "empty tree".  You are already using "merged common ancestors"
> literal phrase without any special marker syntax.

Oh good point; will drop.

Patch
diff mbox series

diff --git a/merge-recursive.c b/merge-recursive.c
index a67ea4957a..3a7a9514b9 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3507,6 +3507,11 @@  int merge_recursive(struct merge_options *opt,
 	struct commit *merged_common_ancestors;
 	struct tree *mrtree;
 	int clean;
+	int num_merge_bases;
+	struct strbuf merge_base_abbrev = STRBUF_INIT;
+
+	if (!opt->call_depth)
+		assert(opt->ancestor == NULL);
 
 	if (show(opt, 4)) {
 		output(opt, 4, _("Merging:"));
@@ -3528,6 +3533,7 @@  int merge_recursive(struct merge_options *opt,
 			output_commit_title(opt, iter->item);
 	}
 
+	num_merge_bases = commit_list_count(ca);
 	merged_common_ancestors = pop_commit(&ca);
 	if (merged_common_ancestors == NULL) {
 		/* if there is no common ancestor, use an empty tree */
@@ -3568,10 +3574,23 @@  int merge_recursive(struct merge_options *opt,
 	if (!opt->call_depth)
 		repo_read_index(opt->repo);
 
-	opt->ancestor = "merged common ancestors";
+	switch (num_merge_bases) {
+	case 0:
+		opt->ancestor = "<empty tree>";
+		break;
+	case 1:
+		strbuf_add_unique_abbrev(&merge_base_abbrev,
+					 &merged_common_ancestors->object.oid,
+					 DEFAULT_ABBREV);
+		opt->ancestor = merge_base_abbrev.buf;
+		break;
+	default:
+		opt->ancestor = "merged common ancestors";
+	}
 	clean = merge_trees(opt, get_commit_tree(h1), get_commit_tree(h2),
 			    get_commit_tree(merged_common_ancestors),
 			    &mrtree);
+	strbuf_release(&merge_base_abbrev);
 	if (clean < 0) {
 		flush_output(opt);
 		return clean;
diff --git a/t/t6036-recursive-corner-cases.sh b/t/t6036-recursive-corner-cases.sh
index d23b948f27..7fddcc8c73 100755
--- a/t/t6036-recursive-corner-cases.sh
+++ b/t/t6036-recursive-corner-cases.sh
@@ -1562,6 +1562,7 @@  test_expect_success 'check nested conflicts' '
 		cd nested_conflicts &&
 
 		git clean -f &&
+		MASTER=$(git rev-parse --short master) &&
 		git checkout L2^0 &&
 
 		# Merge must fail; there is a conflict
@@ -1582,7 +1583,7 @@  test_expect_success 'check nested conflicts' '
 		git cat-file -p R1:a >theirs &&
 		test_must_fail git merge-file --diff3 \
 			-L "Temporary merge branch 1" \
-			-L "merged common ancestors"  \
+			-L "$MASTER"  \
 			-L "Temporary merge branch 2" \
 			ours  \
 			base  \
@@ -1594,7 +1595,7 @@  test_expect_success 'check nested conflicts' '
 		git cat-file -p R1:b >theirs &&
 		test_must_fail git merge-file --diff3 \
 			-L "Temporary merge branch 1" \
-			-L "merged common ancestors"  \
+			-L "$MASTER"  \
 			-L "Temporary merge branch 2" \
 			ours  \
 			base  \
@@ -1732,6 +1733,7 @@  test_expect_success 'check virtual merge base with nested conflicts' '
 	(
 		cd virtual_merge_base_has_nested_conflicts &&
 
+		MASTER=$(git rev-parse --short master) &&
 		git checkout L3^0 &&
 
 		# Merge must fail; there is a conflict
@@ -1760,7 +1762,7 @@  test_expect_success 'check virtual merge base with nested conflicts' '
 		cp left merged-once &&
 		test_must_fail git merge-file --diff3 \
 			-L "Temporary merge branch 1" \
-			-L "merged common ancestors"  \
+			-L "$MASTER"  \
 			-L "Temporary merge branch 2" \
 			merged-once \
 			base        \
diff --git a/t/t6047-diff3-conflict-markers.sh b/t/t6047-diff3-conflict-markers.sh
new file mode 100755
index 0000000000..f69c8256bc
--- /dev/null
+++ b/t/t6047-diff3-conflict-markers.sh
@@ -0,0 +1,189 @@ 
+#!/bin/sh
+
+test_description='recursive merge diff3 style conflict markers'
+
+. ./test-lib.sh
+
+# Setup:
+#          L1
+#            \
+#             ?
+#            /
+#          R1
+#
+# Where:
+#   L1 and R1 both have a file named 'content' but have no common history
+#
+
+test_expect_success 'setup no merge base' '
+	test_create_repo no_merge_base &&
+	(
+		cd no_merge_base &&
+
+		git checkout -b L &&
+		test_commit A content A &&
+
+		git checkout --orphan R &&
+		test_commit B content B
+	)
+'
+
+test_expect_success 'check no merge base' '
+	(
+		cd no_merge_base &&
+
+		git checkout L^0 &&
+
+		test_must_fail git -c merge.conflictstyle=diff3 merge --allow-unrelated-histories -s recursive R^0 &&
+
+		grep "|||||| <empty tree>" content
+	)
+'
+
+# Setup:
+#          L1
+#         /  \
+#   master    ?
+#         \  /
+#          R1
+#
+# Where:
+#   L1 and R1 have modified the same file ('content') in conflicting ways
+#
+
+test_expect_success 'setup unique merge base' '
+	test_create_repo unique_merge_base &&
+	(
+		cd unique_merge_base &&
+
+		test_commit base content "1
+2
+3
+4
+5
+" &&
+
+		git branch L &&
+		git branch R &&
+
+		git checkout L &&
+		test_commit L content "1
+2
+3
+4
+5
+7" &&
+
+		git checkout R &&
+		git rm content &&
+		test_commit R renamed "1
+2
+3
+4
+5
+six"
+	)
+'
+
+test_expect_success 'check unique merge base' '
+	(
+		cd unique_merge_base &&
+
+		git checkout L^0 &&
+		MASTER=$(git rev-parse --short master) &&
+
+		test_must_fail git -c merge.conflictstyle=diff3 merge -s recursive R^0 &&
+
+		grep "|||||| $MASTER:content" renamed
+	)
+'
+
+# Setup:
+#          L1---L2--L3
+#         /  \ /      \
+#   master    X1       ?
+#         \  / \      /
+#          R1---R2--R3
+#
+# Where:
+#   commits L1 and R1 have modified the same file in non-conflicting ways
+#   X1 is an auto-generated merge-base used when merging L1 and R1
+#   commits L2 and R2 are merges of R1 and L1 into L1 and R1, respectively
+#   commits L3 and R3 both modify 'content' in conflicting ways
+#
+
+test_expect_success 'setup multiple merge bases' '
+	test_create_repo multiple_merge_bases &&
+	(
+		cd multiple_merge_bases &&
+
+		test_commit initial content "1
+2
+3
+4
+5" &&
+
+		git branch L &&
+		git branch R &&
+
+		# Create L1
+		git checkout L &&
+		test_commit L1 content "0
+1
+2
+3
+4
+5" &&
+
+		# Create R1
+		git checkout R &&
+		test_commit R1 content "1
+2
+3
+4
+5
+6" &&
+
+		# Create L2
+		git checkout L &&
+		git merge R1 &&
+
+		# Create R2
+		git checkout R &&
+		git merge L1 &&
+
+		# Create L3
+		git checkout L &&
+		test_commit L3 content "0
+1
+2
+3
+4
+5
+A" &&
+
+		# Create R3
+		git checkout R &&
+		git rm content &&
+		test_commit R3 renamed "0
+2
+3
+4
+5
+six"
+	)
+'
+
+test_expect_success 'check multiple merge bases' '
+	(
+		cd multiple_merge_bases &&
+
+		git checkout L^0 &&
+
+		test_must_fail git -c merge.conflictstyle=diff3 merge -s recursive R^0 &&
+
+		grep "|||||| merged common ancestors:content" renamed
+	)
+'
+
+test_done