merge-tree: allow ls-files -u style info to be NUL terminated

Much as `git ls-files` has a -z option, let's add one to merge-tree so
that the conflict-info section can be NUL terminated (and avoid quoting
of unusual filenames).

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-merge-tree.txt

@@ -40,6 +40,12 @@ After the merge completes, a new toplevel tree object is created.  See
 OPTIONS
 -------
 
+-z::
+	Do not quote filenames in the <Conflicted file info> section,
+	and end each filename with a NUL character rather than
+	newline.  Also begin the messages section with a NUL character
+	instead of a newline.  See <<OUTPUT>> below for more information.
+
 --name-only::
 	In the Conflicted file info section, instead of writing a list
 	of (mode, oid, stage, path) tuples to output for conflicted
@@ -76,7 +82,8 @@ OID of toplevel tree
 
 This is a tree object that represents what would be checked out in the
 working tree at the end of `git merge`.  If there were conflicts, then
-files within this tree may have embedded conflict markers.
+files within this tree may have embedded conflict markers.  This section
+is always followed by a newline (or NUL if `-z` is passed).
 
 [[CFI]]
 Conflicted file info
@@ -89,20 +96,26 @@ This is a sequence of lines with the format
 The filename will be quoted as explained for the configuration
 variable `core.quotePath` (see linkgit:git-config[1]).  However, if
 the `--name-only` option is passed, the mode, object, and stage will
-be omitted.
+be omitted.  If `-z` is passed, the "lines" are terminated by a NUL
+character instead of a newline character.
 
 [[IM]]
 Informational messages
 ~~~~~~~~~~~~~~~~~~~~~~
 
-This always starts with a blank line to separate it from the previous
+This always starts with a blank line (or NUL if `-z` is passed) to
-sections, and then has free-form messages about the merge, such as:
+separate it from the previous sections, and then has free-form
+messages about the merge, such as:
 
   * "Auto-merging <file>"
   * "CONFLICT (rename/delete): <oldfile> renamed...but deleted in..."
   * "Failed to merge submodule <submodule> (<reason>)"
   * "Warning: cannot merge binary files: <filename>"
 
+Note that these free-form messages will never have a NUL character
+in or between them, even if -z is passed.  It is simply a large block
+of text taking up the remainder of the output.
+
 EXIT STATUS
 -----------
 

builtin/merge-tree.c

@@ -445,7 +445,7 @@ static int real_merge(struct merge_tree_options *o,
 	if (o->show_messages == -1)
 		o->show_messages = !result.clean;
 
-	puts(oid_to_hex(&result.tree->object.oid));
+	printf("%s%c", oid_to_hex(&result.tree->object.oid), line_termination);
 	if (!result.clean) {
 		struct string_list conflicted_files = STRING_LIST_INIT_NODUP;
 		const char *last = NULL;
@@ -494,6 +494,8 @@ int cmd_merge_tree(int argc, const char **argv, const char *prefix)
 			    N_("do a trivial merge only"), MODE_TRIVIAL),
 		OPT_BOOL(0, "messages", &o.show_messages,
 			 N_("also show informational/conflict messages")),
+		OPT_SET_INT('z', NULL, &line_termination,
+			    N_("separate paths with the NUL character"), '\0'),
 		OPT_BOOL_F(0, "name-only",
 			   &o.name_only,
 			   N_("list filenames without modes/oids/stages"),

t/t4301-merge-tree-write-tree.sh

@@ -173,4 +173,46 @@ test_expect_success 'Check conflicted oids and modes without messages' '
 	test_cmp conflicted-file-info actual
 '
 
+test_expect_success 'NUL terminated conflicted file "lines"' '
+	git checkout -b tweak1 side1 &&
+	test_write_lines zero 1 2 3 4 5 6 >numbers &&
+	git add numbers &&
+	git mv numbers "Αυτά μου φαίνονται κινέζικα" &&
+	git commit -m "Renamed numbers" &&
+
+	test_expect_code 1 git merge-tree --write-tree -z tweak1 side2 >out &&
+	anonymize_hash out >actual &&
+	printf "\\n" >>actual &&
+
+	# Expected results:
+	#   "greeting" should merge with conflicts
+	#   "whatever" has *both* a modify/delete and a file/directory conflict
+	#   "Αυτά μου φαίνονται κινέζικα" should have a conflict
+	echo HASH | lf_to_nul >expect &&
+
+	q_to_tab <<-EOF | lf_to_nul >>expect &&
+	100644 HASH 1Qgreeting
+	100644 HASH 2Qgreeting
+	100644 HASH 3Qgreeting
+	100644 HASH 1Qwhatever~tweak1
+	100644 HASH 2Qwhatever~tweak1
+	100644 HASH 1QΑυτά μου φαίνονται κινέζικα
+	100644 HASH 2QΑυτά μου φαίνονται κινέζικα
+	100644 HASH 3QΑυτά μου φαίνονται κινέζικα
+
+	EOF
+
+	q_to_nul <<-EOF >>expect &&
+	1QgreetingQAuto-mergingQAuto-merging greeting
+	Q1QgreetingQCONFLICT (contents)QCONFLICT (content): Merge conflict in greeting
+	Q2Qwhatever~tweak1QwhateverQCONFLICT (file/directory)QCONFLICT (file/directory): directory in the way of whatever from tweak1; moving it to whatever~tweak1 instead.
+	Q1Qwhatever~tweak1QCONFLICT (modify/delete)QCONFLICT (modify/delete): whatever~tweak1 deleted in side2 and modified in tweak1.  Version tweak1 of whatever~tweak1 left in tree.
+	Q1QΑυτά μου φαίνονται κινέζικαQAuto-mergingQAuto-merging Αυτά μου φαίνονται κινέζικα
+	Q1QΑυτά μου φαίνονται κινέζικαQCONFLICT (contents)QCONFLICT (content): Merge conflict in Αυτά μου φαίνονται κινέζικα
+	Q
+	EOF
+
+	test_cmp expect actual
+'
+
 test_done