stash: add --ours-label, --theirs-label, --base-label for apply

Allow callers of "git stash apply" to pass custom labels for conflict
markers instead of the default "Updated upstream" and "Stashed changes".
Document the new options and add a test.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>

Author: HaraldNordgren

Documentation/git-stash.adoc

@@ -12,7 +12,7 @@ git stash list [<log-options>]
 git stash show [-u | --include-untracked | --only-untracked] [<diff-options>] [<stash>]
 git stash drop [-q | --quiet] [<stash>]
 git stash pop [--index] [-q | --quiet] [<stash>]
-git stash apply [--index] [-q | --quiet] [<stash>]
+git stash apply [--index] [-q | --quiet] [--ours-label=<label>] [--theirs-label=<label>] [--base-label=<label>] [<stash>]
 git stash branch <branchname> [<stash>]
 git stash [push] [-p | --patch] [-S | --staged] [-k | --[no-]keep-index] [-q | --quiet]
 	     [-u | --include-untracked] [-a | --all] [(-m | --message) <message>]
@@ -195,6 +195,15 @@ the index's ones. However, this can fail, when you have conflicts
 (which are stored in the index, where you therefore can no longer
 apply the changes as they were originally).
 
+`--ours-label=<label>`::
+`--theirs-label=<label>`::
+`--base-label=<label>`::
+	These options are only valid for the `apply` command.
++
+Use the given labels in conflict markers instead of the default
+"Updated upstream", "Stashed changes", and "Stash base".
+`--base-label` only has an effect with merge.conflictStyle=diff3.
+
 `-k`::
 `--keep-index`::
 `--no-keep-index`::

builtin/stash.c

@@ -44,7 +44,7 @@
 #define BUILTIN_STASH_POP_USAGE \
 	N_("git stash pop [--index] [-q | --quiet] [<stash>]")
 #define BUILTIN_STASH_APPLY_USAGE \
-	N_("git stash apply [--index] [-q | --quiet] [<stash>]")
+	N_("git stash apply [--index] [-q | --quiet] [--ours-label=<label>] [--theirs-label=<label>] [--base-label=<label>] [<stash>]")
 #define BUILTIN_STASH_BRANCH_USAGE \
 	N_("git stash branch <branchname> [<stash>]")
 #define BUILTIN_STASH_STORE_USAGE \

t/t3903-stash.sh

@@ -1666,6 +1666,43 @@ test_expect_success 'restore untracked files even when we hit conflicts' '
 	)
 '
 
+test_expect_success 'apply with custom conflict labels' '
+	git init conflict_labels &&
+	(
+		cd conflict_labels &&
+		echo base >file &&
+		git add file &&
+		git commit -m base &&
+		echo stashed >file &&
+		git stash push -m "stashed" &&
+		echo upstream >file &&
+		git add file &&
+		git commit -m upstream &&
+		test_must_fail git -c merge.conflictStyle=diff3 stash apply --ours-label=UP --theirs-label=STASH &&
+		test_grep "^<<<<<<< UP" file &&
+		test_grep "^||||||| Stash base" file &&
+		test_grep "^>>>>>>> STASH" file
+	)
+'
+
+test_expect_success 'apply with empty conflict labels' '
+	git init empty_labels &&
+	(
+		cd empty_labels &&
+		echo base >file &&
+		git add file &&
+		git commit -m base &&
+		echo stashed >file &&
+		git stash push -m "stashed" &&
+		echo upstream >file &&
+		git add file &&
+		git commit -m upstream &&
+		test_must_fail git stash apply --ours-label= --theirs-label= &&
+		test_grep "^<<<<<<<$" file &&
+		test_grep "^>>>>>>>$" file
+	)
+'
+
 test_expect_success 'stash create reports a locked index' '
 	test_when_finished "rm -rf repo" &&
 	git init repo &&

xdiff/xmerge.c

@@ -199,9 +199,9 @@ static int fill_conflict_hunk(xdfenv_t *xe1, const char *name1,
 			      int size, int i, int style,
 			      xdmerge_t *m, char *dest, int marker_size)
 {
-	int marker1_size = (name1 ? strlen(name1) + 1 : 0);
-	int marker2_size = (name2 ? strlen(name2) + 1 : 0);
-	int marker3_size = (name3 ? strlen(name3) + 1 : 0);
+	int marker1_size = (name1 && *name1 ? strlen(name1) + 1 : 0);
+	int marker2_size = (name2 && *name2 ? strlen(name2) + 1 : 0);
+	int marker3_size = (name3 && *name3 ? strlen(name3) + 1 : 0);
 	int needs_cr = is_cr_needed(xe1, xe2, m);
 
 	if (marker_size <= 0)