Merge branch 'ad/custom-merge-placeholder-for-symbolic-pathnames' into seen

The labels on conflict markers for the common ancestor, our version,
and the other version are available to custom 3-way merge driver
via %S, %X, and %Y placeholders.

* ad/custom-merge-placeholder-for-symbolic-pathnames:
  merge-ll: expose revision names to custom drivers

3 files changed, 33 insertions, 12 deletions

diff --git a/Documentation/gitattributes.txt b/Documentation/gitattributes.txt
index 201bdf5edb..86a0946bb9 100644
--- a/Documentation/gitattributes.txt
+++ b/Documentation/gitattributes.txt
@@ -1137,11 +1137,11 @@ The `merge.*.name` variable gives the driver a human-readable
 name.
 
 The `merge.*.driver` variable's value is used to construct a
-command to run to merge ancestor's version (`%O`), current
+command to run to common ancestor's version (`%O`), current
 version (`%A`) and the other branches' version (`%B`).  These
 three tokens are replaced with the names of temporary files that
 hold the contents of these versions when the command line is
-built. Additionally, %L will be replaced with the conflict marker
+built. Additionally, `%L` will be replaced with the conflict marker
 size (see below).
 
 The merge driver is expected to leave the result of the merge in
@@ -1159,8 +1159,12 @@ When left unspecified, the driver itself is used for both
 internal merge and the final merge.
 
 The merge driver can learn the pathname in which the merged result
-will be stored via placeholder `%P`.
-
+will be stored via placeholder `%P`. Additionally, the names of the
+common ancestor revision (`%S`), of the current revision (`%X`) and
+of the other branch (`%Y`) can also be supplied. Those are short
+revision names, optionally joined with the paths of the file in each
+revision. Those paths are only present if they differ and are separated
+from the revision by a colon.
 
 `conflict-marker-size`
 ^^^^^^^^^^^^^^^^^^^^^^
diff --git a/merge-ll.c b/merge-ll.c
index 1df58ebaac..13e0713fe8 100644
--- a/merge-ll.c
+++ b/merge-ll.c
@@ -185,9 +185,9 @@ static void create_temp(mmfile_t *src, char *path, size_t len)
 static enum ll_merge_result ll_ext_merge(const struct ll_merge_driver *fn,
 			mmbuffer_t *result,
 			const char *path,
-			mmfile_t *orig, const char *orig_name UNUSED,
-			mmfile_t *src1, const char *name1 UNUSED,
-			mmfile_t *src2, const char *name2 UNUSED,
+			mmfile_t *orig, const char *orig_name,
+			mmfile_t *src1, const char *name1,
+			mmfile_t *src2, const char *name2,
 			const struct ll_merge_options *opts,
 			int marker_size)
 {
@@ -222,6 +222,12 @@ static enum ll_merge_result ll_ext_merge(const struct ll_merge_driver *fn,
 			strbuf_addf(&cmd, "%d", marker_size);
 		else if (skip_prefix(format, "P", &format))
 			sq_quote_buf(&cmd, path);
+		else if (skip_prefix(format, "S", &format))
+			sq_quote_buf(&cmd, orig_name);
+		else if (skip_prefix(format, "X", &format))
+			sq_quote_buf(&cmd, name1);
+		else if (skip_prefix(format, "Y", &format))
+			sq_quote_buf(&cmd, name2);
 		else
 			strbuf_addch(&cmd, '%');
 	}
@@ -315,7 +321,12 @@ static int read_merge_config(const char *var, const char *value,
 		 *    %B - temporary file name for the other branches' version.
 		 *    %L - conflict marker length
 		 *    %P - the original path (safely quoted for the shell)
+		 *    %S - the revision for the merge base
+		 *    %X - the revision for our version
+		 *    %Y - the revision for their version
 		 *
+		 * If the file is not named indentically in all versions, then each
+		 * revision is joined with the corresponding path, separated by a colon.
 		 * The external merge driver should write the results in the
 		 * file named by %A, and signal that it has done with zero exit
 		 * status.
diff --git a/t/t6406-merge-attr.sh b/t/t6406-merge-attr.sh
index 72f8c1722f..156a1efacf 100755
--- a/t/t6406-merge-attr.sh
+++ b/t/t6406-merge-attr.sh
@@ -42,11 +42,15 @@ test_expect_success setup '
 	#!/bin/sh
 
 	orig="$1" ours="$2" theirs="$3" exit="$4" path=$5
+	orig_name="$6" our_name="$7" their_name="$8"
 	(
 		echo "orig is $orig"
 		echo "ours is $ours"
 		echo "theirs is $theirs"
 		echo "path is $path"
+		echo "orig_name is $orig_name"
+		echo "our_name is $our_name"
+		echo "their_name is $their_name"
 		echo "=== orig ==="
 		cat "$orig"
 		echo "=== ours ==="
@@ -121,7 +125,7 @@ test_expect_success 'custom merge backend' '
 
 	git reset --hard anchor &&
 	git config --replace-all \
-	merge.custom.driver "./custom-merge %O %A %B 0 %P" &&
+	merge.custom.driver "./custom-merge %O %A %B 0 %P %S %X %Y" &&
 	git config --replace-all \
 	merge.custom.name "custom merge driver for testing" &&
 
@@ -132,7 +136,8 @@ test_expect_success 'custom merge backend' '
 	o=$(git unpack-file main^:text) &&
 	a=$(git unpack-file side^:text) &&
 	b=$(git unpack-file main:text) &&
-	sh -c "./custom-merge $o $a $b 0 text" &&
+	base_revid=$(git rev-parse --short main^) &&
+	sh -c "./custom-merge $o $a $b 0 text $base_revid HEAD main" &&
 	sed -e 1,3d $a >check-2 &&
 	cmp check-1 check-2 &&
 	rm -f $o $a $b
@@ -142,7 +147,7 @@ test_expect_success 'custom merge backend' '
 
 	git reset --hard anchor &&
 	git config --replace-all \
-	merge.custom.driver "./custom-merge %O %A %B 1 %P" &&
+	merge.custom.driver "./custom-merge %O %A %B 1 %P %S %X %Y" &&
 	git config --replace-all \
 	merge.custom.name "custom merge driver for testing" &&
 
@@ -159,7 +164,8 @@ test_expect_success 'custom merge backend' '
 	o=$(git unpack-file main^:text) &&
 	a=$(git unpack-file anchor:text) &&
 	b=$(git unpack-file main:text) &&
-	sh -c "./custom-merge $o $a $b 0 text" &&
+	base_revid=$(git rev-parse --short main^) &&
+	sh -c "./custom-merge $o $a $b 0 text $base_revid HEAD main" &&
 	sed -e 1,3d $a >check-2 &&
 	cmp check-1 check-2 &&
 	sed -e 1,3d -e 4q $a >check-3 &&
@@ -173,7 +179,7 @@ test_expect_success !WINDOWS 'custom merge driver that is killed with a signal'
 
 	git reset --hard anchor &&
 	git config --replace-all \
-	merge.custom.driver "./custom-merge %O %A %B 0 %P" &&
+	merge.custom.driver "./custom-merge %O %A %B 0 %P %S %X %Y" &&
 	git config --replace-all \
 	merge.custom.name "custom merge driver for testing" &&