merge-ll: expose revision names to custom drivers

Custom merge drivers need access to the names of the revisions they
are working on, so that the merge conflict markers they introduce
can refer to those revisions. The placeholders '%S', '%X' and '%Y'
are introduced to this end.

Signed-off-by: Antonin Delpeuch <antonin@delpeuch.eu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: wetneb

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 +1159,9 @@ 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`. The conflict labels to be used
+for the common ancestor, local head and other head can be passed by
+using '%S', '%X' and '%Y` respectively.
 
 `conflict-marker-size`
 ^^^^^^^^^^^^^^^^^^^^^^

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 ? orig_name : "");
+		else if (skip_prefix(format, "X", &format))
+			sq_quote_buf(&cmd, name1 ? name1 : "");
+		else if (skip_prefix(format, "Y", &format))
+			sq_quote_buf(&cmd, name2 ? 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.

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" &&