Add builtin merge-file, a minimal replacement for RCS merge

merge-file has the same syntax as RCS merge, but supports only the
"-L" option.

For good measure, a test is added, which is quite minimal, though.

[jc: further fix for compliation errors included.]

Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

builtin-merge-file.c

@@ -0,0 +1,72 @@
+#include "cache.h"
+#include "xdiff/xdiff.h"
+
+static const char merge_file_usage[] =
+"git merge-file [-L name1 [-L orig [-L name2]]] file1 orig_file file2";
+
+static int read_file(mmfile_t *ptr, const char *filename)
+{
+	struct stat st;
+	FILE *f;
+
+	if (stat(filename, &st))
+		return error("Could not stat %s", filename);
+	if ((f = fopen(filename, "rb")) == NULL)
+		return error("Could not open %s", filename);
+	ptr->ptr = xmalloc(st.st_size);
+	if (fread(ptr->ptr, st.st_size, 1, f) != 1)
+		return error("Could not read %s", filename);
+	fclose(f);
+	ptr->size = st.st_size;
+	return 0;
+}
+
+int cmd_merge_file(int argc, char **argv, char **envp)
+{
+	char *names[3];
+	mmfile_t mmfs[3];
+	mmbuffer_t result = {NULL, 0};
+	xpparam_t xpp = {XDF_NEED_MINIMAL};
+	int ret = 0, i = 0;
+
+	while (argc > 4) {
+		if (!strcmp(argv[1], "-L")) {
+			names[i++] = argv[2];
+			argc -= 2;
+			argv += 2;
+			continue;
+		}
+		usage(merge_file_usage);
+	}
+
+	if (argc != 4)
+		usage(merge_file_usage);
+
+	for (; i < 3; i++)
+		names[i] = argv[i + 1];
+
+	for (i = 0; i < 3; i++)
+		if (read_file(mmfs + i, argv[i + 1]))
+			return -1;
+
+	ret = xdl_merge(mmfs + 1, mmfs + 0, names[0], mmfs + 2, names[2],
+			&xpp, XDL_MERGE_ZEALOUS, &result);
+
+	for (i = 0; i < 3; i++)
+		free(mmfs[i].ptr);
+
+	if (ret >= 0) {
+		char *filename = argv[1];
+		FILE *f = fopen(filename, "wb");
+
+		if (!f)
+			ret = error("Could not open %s for writing", filename);
+		else if (fwrite(result.ptr, result.size, 1, f) != 1)
+			ret = error("Could not write to %s", filename);
+		else if (fclose(f))
+			ret = error("Could not close %s", filename);
+		free(result.ptr);
+	}
+
+	return ret;
+}