cat-file: introduce the --filters option

The --filters option applies the convert_to_working_tree() filter for
the path when showing the contents of a regular file blob object;
the contents are written out as-is for other types of objects.

This feature comes in handy when a 3rd-party tool wants to work with
the contents of files from past revisions as if they had been checked
out, but without detouring via temporary files.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 35 insertions, 1 deletions

diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index 2dfe6265f..96007cb1a 100644
--- a/builtin/cat-file.c
+++ b/builtin/cat-file.c
@@ -20,6 +20,28 @@ struct batch_options {
 	const char *format;
 };
 
+static int filter_object(const char *path, unsigned mode,
+			 const unsigned char *sha1,
+			 char **buf, unsigned long *size)
+{
+	enum object_type type;
+
+	*buf = read_sha1_file(sha1, &type, size);
+	if (!*buf)
+		return error(_("cannot read object %s '%s'"),
+			sha1_to_hex(sha1), path);
+	if ((type == OBJ_BLOB) && S_ISREG(mode)) {
+		struct strbuf strbuf = STRBUF_INIT;
+		if (convert_to_working_tree(path, *buf, *size, &strbuf)) {
+			free(*buf);
+			*size = strbuf.len;
+			*buf = strbuf_detach(&strbuf, NULL);
+		}
+	}
+
+	return 0;
+}
+
 static int cat_one_file(int opt, const char *exp_type, const char *obj_name,
 			int unknown_type)
 {
@@ -61,6 +83,16 @@ static int cat_one_file(int opt, const char *exp_type, const char *obj_name,
 	case 'e':
 		return !has_sha1_file(sha1);
 
+	case 'w':
+		if (!obj_context.path[0])
+			die("git cat-file --filters %s: <object> must be "
+			    "<sha1:path>", obj_name);
+
+		if (filter_object(obj_context.path, obj_context.mode,
+				  sha1, &buf, &size))
+			return -1;
+		break;
+
 	case 'c':
 		if (!obj_context.path[0])
 			die("git cat-file --textconv %s: <object> must be <sha1:path>",
@@ -440,7 +472,7 @@ static int batch_objects(struct batch_options *opt)
 }
 
 static const char * const cat_file_usage[] = {
-	N_("git cat-file (-t [--allow-unknown-type]|-s [--allow-unknown-type]|-e|-p|<type>|--textconv) <object>"),
+	N_("git cat-file (-t [--allow-unknown-type]|-s [--allow-unknown-type]|-e|-p|<type>|--textconv|--filters) <object>"),
 	N_("git cat-file (--batch | --batch-check) [--follow-symlinks]"),
 	NULL
 };
@@ -486,6 +518,8 @@ int cmd_cat_file(int argc, const char **argv, const char *prefix)
 		OPT_CMDMODE('p', NULL, &opt, N_("pretty-print object's content"), 'p'),
 		OPT_CMDMODE(0, "textconv", &opt,
 			    N_("for blob objects, run textconv on object's content"), 'c'),
+		OPT_CMDMODE(0, "filters", &opt,
+			    N_("for blob objects, run filters on object's content"), 'w'),
 		OPT_BOOL(0, "allow-unknown-type", &unknown_type,
 			  N_("allow -s and -t to work with broken/corrupt objects")),
 		OPT_BOOL(0, "buffer", &batch.buffer_output, N_("buffer --batch output")),