rev-list: teach --no-object-names to enable piping

Allow easier parsing by cat-file by giving rev-list an option to print
only the OID of a non-commit object without any additional information.
This is a short-term shim; later on, rev-list should be taught how to
print the types of objects it finds in a format similar to cat-file's.

Before this commit, the output from rev-list needed to be massaged
before being piped to cat-file, like so:

  git rev-list --objects HEAD | cut -f 1 -d ' ' |
    git cat-file --batch-check

This was especially unexpected when dealing with root trees, as an
invisible whitespace exists at the end of the OID:

  git rev-list --objects --filter=tree:1 --max-count=1 HEAD |
    xargs -I% echo "AA%AA"

Now, it can be piped directly, as in the added test case:

  git rev-list --objects --no-object-names HEAD | git cat-file --batch-check

Signed-off-by: Emily Shaffer <emilyshaffer@google.com>
Change-Id: I489bdf0a8215532e540175188883ff7541d70e1b
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-rev-list.txt

@@ -48,6 +48,7 @@ SYNOPSIS
 	     [ --date=<format>]
 	     [ [ --objects | --objects-edge | --objects-edge-aggressive ]
 	       [ --unpacked ]
+	       [ --object-names | --no-object-names ]
 	       [ --filter=<filter-spec> [ --filter-print-omitted ] ] ]
 	     [ --missing=<missing-action> ]
 	     [ --pretty | --header ]

Documentation/rev-list-options.txt

@@ -708,6 +708,16 @@ ifdef::git-rev-list[]
 	Only useful with `--objects`; print the object IDs that are not
 	in packs.
 
+--object-names::
+	Only useful with `--objects`; print the names of the object IDs
+	that are found. This is the default behavior.
+
+--no-object-names::
+	Only useful with `--objects`; does not print the names of the object
+	IDs that are found. This inverts `--object-names`. This flag allows
+	the output to be more easily parsed by commands such as
+	linkgit:git-cat-file[1].
+
 --filter=<filter-spec>::
 	Only useful with one of the `--objects*`; omits objects (usually
 	blobs) from the list of printed objects.  The '<filter-spec>'

builtin/rev-list.c

@@ -49,6 +49,7 @@ static const char rev_list_usage[] =
 "    --objects | --objects-edge\n"
 "    --unpacked\n"
 "    --header | --pretty\n"
+"    --[no-]object-names\n"
 "    --abbrev=<n> | --no-abbrev\n"
 "    --abbrev-commit\n"
 "    --left-right\n"
@@ -75,6 +76,9 @@ enum missing_action {
 };
 static enum missing_action arg_missing_action;
 
+/* display only the oid of each object encountered */
+static int arg_show_object_names = 1;
+
 #define DEFAULT_OIDSET_SIZE     (16*1024)
 
 static void finish_commit(struct commit *commit);
@@ -255,7 +259,10 @@ static void show_object(struct object *obj, const char *name, void *cb_data)
 	display_progress(progress, ++progress_counter);
 	if (info->flags & REV_LIST_QUIET)
 		return;
-	show_object_with_name(stdout, obj, name);
+	if (arg_show_object_names)
+		show_object_with_name(stdout, obj, name);
+	else
+		printf("%s\n", oid_to_hex(&obj->oid));
 }
 
 static void show_edge(struct commit *commit)
@@ -484,6 +491,16 @@ int cmd_rev_list(int argc, const char **argv, const char *prefix)
 		if (skip_prefix(arg, "--missing=", &arg))
 			continue; /* already handled above */
 
+		if (!strcmp(arg, ("--no-object-names"))) {
+			arg_show_object_names = 0;
+			continue;
+		}
+
+		if (!strcmp(arg, ("--object-names"))) {
+			arg_show_object_names = 1;
+			continue;
+		}
+
 		usage(rev_list_usage);
 
 	}

t/t6000-rev-list-misc.sh

@@ -48,6 +48,26 @@ test_expect_success 'rev-list --objects with pathspecs and copied files' '
 	! grep one output
 '
 
+test_expect_success 'rev-list --objects --no-object-names has no space/names' '
+	git rev-list --objects --no-object-names HEAD >output &&
+	! grep wanted_file output &&
+	! grep unwanted_file output &&
+	! grep " " output
+'
+
+test_expect_success 'rev-list --objects --no-object-names works with cat-file' '
+	git rev-list --objects --no-object-names --all >list-output &&
+	git cat-file --batch-check <list-output >cat-output &&
+	! grep missing cat-output
+'
+
+test_expect_success '--no-object-names and --object-names are last-one-wins' '
+	git rev-list --objects --no-object-names --object-names --all >output &&
+	grep wanted_file output &&
+	git rev-list --objects --object-names --no-object-names --all >output &&
+	! grep wanted_file output
+'
+
 test_expect_success 'rev-list A..B and rev-list ^A B are the same' '
 	git commit --allow-empty -m another &&
 	git tag -a -m "annotated" v1.0 &&