[PATCH 3/3] builtin/describe: describe blobs

[Stefan Beller <sbeller@google.com>]

Sometimes users are given a hash of an object and they want to
identify it further (ex.: Use verify-pack to find the largest blobs,
but what are these? or [1])

The best identification of a blob hash is done via a its path at a
given commit, which this implements.

[1] https://stackoverflow.com/questions/223678/which-commit-has-this-blob

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 builtin/describe.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 54 insertions(+), 4 deletions(-)

diff --git a/builtin/describe.c b/builtin/describe.c
index 29075dbd0f..752de5843b 100644
--- a/builtin/describe.c
+++ b/builtin/describe.c
@@ -11,8 +11,9 @@
 #include "hashmap.h"
 #include "argv-array.h"
 #include "run-command.h"
+#include "revision.h"
+#include "list-objects.h"
 
-#define SEEN		(1u << 0)
 #define MAX_TAGS	(FLAG_BITS - 1)
 
 static const char * const describe_usage[] = {
@@ -282,6 +283,50 @@ static void show_suffix(int depth, const struct object_id *oid)
 	printf("-%d-g%s", depth, find_unique_abbrev(oid->hash, abbrev));
 }
 
+struct blob_descriptor {
+	struct object_id current_commit;
+	struct object_id looking_for;
+};
+
+static void process_commit(struct commit *commit, void *data)
+{
+	struct blob_descriptor *bd = data;
+
+	bd->current_commit = commit->object.oid;
+}
+
+static void process_object(struct object *obj, const char *name, void *data)
+{
+	struct blob_descriptor *bd = data;
+
+	if (!oidcmp(&bd->looking_for, &obj->oid))
+		printf(_("blob %s present at path %s in commit %s\n"),
+			oid_to_hex(&bd->looking_for), name,
+			oid_to_hex(&bd->current_commit));
+}
+
+static void describe_blob(struct object_id oid)
+{
+	struct rev_info revs;
+	struct argv_array args = ARGV_ARRAY_INIT;
+	struct blob_descriptor bd = { null_oid, oid };
+
+	argv_array_pushl(&args, "internal: The first arg is not parsed",
+		"--all", "--single-worktree", "--objects", NULL);
+
+	revs.tree_blobs_in_commit_order = 1;
+
+	init_revisions(&revs, NULL);
+
+	if (setup_revisions(args.argc, args.argv, &revs, NULL) > 1)
+		BUG("setup_revisions could not handle all args?");
+
+	if (prepare_revision_walk(&revs))
+		die("revision walk setup failed");
+
+	traverse_commit_list(&revs, process_commit, process_object, &bd);
+}
+
 static void describe(const char *arg, int last_one)
 {
 	struct object_id oid;
@@ -295,9 +340,14 @@ static void describe(const char *arg, int last_one)
 
 	if (get_oid(arg, &oid))
 		die(_("Not a valid object name %s"), arg);
-	cmit = lookup_commit_reference(&oid);
-	if (!cmit)
-		die(_("%s is not a valid '%s' object"), arg, commit_type);
+	cmit = lookup_commit_reference_gently(&oid, 1);
+	if (!cmit) {
+		if (lookup_blob(&oid))
+			describe_blob(oid);
+		else
+			die(_("%s is not a commit nor blob"), arg);
+		return;
+	}
 
 	n = find_commit_name(&cmit->object.oid);
 	if (n && (tags || all || n->prio == 2)) {
-- 
2.15.0.rc2.443.gfcc3b81c0a