rev-parse --disambiguate=<prefix>

The new option allows you to feed an ambiguous prefix and enumerate
all the objects that share it as a prefix of their object names.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-rev-parse.txt

@@ -101,6 +101,12 @@ OPTIONS
 	The option core.warnAmbiguousRefs is used to select the strict
 	abbreviation mode.
 
+--disambiguate=<prefix>::
+	Show every object whose name begins with the given prefix.
+	The <prefix> must be at least 4 hexadecimal digits long to
+	avoid listing each and every object in the repository by
+	mistake.
+
 --all::
 	Show all refs found in `refs/`.
 

builtin/rev-parse.c

@@ -195,6 +195,12 @@ static int anti_reference(const char *refname, const unsigned char *sha1, int fl
 	return 0;
 }
 
+static int show_abbrev(const unsigned char *sha1, void *cb_data)
+{
+	show_rev(NORMAL, sha1, NULL);
+	return 0;
+}
+
 static void show_datestring(const char *flag, const char *datestr)
 {
 	static char buffer[100];
@@ -589,6 +595,10 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 				for_each_ref(show_reference, NULL);
 				continue;
 			}
+			if (!prefixcmp(arg, "--disambiguate=")) {
+				for_each_abbrev(arg + 15, show_abbrev, NULL);
+				continue;
+			}
 			if (!strcmp(arg, "--bisect")) {
 				for_each_ref_in("refs/bisect/bad", show_reference, NULL);
 				for_each_ref_in("refs/bisect/good", anti_reference, NULL);

cache.h

@@ -828,6 +828,9 @@ extern int get_sha1_blob(const char *str, unsigned char *sha1);
 extern void maybe_die_on_misspelt_object_name(const char *name, const char *prefix);
 extern int get_sha1_with_context(const char *str, unsigned flags, unsigned char *sha1, struct object_context *orc);
 
+typedef int each_abbrev_fn(const unsigned char *sha1, void *);
+extern int for_each_abbrev(const char *prefix, each_abbrev_fn, void *);
+
 /*
  * Try to read a SHA1 in hexadecimal format from the 40 characters
  * starting at hex.  Write the 20-byte result to sha1 in binary form.

sha1_name.c

@@ -20,10 +20,15 @@ struct disambiguate_state {
 	unsigned candidate_ok:1;
 	unsigned disambiguate_fn_used:1;
 	unsigned ambiguous:1;
+	unsigned always_call_fn:1;
 };
 
 static void update_candidates(struct disambiguate_state *ds, const unsigned char *current)
 {
+	if (ds->always_call_fn) {
+		ds->ambiguous = ds->fn(current, ds->cb_data) ? 1 : 0;
+		return;
+	}
 	if (!ds->candidate_exists) {
 		/* this is the first candidate */
 		hashcpy(ds->candidate, current);
@@ -272,17 +277,12 @@ static int disambiguate_blob_only(const unsigned char *sha1, void *cb_data_unuse
 	return kind == OBJ_BLOB;
 }
 
-static int get_short_sha1(const char *name, int len, unsigned char *sha1,
+static int prepare_prefixes(const char *name, int len,
-			  unsigned flags)
+			    unsigned char *bin_pfx,
+			    char *hex_pfx)
 {
-	int i, status;
+	int i;
-	char hex_pfx[40];
-	unsigned char bin_pfx[20];
-	struct disambiguate_state ds;
-	int quietly = !!(flags & GET_SHA1_QUIETLY);
 
-	if (len < MINIMUM_ABBREV || len > 40)
-		return -1;
 	hashclr(bin_pfx);
 	memset(hex_pfx, 'x', 40);
 	for (i = 0; i < len ;i++) {
@@ -303,6 +303,22 @@ static int get_short_sha1(const char *name, int len, unsigned char *sha1,
 			val <<= 4;
 		bin_pfx[i >> 1] |= val;
 	}
+	return 0;
+}
+
+static int get_short_sha1(const char *name, int len, unsigned char *sha1,
+			  unsigned flags)
+{
+	int status;
+	char hex_pfx[40];
+	unsigned char bin_pfx[20];
+	struct disambiguate_state ds;
+	int quietly = !!(flags & GET_SHA1_QUIETLY);
+
+	if (len < MINIMUM_ABBREV || len > 40)
+		return -1;
+	if (prepare_prefixes(name, len, bin_pfx, hex_pfx) < 0)
+		return -1;
 
 	prepare_alt_odb();
 
@@ -327,6 +343,31 @@ static int get_short_sha1(const char *name, int len, unsigned char *sha1,
 	return status;
 }
 
+
+int for_each_abbrev(const char *prefix, each_abbrev_fn fn, void *cb_data)
+{
+	char hex_pfx[40];
+	unsigned char bin_pfx[20];
+	struct disambiguate_state ds;
+	int len = strlen(prefix);
+
+	if (len < MINIMUM_ABBREV || len > 40)
+		return -1;
+	if (prepare_prefixes(prefix, len, bin_pfx, hex_pfx) < 0)
+		return -1;
+
+	prepare_alt_odb();
+
+	memset(&ds, 0, sizeof(ds));
+	ds.always_call_fn = 1;
+	ds.cb_data = cb_data;
+	ds.fn = fn;
+
+	find_short_object_filename(len, hex_pfx, &ds);
+	find_short_packed_object(len, bin_pfx, &ds);
+	return ds.ambiguous;
+}
+
 const char *find_unique_abbrev(const unsigned char *sha1, int len)
 {
 	int status, exists;

t/t1512-rev-parse-disambiguation.sh

@@ -252,4 +252,13 @@ test_expect_success 'ambiguous commit-ish' '
 	test_must_fail git log 000000000...
 '
 
+test_expect_success 'rev-parse --disambiguate' '
+	# The test creates 16 objects that share the prefix and two
+	# commits created by commit-tree in earlier tests do not share
+	# the prefix.
+	git rev-parse --disambiguate=000000000 >actual &&
+	test "$(wc -l <actual)" = 16 &&
+	test "$(sed -e "s/^\(.........\).*/\1/" actual | sort -u)" = 000000000
+'
+
 test_done