sha1_name.c: introduce get_sha1_committish()

Many callers know that the user meant to name a committish by
syntactical positions where the object name appears.  Calling this
function allows the machinery to disambiguate shorter-than-unique
abbreviated object names between committish and others.

Note that this does NOT error out when the named object is not a
committish. It is merely to give a hint to the disambiguation
machinery.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

cache.h

@@ -817,6 +817,7 @@ struct object_context {
 #define GET_SHA1_ONLY_TO_DIE 04000
 
 extern int get_sha1(const char *str, unsigned char *sha1);
+extern int get_sha1_committish(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);
 

commit.c

@@ -67,7 +67,7 @@ struct commit *lookup_commit_reference_by_name(const char *name)
 	unsigned char sha1[20];
 	struct commit *commit;
 
-	if (get_sha1(name, sha1))
+	if (get_sha1_committish(name, sha1))
 		return NULL;
 	commit = lookup_commit_reference(sha1);
 	if (!commit || parse_commit(commit))

revision.c

@@ -979,7 +979,7 @@ static int add_parents_only(struct rev_info *revs, const char *arg_, int flags)
 		flags ^= UNINTERESTING;
 		arg++;
 	}
-	if (get_sha1(arg, sha1))
+	if (get_sha1_committish(arg, sha1))
 		return 0;
 	while (1) {
 		it = get_reference(revs, arg, sha1, 0);
@@ -1120,8 +1120,8 @@ int handle_revision_arg(const char *arg_, struct rev_info *revs,
 			next = "HEAD";
 		if (dotdot == arg)
 			this = "HEAD";
-		if (!get_sha1(this, from_sha1) &&
-		    !get_sha1(next, sha1)) {
+		if (!get_sha1_committish(this, from_sha1) &&
+		    !get_sha1_committish(next, sha1)) {
 			struct commit *a, *b;
 			struct commit_list *exclude;
 

sha1_name.c

@@ -872,7 +872,7 @@ int get_sha1_mb(const char *name, unsigned char *sha1)
 		struct strbuf sb;
 		strbuf_init(&sb, dots - name);
 		strbuf_add(&sb, name, dots - name);
-		st = get_sha1(sb.buf, sha1_tmp);
+		st = get_sha1_committish(sb.buf, sha1_tmp);
 		strbuf_release(&sb);
 	}
 	if (st)
@@ -881,7 +881,7 @@ int get_sha1_mb(const char *name, unsigned char *sha1)
 	if (!one)
 		return -1;
 
-	if (get_sha1(dots[3] ? (dots + 3) : "HEAD", sha1_tmp))
+	if (get_sha1_committish(dots[3] ? (dots + 3) : "HEAD", sha1_tmp))
 		return -1;
 	two = lookup_commit_reference_gently(sha1_tmp, 0);
 	if (!two)
@@ -999,6 +999,23 @@ int get_sha1(const char *name, unsigned char *sha1)
 	return get_sha1_with_context(name, 0, sha1, &unused);
 }
 
+/*
+ * Many callers know that the user meant to name a committish by
+ * syntactical positions where the object name appears.  Calling this
+ * function allows the machinery to disambiguate shorter-than-unique
+ * abbreviated object names between committish and others.
+ *
+ * Note that this does NOT error out when the named object is not a
+ * committish. It is merely to give a hint to the disambiguation
+ * machinery.
+ */
+int get_sha1_committish(const char *name, unsigned char *sha1)
+{
+	struct object_context unused;
+	return get_sha1_with_context(name, GET_SHA1_COMMITTISH,
+				     sha1, &unused);
+}
+
 /* Must be called only when object_name:filename doesn't exist. */
 static void diagnose_invalid_sha1_path(const char *prefix,
 				       const char *filename,

t/t1512-rev-parse-disambiguation.sh

@@ -102,7 +102,7 @@ test_expect_failure 'disambiguate commit' '
 	test $(git rev-parse $commit^) = $(git rev-parse 0000000000e4f)
 '
 
-test_expect_failure 'log name1..name2 takes only commit-ishes on both ends' '
+test_expect_success 'log name1..name2 takes only commit-ishes on both ends' '
 	git log 000000000..000000000 &&
 	git log ..000000000 &&
 	git log 000000000.. &&