get_short_sha1: NUL-terminate hex prefix

We store the hex prefix in a 40-byte buffer with the prefix
itself followed by 40-minus-len "x" characters. These x's
serve no purpose, and the lack of NUL termination makes the
prefix string annoying to use. Let's just terminate it.

Note that this is in contrast to the binary prefix, which
_must_ be zero-padded, because we look at the whole thing
during a binary search to find the first potential match in
each pack index. The loose-object hex search cannot use the
same trick because it has to do a linear walk through the
unsorted results of readdir() (and even if it could, you'd
want zeroes instead of x's).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sha1_name.c

@@ -14,7 +14,7 @@ typedef int (*disambiguate_hint_fn)(const unsigned char *, void *);
 
 struct disambiguate_state {
 	int len; /* length of prefix in hex chars */
-	char hex_pfx[GIT_SHA1_HEXSZ];
+	char hex_pfx[GIT_SHA1_HEXSZ + 1];
 	unsigned char bin_pfx[GIT_SHA1_RAWSZ];
 
 	disambiguate_hint_fn fn;
@@ -291,7 +291,6 @@ static int init_object_disambiguation(const char *name, int len,
 		return -1;
 
 	memset(ds, 0, sizeof(*ds));
-	memset(ds->hex_pfx, 'x', GIT_SHA1_HEXSZ);
 
 	for (i = 0; i < len ;i++) {
 		unsigned char c = name[i];
@@ -313,6 +312,7 @@ static int init_object_disambiguation(const char *name, int len,
 	}
 
 	ds->len = len;
+	ds->hex_pfx[len] = '\0';
 	prepare_alt_odb();
 	return 0;
 }
@@ -346,7 +346,7 @@ static int get_short_sha1(const char *name, int len, unsigned char *sha1,
 	status = finish_object_disambiguation(&ds, sha1);
 
 	if (!quietly && (status == SHORT_NAME_AMBIGUOUS))
-		return error("short SHA1 %.*s is ambiguous.", ds.len, ds.hex_pfx);
+		return error("short SHA1 %s is ambiguous.", ds.hex_pfx);
 	return status;
 }