use skip_prefix to avoid magic numbers

It's a common idiom to match a prefix and then skip past it
with a magic number, like:

  if (starts_with(foo, "bar"))
	  foo += 3;

This is easy to get wrong, since you have to count the
prefix string yourself, and there's no compiler check if the
string changes.  We can use skip_prefix to avoid the magic
numbers here.

Note that some of these conversions could be much shorter.
For example:

  if (starts_with(arg, "--foo=")) {
	  bar = arg + 6;
	  continue;
  }

could become:

  if (skip_prefix(arg, "--foo=", &bar))
	  continue;

However, I have left it as:

  if (skip_prefix(arg, "--foo=", &v)) {
	  bar = v;
	  continue;
  }

to visually match nearby cases which need to actually
process the string. Like:

  if (skip_prefix(arg, "--foo=", &v)) {
	  bar = atoi(v);
	  continue;
  }

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

1 files changed, 2 insertions, 2 deletions

diff --git a/convert.c b/convert.c
index ab80b72357..cb5fbb45ea 100644
--- a/convert.c
+++ b/convert.c
@@ -1121,9 +1121,9 @@ static int is_foreign_ident(const char *str)
 {
 	int i;
 
-	if (!starts_with(str, "$Id: "))
+	if (!skip_prefix(str, "$Id: ", &str))
 		return 0;
-	for (i = 5; str[i]; i++) {
+	for (i = 0; str[i]; i++) {
 		if (isspace(str[i]) && str[i+1] != '$')
 			return 1;
 	}