Re: [PATCH v3 08/14] remote.c: report specific errors from branch_get_upstream
- From
Junio C Hamano <gitster@pobox.com>
- Date
- May 21, 2015, 18:33 UTC
- Message-ID
- <xmqq7fs1kcfd.fsf@gitster.dls.corp.google.com>
- In-Reply-To
- <20150521044532.GH23409@peff.net>
Jeff King <peff@peff.net> writes:
Show 22 quoted lines
> diff --git a/remote.c b/remote.c
> index dca3442..1b7051a 100644
> --- a/remote.c
> +++ b/remote.c
> @@ -1705,10 +1705,35 @@ int branch_merge_matches(struct branch *branch,
> return refname_match(branch->merge[i]->src, refname);
> }
>
> -const char *branch_get_upstream(struct branch *branch)
> +__attribute((format (printf,2,3)))
> +static const char *error_buf(struct strbuf *err, const char *fmt, ...)
> {
> - if (!branch || !branch->merge || !branch->merge[0])
> - return NULL;
> + if (err) {
> + va_list ap;
> + va_start(ap, fmt);
> + strbuf_vaddf(err, fmt, ap);
> + va_end(ap);
> + }
> + return NULL;
> +}Many of our functions return -1 to signal an error, and that is why it makes sense for our error() helper to return -1 to save code in the caller, but only because the callers of this private helper use a NULL to signal an error, this also returns NULL. If we were to use the "callers can opt into detailed message by passing strbuf" pattern more widely, we would want a variant of the above that returns -1, too. And such a helper would do the same thing as above, with only difference from the above is to return -1.
It's a shame that we have to return something from this function, whose primary purpose is "we may or may not want an error message in a strbuf, so format the message when and only when we give you a strbuf", but C forces us to make it "always return NULL to signal an error to the caller, and optionally format the message into a strbuf if given".
And the name of this helper function only captures the "optionally format the message" part, not the "always return NULL" part.
Show 19 quoted lines
> +const char *branch_get_upstream(struct branch *branch, struct strbuf *err)
> +{
> + if (!branch)
> + return error_buf(err, _("HEAD does not point to a branch"));
> + if (!branch->merge || !branch->merge[0] || !branch->merge[0]->dst) {
> + if (!ref_exists(branch->refname))
> + return error_buf(err, _("no such branch: '%s'"),
> + branch->name);
> + if (!branch->merge)
> + return error_buf(err,
> + _("no upstream configured for branch '%s'"),
> + branch->name);
> + return error_buf(err,
> + _("upstream branch '%s' not stored as a remote-tracking branch"),
> + branch->merge[0]->src);
> + }
> +
> return branch->merge[0]->dst;
> }This is a faithful conversion of what the get_upstream_branch() used to do, but that ref_exists() check and the error checking there look somewhat out of place.
It makes the reader wonder what should happen when "branch->refname" does not exist as a ref, but "branch->merge[0]->dst" can be fully dereferenced. Should it be an error, or if it is OK, the reason why it is OK is...?