Subject: Re: [PATCH v2 1/4] fetch: extract writing to FETCH_HEAD

From: Patrick Steinhardt <[email-masked]>
Date: Mon, 11 Jan 2021 11:26:13 +0100

On Fri, Jan 08, 2021 at 03:40:17PM -0800, Junio C Hamano wrote:
> Patrick Steinhardt <[email-masked]> writes:
> > +static void append_fetch_head(struct fetch_head *fetch_head, const char *old_oid,
> 
> It is clear from the type these days but variable names like
> "old_oid" hint the readers that they are not a hexadecimal object
> name string but either an array of uchar[40] or a struct object_id;
> perhaps "old_oid_hex" would be less misleading.
> 
> If the caller does have struct object_id, then it would be even
> better to take it as-is as a parameter and use oid_to_hex_r() on it in
> this function when it is given to fprintf().  [Nit #1]

Agreed.

[snip]
> > +	fprintf(fetch_head->fp, "%s\t%s\t%s",
> > +		old_oid, merge_status_marker, note);
> > +	for (i = 0; i < url_len; ++i)
> > +		if ('\n' == url[i])
> > +			fputs("\\n", fetch_head->fp);
> > +		else
> > +			fputc(url[i], fetch_head->fp);
> > +	fputc('\n', fetch_head->fp);
> > +}
> 
> OK.  This is the "case FETCH_HEAD_NOT_FOR_MERGE" and "case
> FETCH_HEAD_MERGE" parts in the original.
> 
> As an abstraction, it may be better to make the caller pass a
> boolean "is this for merge?" and keep the knowledge of what exact
> string is used for merge_status_marker to this function, instead of
> letting the caller passing it as a parameter in the string form.
> After all, we never allow anything other than an empty string or a
> fixed "not-for-merge" string in that place in the file format.
> [Nit #2]

I think it's even nicer to just pass in `rm->fetch_head_status`
directly, which allows us to move below switch into `append_fetch_head`.

[snip]
> > +	fclose(fetch_head->fp);
> > +}
> 
> > @@ -909,22 +959,19 @@ N_("It took %.2f seconds to check forced updates. You can use\n"
> >  static int store_updated_refs(const char *raw_url, const char *remote_name,
> >  			      int connectivity_checked, struct ref *ref_map)
> >  {
> > -	FILE *fp;
> > +	struct fetch_head fetch_head;
> 
> And that is why this variable is left uninitialised on stack and it
> is OK.  An alternative design would be to initialize fetch_head.fp
> to NULL, and return early with "if (!fetch_head->fp)" in the two
> functions that take fetch_head struct.  That way, we have less
> reliance on the global variable write_fetch_head.

I like your proposal more. I wasn't quite happy with leaving `fp`
uninitialized, and using it as a sentinel for whether to write something
or not feels natural to me.

[snip]
> > @@ -1016,16 +1063,10 @@ static int store_updated_refs(const char *raw_url, const char *remote_name,
> >  				merge_status_marker = "not-for-merge";
> >  				/* fall-through */
> >  			case FETCH_HEAD_MERGE:
> > -				fprintf(fp, "%s\t%s\t%s",
> > -					oid_to_hex(&rm->old_oid),
> > -					merge_status_marker,
> > -					note.buf);
> > -				for (i = 0; i < url_len; ++i)
> > -					if ('\n' == url[i])
> > -						fputs("\\n", fp);
> > -					else
> > -						fputc(url[i], fp);
> > -				fputc('\n', fp);
> > +				append_fetch_head(&fetch_head,
> > +						  oid_to_hex(&rm->old_oid),
> > +						  merge_status_marker,
> > +						  note.buf, url, url_len);
> 
> Here, we can lose merge_status_marker variable from this caller, and
> then this caller becomes:
> 
> 		switch (rm->fetch_head_status) {
> 		case FETCH_HEAD_NOT_FOR_MERGE:
> 		case FETCH_HEAD_MERGE:
> 			append_fetch_head(&fetch_head, &rm->old_oid,
> 				rm->fetch_head_status == FETCH_HEAD_MERGE,
>                                 note.buf, url, url_len);
> 
> Note that I am passing "is this a ref to be merged?" boolean to keep
> the exact string of "not-for-merge" in the callee.

As said above, I'm just moving this complete switch into
`append_fetch_head` and pass `rm->fetch_head_status`.

Patrick