On Mon, May 16 2022, Derrick Stolee wrote:
> On 5/12/2022 7:39 PM, Junio C Hamano wrote:
> [...]
> This switch statement was recently added to make it clear that
> unpack_loose_header() returns an enum value, not an int. This adds
> complications for future developers if that enum gains new values, since
> that developer would need to add a case statement to this switch for
> little real value.
>
> Instead, we can revert back to an 'if' statement, but make the enum
> explicit by using "!= ULHR_OK" instead of assuming it has the numerical
> value zero.
>
> Co-authored-by: Junio C Hamano <gitster@xxxxxxxxx>
> Signed-off-by: Derrick Stolee <derrickstolee@xxxxxxxxxx>
> ---
>
> object-file.c | 8 ++------
> 1 file changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/object-file.c b/object-file.c
> index b5d1d12b68a..52e4ae1b5f0 100644
> --- a/object-file.c
> +++ b/object-file.c
> @@ -2623,12 +2623,8 @@ int read_loose_object(const char *path,
> goto out;
> }
>
> - switch (unpack_loose_header(&stream, map, mapsize, hdr, sizeof(hdr),
> - NULL)) {
> - case ULHR_OK:
> - break;
> - case ULHR_BAD:
> - case ULHR_TOO_LONG:
> + if (unpack_loose_header(&stream, map, mapsize, hdr, sizeof(hdr),
> + NULL) != ULHR_OK) {
> error(_("unable to unpack header of %s"), path);
> goto out;
> }
This whole topic-at-large is a stylistic fix-up for a case where I
obviously got it wrong, so take this with a double grain of salt.
Re the "What's Cooking" mention of
ds/object-file-unpack-loose-header-fix: I don't mind it being merged
down at all. The below is all small potatoes.
I don't think the rationale ("adds complications for future
developers") makes sense in this case.
Let's leave aside the question of whether we exhaustively check enum
arms as in the pre-image, or check "not ok" as in the post-image.
Surely we can agree that whatever pattern is preferred we're better
off consistently picking one or the other?
I think this proposed change would make more sense and be in line with
its commit message if it also proposed this:
diff --git a/streaming.c b/streaming.c
index fe54665d86e..bb4ed198463 100644
--- a/streaming.c
+++ b/streaming.c
@@ -230,15 +230,10 @@ static int open_istream_loose(struct git_istream *st, struct repository *r,
st->u.loose.mapped = map_loose_object(r, oid, &st->u.loose.mapsize);
if (!st->u.loose.mapped)
return -1;
- switch (unpack_loose_header(&st->z, st->u.loose.mapped,
- st->u.loose.mapsize, st->u.loose.hdr,
- sizeof(st->u.loose.hdr), NULL)) {
- case ULHR_OK:
- break;
- case ULHR_BAD:
- case ULHR_TOO_LONG:
+ if (unpack_loose_header(&st->z, st->u.loose.mapped,
+ st->u.loose.mapsize, st->u.loose.hdr,
+ sizeof(st->u.loose.hdr), NULL) != ULHR_OK)
goto error;
- }
if (parse_loose_header(st->u.loose.hdr, &oi) < 0 || *type < 0)
goto error;
I.e. now we've converted the 2/3 callers of the API that only cared
about "not OK", there's a third one that cares about all the enum arms
currently, so that one remains a "switch".
The reason I think the rationale doesn't make sense is because of this
inconsistency. I.e. if we suppose a developer adds another enum value,
they'll then discover those three callers.
Surely whatever our preference for how to handle those 2/3 callers
it's less complicated if they don't use different patterns for no
obvious reason.
But anyway. Looking a bit deeper at this code again I think these two
patches are where we'd eventually want to head with this API. I.e. I
think the whole business of making this a tri-state return was
premature on my part.
After this RFC unpack_loose_header() is again a function that returns
a negative value on error, and the enum is gone. As noted in 2/2
there's a slight trade-off there, which I think is for the better,
both in terms of API simplicity, and in the new "error" output we'll
omit in these obscure cases. I.e.:
- error: header for $bogus_long_sha1 too long, exceeds 32 bytes
+ error: header too long, exceeds 32 bytes
+ error: unable to unpack $bogus_long_sha1 header
This whole "switch" complexity was because the old error message
wanted to note the OID in the "header too long" message.
Again, I'm perfectly fine with ds/object-file-unpack-loose-header-fix
advancing to "next", I can rebase this on top, or drop it depending on
the consensus about whether it's worthwile. I did want to un-block
that topic one way or the other, so to the extent that it was waiting
on my feedback...
Ævar Arnfjörð Bjarmason (2):
object-file API: fix obscure unpack_loose_header() return
object-file API: have unpack_loose_header() return "int" again
cache.h | 25 +++++-------------------
object-file.c | 46 +++++++++++++++++----------------------------
streaming.c | 11 +++--------
t/t1006-cat-file.sh | 6 ++++--
4 files changed, 29 insertions(+), 59 deletions(-)
--
2.36.1.957.g2c13267e09b
