* ref-filter: how to improve the code
@ 2018-02-25 18:28 Оля Тележная
2018-02-28 13:25 ` Jeff King
0 siblings, 1 reply; 4+ messages in thread
From: Оля Тележная @ 2018-02-25 18:28 UTC (permalink / raw)
To: git, Junio C Hamano; +Cc: Jeff King, Christian Couder
Hi everyone,
I am trying to remove cat-file formatting part and reuse same
functionality from ref-filter.
I have a problem that cat-file sometimes needs to continue running
even if the request is broken, while in ref-filter we invoke die() in
many places everywhere during formatting process. I write this email
because I want to discuss how to implement the solution better.
ref-filter has 2 functions which could be interesting for us:
format_ref_array_item() and show_ref_array_item(). I guess it's a good
idea to print everything in show_ref_array_item(), including all
errors. In that case all current users of ref-filter will invoke
show_ref_array_item() (as they did it before), and cat-file could use
format_ref_array_item() and work with the result in its own logic.
I tried to replace all die("...") with `return error("...")` and
finally exit(), but actual problem is that we print "error:..."
instead of "fatal:...", and it looks funny.
The draft of the code is here: https://github.com/telezhnaya/git/commits/p2
One of the easiest solutions is to add strbuf parameter for errors to
all functions that we use during formatting process, fill it in and
print in show_ref_array_item() if necessary. What do you think about
this idea?
Another way is to change the resulting error message, print current
message with "error" prefix and then print something like "fatal:
could not format the output". It is easier but I am not sure that it's
a good idea to change the interface.
If you have another ideas - please share them with me. It is really
important step to make formatting logic more general and easier to
reuse.
Thanks!
Olga
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: ref-filter: how to improve the code
2018-02-25 18:28 ref-filter: how to improve the code Оля Тележная
@ 2018-02-28 13:25 ` Jeff King
2018-03-01 11:17 ` Оля Тележная
0 siblings, 1 reply; 4+ messages in thread
From: Jeff King @ 2018-02-28 13:25 UTC (permalink / raw)
To: Оля Тележная
Cc: git, Junio C Hamano, Christian Couder
On Sun, Feb 25, 2018 at 09:28:25PM +0300, Оля Тележная wrote:
> I am trying to remove cat-file formatting part and reuse same
> functionality from ref-filter.
> I have a problem that cat-file sometimes needs to continue running
> even if the request is broken, while in ref-filter we invoke die() in
> many places everywhere during formatting process. I write this email
> because I want to discuss how to implement the solution better.
>
> ref-filter has 2 functions which could be interesting for us:
> format_ref_array_item() and show_ref_array_item(). I guess it's a good
> idea to print everything in show_ref_array_item(), including all
> errors. In that case all current users of ref-filter will invoke
> show_ref_array_item() (as they did it before), and cat-file could use
> format_ref_array_item() and work with the result in its own logic.
Yes, that arrangement makes sense to me.
> I tried to replace all die("...") with `return error("...")` and
> finally exit(), but actual problem is that we print "error:..."
> instead of "fatal:...", and it looks funny.
If you do that, then format_ref_array_item() is still going to print
things, even if it doesn't die(). But for "cat-file --batch", we usually
do not print errors at all, but instead just say "... missing" (although
it depends on the error; syntactic errors in the format string would
still cause us to write to stderr).
> One of the easiest solutions is to add strbuf parameter for errors to
> all functions that we use during formatting process, fill it in and
> print in show_ref_array_item() if necessary. What do you think about
> this idea?
>
> Another way is to change the resulting error message, print current
> message with "error" prefix and then print something like "fatal:
> could not format the output". It is easier but I am not sure that it's
> a good idea to change the interface.
For reference, the first one is what we've been switching to in the refs
code. And I think it's been fairly successful there.
-Peff
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: ref-filter: how to improve the code
2018-02-28 13:25 ` Jeff King
@ 2018-03-01 11:17 ` Оля Тележная
2018-03-01 15:04 ` Jeff King
0 siblings, 1 reply; 4+ messages in thread
From: Оля Тележная @ 2018-03-01 11:17 UTC (permalink / raw)
To: Jeff King; +Cc: git, Junio C Hamano, Christian Couder
2018-02-28 16:25 GMT+03:00 Jeff King <peff@peff.net>:
> On Sun, Feb 25, 2018 at 09:28:25PM +0300, Оля Тележная wrote:
>
>> I am trying to remove cat-file formatting part and reuse same
>> functionality from ref-filter.
>> I have a problem that cat-file sometimes needs to continue running
>> even if the request is broken, while in ref-filter we invoke die() in
>> many places everywhere during formatting process. I write this email
>> because I want to discuss how to implement the solution better.
>>
>> ref-filter has 2 functions which could be interesting for us:
>> format_ref_array_item() and show_ref_array_item(). I guess it's a good
>> idea to print everything in show_ref_array_item(), including all
>> errors. In that case all current users of ref-filter will invoke
>> show_ref_array_item() (as they did it before), and cat-file could use
>> format_ref_array_item() and work with the result in its own logic.
>
> Yes, that arrangement makes sense to me.
>
>> I tried to replace all die("...") with `return error("...")` and
>> finally exit(), but actual problem is that we print "error:..."
>> instead of "fatal:...", and it looks funny.
>
> If you do that, then format_ref_array_item() is still going to print
> things, even if it doesn't die(). But for "cat-file --batch", we usually
> do not print errors at all, but instead just say "... missing" (although
> it depends on the error; syntactic errors in the format string would
> still cause us to write to stderr).
Not sure if you catch my idea. format_ref_array_item() will not print
anything, it will just return an error code. And if there was an error
- we will print it in show_ref_array_item() (or go back to cat-file
and print what we want).
>
>> One of the easiest solutions is to add strbuf parameter for errors to
>> all functions that we use during formatting process, fill it in and
>> print in show_ref_array_item() if necessary. What do you think about
>> this idea?
>>
>> Another way is to change the resulting error message, print current
>> message with "error" prefix and then print something like "fatal:
>> could not format the output". It is easier but I am not sure that it's
>> a good idea to change the interface.
>
> For reference, the first one is what we've been switching to in the refs
> code. And I think it's been fairly successful there.
>
> -Peff
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: ref-filter: how to improve the code
2018-03-01 11:17 ` Оля Тележная
@ 2018-03-01 15:04 ` Jeff King
0 siblings, 0 replies; 4+ messages in thread
From: Jeff King @ 2018-03-01 15:04 UTC (permalink / raw)
To: Оля Тележная
Cc: git, Junio C Hamano, Christian Couder
On Thu, Mar 01, 2018 at 02:17:09PM +0300, Оля Тележная wrote:
> >> I tried to replace all die("...") with `return error("...")` and
> >> finally exit(), but actual problem is that we print "error:..."
> >> instead of "fatal:...", and it looks funny.
> >
> > If you do that, then format_ref_array_item() is still going to print
> > things, even if it doesn't die(). But for "cat-file --batch", we usually
> > do not print errors at all, but instead just say "... missing" (although
> > it depends on the error; syntactic errors in the format string would
> > still cause us to write to stderr).
>
> Not sure if you catch my idea. format_ref_array_item() will not print
> anything, it will just return an error code. And if there was an error
> - we will print it in show_ref_array_item() (or go back to cat-file
> and print what we want).
OK, I think I misunderstood. It seems like there are three possible
strategies on the table:
- low-level functions call error() and return -1, that gets passed up
through mid-level functions like format_ref_array_item(), and then
higher-level functions like show_ref_array_item() act on the error
code and call die(). The user sees something like:
error: unable to parse object 1234abcd
fatal: unable to format object
- low-level functions return a numeric error code, which is then
formatted by higher-level functions like show_ref_array_item() to
produce a specific message
- low-level functions stuff an error code into a strbuf and return -1,
and then higher-level functions like show_ref_array_item() will feed
that message to die("%s", err.buf).
I think the first one, besides changing the output, is going to produce
error() messages even for cases where we're calling
format_ref_array_item() directly, because error() writes its output
immediately.
The second is a pain in practice, because it doubles the work: you have
to come up with a list of error codes, and then translate it them into
strings. And there's no room to mention variable strings (like the name
of the object).
So I think the third is really the only viable option.
-Peff
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2018-03-01 15:04 UTC | newest]
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2018-02-25 18:28 ref-filter: how to improve the code Оля Тележная
2018-02-28 13:25 ` Jeff King
2018-03-01 11:17 ` Оля Тележная
2018-03-01 15:04 ` Jeff King
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