Xen Coding style

Xen Coding style

[Julien Grall]

Hi all,

This was originally discussed during the last community call.

A major part of the comments during review is related to coding style 
issues. This can lead to frustration from the contributor as the current 
CODING_STYLE is quite light and the choice often down to a matter of 
taste from the maintainers.

In the past, Lars tried to address the problem by introducing a coding 
style checker (see [1] and [2]). However, the work came to stop because 
we couldn't agree on what is Xen coding style.

I would like to suggest a different approach. Rather than trying to 
agree on all the rules one by one, I propose to have a vote on different 
coding styles and pick the preferred one.

The list of coding styles would come from the community. It could be 
coding styles already used in the open source community or new coding 
styles (for instance a contributor could write down his/her 
understanding of Xen Coding Style).

Are the committers happy with this appraoch? If so, I could send a 
formal call for coding style?

Cheers,

[1] <20190718144317.23307-1-tamas@tklengyel.com>
[2] <CAOcoXZavLnHhNc7mmHnO5Gi_vq-0j1FCgvpXh0NimAewXX8e1g@mail.gmail.com>

Re: Xen Coding style

[Jan Beulich]

On 07.05.2020 16:43, Julien Grall wrote:
> This was originally discussed during the last community call.
> 
> A major part of the comments during review is related to coding style issues. This can lead to frustration from the contributor as the current CODING_STYLE is quite light and the choice often down to a matter of taste from the maintainers.
> 
> In the past, Lars tried to address the problem by introducing a coding style checker (see [1] and [2]). However, the work came to stop because we couldn't agree on what is Xen coding style.
> 
> I would like to suggest a different approach. Rather than trying to agree on all the rules one by one, I propose to have a vote on different coding styles and pick the preferred one.
> 
> The list of coding styles would come from the community. It could be coding styles already used in the open source community or new coding styles (for instance a contributor could write down his/her understanding of Xen Coding Style).
> 
> Are the committers happy with this appraoch?

I'm not, sorry, and I'm pretty sure I indicated so before. For one I
don't think picking an arbitrary other style than what we currently use
is going to be helpful: It'll be a significant amount of code churn all
over the code base. Instead I think the basic current principle should
remain: Imported files, if not heavily changed, are permitted to retain
their original style, while "our" files get written in "our" style.
(Recording which one's which is still tbd.)

I don't think though this necessarily implies "to agree on all the rules
one by one" - we could also settle on there explicitly being freedom
beyond what's spelled out explicitly. I'd not be happy with this, as it
would lead to a lot of inconsistencies over time, but it's still an
option. Obviously there's the wide range of middle ground to agree on
some more rules to become written down (I did propose a few over time,
without - iirc - getting helpful, if any, feedback), while leaving the
rest up to the author.

The main thing we need to settle on imo is whether unwritten rules
count. Me being picky isn't because of me liking to be, but because of
me thinking that a consistent code base is quite helpful. If consensus
is that consistency is not a goal, I'll accept this (with some
grumbling).

Jan

Re: Xen Coding style

[Julien Grall]

On 08/05/2020 09:36, Jan Beulich wrote:
> On 07.05.2020 16:43, Julien Grall wrote:
>> This was originally discussed during the last community call.
>>
>> A major part of the comments during review is related to coding style issues. This can lead to frustration from the contributor as the current CODING_STYLE is quite light and the choice often down to a matter of taste from the maintainers.
>>
>> In the past, Lars tried to address the problem by introducing a coding style checker (see [1] and [2]). However, the work came to stop because we couldn't agree on what is Xen coding style.
>>
>> I would like to suggest a different approach. Rather than trying to agree on all the rules one by one, I propose to have a vote on different coding styles and pick the preferred one.
>>
>> The list of coding styles would come from the community. It could be coding styles already used in the open source community or new coding styles (for instance a contributor could write down his/her understanding of Xen Coding Style).
>>
>> Are the committers happy with this appraoch?
> 
> I'm not, sorry, and I'm pretty sure I indicated so before. For one I
> don't think picking an arbitrary other style than what we currently use
> is going to be helpful: It'll be a significant amount of code churn all
> over the code base. Instead I think the basic current principle should
> remain: Imported files, if not heavily changed, are permitted to retain
> their original style, while "our" files get written in "our" style.
> (Recording which one's which is still tbd.)

There are existing coding styles that are quite close to the one used by 
Xen (such as BSD). We could either use them as-is or make small changes 
to fit Xen.

> 
> I don't think though this necessarily implies "to agree on all the rules
> one by one" - we could also settle on there explicitly being freedom
> beyond what's spelled out explicitly. I'd not be happy with this, as it
> would lead to a lot of inconsistencies over time, but it's still an
> option. Obviously there's the wide range of middle ground to agree on
> some more rules to become written down (I did propose a few over time,
> without - iirc - getting helpful, if any, feedback), while leaving the
> rest up to the author.
> 
> The main thing we need to settle on imo is whether unwritten rules
> count. Me being picky isn't because of me liking to be, but because of
> me thinking that a consistent code base is quite helpful. If consensus
> is that consistency is not a goal, I'll accept this (with some
> grumbling).

Consistency is important, but this should not be based on unwritten 
rules. We should be able to write a script that can check whether a 
patch contain any violations.

The end goal is to reduce the workload on the reviewer and the tension 
within the community.

You seem to be the maintainer with the most unwritten rules. Would you 
mind to have a try at writing a coding style based on it?

Cheers,

-- 
Julien Grall

Re: Xen Coding style

[Jan Beulich]

On 08.05.2020 12:00, Julien Grall wrote:
> You seem to be the maintainer with the most unwritten rules. Would
> you mind to have a try at writing a coding style based on it?

On the basis that even small, single aspect patches to CODING_STYLE
have been ignored [1], I don't think this would be a good use of my
time. If I was promised (reasonable) feedback, I could take what I
have and try to add at least a few more things based on what I find
myself commenting on more frequently. But really I'd prefer it to
be done the other way around - for people to look at the patches
already sent, and for me to only subsequently send more. After all,
if already those adjustments are controversial, I don't think we
could settle on others.

Jan

[1] https://lists.xenproject.org/archives/html/xen-devel/2019-07/msg01234.html

Re: Xen Coding style

[Julien Grall]

Hi Jan,

On 08/05/2020 12:20, Jan Beulich wrote:
> On 08.05.2020 12:00, Julien Grall wrote:
>> You seem to be the maintainer with the most unwritten rules. Would
>> you mind to have a try at writing a coding style based on it?
> 
> On the basis that even small, single aspect patches to CODING_STYLE
> have been ignored [1],

Your thread is one of the example why I started this thread. Agreeing on 
specific rule doesn't work because it either result to bikesheding or 
there is not enough interest to review rule by rule.

> I don't think this would be a good use of my
> time.

I would have assumed that the current situation (i.e 
nitpicking/bikeshedding on the ML) is not a good use of your time :).

I would be happy to put some effort to help getting the coding style 
right, however I believe focusing on an overall coding style would value 
everyone's time better than a rule by rule discussion.

> If I was promised (reasonable) feedback, I could take what I
> have and try to add at least a few more things based on what I find
> myself commenting on more frequently. But really I'd prefer it to
> be done the other way around - for people to look at the patches
> already sent, and for me to only subsequently send more. After all,
> if already those adjustments are controversial, I don't think we
> could settle on others.
While I understand this requires another investment from your part, I am 
afraid it is going to be painful for someone else to go through all the 
existing coding style bikeshedding and infer your unwritten rules.

It might be more beneficial for that person to pursue the work done by 
Tamas and Viktor in the past (see my previous e-mail). This may mean to 
adopt an existing coding style (BSD) and then tweak it.

Cheers,

-- 
Julien Grall

Re: Xen Coding style

[Tamas K Lengyel]

On Fri, May 8, 2020 at 6:21 AM Julien Grall <julien@xen.org> wrote:
>
> Hi Jan,
>
> On 08/05/2020 12:20, Jan Beulich wrote:
> > On 08.05.2020 12:00, Julien Grall wrote:
> >> You seem to be the maintainer with the most unwritten rules. Would
> >> you mind to have a try at writing a coding style based on it?
> >
> > On the basis that even small, single aspect patches to CODING_STYLE
> > have been ignored [1],
>
> Your thread is one of the example why I started this thread. Agreeing on
> specific rule doesn't work because it either result to bikesheding or
> there is not enough interest to review rule by rule.
>
> > I don't think this would be a good use of my
> > time.
>
> I would have assumed that the current situation (i.e
> nitpicking/bikeshedding on the ML) is not a good use of your time :).
>
> I would be happy to put some effort to help getting the coding style
> right, however I believe focusing on an overall coding style would value
> everyone's time better than a rule by rule discussion.
>
> > If I was promised (reasonable) feedback, I could take what I
> > have and try to add at least a few more things based on what I find
> > myself commenting on more frequently. But really I'd prefer it to
> > be done the other way around - for people to look at the patches
> > already sent, and for me to only subsequently send more. After all,
> > if already those adjustments are controversial, I don't think we
> > could settle on others.
> While I understand this requires another investment from your part, I am
> afraid it is going to be painful for someone else to go through all the
> existing coding style bikeshedding and infer your unwritten rules.
>
> It might be more beneficial for that person to pursue the work done by
> Tamas and Viktor in the past (see my previous e-mail). This may mean to
> adopt an existing coding style (BSD) and then tweak it.

Thanks Julien for restarting this discussion. IMHO agreeing on a set
of style rules ahead and then applying universally all at once is not
going to be productive since we are so all over the place. Instead, I
would recommend we start piece-by-piece. We introduce a baseline style
checker, then maintainers can decide when and if they want to move
their code-base to be under the automated style checker. That way we
have a baseline and each maintainer can decide on their own term when
they want to have their files be also style checked and in what form.
The upside of this route I think is pretty clear: we can have at least
partial automation even while we figure out what to do with some of
the more problematic files and quirks that are in our code-base. I
would highly prefer this route since I would immediately bring all
files I maintain over to the automated checker just so I never ever
have to deal with this again manually. What style is in use to me
really doesn't matter, BSD was very close with some minor tweaks, or
even what we use to check the style just as long as we have
_something_.

Cheers,
Tamas

Re: Xen Coding style

[Jürgen Groß]

On 08.05.20 14:55, Tamas K Lengyel wrote:
> On Fri, May 8, 2020 at 6:21 AM Julien Grall <julien@xen.org> wrote:
>>
>> Hi Jan,
>>
>> On 08/05/2020 12:20, Jan Beulich wrote:
>>> On 08.05.2020 12:00, Julien Grall wrote:
>>>> You seem to be the maintainer with the most unwritten rules. Would
>>>> you mind to have a try at writing a coding style based on it?
>>>
>>> On the basis that even small, single aspect patches to CODING_STYLE
>>> have been ignored [1],
>>
>> Your thread is one of the example why I started this thread. Agreeing on
>> specific rule doesn't work because it either result to bikesheding or
>> there is not enough interest to review rule by rule.
>>
>>> I don't think this would be a good use of my
>>> time.
>>
>> I would have assumed that the current situation (i.e
>> nitpicking/bikeshedding on the ML) is not a good use of your time :).
>>
>> I would be happy to put some effort to help getting the coding style
>> right, however I believe focusing on an overall coding style would value
>> everyone's time better than a rule by rule discussion.
>>
>>> If I was promised (reasonable) feedback, I could take what I
>>> have and try to add at least a few more things based on what I find
>>> myself commenting on more frequently. But really I'd prefer it to
>>> be done the other way around - for people to look at the patches
>>> already sent, and for me to only subsequently send more. After all,
>>> if already those adjustments are controversial, I don't think we
>>> could settle on others.
>> While I understand this requires another investment from your part, I am
>> afraid it is going to be painful for someone else to go through all the
>> existing coding style bikeshedding and infer your unwritten rules.
>>
>> It might be more beneficial for that person to pursue the work done by
>> Tamas and Viktor in the past (see my previous e-mail). This may mean to
>> adopt an existing coding style (BSD) and then tweak it.
> 
> Thanks Julien for restarting this discussion. IMHO agreeing on a set
> of style rules ahead and then applying universally all at once is not
> going to be productive since we are so all over the place. Instead, I
> would recommend we start piece-by-piece. We introduce a baseline style
> checker, then maintainers can decide when and if they want to move
> their code-base to be under the automated style checker. That way we
> have a baseline and each maintainer can decide on their own term when
> they want to have their files be also style checked and in what form.
> The upside of this route I think is pretty clear: we can have at least
> partial automation even while we figure out what to do with some of
> the more problematic files and quirks that are in our code-base. I
> would highly prefer this route since I would immediately bring all
> files I maintain over to the automated checker just so I never ever
> have to deal with this again manually. What style is in use to me
> really doesn't matter, BSD was very close with some minor tweaks, or
> even what we use to check the style just as long as we have
> _something_.

Wouldn't it make more sense to have a patch checker instead and accept
only patches which change code according to the style guide? This
wouldn't require to change complete files at a time.


Juergen

Re: Xen Coding style

[Tamas K Lengyel]

On Fri, May 8, 2020 at 8:18 AM Jürgen Groß <jgross@suse.com> wrote:
>
> On 08.05.20 14:55, Tamas K Lengyel wrote:
> > On Fri, May 8, 2020 at 6:21 AM Julien Grall <julien@xen.org> wrote:
> >>
> >> Hi Jan,
> >>
> >> On 08/05/2020 12:20, Jan Beulich wrote:
> >>> On 08.05.2020 12:00, Julien Grall wrote:
> >>>> You seem to be the maintainer with the most unwritten rules. Would
> >>>> you mind to have a try at writing a coding style based on it?
> >>>
> >>> On the basis that even small, single aspect patches to CODING_STYLE
> >>> have been ignored [1],
> >>
> >> Your thread is one of the example why I started this thread. Agreeing on
> >> specific rule doesn't work because it either result to bikesheding or
> >> there is not enough interest to review rule by rule.
> >>
> >>> I don't think this would be a good use of my
> >>> time.
> >>
> >> I would have assumed that the current situation (i.e
> >> nitpicking/bikeshedding on the ML) is not a good use of your time :).
> >>
> >> I would be happy to put some effort to help getting the coding style
> >> right, however I believe focusing on an overall coding style would value
> >> everyone's time better than a rule by rule discussion.
> >>
> >>> If I was promised (reasonable) feedback, I could take what I
> >>> have and try to add at least a few more things based on what I find
> >>> myself commenting on more frequently. But really I'd prefer it to
> >>> be done the other way around - for people to look at the patches
> >>> already sent, and for me to only subsequently send more. After all,
> >>> if already those adjustments are controversial, I don't think we
> >>> could settle on others.
> >> While I understand this requires another investment from your part, I am
> >> afraid it is going to be painful for someone else to go through all the
> >> existing coding style bikeshedding and infer your unwritten rules.
> >>
> >> It might be more beneficial for that person to pursue the work done by
> >> Tamas and Viktor in the past (see my previous e-mail). This may mean to
> >> adopt an existing coding style (BSD) and then tweak it.
> >
> > Thanks Julien for restarting this discussion. IMHO agreeing on a set
> > of style rules ahead and then applying universally all at once is not
> > going to be productive since we are so all over the place. Instead, I
> > would recommend we start piece-by-piece. We introduce a baseline style
> > checker, then maintainers can decide when and if they want to move
> > their code-base to be under the automated style checker. That way we
> > have a baseline and each maintainer can decide on their own term when
> > they want to have their files be also style checked and in what form.
> > The upside of this route I think is pretty clear: we can have at least
> > partial automation even while we figure out what to do with some of
> > the more problematic files and quirks that are in our code-base. I
> > would highly prefer this route since I would immediately bring all
> > files I maintain over to the automated checker just so I never ever
> > have to deal with this again manually. What style is in use to me
> > really doesn't matter, BSD was very close with some minor tweaks, or
> > even what we use to check the style just as long as we have
> > _something_.
>
> Wouldn't it make more sense to have a patch checker instead and accept
> only patches which change code according to the style guide? This
> wouldn't require to change complete files at a time.

In theory, yes. But in practice this would require that we can agree
on a style that applies to all patches that touch any file within Xen.
We can't seem to do that because there are too many exceptions and
corner-cases and personal-preferences of maintainers that apply only
to a subset of the codebase. So AFAICT what you propose doesn't seem
to be a viable way to start.

Tamas

Re: Xen Coding style

[Jürgen Groß]

On 08.05.20 16:23, Tamas K Lengyel wrote:
> On Fri, May 8, 2020 at 8:18 AM Jürgen Groß <jgross@suse.com> wrote:
>>
>> On 08.05.20 14:55, Tamas K Lengyel wrote:
>>> On Fri, May 8, 2020 at 6:21 AM Julien Grall <julien@xen.org> wrote:
>>>>
>>>> Hi Jan,
>>>>
>>>> On 08/05/2020 12:20, Jan Beulich wrote:
>>>>> On 08.05.2020 12:00, Julien Grall wrote:
>>>>>> You seem to be the maintainer with the most unwritten rules. Would
>>>>>> you mind to have a try at writing a coding style based on it?
>>>>>
>>>>> On the basis that even small, single aspect patches to CODING_STYLE
>>>>> have been ignored [1],
>>>>
>>>> Your thread is one of the example why I started this thread. Agreeing on
>>>> specific rule doesn't work because it either result to bikesheding or
>>>> there is not enough interest to review rule by rule.
>>>>
>>>>> I don't think this would be a good use of my
>>>>> time.
>>>>
>>>> I would have assumed that the current situation (i.e
>>>> nitpicking/bikeshedding on the ML) is not a good use of your time :).
>>>>
>>>> I would be happy to put some effort to help getting the coding style
>>>> right, however I believe focusing on an overall coding style would value
>>>> everyone's time better than a rule by rule discussion.
>>>>
>>>>> If I was promised (reasonable) feedback, I could take what I
>>>>> have and try to add at least a few more things based on what I find
>>>>> myself commenting on more frequently. But really I'd prefer it to
>>>>> be done the other way around - for people to look at the patches
>>>>> already sent, and for me to only subsequently send more. After all,
>>>>> if already those adjustments are controversial, I don't think we
>>>>> could settle on others.
>>>> While I understand this requires another investment from your part, I am
>>>> afraid it is going to be painful for someone else to go through all the
>>>> existing coding style bikeshedding and infer your unwritten rules.
>>>>
>>>> It might be more beneficial for that person to pursue the work done by
>>>> Tamas and Viktor in the past (see my previous e-mail). This may mean to
>>>> adopt an existing coding style (BSD) and then tweak it.
>>>
>>> Thanks Julien for restarting this discussion. IMHO agreeing on a set
>>> of style rules ahead and then applying universally all at once is not
>>> going to be productive since we are so all over the place. Instead, I
>>> would recommend we start piece-by-piece. We introduce a baseline style
>>> checker, then maintainers can decide when and if they want to move
>>> their code-base to be under the automated style checker. That way we
>>> have a baseline and each maintainer can decide on their own term when
>>> they want to have their files be also style checked and in what form.
>>> The upside of this route I think is pretty clear: we can have at least
>>> partial automation even while we figure out what to do with some of
>>> the more problematic files and quirks that are in our code-base. I
>>> would highly prefer this route since I would immediately bring all
>>> files I maintain over to the automated checker just so I never ever
>>> have to deal with this again manually. What style is in use to me
>>> really doesn't matter, BSD was very close with some minor tweaks, or
>>> even what we use to check the style just as long as we have
>>> _something_.
>>
>> Wouldn't it make more sense to have a patch checker instead and accept
>> only patches which change code according to the style guide? This
>> wouldn't require to change complete files at a time.
> 
> In theory, yes. But in practice this would require that we can agree
> on a style that applies to all patches that touch any file within Xen.
> We can't seem to do that because there are too many exceptions and
> corner-cases and personal-preferences of maintainers that apply only
> to a subset of the codebase. So AFAICT what you propose doesn't seem
> to be a viable way to start.

I think long ago we already agreed to have a control file which tells a
style checker which style to apply (if any). As a start we could have a
patch checker checking only the commit message (has it a Signed-off-by:
etc.). The next step would be to add the control file, and the framework
to split the patch into the changed file hunks and passing each hunk to
the correct checking script (might be doing nothing in the beginning).
And then we could add some logic to the single checkers.


Juergen

Re: Xen Coding style

[Julien Grall]

On 08/05/2020 15:42, Jürgen Groß wrote:
> On 08.05.20 16:23, Tamas K Lengyel wrote:
>> On Fri, May 8, 2020 at 8:18 AM Jürgen Groß <jgross@suse.com> wrote:
>>>
>>> On 08.05.20 14:55, Tamas K Lengyel wrote:
>>>> On Fri, May 8, 2020 at 6:21 AM Julien Grall <julien@xen.org> wrote:
>>>>>
>>>>> Hi Jan,
>>>>>
>>>>> On 08/05/2020 12:20, Jan Beulich wrote:
>>>>>> On 08.05.2020 12:00, Julien Grall wrote:
>>>>>>> You seem to be the maintainer with the most unwritten rules. Would
>>>>>>> you mind to have a try at writing a coding style based on it?
>>>>>>
>>>>>> On the basis that even small, single aspect patches to CODING_STYLE
>>>>>> have been ignored [1],
>>>>>
>>>>> Your thread is one of the example why I started this thread. 
>>>>> Agreeing on
>>>>> specific rule doesn't work because it either result to bikesheding or
>>>>> there is not enough interest to review rule by rule.
>>>>>
>>>>>> I don't think this would be a good use of my
>>>>>> time.
>>>>>
>>>>> I would have assumed that the current situation (i.e
>>>>> nitpicking/bikeshedding on the ML) is not a good use of your time :).
>>>>>
>>>>> I would be happy to put some effort to help getting the coding style
>>>>> right, however I believe focusing on an overall coding style would 
>>>>> value
>>>>> everyone's time better than a rule by rule discussion.
>>>>>
>>>>>> If I was promised (reasonable) feedback, I could take what I
>>>>>> have and try to add at least a few more things based on what I find
>>>>>> myself commenting on more frequently. But really I'd prefer it to
>>>>>> be done the other way around - for people to look at the patches
>>>>>> already sent, and for me to only subsequently send more. After all,
>>>>>> if already those adjustments are controversial, I don't think we
>>>>>> could settle on others.
>>>>> While I understand this requires another investment from your part, 
>>>>> I am
>>>>> afraid it is going to be painful for someone else to go through all 
>>>>> the
>>>>> existing coding style bikeshedding and infer your unwritten rules.
>>>>>
>>>>> It might be more beneficial for that person to pursue the work done by
>>>>> Tamas and Viktor in the past (see my previous e-mail). This may 
>>>>> mean to
>>>>> adopt an existing coding style (BSD) and then tweak it.
>>>>
>>>> Thanks Julien for restarting this discussion. IMHO agreeing on a set
>>>> of style rules ahead and then applying universally all at once is not
>>>> going to be productive since we are so all over the place. Instead, I
>>>> would recommend we start piece-by-piece. We introduce a baseline style
>>>> checker, then maintainers can decide when and if they want to move
>>>> their code-base to be under the automated style checker. That way we
>>>> have a baseline and each maintainer can decide on their own term when
>>>> they want to have their files be also style checked and in what form.
>>>> The upside of this route I think is pretty clear: we can have at least
>>>> partial automation even while we figure out what to do with some of
>>>> the more problematic files and quirks that are in our code-base. I
>>>> would highly prefer this route since I would immediately bring all
>>>> files I maintain over to the automated checker just so I never ever
>>>> have to deal with this again manually. What style is in use to me
>>>> really doesn't matter, BSD was very close with some minor tweaks, or
>>>> even what we use to check the style just as long as we have
>>>> _something_.
>>>
>>> Wouldn't it make more sense to have a patch checker instead and accept
>>> only patches which change code according to the style guide? This
>>> wouldn't require to change complete files at a time.

So what are you going to do if a new contributor is unfortunate enough 
to modify code that doesn't pass the coding style checker? Are we going 
to impose him/her to fix the coding style before submitting his patch?

>>
>> In theory, yes. But in practice this would require that we can agree
>> on a style that applies to all patches that touch any file within Xen.
>> We can't seem to do that because there are too many exceptions and
>> corner-cases and personal-preferences of maintainers that apply only
>> to a subset of the codebase. So AFAICT what you propose doesn't seem
>> to be a viable way to start.
> 
> I think long ago we already agreed to have a control file which tells a
> style checker which style to apply (if any). As a start we could have a
> patch checker checking only the commit message (has it a Signed-off-by:
> etc.). The next step would be to add the control file, and the framework
> to split the patch into the changed file hunks and passing each hunk to
> the correct checking script (might be doing nothing in the beginning).
> And then we could add some logic to the single checkers.

Yes the framework can be written down now (patches are welcomed). But 
this doesn't resolve the underlying problem. Aside files imported from 
Linux, what is the coding style of Xen?

The best way to describe it at the moment is a collection of unwritten 
rules that can differ even between maintainers of the same component. I 
don't really see how we could write a style checker based on this.

The best way to reduce the burden on reviewer and bikeshedding is by 
formalizing what our coding style. With that, we can write a style 
checker effectively and all sort of other tools.

It would prefer to have a common one but we could consider small quirks 
per components if it is necessary.

Cheers,

-- 
Julien Grall

Re: Xen Coding style

[Jürgen Groß]

On 08.05.20 17:50, Julien Grall wrote:
> 
> 
> On 08/05/2020 15:42, Jürgen Groß wrote:
>> On 08.05.20 16:23, Tamas K Lengyel wrote:
>>> On Fri, May 8, 2020 at 8:18 AM Jürgen Groß <jgross@suse.com> wrote:
>>>>
>>>> On 08.05.20 14:55, Tamas K Lengyel wrote:
>>>>> On Fri, May 8, 2020 at 6:21 AM Julien Grall <julien@xen.org> wrote:
>>>>>>
>>>>>> Hi Jan,
>>>>>>
>>>>>> On 08/05/2020 12:20, Jan Beulich wrote:
>>>>>>> On 08.05.2020 12:00, Julien Grall wrote:
>>>>>>>> You seem to be the maintainer with the most unwritten rules. Would
>>>>>>>> you mind to have a try at writing a coding style based on it?
>>>>>>>
>>>>>>> On the basis that even small, single aspect patches to CODING_STYLE
>>>>>>> have been ignored [1],
>>>>>>
>>>>>> Your thread is one of the example why I started this thread. 
>>>>>> Agreeing on
>>>>>> specific rule doesn't work because it either result to bikesheding or
>>>>>> there is not enough interest to review rule by rule.
>>>>>>
>>>>>>> I don't think this would be a good use of my
>>>>>>> time.
>>>>>>
>>>>>> I would have assumed that the current situation (i.e
>>>>>> nitpicking/bikeshedding on the ML) is not a good use of your time :).
>>>>>>
>>>>>> I would be happy to put some effort to help getting the coding style
>>>>>> right, however I believe focusing on an overall coding style would 
>>>>>> value
>>>>>> everyone's time better than a rule by rule discussion.
>>>>>>
>>>>>>> If I was promised (reasonable) feedback, I could take what I
>>>>>>> have and try to add at least a few more things based on what I find
>>>>>>> myself commenting on more frequently. But really I'd prefer it to
>>>>>>> be done the other way around - for people to look at the patches
>>>>>>> already sent, and for me to only subsequently send more. After all,
>>>>>>> if already those adjustments are controversial, I don't think we
>>>>>>> could settle on others.
>>>>>> While I understand this requires another investment from your 
>>>>>> part, I am
>>>>>> afraid it is going to be painful for someone else to go through 
>>>>>> all the
>>>>>> existing coding style bikeshedding and infer your unwritten rules.
>>>>>>
>>>>>> It might be more beneficial for that person to pursue the work 
>>>>>> done by
>>>>>> Tamas and Viktor in the past (see my previous e-mail). This may 
>>>>>> mean to
>>>>>> adopt an existing coding style (BSD) and then tweak it.
>>>>>
>>>>> Thanks Julien for restarting this discussion. IMHO agreeing on a set
>>>>> of style rules ahead and then applying universally all at once is not
>>>>> going to be productive since we are so all over the place. Instead, I
>>>>> would recommend we start piece-by-piece. We introduce a baseline style
>>>>> checker, then maintainers can decide when and if they want to move
>>>>> their code-base to be under the automated style checker. That way we
>>>>> have a baseline and each maintainer can decide on their own term when
>>>>> they want to have their files be also style checked and in what form.
>>>>> The upside of this route I think is pretty clear: we can have at least
>>>>> partial automation even while we figure out what to do with some of
>>>>> the more problematic files and quirks that are in our code-base. I
>>>>> would highly prefer this route since I would immediately bring all
>>>>> files I maintain over to the automated checker just so I never ever
>>>>> have to deal with this again manually. What style is in use to me
>>>>> really doesn't matter, BSD was very close with some minor tweaks, or
>>>>> even what we use to check the style just as long as we have
>>>>> _something_.
>>>>
>>>> Wouldn't it make more sense to have a patch checker instead and accept
>>>> only patches which change code according to the style guide? This
>>>> wouldn't require to change complete files at a time.
> 
> So what are you going to do if a new contributor is unfortunate enough 
> to modify code that doesn't pass the coding style checker? Are we going 
> to impose him/her to fix the coding style before submitting his patch?

The modified portions should comply to the coding style. Same as in the
Linux kernel.

> 
>>>
>>> In theory, yes. But in practice this would require that we can agree
>>> on a style that applies to all patches that touch any file within Xen.
>>> We can't seem to do that because there are too many exceptions and
>>> corner-cases and personal-preferences of maintainers that apply only
>>> to a subset of the codebase. So AFAICT what you propose doesn't seem
>>> to be a viable way to start.
>>
>> I think long ago we already agreed to have a control file which tells a
>> style checker which style to apply (if any). As a start we could have a
>> patch checker checking only the commit message (has it a Signed-off-by:
>> etc.). The next step would be to add the control file, and the framework
>> to split the patch into the changed file hunks and passing each hunk to
>> the correct checking script (might be doing nothing in the beginning).
>> And then we could add some logic to the single checkers.
> 
> Yes the framework can be written down now (patches are welcomed). But 
> this doesn't resolve the underlying problem. Aside files imported from 
> Linux, what is the coding style of Xen?

The checker for Xen style needs to be written, yes.

> The best way to describe it at the moment is a collection of unwritten 
> rules that can differ even between maintainers of the same component. I 
> don't really see how we could write a style checker based on this.

The style checker's rules must be written down, of course.

And today there are already some rules documented.

> 
> The best way to reduce the burden on reviewer and bikeshedding is by 
> formalizing what our coding style. With that, we can write a style 
> checker effectively and all sort of other tools.

Correct. A checker should only check what is written down. Not more,
maybe less in the beginning.

> It would prefer to have a common one but we could consider small quirks 
> per components if it is necessary.

I would say: only Xen style, Linux kernel style, libxl style (why do we
have different styles in one project???), maybe BSD, and maybe no style
at all.

Ah yes, and Makefile style, doc style, Kconfig style, ...


Juergen