[flang-dev] Code formatting alignment with LLVM

[Mehdi AMINI via flang-dev]

On Mon, Mar 2, 2020 at 7:08 AM David Truby via flang-dev <
flang-dev at lists.llvm.org> wrote:

> Hi all,
>
> Since we haven’t seen any movement on this in quite a while and our
> projected merge date is moving ever closer, I wonder if I could summarise
> the positions that have been given so far so we can decide on a way
> forward. If I misrepresent what you’ve stated at all please reply to
> correct me, I’m just trying to give a brief summary.
>
> I opened the discussion with a PR to see what the projected changes would
> look like; I did this for two reasons, firstly that we were requested to in
> a discussion about merging on llvm-dev, but also because I believe we
> should align with the rest of the community on a single coding style. My
> position is that I have no preference at all in what the style is, I just
> think there should be a single one across the community. My reason for
> thinking this is that fairly likely that changes to f18, mlir and llvm
> will be mixed in together once we land, and working on a single change that
> has multiple different coding styles within it may lead to some issues for
> anyone working on those.
>
> Tim Keith and Peter Klausler from Nvidia replied to say that comment
> alignment (and code alignment in general) cause spurious changes to a
> appear when submitting diffs, making it more difficult to see what has
> changed.
>

Can you clarify the concern here? If there is a one-time formatting of the
codebase now (LLDB did such a one-time formatting change to align with LLVM
a few years ago), then any future patches correctly formatted should not
have any spurious change right?


> Tim Keith also pointed out that clang and llvm are not properly
> clang-formatted entirely themselves, which weakens the “common code style
> across the board” desire.
>

It is worth noting that a lot of the codebase predates clang-format, when
there wasn't any tool to help formatting we could only rely on code review
and best effort.


> Eric Schweitz replied to show MLIR’s clang-format file, which is also the
> one used for the lib/Lower subdirectory of f18. This style has only one
> small change from the LLVM style, but it is nonetheless a diversion.
>
Eric also pointed out that clang-formatting for new code is enforced on
> Phabricator by pre-commit bots. This is the case not only for mlir, but for
> new code heading to clang and llvm too. This is consistent with the Coding
> Guidelines which do not require that all code is properly clang-formatted,
> only all new code. Eric also suggested that we could submit diffs without
> running clang-format, so that the changes are clear, and then once approved
> run clang-format to match the code with the rest of the project. This might
> mitigate the code alignment issues.
>

> Johannes Doerfert stated his preference for minimizing clang-format
> differences from the rest of the project, in part to ease our acceptance by
> the community. He also stated that he is used to the llvm settings and so
> anything different makes his workflow uneasy. I believe this goes hand in
> hand with my statement about working with different coding styles in a
> single change.
>
> On the F18 community call, Hal Finkel explained the reasoning behind the
> LLVM coding style decisions. He stated that LLVM prefers readability of
> code over writability (or reviewability) as code is much more likely to be
> read than written or reviewed. This is why LLVM uses code and comment
> alignment in its coding style. On the call it was also discussed that some
> people do not find that the alignment makes code easier to read and that
> this seems to be subjective.
>
> I think that this is the point the discussions have reached so far, if I
> have missed anything or misrepresented anyone’s position please reply to
> this to clarify.
>
> Given the impasse we have got to, I suggest that if we cannot find a
> compromise here we should take the discussion to llvm-dev and see how the
> wider community feels about a large diversion from the coding style for a
> specific sub-project. It may be that this is not a hard block for merging,
> however it is something that was requested of us initially so it is
> something we need to discuss there if we decide not to do it.
>
> I hope this helps to move the conversation forward.
>
> Thanks
> David Truby
>
> On 11 Feb 2020, at 10:20, David Truby via flang-dev <
> flang-dev at lists.llvm.org> wrote:
>
> Hi all,
>
> We have been having a discussion on the GitHub issue tracker about code
> formatting (and specifically clang-format settings) and whether to align
> closer with the rest of the project, which you can find here:
> https://github.com/flang-compiler/f18/pull/945. Since the discussion
> there hasn’t moved much recently I’d like to start a discussion here so we
> can get input from a wider group of people.
>
> My opinion is that regardless of technical preferences we shouldn’t
> diverge from the style of the rest of the project as much as we currently
> do, or at least if we want to do that then we should have a discussion with
> the wider community about whether that is acceptable to them.
>
> Does anyone else have any input on this?
>
> Thanks
> David Truby
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