[llvm-dev] Change coding style for argument alignment?

[David Blaikie via llvm-dev]

(probably worth using a monospaced font when discussing indent styles in
HTML email, otherwise it's a bit hard to tell what's being discussed)

On Thu, Dec 3, 2020 at 1:33 PM Krzysztof Parzyszek via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> I support this proposal.  I very much dislike the current function
> parameter formatting (in function declarations/definitions).  It just adds
> a bunch of whitespace without improvement in readability.
>
>
>
> In practice there are already various mixtures of formatting being used.
> For example:
>
>
>
>   bool tailDuplicate(bool IsSimple,
>
>                      MachineBasicBlock *TailBB,
>
>                      MachineBasicBlock *ForcedLayoutPred,
>
>                      SmallVectorImpl<MachineBasicBlock *> &TDBBs,
>
>                      SmallVectorImpl<MachineInstr *> &Copies,
>
>                      SmallVectorImpl<MachineBasicBlock *> *CandidatePtr);
>
>   void appendCopies(MachineBasicBlock *MBB,
>
>                  SmallVectorImpl<std::pair<Register, RegSubRegPair>>
> &CopyInfos,
>
>                  SmallVectorImpl<MachineInstr *> &Copies);
>
>
>

Looks like "appendCopies" is the odd one out here. Probably someone didn't
reindent when the name was changed. Hmm, nope, it was checked in that way -
but it doesn't match any style I think we've ever had, so it's not really
an argument for/against any particular format - the author seems to have
uesd right alignment to fit the long name. (possible that our style guide
didn't or doesn't specify what to do when things are too long - but I think
generally, the answer is what's done for removeDeadBlock: Fallback to a
double indent from the start, and this is what clang-format does with its
LLVM style interpretation)


>   void removeDeadBlock(
>
>       MachineBasicBlock *MBB,
>
>       function_ref<void(MachineBasicBlock *)> *RemovalCallback = nullptr);
>
>
>
> These are 3 adjacent declarations in the same file
> (llvm/include/llvm/CodeGen/TailDuplicator.h).
>
>
>
>
>
> I don’t think that the alternative format would make call sites immune to
> renaming, since it can still cause fewer or more function arguments to fit
> in a given line of code.  I still think it’s a worthwhile change in style.
>

I don't have strong feelings either way - mostly of the opinion that it's a
"clang-format and forget about it" sort of thing. (which isn't to say
formatting issues can't rise to the level of "this is actively harmful to
readability of the code" but this one doesn't rise to that level from my
perspective at least)

- Dave


>
>
> --
>
> Krzysztof Parzyszek  kparzysz at quicinc.com   AI tools development
>
>
>
> *From:* llvm-dev <llvm-dev-bounces at lists.llvm.org> *On Behalf Of *Nikita
> Popov via llvm-dev
> *Sent:* Thursday, December 3, 2020 3:01 PM
> *To:* llvm-dev <llvm-dev at lists.llvm.org>
> *Subject:* [EXT] [llvm-dev] Change coding style for argument alignment?
>
>
>
> Hi,
>
>
>
> LLVM currently uses a coding style where arguments and parameters need to
> be aligned to the opening parenthesis "(".
>
>
>
>     someFunctionCall(Arg1, Arg2,
>
>                      Arg3, Arg4);
>
>
>
> This style guideline is unfortunate for a couple of reasons:
>
>
>
> 1. If a function is renamed, it is necessary to also reindent the
> arguments at all call-sites. For functions with many or complex arguments,
> this may require significant reflow.
>
>
>
> 2. It causes significant right-ward drift. Especially for declarations,
> it's somewhat common for code ending up like this...
>
>
>
>    Foo SomeClassName::someMethodName(Bar &Arg1,
>                                       Bar &Arg2,
>                                       Bar &Arg3,
>                                       Bar &Arg4) {
>
>
>
> ... because there is just enough space to fit each argument individually,
> but still a need to break each one out on a separate line. Closure
> arguments are another common case of very awkward formatting.
>
>
>
> 3. There are some arcane rules about when this is not the preferred style
> and you're supposed to indent arguments on the following line instead.
>
>
>
> Is there any chance that the style could be changed towards indenting (but
> not aligning) the following line instead?
>
>
>
>     someFunctionCall(
>
>         Arg1, Arg2, Arg3, Arg4);
>
>
>
> This is unaffected by renames, does not cause rightward drift and results
> in very predictable formatting.
>
>
>
> Based on past discussions, LLVM seems to be open to improving coding style
> for the better, so I thought I'd give this a shot, as this is a continuous
> source of friction for me.
>
>
>
> Regards,
>
> Nikita
> _______________________________________________
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> llvm-dev at lists.llvm.org
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>
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