[llvm-dev] [cfe-dev] [RFC] Adding support for clang-format making further code modifying changes

[Renato Golin via llvm-dev]

On Tue, 10 Aug 2021 at 15:55, Manuel Klimek via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> I agree that that was probably not obvious or stated very clearly anywhere
> - clang-format for years was basically developed by a small team without
> much interest in input by the rest of the world, for a very specific use
> case.
> At the time we did not do a great job at spreading our thoughts with the
> world, as a lot of discussions were in person.
>

I think there's more to that than what was created by the people who
created it.

After being used extensively by people around the world, clang-format has
perhaps grown to something that the original team did not envision.

However, as a public clang tool, and as part of the LLVM "family", it's no
longer "a tool used by the team that created it", and not even "a tool used
by LLVM developers". It is truly a public tool maintained by the LLVM
community.

As such, I think we shouldn't restrict the design goals to the original
design, or to what a small sub-group uses it for. Clang-format is an
official tool like other visible stuff and should have the same community
oversight as everything else.

There is a high demand for a formatting tool that can do so much more than
the original design and people have been using it, albeit precariously, for
that purpose already.

So I believe the original policy that "breaking changes are a benefit" can
still be valid in a number of places, but it does not (and should not) need
to be the only valid case. Definitely not the default, either.

I think we need to take a step back and ask users what they expect, rather
than push forward a policy that people never really wanted but coped with
it anyway because there's nothing better.

FWIW, borrowing suggestions from others in this thread, I propose we change
the policy to:
 * Breaking changes off by default, override behaviour with configuration
files
 * All behaviour must be controlled by a configuration flag with options
explicit on doc/config
 * Make explicit some options are breaking (comment/naming)
 * Backwards compatibility is pursued, but can be broken in case of clear
bugs

An easy way to manage the configuration in this case is to have a dump
function (`clang-format --dump --config foo.cfg`) that reads a config file
and dumps all missing parameters and their current values.

Inline comments would be nice but make configuration management hard, so
there could be a webpage that describes all options and the URL is dumped
on the config file.

cheers,
--renato
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