Use autoformatting, enforced by CI

[certik]

@zbeekman wrote:

Best thing I've found so far is findent and eclint for Fortran. findent works off an actual AST and claims to test against all code examples in the latest Modern Fortran Explained by MRC, so it should be robust. Probably won't help with this particular style issue, but I haven't been using it in earnest yet as I just discovered it (and added it to Homebrew).

[zbeekman]

What about local pre-commit hooks too? The pre-commit project is pretty great.

I also think we should get an editorconfig file going asap

[certik]

What happens when people submit a PR without setting up pre commit hooks? For example by directly modifying files at GitHub and submitting the PR online?

[zbeekman]

We can have the PR run the pre-commit hooks during CI too... We could even have running CMake (or at build time) detect a build from git, see if the current author has made any commits and install hooks for them if they have... I'm happy to use it or not use it, but I've found it very helpful personally.

[certik]

Let's setup automatic formatting check on a CI:

• Use a tool (findent if it works)
• Write documentation how each developer can use it before submitting a PR
• Run this on CI for each PR and fail the tests if they are not formatted correctly
• If it is not formatted correctly, make a patch available somehow that the PR author can simply apply (in case they do not have the findent installed). Here is an example how to do that in SymEngine: https://github.com/symengine/symengine/blob/861c64569a3543744f166dc63b6ff574c7344b02/bin/travis_clang_format.sh

Later, let's also:

• Create a bot that will provide the correct patch. Here is an example PR that shows how it works: Add some small functions to the Expression class symengine/symengine#1530, I can't find a PR now where the formatting is incorrect (the bot provides copy & paste instructions how to fix it by downloading the patch and applying it).

[zbeekman]

Let's get some of those ready to merge PRs in before I start work on any of this. There are a bunch that are ready to ship. I'd merge them myself because I think everyone is in agreement, but I'm not part of the fortran-lang org.