[RFC] clang tooling cleanups

[Finn Thain]

On Tue, 27 Oct 2020, trix at redhat.com wrote:

> This rfc will describe
> An upcoming treewide cleanup.
> How clang tooling was used to programatically do the clean up.
> Solicit opinions on how to generally use clang tooling.
> 

This tooling is very impressive. It makes possible an idea that I had a 
while ago, to help make code review more efficient. It works like this. 

Suppose a patch, p, is the difference between the new tree, n, and the old 
tree, o. That is, p = n - o.

Now let clang-tidy be the transformation 't'. This gets you a much more 
readable patch submission, P = t(n) - t(o).

The only difficulty is that, if I submit P intead of p then 'git am' will 
probably reject it. This is solved by a little tooling around git, such 
that, should a patch P fail to apply, the relevant files are automatically 
reformatted with the officially endorsed transformation t, to generate a 
minimal cleanup patch, such that P can be automatically applied on top.

If the patch submission process required* that every patch submission was 
generated like P and not like p, it would immediately eliminate all 
clean-up patches from the workload of all reviewers, and also make the 
reviewers' job easier because all submissions are now formatted correctly, 
and also avoid time lost to round-trips, such as, "you can have a 
reviewed-by if you respin to fix some minor style issues".

* Enforcing this, e.g. with checkpatch, is slightly more complicated, but 
it works the same way: generate a minimal cleanup patch for the relevant 
files, apply the patch-to-be-submitted, and finally confirm that the 
modified files are unchanged under t.