[PATCH v2] Add .clang-format style file

[Joseph Myers]

On Wed, 30 Mar 2022, Noah Goldstein via Libc-alpha wrote:

> clang-format cleans up excess whitespace before the first comment
> [MaxEmptyLinesToKeep: 1] and realigns part of the comments:
> 
> -
>  /* A reader--writer lock that fulfills the POSIX requirements (but operations
>     on this lock are not necessarily full barriers, as one may interpret the
>     POSIX requirement about "synchronizing memory").  All critical sections are
> @@ -71,18 +70,18 @@
>     #1    0   0   0   0   Lock is idle (and in a read phase).
>     #2    0   0   >0  0   Readers have acquired the lock.
>     #3    0   1   0   0   Lock is not acquired; a writer will try to start a
> - write phase.
> +                         write phase.

But the indentation is correct as-is.  The general rule in glibc is that 
any multiple of 8 blank columns at the start of a line is represented by 
the corresponding number of TAB characters.  There may be a case for using 
spaces instead of tabs, but that's not the current style (except maybe for 
some files shared with gnulib).

> It also fixes difficult to ready indentation:
> 
>      {
>        rnew = r - (1 << PTHREAD_RWLOCK_READER_SHIFT);
>        /* If we are the last reader, we also need to unblock any readers
> - that are waiting for a writer to go first (PTHREAD_RWLOCK_RWAITING)
> - so that they can register while the writer is active.  */
> +         that are waiting for a writer to go first (PTHREAD_RWLOCK_RWAITING)
> +         so that they can register while the writer is active.  */
>        if ((rnew >> PTHREAD_RWLOCK_READER_SHIFT) == 0)
> - {
> -   if ((rnew & PTHREAD_RWLOCK_WRLOCKED) != 0)
> -     rnew |= PTHREAD_RWLOCK_WRPHASE;
> -   rnew &= ~(unsigned int) PTHREAD_RWLOCK_RWAITING;
> - }
> +        {
> +          if ((rnew & PTHREAD_RWLOCK_WRLOCKED) != 0)
> +            rnew |= PTHREAD_RWLOCK_WRPHASE;
> +          rnew &= ~(unsigned int) PTHREAD_RWLOCK_RWAITING;
> +        }

Again, the indentation looks fine as-is; it's using TABs.

> aligns conditions nicely:
> 
>        while ((r & PTHREAD_RWLOCK_WRPHASE) == 0
> -      && (r & PTHREAD_RWLOCK_WRLOCKED) != 0
> -      && (r >> PTHREAD_RWLOCK_READER_SHIFT) > 0)
> 
> +             && (r & PTHREAD_RWLOCK_WRLOCKED) != 0
> +             && (r >> PTHREAD_RWLOCK_READER_SHIFT) > 0)

Likewise, the indentation is already correct, using TABs.

> and cleans up some obvious style mistakes
> 
> - done:
> +done:

I don't think that's a style mistake either.  Emacs indents a label in the 
outermost block of a function like that (one-column indent rather than 
zero columns), and I think it's deliberate to support tools such as "diff 
-p", where it's desirable that, at any point within a function, the 
previous line starting with a letter is the line with the function name, 
not a line with a label somewhere within the function.

-- 
Joseph S. Myers
joseph@codesourcery.com