On 1/10/24 15:59, Marek Polacek wrote:
On Wed, Jan 10, 2024 at 02:58:03PM -0500, Jason Merrill via Gcc wrote:
What formatting style do we want for non-trivial lambdas in GCC sources?
I'm thinking the most consistent choice would be

auto l = [&] (parms) // space between ] (
   {                  // brace on new line, indented two spaces
     return stuff;
   };

Sure, why not.  Consistency is what matters.  Thus far we seem
to have been very inconsistent.  ;)
By default, recent emacs lines up the { with the previous line, like an
in-class function definition; I talked it into the above indentation with

(defun lambda-offset (elem)
   (if (assq 'inline-open c-syntactic-context) '+ 0))
(add-to-hook 'c++-mode-hook '(c-set-offset 'inlambda 'lambda-offset))

I think we probably want the same formatting for lambdas in function
argument lists, e.g.

algorithm ([] (parms)
   {
     return foo;
   });

And what about lambdas in conditions:

if (foo ()
     && [&] (params) mutable
        {
         return 42;
        } ())

should the { go just below [?

I think we don't want the { to go below the [ in general; that was the old emacs default behavior, and it produced lambda bodies with excessive indentation.

With my adjustment above, emacs indents the { two spaces from the &&, which seems a bit arbitrary but reasonable.

Jason

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