Formatter moves an attribute in front of ~a as x: int onto x #9101

Found by a bug hunt over the 16 commits from eb087382 to cd641cbc.

let g = (@attr ~a as x: int) => x

bsc -format prints:

let g = (~a as @attr x: int) => x

The attribute is on the Ppat_constraint pattern before formatting and on the inner Ppat_var "x" after, so formatting changes the AST. The same happens at b123b7c3.

Since #9055 a doc comment is accepted in the same position, and it is printed in the same place:

let h = (/** a */ ~a as x: int=3) => x

prints as ~a as /** a */ with x: int=3 on the next line.

Cause

The ~b as c arm of print_exp_fun_parameter (res_printer.ml#L5650-L5658) prints ~lbl as, then the whole pattern including its attributes.

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