How to control indentation after an open parenthesis in Emacs - actionscript-3

Question

When I use emacs python-mode, if the last character of a line is an open parenthesis it indents the next line just one step in from the indentation of the previous line.
call_some_function(
some_very_long_argument_that_I_want_to_put_on_its_own_line)
I like that. Now in ecmascript-mode (which I am using for actionscript 3), it always indents to the level of the previous parenthesis.
call_some_function(
this_is_not_really_saving_me_any_horizontal_space);
How can I make ecmascript-mode indent like python-mode in this respect?

Answer 1

Since ecmascript-mode is based on cc-mode, you can use c-set-offset which allows you to customize any syntactic symbol's offset with the preferred value.
In your case, go to the point which is indented in the wrong level, hit C-c C-o (or type M-x c-set-offset), accept the suggested symbol (arglist-intro), and set it a new value (e.g. +, the default offset).
You can also do it programmatically in your dotemacs, for instance, with:
(add-hook 'ecmascript-mode-hook
(lambda ()
(c-set-offset 'arglist-intro '+)
(c-set-offset 'arglist-close 0)))

Answer 2

ecmascript-mode seems to be based on cc-mode. If you set the indentation style for cc-mode,
it will also work for ecmascript-mode. I have the following code in my .emacs. When I use
ecmascript-mode it indents as desired:
;;{{{ c/c++ indent style variables
(require 'cc-mode)
(defconst my-c-style
'(
(c-electric-pound-behavior . 'alignleft)
(c-tab-always-indent . t)
(c-hanging-braces-alist . ((block-open)
(brace-list-open)
(substatement-open)
(defun-open before after)
(defun-close before after)
))
(c-hanging-colons-alist . ((member-init-intro before)
(inher-intro)
(case-label)
(access-label after)
(label after)
(access-key after)))
(c-cleanup-list . (scope-operator
empty-defun-braces
defun-close-semi))
(c-offsets-alist . ((arglist-close . c-lineup-arglist)
(case-label . 4)
(statement-case-intro . 4)
(access-label . -4)
(label . -)
(substatement-open . 0)
(block-open . 0)
(knr-argdecl-intro . -)))
)
"My C++/C Programming Style")
; Customizations for both c-mode and c++-mode
(defun my-c-mode-common-hook ()
; set up for my perferred indentation style, but only do it once
(c-add-style "My" my-c-style 'set-this-style)
; we like auto-newline and hungry-delete
(c-toggle-auto-hungry-state 1)
; keybindings for both C and C++. We can put these in c-mode-map
; because c++-mode-map inherits it
(define-key c-mode-map "\C-m" 'newline-and-indent)
; insert 8 tabs
(setq tab-width 8)
)
;;}}}

Answer 3

Thank you Török Gábor, in my case I prefered to set
(add-hook 'XXX-mode-hook
(lambda ()
(c-set-offset 'arglist-cont-nonempty '+)))
I was looking for something like this :
veryLongFunctionName (bar,
bar,
bar)
For a more exhaustive list of variables : read emacs documentation