bug#18346: Missing feature; smart contextual documentation (help buffers)

[user3341592 <user47795-cAwOlEar6MYS+FvcfC7Uqw@public.gmane.org>]

Here is a missing feature which Stefan asked to report.

See http://stackoverflow.com/questions/25551120/bind-f1-to-smart-contextual-documentation-help-buffers.

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Is there a function which I could bind on F1 in Emacs, which would give
me (in a temporary or persistent buffer) contextual documentation on the
"symbol" under point?

IIUC, that'd give the same results as:

- C-c C-v RET in ESS buffers (= ess-display-help-on-object)
- C-h f/v RET in Emacs Lisp buffers (= describe-function/variable)
- C-h S in Shell buffers (= info-lookup-symbol) + M-x man-follow?
- ??? in AWK, C, Java
- ??? in AUCTeX buffers (well, that may be a big dream ;-))
- ...

Somehow, Auto-Complete does that job (at least in ESS and Emacs Lisp
buffers), as it displays the right help (on functions, on variables,
etc.) in its "quick help" tooltip. Though, it's only displayed in the
completion process, not after.

I first thought that info-lookup-symbol would be (part of) the solution,
but it already does NOT work in ESS, so it's pretty very limited...

What should I bind onto F1, then?
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