Help understanding ruby.el percent literal syntax

Help understanding ruby.el percent literal syntax

[Philippe Vaucher]

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Hello,

We are trying to solve a bug in evil-surround at
https://github.com/emacs-evil/evil-surround/issues/154. The bug is that
percent literals refuse to be replaced when you try to replace a pair of
"{}" with "()" using evil-surround, because ruby.el modifies the percent
literal syntax table in a special way (when we use `fundamental-mode' then
things works as expected).

Thus we are trying to understand the purpose of
`ruby-syntax-propertize-percent-literal' function (
https://github.com/emacs-mirror/emacs/blob/master/lisp/progmodes/ruby-mode.el#L1971-L1999)
which is called from `ruby-syntax-propertize' (
https://github.com/emacs-mirror/emacs/blob/master/lisp/progmodes/ruby-mode.el#L1929
).

If I comment out the call to `ruby-syntax-propertize-percent-literal', then
the bug in evil-surround is gone, and everything just looks the same
visually (the percent literals are correctly highlighted). I don't
understand what purpose this function has. Maybe some other parts of
ruby.el rely on this syntax-table modification?

If someone can point to other parts in ruby.el that require this function
to be called, maybe we can then figure out what the "bug" is in that
function, and possibly offer a patch.

Kind regards,
Philippe

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Re: Help understanding ruby.el percent literal syntax

[Stefan Monnier]

> We are trying to solve a bug in evil-surround at
> https://github.com/emacs-evil/evil-surround/issues/154. The bug is that
> percent literals refuse to be replaced when you try to replace a pair of
> "{}" with "()" using evil-surround, because ruby.el modifies the percent
> literal syntax table in a special way (when we use `fundamental-mode' then
> things works as expected).

ruby-mode uses syntax-propertize to make it so that

    config.allow_sites = %w{twitter facebook pinterest linkedin}
    
is treated somewhat like

    config.allow_sites = "w{twitter facebook pinterest linkedin"

So if you go to the end of the line and try to skip back over the
previous `sexp` you'll end up in front of the `%` rather than in front
of the `{`.

The purpose is probably to handle things like:

    config.allow_sites = %w{twitter facebook # pinterest linkedin}

where the `#` would otherwise be taken as the beginning of a comment.

> If I comment out the call to `ruby-syntax-propertize-percent-literal', then
> the bug in evil-surround is gone, and everything just looks the same
> visually (the percent literals are correctly highlighted).

Not sure what "comment out the call" means exactly, but from my reading
of the code, it would result in mayhem (the %w{ above would probably
be highlighted as if he extended to the end of the buffer).

In order to interact better with things like Evil's
delimiter-replacement, ruby-mode.el could be changed so that instead of
marking the opening `%` and the closing `}` with the `|` syntax, it
would mark the `%` and `w` part with `'` syntax and then arrange to mark
the inside of the delimited text with an ad-hoc syntax table that
doesn't treat `#` as a comment started nor `"` as a string delimiter
(i.e., the same syntax-table used by the `with-syntax-table`
in `ruby-syntax-propertize-percent-literal`).  Or alternatively, it
could look for things like `#` and `"` and give them a `.` syntax.


        Stefan

Re: Help understanding ruby.el percent literal syntax

[Philippe Vaucher]

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>
> ruby-mode uses syntax-propertize to make it so that
>
>     config.allow_sites = %w{twitter facebook pinterest linkedin}
>
> is treated somewhat like
>
>     config.allow_sites = "w{twitter facebook pinterest linkedin"
>
> So if you go to the end of the line and try to skip back over the
> previous `sexp` you'll end up in front of the `%` rather than in front
> of the `{`.
>
> The purpose is probably to handle things like:
>
>     config.allow_sites = %w{twitter facebook # pinterest linkedin}
>
> where the `#` would otherwise be taken as the beginning of a comment.
>

Ah right, that makes sense.



> > If I comment out the call to `ruby-syntax-propertize-percent-literal',
> then
> > the bug in evil-surround is gone, and everything just looks the same
> > visually (the percent literals are correctly highlighted).
>
> Not sure what "comment out the call" means exactly, but from my reading
> of the code, it would result in mayhem (the %w{ above would probably
> be highlighted as if he extended to the end of the buffer).
>

What I meant was "if I edit `ruby-syntax-propertize' so it never calls
`ruby-syntax-propertize-percent-literal' at line 1929". But I think you are
right, it would probably break on your example with the comment above.


In order to interact better with things like Evil's
> delimiter-replacement, ruby-mode.el could be changed so that instead of
> marking the opening `%` and the closing `}` with the `|` syntax, it
> would mark the `%` and `w` part with `'` syntax and then arrange to mark
> the inside of the delimited text with an ad-hoc syntax table that
> doesn't treat `#` as a comment started nor `"` as a string delimiter
> (i.e., the same syntax-table used by the `with-syntax-table`
> in `ruby-syntax-propertize-percent-literal`).  Or alternatively, it
> could look for things like `#` and `"` and give them a `.` syntax.


Thank you a lot for the explanation and the suggestion! We'll see what we
can do :-)

Kind regards,
Philippe

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