[erlang-bugs] erlang.el mis-indents whole-buffer selection

[Magnus Henoch]

Tuncer Ayaz <tuncer.ayaz@REDACTED> writes:

> Previously it was just a certain[1] function in rebar.erl which got
> mis-indented when you did a whole-buffer indent, but now there's also
> a second[2] function which gets mis-indented.
>
> In both cases indenting the function itself separately works, and the
> bug happens if you select the whole buffer and indent that with
> erlang.el (C-x C-q).
>
> I'm using Emacs 24.3.1 with latest erlang.el from maint.
>
> Is it possible to fix this in the existing indenter?
>
> [1] https://github.com/rebar/rebar/blob/620c4b01c/src/rebar.erl#L318-L365
> [2] https://github.com/rebar/rebar/blob/620c4b01c/src/rebar_erlc_compiler.erl#L92-L112

It seems like this happens when the code being indented has not yet been
made visible, and thus lazy syntax highlighting has not yet happened.
The syntax table for erlang-mode is unable to handle some combinations
of characters; in particular, when a string ends with a dollar sign (as
in "foo$"), the dollar sign plus the double quote would be treated as a
character constant were it not for some magic regexps in
font-lock-syntactic-keywords.  Manually scrolling through the buffer
before reindenting seems to make the problem go away.

This is less than satisfactory, of course.  Looking up online help for
font-lock-syntactic-keywords in a modern Emacs gives:

  This variable is obsolete since 24.1;
  use `syntax-propertize-function' instead.

And the NEWS file for Emacs 24.1 contains:

  *** New variable `syntax-propertize-function'.
  This replaces `font-lock-syntactic-keywords' which is now obsolete.
  This allows syntax-table properties to be set independently from font-lock:
  just call syntax-propertize to make sure the text is propertized.
  Together with this new variable come a new hook
  syntax-propertize-extend-region-functions, as well as two helper functions:
  syntax-propertize-via-font-lock to reuse old font-lock-syntactic-keywords
  as-is; and syntax-propertize-rules which provides a new way to specify
  syntactic rules.

This sounds like the right way to solve the problem, though of course
you won't know until you try...

Regards,
Magnus