Re: Help Understanding syntax-propertize-function

[Stefan Monnier]

> Could someone help explain the following code:

I'm not sure which part you don't understand, so I'll stick to
generic ideas:

> (defun hcl--syntax-propertize-function (start end)
>   (goto-char start)
>   (hcl--syntax-propertize-heredoc end)
>   (funcall
>    (syntax-propertize-rules
>     (hcl--here-doc-beg-re
>      (2 (hcl--font-lock-open-heredoc
>          (match-beginning 0) (match-string 1) (match-beginning 2))))
>     ("\\s|" (0 (prog1 nil (hcl--syntax-propertize-heredoc end)))))
>    (point) end))

Since we don't know where `start` will be, it can be within a heredoc.
So we first call `hcl--syntax-propertize-heredoc` which should detect
when we're inside a heredoc and if so process it until its end and if not
do nothing.

Once that's done, we know we're not in a heredoc, hence we're in
"normal code" and we then use `syntax-propertize-rules` to try and
detect a few interesting conditions.  One of them is when we find
a match for `hcl--here-doc-beg-re`, in that case we call
`hcl--font-lock-open-heredoc` to place some syntactic marker at the
beginning of the heredoc.  The other is when we see a char of
syntactic category `|`, which doesn't occur in the wild but should
presumably be the result of `hcl--font-lock-open-heredoc` having placed
it there, so it announces the beginning of a heredoc, in which case we
can call `hcl--syntax-propertize-heredoc` to process it.


        Stefan