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Re: Using incremental parsing in Emacs

From: Stefan Monnier
Subject: Re: Using incremental parsing in Emacs
Date: Mon, 06 Jan 2020 08:47:31 -0500
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux)

> I see the buffer is fontified correctly. Does it parse the whole buffer?

We have different levels of parsing.  At the bottom we have
`syntax-ppss` (whose workhorse, implemented in C, is
`parse-partial-sexp`) which only counts parentheses and looks for
comment and string markers.  In the above case, `syntax-ppss` indeed
parses the whole buffer, but given its limited scope this parsing is
usually fast (it can be slow in some cases, because `parse-partial-sexp`
is supplemented by `syntax-propertize-function` to handle the "unusual"
cases of "strings/comments" (a typical example would be here-documents
in shell scripts) and this is all implemented in Elisp using regexp

After this parsing is done, font-lock looks at the few lines actually
displayed using its Elisp/regexps rules to apply the actual highlighting.
This may look at more parts of the buffer, tho, depending on the actual
font-lock rules.


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