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From: | Dmitry Gutov |
Subject: | bug#31290: Fundamental bugs in syntax-propertize |
Date: | Tue, 8 May 2018 15:35:14 +0300 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 |
On 4/28/18 12:08 AM, Alan Mackenzie wrote:
At least that would be true if syntax-propertize--done hadn't been prematurely and spuriously increased, crudely to prevent an infinite recursion, falsely indicating to the syntax-ppss infrastructure that the syntax-table properties have already been applied to the region (BEGIN END). .... but it should not call `syntax-ppss-flush-cache', .... Why not? Because syntax-ppss-flush-cache sets syntax-propertize--done back to its true value, allowing the wrongly allowed syntax-ppss calls at a later position to cause a recursive loop.
Maybe we should "allow" it to loop, in certain cases? Leaving it to be the responsibility of the programmer, to make sure the result doesn't infloop, even if these rules are violated.
.... which means that it should not call `syntax-ppss' on some position and later modify the buffer on some earlier position. This is a bad restriction, because sometimes syntax-table properties can only be correctly determined by examining the syntax of later buffer positions. An example of this is giving the string-fence syntax-table text property to an unbalanced opening string quote, but not to correctly matched quotes.
I'm not exactly convinced by the given example (why would we use the string-fence in that case?), but it might be better if something like this was possible, indeed.
2. syntax-propertize-function's are banned from using syntax-ppss, the documentation instead directing them to use parse-partial-sexp directly.
The ones that currently call syntax-ppss, can't simply switch over to parse-partial-sexp without becoming slower due to the lack of cache.
Before tackling this bug, I'd rather we see a real-world problem that it caused, and pick a particular approach based on it.
But off the top of my head, we could introduce a "stricter but somewhat slower" variation of syntax-ppss to be called inside syntax-propertize-function's, which would treat the values in question more carefully, somehow.
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