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From: | JD Smith |
Subject: | bug#71345: Feature: unleash font-lock's secret weapon; handle Qfontified = non-nil |
Date: | Tue, 4 Jun 2024 08:08:40 -0400 |
In my situation, the most likely scenario is that fontified=nil is noticed during redisplay when there is a fairly large stretch of already-fontified property having the same value. So jit-lock-fontify-now will quickly find a nice large chunk to call my FONTIFICATION-FUNCTION=F-F with. Since jit-lock-after-change will likely clear away already-fontified and set fontified=nil, a single additional F-F on top of jit-lock-function will probably be very well handled. A good question is how it would scale with more functions all operating in the same region. One idea is to rig up a test file, do some fake jit-lock-flushing on it, and check performance of just subtracting/searching/dividing the already-fontified property as you add more (fake) F-F's. For me, jit-lock-fontify-now of a 2500 char chunk in a heavy treesitter buffer is in the 2-5ms range. Individual F-F's could be much lighter weight.
Nice idea. Since redisplay just directs jit-lock to a "starting position", it would be free to update however much buffer text it wants. To overcome the issue of "many small domains", jit-lock could cheat, for example checking if ANY chars in the next block need a particular F-F, and running it on the full block if so. That's already implicitly how jit-lock works now if I understand correctly. But things like `text-property-any' will be quickly defeated by the combinatorics of a large F-F set. Also, an advantage of keeping the fontified=nil semantics is that changes to jit-lock could be back-ported to earlier Emacs versions. So here's an idea. You could invert the logic, and have a set of `fontified-pending' properties which jit-lock-flush adds to as it sets fontified=nil, maintaining one property symbol for each F-F (e.g. fontified-pending-N). Then jit-lock-flush's only job is to select and apply one such property over the region, and fontify-now can use a simple and very fast `text-property-any' as it loops through the list of F-F's, and a final `remove-list-of-text-properties' to strip them all away. For the convenience of jit-lock-after-change, setting a "single property to rule them all" (fontified-pending=t) directs jit-lock to run all the F-F's, there. fontify-now could check for that first, then only bother to look for the individual (-N) properties if it is not set. Is there code out there that sets fontified=nil on its own or is that an internal detail of jit-lock?
Great, so this information could be put into action using one of these approaches. |
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