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* Closes <https://github.com/emilk/egui/issues/3964>
* [X] I have followed the instructions in the PR template
This PR adds support for syntax highlighting with custom
`syntect::parsing::SyntaxSet` and `syntect::highlighting::ThemeSet`. It
adds a new `egui_extras::highlight_with` function (enabled with `feature
= "syntect"`), which takes a new public`struct SyntectSettings`
containing the syntax and theme sets.
```rust
let mut builder = SyntaxSetBuilder::new();
builder.add_from_folder("syntax", true).unwrap();
let ps = builder.build();
let ts = syntect::highlighting::ThemeSet::load_defaults();
let syntax =
egui_extras::syntax_highlighting::SyntectSettings { ps, ts };
// ...elsewhere
egui_extras::syntax_highlighting::highlight_with(
ui.ctx(),
ui.style(),
&theme,
buf,
"rhai",
&syntax,
);
```
There's a little bit of architectural complexity, but it all emerges
naturally from the problem's constraints.
Previously, the `Highlighter` both contained the `syntect` settings
_and_ implemented `egui::cache::ComputerMut` to highlight a string; the
settings would never change. After this change, the `syntect` settings
have become part of the cache key, so we should redo highlighting if
they change. The `Highlighter` becomes an empty `struct` which just
serves to implement `ComputerMut`.
`SyntaxSet` and `ThemeSet` are not hasheable themselves, so can't be
used as cache keys direction. Instead, we can use the *address* of the
`&SyntectSettings` as the key. This requires an object with a custom
`Hash` implementation, so I added a new `HighlightSettings(&'a
SyntectSettings)`, implementing `Hash` using `std::ptr::hash` on the
reference. I think using the address is reasonable – it would be _weird_
for a user to be constantly moving around their `SyntectSettings`, and
there's a warning in the docstring to this effect.
To work _without_ custom settings, `SyntectSettings::default` preserves
the same behavior as before, using `SyntaxSet::load_defaults_newlines`
and `ThemeSet::load_defaults`. If the user doesn't provide custom
settings, then we instantiate a singleton `SyntectSettings` in `data`
and use it; this will only be constructed once.
Finally, in cases where the `syntect` feature is disabled,
`SyntectSettings` are replaced with a unit `()`. This adds a _tiny_
amount of overhead – one singleton `Arc<()>` allocation and a lookup in
`data` per `highlight` – but I think that's better than dramatically
different implementations. If this is an issue, I can refactor to make
it zero-cost when the feature is disabled.
f11a3510ba