Use giallo instead of syntect (#3044)

* Use giallo instead of syntect

* Update

* Remove all submodules

* Update contributing docs

* Update docs

* Update changelog

Author: Keats

.gitmodules

@@ -2,6 +2,53 @@
 
 ## 0.22.0 (unreleased)
 
+### Breaking
+Syntect has been replaced with [Giallo](https://github.com/getzola/giallo) and all the highlighting options
+of the `markdown` section in the config file have been moved/changed in `[markdown.highlighting].
+
+The themes are different so you will need to find something you like from <https://textmate-grammars-themes.netlify.app/>.
+
+Migration:
+
+**Single theme:**
+```toml
+# Before
+[markdown]
+highlight_code = true
+highlight_theme = "base16-ocean-dark"
+
+# Now
+[markdown.highlighting]
+theme = "gruvbox-dark"
+```
+
+**Class output:**
+```toml
+# Before
+[markdown]
+highlight_code = true
+highlight_theme = "css"
+highlight_themes_css = [
+  { theme = "base16-ocean-dark", filename = "syntax-theme-dark.css" },
+  { theme = "base16-ocean-light", filename = "syntax-theme-light.css" },
+]
+
+# Now
+[markdown.highlighting]
+theme = "gruvbox-dark"
+style = "class"
+```
+
+For more information on how to handle light/dark themes as well as details about CSS generation and required CSS, 
+see the [documentation](https://www.getzola.org/documentation/content/syntax-highlighting/).
+
+Some grammar names have changed as well, I recommend to set up the following:
+
+```toml
+[markdown.highlighting]
+error_on_missing_language = true
+```
+
 ## 0.21.0 (2025-07-14)
 
 - Allow `github_alerts` at config.toml level

CHANGELOG.md

@@ -19,60 +19,6 @@ If you want to work on an issue, please mention it in a comment to avoid potenti
 any questions on how to approach it do not hesitate to ping me (@keats).
 Easy issues are tagged with `help wanted` and/or `good first issue`
 
-## Adding syntax highlighting languages and themes
+## Adding syntax highlighting languages, themes or aliases
 
-### Adding a syntax
-Syntax highlighting depends on submodules so ensure you load them first:
-
-```bash
-$ git submodule update --init
-```
-
-Zola only works with syntaxes in the `.sublime-syntax` format. If your syntax
-is in `.tmLanguage` format, open it in Sublime Text and convert it to `sublime-syntax` by clicking on
-Tools > Developer > New Syntax from ... and put it in the `sublime/syntaxes` directory.
-
-You can also add a submodule to the repository of the wanted syntax:
-
-```bash
-$ cd sublime/syntaxes/extra
-$ git submodule add https://github.com/elm-community/SublimeElmLanguageSupport
-```
-
-Note that you can also only copy manually the updated syntax definition file but this means
-Zola won't be able to automatically update it.
-
-You can check for any updates to the current packages by running:
-
-```bash
-$ git submodule update --remote --merge
-```
-
-And finally from the root of the components/config crate run the following command:
-
-```bash
-$ cargo run --example generate_sublime synpack ../../sublime/syntaxes ../../sublime/syntaxes/newlines.packdump
-```
-
-### Adding a theme
-A gallery containing lots of themes is located at https://tmtheme-editor.glitch.me/#!/editor/theme/Solarized%20(light).
-More themes can be easily added to Zola, just make a PR with the wanted theme added in the `sublime/themes` directory.
-
-If you want to test Zola with a new theme, it needs to be built into the syntect file `all.themedump`.
-
-First build the tool to generate the syntect file:
-
-```bash
-$ git clone https://github.com/getzola/zola.git && cd zola/components/config
-$ cargo build --example generate_sublime
-```
-
-copy your theme in `sublime/themes/`, then regenerate the syntect file:
-
-``` bash
-$ ./target/debug/examples/generate_sublime themepack sublime/themes/ sublime/themes/all.themedump
-```
-
-You should see the list of themes being added.
-
-To test your new theme, rebuild Zola with `cargo build`.
+Open an issue on the [Giallo repository](https://github.com/getzola/giallo).