feat: Add a debug command to save css file for a theme

This adds a new command `debug highlight save-theme-css` that can
generate a CSS file for a theme to migrate to the "css" theme.

Author: vbfox

crates/engarde/src/syntax.rs

@@ -3,7 +3,7 @@ use syntect::easy::HighlightLines;
 use syntect::highlighting::ThemeSet;
 use syntect::html::{
     ClassStyle, ClassedHTMLGenerator, IncludeBackground, append_highlighted_html_for_styled_line,
-    start_highlighted_html_snippet,
+    css_for_theme_with_class_style, start_highlighted_html_snippet,
 };
 use syntect::parsing::{SyntaxReference, SyntaxSet};
 use syntect::util::LinesWithEndings;
@@ -34,6 +34,10 @@ impl Syntax {
         self.syntax_set = builder.build();
     }
 
+    pub fn css_theme_name() -> &'static str {
+        CSS_THEME
+    }
+
     pub fn has_theme(&self, name: &str) -> bool {
         name == CSS_THEME || self.theme_set.themes.contains_key(name)
     }
@@ -46,6 +50,16 @@ impl Syntax {
         themes.into_iter()
     }
 
+    fn css_class_style() -> ClassStyle {
+        ClassStyle::SpacedPrefixed { prefix: "c-" }
+    }
+
+    /// Get the content of a css file to apply the specified color theme when using the 'css' theme
+    pub fn css_for_theme(&self, name: &str) -> String {
+        let theme = &self.theme_set.themes[name];
+        css_for_theme_with_class_style(theme, Self::css_class_style()).unwrap()
+    }
+
     pub fn syntaxes(&self) -> impl Iterator<Item = String> + '_ {
         fn reference_to_string(sd: &SyntaxReference) -> String {
             let extensions = sd.file_extensions.join(", ");
@@ -101,7 +115,7 @@ impl Syntax {
         let mut html_generator = ClassedHTMLGenerator::new_with_class_style(
             syntax,
             &self.syntax_set,
-            ClassStyle::SpacedPrefixed { prefix: "c-" },
+            Self::css_class_style(),
         );
 
         for line in LinesWithEndings::from(code) {

src/bin/cobalt/debug.rs

@@ -1,5 +1,7 @@
 use crate::args;
 use crate::error::Result;
+#[cfg(feature = "syntax-highlight")]
+use std::path::PathBuf;
 
 /// Print site debug information
 #[derive(Clone, Debug, PartialEq, Eq, clap::Subcommand)]
@@ -34,6 +36,19 @@ pub(crate) enum HighlightCommands {
         #[command(flatten, next_help_heading = "Config")]
         config: args::ConfigArgs,
     },
+
+    /// Save the css file for a theme
+    #[cfg(feature = "syntax-highlight")]
+    SaveThemeCss {
+        #[command(flatten, next_help_heading = "Config")]
+        config: args::ConfigArgs,
+
+        /// Name of the theme to generate a css file for
+        name: String,
+
+        /// Path of the css file
+        path: PathBuf,
+    },
 }
 
 impl DebugCommands {
@@ -58,6 +73,23 @@ impl DebugCommands {
                     println!("{name}");
                 }
             }
+            #[cfg(feature = "syntax-highlight")]
+            Self::Highlight(HighlightCommands::SaveThemeCss { config, name, path }) => {
+                let config = config.load_config()?;
+                let config = cobalt::cobalt_model::Config::from_config(config)?;
+                if name == engarde::Syntax::css_theme_name() || !config.syntax.has_theme(name) {
+                    return Err(anyhow::anyhow!("Unknown theme: {name}"));
+                }
+
+                let css = config.syntax.css_for_theme(name);
+
+                std::fs::write(path, css)?;
+
+                println!(
+                    "CSS theme '{name}' successfully saved to: {}",
+                    path.display()
+                );
+            }
             Self::Files { collection, config } => {
                 let config = config.load_config()?;
                 let config = cobalt::cobalt_model::Config::from_config(config)?;