inject site config during Sass compilation

it is helpful to be able to use site config during Sass compilation,
for example to allow a site owner to set header color in a Sass
template.  in this change we serialize a subset of the site's config
to a `.scss` file as a Sass map literal, allowing config content to
be referenced in site Sass or theme Sass.

components/config/src/config/mod.rs

@@ -111,6 +111,13 @@ pub struct SerializedConfig<'a> {
     markdown: &'a markup::Markdown,
 }
 
+#[derive(Serialize)]
+pub struct SassConfig<'a> {
+    base_url: &'a str,
+    theme: &'a Option<String>,
+    extra: &'a HashMap<String, Toml>,
+}
+
 impl Config {
     // any extra syntax and highlight themes have been loaded and validated already by the from_file method before parsing the config
     /// Parses a string containing TOML to our Config struct
@@ -333,6 +340,10 @@ impl Config {
             markdown: &self.markdown,
         }
     }
+
+    pub fn sass_config(&self) -> SassConfig {
+        SassConfig { base_url: &self.base_url, theme: &self.theme, extra: &self.extra }
+    }
 }
 
 // merge TOML data that can be a table, or anything else

components/site/Cargo.toml

@@ -7,6 +7,7 @@ include = ["src/**/*"]
 
 [dependencies]
 serde = { version = "1.0", features = ["derive"] }
+tempfile = "3"
 
 errors = { path = "../errors" }
 config = { path = "../config" }
@@ -20,5 +21,4 @@ libs = { path = "../libs" }
 content = { path = "../content" }
 
 [dev-dependencies]
-tempfile = "3"
 path-slash = "0.2"

components/site/src/lib.rs

@@ -708,13 +708,13 @@ impl Site {
         if let Some(ref theme) = self.config.theme {
             let theme_path = self.base_path.join("themes").join(theme);
             if theme_path.join("sass").exists() {
-                sass::compile_sass(&theme_path, &self.output_path)?;
+                sass::compile_sass(&theme_path, &self.output_path, &self.config)?;
                 start = log_time(start, "Compiled theme Sass");
             }
         }
 
         if self.config.compile_sass {
-            sass::compile_sass(&self.base_path, &self.output_path)?;
+            sass::compile_sass(&self.base_path, &self.output_path, &self.config)?;
             start = log_time(start, "Compiled own Sass");
         }
 

components/site/src/sass/mod.rs

@@ -1,24 +1,27 @@
 use std::fs::create_dir_all;
 use std::path::{Path, PathBuf};
 
+use config::Config;
 use libs::globset::Glob;
 use libs::grass::{from_path as compile_file, Options, OutputStyle};
 use libs::walkdir::{DirEntry, WalkDir};
+use tempfile::{tempdir, TempDir};
 
 use crate::anyhow;
-use errors::{bail, Result};
+use errors::{bail, Context, Result};
 use utils::fs::{create_file, ensure_directory_exists};
 
-pub fn compile_sass(base_path: &Path, output_path: &Path) -> Result<()> {
+mod serde;
+
+pub fn compile_sass(base_path: &Path, output_path: &Path, config: &Config) -> Result<()> {
     ensure_directory_exists(output_path)?;
 
-    let sass_path = {
-        let mut sass_path = PathBuf::from(base_path);
-        sass_path.push("sass");
-        sass_path
-    };
+    let sass_path = PathBuf::from(base_path).join("sass");
+
+    let dependencies_dir = build_dependencies_dir_from_config(config)?;
 
-    let options = Options::default().style(OutputStyle::Compressed);
+    let options =
+        Options::default().style(OutputStyle::Compressed).load_path(dependencies_dir.path());
     let files = get_non_partial_scss(&sass_path);
     let mut compiled_paths = Vec::new();
 
@@ -52,6 +55,24 @@ pub fn compile_sass(base_path: &Path, output_path: &Path) -> Result<()> {
     Ok(())
 }
 
+/// write out a subset of the Zola config document to a temporary SCSS file
+/// as an SCSS map variable literal.  this will allow parts of the site's
+/// config to be usable during Sass compilation.  this enables theme configuration
+/// like allowing the site owner to change header color.  this function returns
+/// a tempdir holding a single `.scss` file.  the tempdir should then be used as
+/// a load directory above when compiling the site's Sass files.  the tempdir
+/// and contained `.scss` file will be deleted on drop of the returned `TempDir`
+/// struct, which should happen after Sass compilation finishes.
+fn build_dependencies_dir_from_config(config: &Config) -> Result<TempDir> {
+    let dir = tempdir().context("failed to create tempdir for SASS dependencies")?;
+
+    let config_serialized = serde::serialize_config(config)?;
+
+    std::fs::write(dir.path().join("zola.scss"), format!("$config: {}", config_serialized))?;
+
+    Ok(dir)
+}
+
 fn is_partial_scss(entry: &DirEntry) -> bool {
     entry.file_name().to_str().map(|s| s.starts_with('_')).unwrap_or(false)
 }