ndg-html: link custom scripts where they are copied

CHANGELOG.md

@@ -37,6 +37,11 @@ changes.
 
 ### Fixed
 
+- Pages now link each script in `script_paths` at `assets/<file name>`, where
+  NDG copies it. Before, the link used the configured source path, so a script
+  from outside the output directory, such as a path in the Nix store, did not
+  load.
+
 - An anchor link that holds only an element, such as
   `<a href="#fig-example"><img src="example.png"></a>`, no longer gets humanized
   text added after the element. Before, the processor treated it as an empty

crates/ndg-html/src/template.rs

@@ -1627,9 +1627,13 @@ fn generate_custom_scripts(
   // replace default content, the user should specify `--template-dir` or
   // `--template` instead.
   for script_path in &config.script_paths {
-    // Relative path to script
+    // `copy_assets` copies each script to `assets/<file name>`, so link there,
+    // not to the configured source path.
+    let Some(file_name) = script_path.file_name() else {
+      continue;
+    };
     let script_relative_path =
-      format!("{}{}", root_prefix, script_path.to_string_lossy());
+      format!("{}assets/{}", root_prefix, file_name.to_string_lossy());
     write!(
       custom_scripts,
       "<script defer src=\"{script_relative_path}\"></script>"

crates/ndg-html/tests/custom_scripts.rs

@@ -0,0 +1,40 @@
+#![allow(clippy::expect_used, reason = "Fine in tests")]
+use std::path::PathBuf;
+
+mod common;
+
+use common::test_config;
+use ndg_html::template::render;
+use tempfile::TempDir;
+
+#[test]
+fn test_custom_script_links_to_copied_asset() {
+  let temp_dir = TempDir::new().expect("Failed to create temp dir");
+  let output_dir = temp_dir.path();
+
+  // A script outside the output directory, as with a path in the Nix store.
+  let config = ndg_config::Config {
+    script_paths: vec![PathBuf::from("/nix/store/abc-scripts/custom.js")],
+    ..test_config(output_dir)
+  };
+
+  let html = render(
+    &config,
+    "<p>Test content</p>",
+    "Test Page",
+    &[],
+    &PathBuf::from("docs/test.html"),
+    None,
+  )
+  .expect("Failed to render page");
+
+  // The script is copied to `assets/<file name>`, so the page must link there.
+  assert!(
+    html.contains("<script defer src=\"../assets/custom.js\"></script>"),
+    "Script should link to the copied asset"
+  );
+  assert!(
+    !html.contains("/nix/store/abc-scripts/custom.js"),
+    "Script should not link to its source path"
+  );
+}