feat(lsp): explain generated targets on hover

hemx-lsp/src/main.rs

@@ -442,7 +442,10 @@ fn hemplate_completion_items(
             items.push(completion_item(
                 &format!("ui::{}", target.name),
                 &format!("ui::{}", target.name),
-                "Generated hemx target discovered by hemx-build in the open `.heml` document.",
+                &format!(
+                    "Generated hemx {} target discovered by hemx-build in the open `.heml` document.",
+                    target.kind
+                ),
             ));
         }
     }
@@ -502,6 +505,21 @@ fn completion_item(label: &str, insert_text: &str, detail: &str) -> serde_json::
 }
 
 fn hemplate_hover(uri: &str, text: &str, position: Option<(usize, usize)>) -> serde_json::Value {
+    if let Some((kind, name)) = position.and_then(|position| generated_target_at(text, position)) {
+        if let Ok(targets) =
+            hemx_build::generated_targets_for_heml_source(path_from_file_uri(uri), text)
+        {
+            if targets
+                .iter()
+                .any(|target| target.kind == kind && target.name == name)
+            {
+                return hover_markdown(&format!(
+                    "Generated hemx `{kind}` target `{name}`.\n\nRust symbol: `ui::{name}`.\n\nSource: hemx-build facts for the current `.heml` document."
+                ));
+            }
+        }
+    }
+
     if let Some((owner, field)) = position.and_then(|position| dotted_name_at(text, position)) {
         if let Ok(Some(facts)) =
             hemx_build::template_context_facts_for_heml_source(path_from_file_uri(uri), text)
@@ -584,6 +602,26 @@ fn line_prefix(text: &str, position: (usize, usize)) -> Option<String> {
     Some(line.chars().take(position.1).collect())
 }
 
+fn generated_target_at(text: &str, position: (usize, usize)) -> Option<(String, String)> {
+    let line = text.lines().nth(position.0)?;
+    let cursor = position.1.min(line.len());
+    [
+        ("root", "data-hemx-root=\""),
+        ("slot", "data-hemx-slot=\""),
+        ("form", "data-hemx-form=\""),
+        ("handle", "data-hemx-handle=\""),
+    ]
+    .into_iter()
+    .find_map(|(kind, prefix)| {
+        line.match_indices(prefix).find_map(|(attribute_start, _)| {
+            let value_start = attribute_start + prefix.len();
+            let value_end = value_start + line[value_start..].find('"')?;
+            (cursor >= value_start && cursor <= value_end)
+                .then(|| (kind.to_owned(), line[value_start..value_end].to_owned()))
+        })
+    })
+}
+
 fn dotted_name_at(text: &str, position: (usize, usize)) -> Option<(String, String)> {
     let line = text.lines().nth(position.0)?;
     let chars = line.chars().collect::<Vec<_>>();
@@ -1083,6 +1121,19 @@ mod tests {
         );
     }
 
+    #[test]
+    fn hover_reports_generated_target_kind_and_rust_symbol() {
+        // req: diag/010
+        let uri = "file:///tmp/workout.heml";
+        let text = r#"<main data-hemx-root="workout"><section data-hemx-slot="progress_panel"></section></main>"#;
+        let cursor = text.find("progress_panel").expect("fixture target") + 2;
+
+        let hover = hemplate_hover(uri, text, Some((0, cursor))).to_string();
+
+        assert!(hover.contains("`slot` target `progress_panel`"), "{hover}");
+        assert!(hover.contains("`ui::progress_panel`"), "{hover}");
+    }
+
     #[test]
     fn source_positions_use_lsp_utf16_columns() {
         assert_eq!(