Keep exported function headers visible in structural diffs

Include export declarations in context scopes and retain multiline JavaScript and TypeScript signatures through the function body opening. Changes deep in a function now retain its name and parameters instead of exposing an orphaned parameter line.

Validation: all 66 plugin tests pass, including a TSX regression; verified the reported ReviewHome commit range. Wrapping behavior is unchanged.

AI assistance: Codex.

Agent-Session: 01a0cf54-8719-7203-a3ab-7b4959428076

Author: sidkmenon

plugins/context/queries/javascript.scm

@@ -22,3 +22,20 @@
   (#set! tag "context:scope"))
 ((return_statement) @fold
   (#set! tag "context:scope"))
+
+; Export prefixes belong to the declaration header. Without the wrapper,
+; whole-line projection starts the function scope on its first parameter.
+((export_statement declaration: [
+  (function_declaration)
+  (generator_function_declaration)
+  (class_declaration)
+]) @fold (#set! tag "context:scope"))
+
+; Keep the complete function header up to the body, including destructured
+; parameters and multiline return types.
+([
+  (function_declaration body: (statement_block "{" @fold.open "}" @fold.close) @fold)
+  (generator_function_declaration body: (statement_block "{" @fold.open "}" @fold.close) @fold)
+  (method_definition body: (statement_block "{" @fold.open "}" @fold.close) @fold)
+  (arrow_function body: (statement_block "{" @fold.open "}" @fold.close) @fold)
+] (#set! tag "context:body"))

plugins/context/src/lib.rs

@@ -45,7 +45,7 @@ pub struct Options {
 }
 
 /// The first and last line of every scope on `source` that holds a changed
-/// line.
+/// line, plus its full header when the query marks the function body.
 ///
 /// A scope region is a whole construct: its first line is the line its
 /// signature or header starts on and its last is the line that closes it,
@@ -63,6 +63,11 @@ fn scope_rows(source: &Source, changed: &BTreeSet<u32>) -> BTreeSet<u32> {
         }
         rows.insert(span.start);
         rows.insert(span.end - 1);
+        if let Node::Fold { children } = &region.node {
+            if let Some(body) = children.iter().find(|child| has_tag(child, "context:body")) {
+                rows.extend(span.start..body.range.start.line);
+            }
+        }
     });
     rows
 }

src/plugin/tests/context.rs

@@ -575,3 +575,20 @@ fn a_scope_keeps_the_line_it_closes_on() {
         );
     }
 }
+
+#[test]
+fn exported_tsx_functions_keep_complete_headers_above_distant_changes() {
+    let body = repeated(0..30, |i| format!("    const value_{i} = {i};\n"));
+    let before = format!("export function ReviewHome({{\n    reviews,\n    setup,\n}}: Props) {{\n{body}    return <h1>Reviews</h1>;\n}}\n");
+    let after = before.replace("<h1>Reviews</h1>", "<h1>Sessions</h1>");
+    let sides = shaped("home.tsx", &before, &after, 3);
+    for source in [lhs(&sides), rhs(&sides)] {
+        let open = open_leaf_lines(&source.regions);
+        assert!(
+            (0..4).all(|line| open.contains(&line)),
+            "header hidden: {open:?}"
+        );
+        assert!(!open.contains(&10), "unrelated body should collapse");
+        assert!(open.contains(&34), "changed JSX should stay visible");
+    }
+}