#1063: find an undefined name's first use from the failing frame on

A ReferenceError's first use was searched across the whole file, so a mention
earlier in a comment, a string or another function could report the wrong line.
The search now starts at the innermost script frame's line, and covers the whole
file only when there is no frame. Follow-up to storytold/effectcraft#1161.

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>

crates/script/src/runtime.rs

@@ -563,27 +563,32 @@ fn position(msg: &str, file: &str, code: &str) -> (Option<u32>, Option<u32>) {
         let mut it = l[i..].split([':', ')']);
         Some((it.next()?.parse().ok()?, it.next()?.parse().ok()?))
     };
+    // The innermost frame in the user's script, or the error's own position.
+    let frames: Vec<&str> = msg.lines().skip(1).collect();
+    let frame = frames.iter().find_map(|l| pick(l)).or_else(|| msg.lines().next().and_then(pick));
     // `ReferenceError: name is not defined`: boa places it at the start of the function that reads
-    // the name, so the first use of the name in the code is the better position (#1063).
+    // the name, so the name's first use from that frame's line on is the better position (#1063).
+    // With no frame to start from, the first use anywhere in the code is (#1161).
     let first = msg.lines().next().unwrap_or("");
     let undefined = first.split("ReferenceError: ").nth(1).and_then(|r| r.split(" is not defined").next());
-    if let Some(at) = undefined.and_then(|name| first_use(name, code)) {
+    let start_line = frame.map_or(1, |(line, _)| line);
+    if let Some(at) = undefined.and_then(|name| first_use(name, code, start_line)) {
         return (Some(at.0), Some(at.1));
     }
-    let frames: Vec<&str> = msg.lines().skip(1).collect();
-    if let Some((a, b)) = frames.iter().find_map(|l| pick(l)).or_else(|| msg.lines().next().and_then(pick)) {
+    if let Some((a, b)) = frame {
         return (Some(a), Some(b));
     }
     (None, None)
 }
 
-/// The first use of `name` as a whole identifier in `code`, as a 1-based line and column.
-fn first_use(name: &str, code: &str) -> Option<(u32, u32)> {
+/// The first use of `name` as a whole identifier in `code` on or after `start_line` (1-based), as a
+/// 1-based line and column.
+fn first_use(name: &str, code: &str, start_line: u32) -> Option<(u32, u32)> {
     if name.is_empty() {
         return None;
     }
     let ident = |c: u8| c.is_ascii_alphanumeric() || c == b'_' || c == b'$';
-    for (n, line) in code.lines().enumerate() {
+    for (n, line) in code.lines().enumerate().skip(start_line.saturating_sub(1) as usize) {
         let b = line.as_bytes();
         let mut from = 0;
         while let Some(i) = line.get(from..).and_then(|rest| rest.find(name)).map(|i| i + from) {

crates/script/src/tests.rs

@@ -187,6 +187,18 @@ fn errors_inside_a_function_wrapper_report_the_failing_line() {
     assert_eq!(e.line, Some(3), "{e:?}");
 }
 
+/// The first use of an undefined name is the one inside the function that reads it: a mention
+/// before it, in a comment, a string or another function, doesn't move the report (#1161).
+#[test]
+fn an_undefined_name_mentioned_earlier_reports_its_use_in_the_reading_function() {
+    let mut s = session();
+    let code = "// nope is mentioned here\nvar text = 'nope';\nfunction other() { return nope; }\n(function () {\n  var a = 1;\n  nope.call();\n})();\n";
+    let o = run_code(&mut s, code, "earlier.jsx");
+    let e = o.error.expect("reference error");
+    assert!(e.message.contains("nope"), "{e:?}");
+    assert_eq!(e.line, Some(6), "{e:?}");
+}
+
 #[test]
 fn match_names_and_lookups() {
     let mut s = session();