#1063: report an undefined name at its first use inside a function wrapper

Inside a function wrapper such as (function () { ... })(), boa places a ReferenceError at the start of
the function, so a script's error was reported at the wrapper's first line rather than the line that
failed. The first use of the undefined name in the code is now the position, and boa's frames remain
the fallback. Thrown errors and object-model errors already report their own lines. A regression
test covers a thrown error, an undefined name, and an object-model error inside a wrapper.

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

crates/script/src/runtime.rs

@@ -547,9 +547,9 @@ pub(crate) fn script_error(e: &boa_engine::JsError, ctx: &mut Context, file: &st
     ScriptError { message, line, column, file: file.to_string() }
 }
 
-/// Line and column of an error: `at line N, col M` (syntax errors), else the innermost backtrace
-/// frame in the user's script (`file:line:col`), else (names boa can't place) the first use of
-/// the undefined name in `code`.
+/// Line and column of an error: `at line N, col M` (syntax errors), else the first use of an
+/// undefined name in `code` (boa places those at a function's start), else the innermost backtrace
+/// frame in the user's script (`file:line:col`).
 fn position(msg: &str, file: &str, code: &str) -> (Option<u32>, Option<u32>) {
     if let Some(i) = msg.find("at line ") {
         let rest = &msg[i + 8..];
@@ -563,28 +563,39 @@ 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()?))
     };
+    // `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).
+    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)) {
+        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)) {
         return (Some(a), Some(b));
     }
-    // `ReferenceError: name is not defined` without a position.
-    let first = msg.lines().next().unwrap_or("");
-    if let Some(name) = first.split("ReferenceError: ").nth(1).and_then(|r| r.split(" is not defined").next()) {
-        for (n, line) in code.lines().enumerate() {
-            let b = line.as_bytes();
-            let mut from = 0;
-            while let Some(i) = line[from..].find(name).map(|i| i + from) {
-                let before = i.checked_sub(1).map(|j| b[j]);
-                let after = b.get(i + name.len()).copied();
-                let ident = |c: u8| c.is_ascii_alphanumeric() || c == b'_' || c == b'$';
-                if !before.is_some_and(|c| ident(c) || c == b'.') && !after.is_some_and(ident) {
-                    return (Some(n as u32 + 1), Some(i as u32 + 1));
-                }
-                from = i + name.len();
+    (None, None)
+}
+
+/// The first use of `name` as a whole identifier in `code`, as a 1-based line and column.
+fn first_use(name: &str, code: &str) -> Option<(u32, u32)> {
+    if name.is_empty() {
+        return None;
+    }
+    let ident = |c: u8| c.is_ascii_alphanumeric() || c == b'_' || c == b'$';
+    for (n, line) in code.lines().enumerate() {
+        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) {
+            let before = i.checked_sub(1).and_then(|j| b.get(j).copied());
+            let after = b.get(i + name.len()).copied();
+            if !before.is_some_and(|c| ident(c) || c == b'.') && !after.is_some_and(ident) {
+                return Some((n as u32 + 1, i as u32 + 1));
             }
+            from = i + name.len();
         }
     }
-    (None, None)
+    None
 }
 
 /// Evaluate `code` in `ctx` and convert the result.

crates/script/src/tests.rs

@@ -142,6 +142,24 @@ fn errors_report_line_and_column() {
     assert_eq!(e.line, Some(3), "{e:?}");
 }
 
+/// A script wrapped in a function (the usual `(function () { ... })();` shape) reports the line
+/// that failed, not the wrapper's line (#1063).
+#[test]
+fn errors_inside_a_function_wrapper_report_the_failing_line() {
+    let mut s = session();
+    let o = run_code(&mut s, "(function () {\n  var a = 1;\n  throw new Error('inside');\n})();\n", "thrown.jsx");
+    let e = o.error.expect("thrown");
+    assert_eq!(e.message, "inside");
+    assert_eq!(e.line, Some(3), "{e:?}");
+    let o = run_code(&mut s, "(function () {\n  var a = 1;\n  nope.call();\n})();\n", "reference.jsx");
+    let e = o.error.expect("reference error");
+    assert_eq!(e.line, Some(3), "{e:?}");
+    let o = run_code(&mut s, "(function () {\n  var c = app.project.items.addComp('C', 10, 10, 1, 1, 24);\n  c.layer(5);\n})();\n", "range.jsx");
+    let e = o.error.expect("range error");
+    assert!(e.message.contains("out of range"), "{e:?}");
+    assert_eq!(e.line, Some(3), "{e:?}");
+}
+
 #[test]
 fn match_names_and_lookups() {
     let mut s = session();