fix(ecmascript): avoid charAt panic on 32-bit (#26244)

## Summary

- Return `OutOfRange` when a `StringCharAt` position cannot fit in `usize`, avoiding a panic on 32-bit targets.
- Cover the `u32` boundary in direct evaluation and minifier constant folding, alongside existing conversion and UTF-16 edge cases.

crates/oxc_ecmascript/src/string_char_at.rs

@@ -14,7 +14,12 @@ impl StringCharAt for &str {
 
         let position = pos.unwrap_or(0.0).to_integer_or_infinity_as_i64();
         let position = match position {
-            ToIntegerOrInfinityResult::Value(v) if v >= 0 => v.to_usize().unwrap(),
+            ToIntegerOrInfinityResult::Value(v)
+                if v >= 0
+                    && let Some(v) = v.to_usize() =>
+            {
+                v
+            }
             _ => return StringCharAtResult::OutOfRange,
         };
 
@@ -47,10 +52,18 @@ mod test {
         assert_eq!(s.char_at(Some(4.0)), StringCharAtResult::OutOfRange);
         assert_eq!(s.char_at(Some(0.5)), StringCharAtResult::Value('t'));
         assert_eq!(s.char_at(None), StringCharAtResult::Value('t'));
+        assert_eq!(s.char_at(Some(f64::NAN)), StringCharAtResult::Value('t'));
         assert_eq!(s.char_at(Some(f64::INFINITY)), StringCharAtResult::OutOfRange);
         assert_eq!(s.char_at(Some(f64::NEG_INFINITY)), StringCharAtResult::OutOfRange);
         assert_eq!(s.char_at(Some(-1.0)), StringCharAtResult::OutOfRange);
         assert_eq!(s.char_at(Some(-1.1)), StringCharAtResult::OutOfRange);
         assert_eq!(s.char_at(Some(-1_073_741_825.0)), StringCharAtResult::OutOfRange);
+        assert_eq!(s.char_at(Some(f64::from(u32::MAX))), StringCharAtResult::OutOfRange);
+        assert_eq!(s.char_at(Some(f64::from(u32::MAX) + 1.0)), StringCharAtResult::OutOfRange);
+
+        let astral = "𝄞";
+        assert_eq!(astral.char_at(Some(0.0)), StringCharAtResult::InvalidChar(0xd834));
+        assert_eq!(astral.char_at(Some(1.0)), StringCharAtResult::InvalidChar(0xdd1e));
+        assert_eq!(astral.char_at(Some(2.0)), StringCharAtResult::OutOfRange);
     }
 }

crates/oxc_minifier/tests/peephole/replace_known_methods.rs

@@ -242,6 +242,8 @@ fn test_fold_string_char_at() {
     test("x = 'abcde'.charAt(3)", "x = 'd'");
     test("x = 'abcde'.charAt(4)", "x = 'e'");
     test("x = 'abcde'.charAt(5)", "x = ''");
+    test("x = 'abcde'.charAt(4294967295)", "x = ''");
+    test("x = 'abcde'.charAt(4294967296)", "x = ''");
     test("x = 'abcde'.charAt(-1)", "x = ''");
     test("x = 'abcde'.charAt()", "x = 'a'");
     test_same("x = 'abcde'.charAt(...foo)");