fix(ecmascript): skip array length evaluation if there are any spread elements (#13162)

https://github.com/oxc-project/oxc/blob/4d0a05e1e7c06598fc92b41bbf785eb6dc6e36fa/crates/oxc_ecmascript/src/constant_evaluation/mod.rs#L501-L502

If there are spread elements in an array, say `[...[1, 2, 3]]`, then
`arr.elements.len()` no longer represents the value of `.length`
property of the array, which will cause mis-optimization.

<details>
  <summary>PoC of the bug</summary>

`test.js`:
``` js
let k = [...[1, 2, 3]].length;
console.log(k);
```

```
$ node test.js
3

$ cargo run --example minifier -- test.js
    Finished `dev` profile [unoptimized] target(s) in 0.08s
     Running `target/debug/examples/minifier`
console.log(1);
```
</details>


This bug was originally discovered in
vitejs/rolldown-vite#375.

Maybe sometimes the `.length` can be evaluated recursively, but here we
just skip the evaluation as a quick fix.

What's more, I think it would be better to add some tests like
`test_eval("[1, 2, 3].length", Some(Number(3.0)))` and
`test_eval("[...a].length", None)`, but I cannot find a suitable place
and found it's not trivial to implement one `Ctx` for `evaluate_value`
in test files. Please let me know if you have any comments. Thanks.

---------

Co-authored-by: GZTime <Time.GZ@outlook.com>
Co-authored-by: Boshen <boshenc@gmail.com>

Author: 3 people

crates/oxc_ecmascript/src/constant_evaluation/mod.rs

@@ -495,15 +495,7 @@ impl<'a> ConstantEvaluation<'a> for StaticMemberExpression<'a> {
         _target_ty: Option<ValueType>,
     ) -> Option<ConstantValue<'a>> {
         match self.property.name.as_str() {
-            "length" => {
-                if let Some(ConstantValue::String(s)) = self.object.evaluate_value(ctx) {
-                    Some(ConstantValue::Number(s.encode_utf16().count().to_f64().unwrap()))
-                } else if let Expression::ArrayExpression(arr) = &self.object {
-                    Some(ConstantValue::Number(arr.elements.len().to_f64().unwrap()))
-                } else {
-                    None
-                }
-            }
+            "length" => evaluate_value_length(&self.object, ctx),
             _ => None,
         }
     }
@@ -517,19 +509,30 @@ impl<'a> ConstantEvaluation<'a> for ComputedMemberExpression<'a> {
     ) -> Option<ConstantValue<'a>> {
         match &self.expression {
             Expression::StringLiteral(s) if s.value == "length" => {
-                if let Some(ConstantValue::String(s)) = self.object.evaluate_value(ctx) {
-                    Some(ConstantValue::Number(s.encode_utf16().count().to_f64().unwrap()))
-                } else if let Expression::ArrayExpression(arr) = &self.object {
-                    Some(ConstantValue::Number(arr.elements.len().to_f64().unwrap()))
-                } else {
-                    None
-                }
+                evaluate_value_length(&self.object, ctx)
             }
             _ => None,
         }
     }
 }
 
+fn evaluate_value_length<'a>(
+    object: &Expression<'a>,
+    ctx: &impl ConstantEvaluationCtx<'a>,
+) -> Option<ConstantValue<'a>> {
+    if let Some(ConstantValue::String(s)) = object.evaluate_value(ctx) {
+        Some(ConstantValue::Number(s.encode_utf16().count().to_f64().unwrap()))
+    } else if let Expression::ArrayExpression(arr) = object {
+        if arr.elements.iter().any(|e| matches!(e, ArrayExpressionElement::SpreadElement(_))) {
+            None
+        } else {
+            Some(ConstantValue::Number(arr.elements.len().to_f64().unwrap()))
+        }
+    } else {
+        None
+    }
+}
+
 impl<'a> ConstantEvaluation<'a> for CallExpression<'a> {
     fn evaluate_value_to(
         &self,

crates/oxc_minifier/src/peephole/fold_constants.rs

@@ -1778,6 +1778,7 @@ mod test {
         // Cannot fold
         fold("x = [foo(), 0].length", "x = [foo(),0].length");
         fold_same("x = y.length");
+        fold_same("[...[1, 2, 3]].length");
     }
 
     #[test]