Use %array_length for Array.length to bring back lost optimizations (#7872)

* Use `%array_length` for `Array.length` to bring back lost optimizations

* CHANGELOG

Author: cknitt

CHANGELOG.md

@@ -31,6 +31,8 @@
 
 #### :nail_care: Polish
 
+- Reactivate optimization for length of array literals. https://github.com/rescript-lang/rescript/pull/7872
+
 #### :house: Internal
 
 - Playground: Add config options for experimental features and jsx preserve mode. https://github.com/rescript-lang/rescript/pull/7865

packages/@rescript/runtime/Js_array.res

@@ -97,8 +97,7 @@ Js.Array.isArray("abcd") == false
 /**
 Returns the number of elements in the array. See [`Array.length`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/length) on MDN.
 */
-@get
-external length: array<'a> => int = "length"
+external length: array<'a> => int = "%array_length"
 
 /* Mutator functions */
 

packages/@rescript/runtime/Js_array2.res

@@ -120,8 +120,7 @@ Returns the number of elements in the array. See
 [`Array.length`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/length)
 on MDN.
 */
-@get
-external length: array<'a> => int = "length"
+external length: array<'a> => int = "%array_length"
 
 /* Mutator functions */
 

packages/@rescript/runtime/Stdlib_Array.res

@@ -42,7 +42,7 @@ let fromInitializer = (~length, f) =>
 
 @val external isArray: 'a => bool = "Array.isArray"
 
-@get external length: array<'a> => int = "length"
+external length: array<'a> => int = "%array_length"
 
 let isEmpty = arr => arr->length === 0
 

packages/@rescript/runtime/Stdlib_Array.resi

@@ -77,8 +77,7 @@ let someArray = ["hi", "hello"]
 someArray->Array.length == 2
 ```
 */
-@get
-external length: array<'a> => int = "length"
+external length: array<'a> => int = "%array_length"
 
 /**
 `isEmpty(array)` returns `true` if the array is empty (has length 0), `false` otherwise.

tests/docstring_tests/DocTest.res.js

@@ -21,7 +21,7 @@ function f(v) {
 }
 
 function fff(x) {
-  return x.length >= 0;
+  return true;
 }
 
 function fff2(x) {
@@ -33,15 +33,11 @@ function fff2(x) {
 }
 
 function fff3(x) {
-  if (x.length >= 0) {
-    return 1;
-  } else {
-    return 2;
-  }
+  return 1;
 }
 
 function fff4(x) {
-  if (x.length > 0) {
+  if (x.length !== 0) {
     return 1;
   } else {
     return 2;
@@ -87,7 +83,7 @@ Mocha.describe("Array_subtle_test", () => {
       3,
       3
     ];
-    while (v.length > 0) {
+    while (v.length !== 0) {
       v.pop();
     };
     Test_utils.eq("File \"array_subtle_test.res\", line 60, characters 7-14", 0, v.length);

tests/tests/src/array_subtle_test.mjs

@@ -6,11 +6,7 @@ import * as Test_utils from "./test_utils.mjs";
 Mocha.describe("Js_array_test", () => {
   Mocha.test("isArray_array", () => Test_utils.eq("File \"js_array_test.res\", line 25, characters 7-14", true, Array.isArray([])));
   Mocha.test("isArray_int", () => Test_utils.eq("File \"js_array_test.res\", line 28, characters 7-14", false, Array.isArray(34)));
-  Mocha.test("length", () => Test_utils.eq("File \"js_array_test.res\", line 31, characters 7-14", 3, [
-    1,
-    2,
-    3
-  ].length));
+  Mocha.test("length", () => Test_utils.eq("File \"js_array_test.res\", line 31, characters 7-14", 3, 3));
   Mocha.test("copyWithin", () => Test_utils.eq("File \"js_array_test.res\", line 35, characters 7-14", [
     1,
     2,