Implement array.fill (#1497)

Perryvw · web-flow · commit 45f607828da4 · 2023-10-03T20:41:58.000+02:00
diff --git a/src/LuaLib.ts b/src/LuaLib.ts
@@ -9,6 +9,7 @@ export enum LuaLibFeature {
     ArrayConcat = "ArrayConcat",
     ArrayEntries = "ArrayEntries",
     ArrayEvery = "ArrayEvery",
+    ArrayFill = "ArrayFill",
     ArrayFilter = "ArrayFilter",
     ArrayForEach = "ArrayForEach",
     ArrayFind = "ArrayFind",
diff --git a/src/lualib/ArrayFill.ts b/src/lualib/ArrayFill.ts
@@ -0,0 +1,19 @@
+// https://tc39.es/ecma262/multipage/indexed-collections.html#sec-array.prototype.fill
+export function __TS__ArrayFill<T>(this: T[], value: T, start?: number, end?: number): T[] {
+    let relativeStart = start ?? 0;
+    let relativeEnd = end ?? this.length;
+
+    if (relativeStart < 0) {
+        relativeStart += this.length;
+    }
+
+    if (relativeEnd < 0) {
+        relativeEnd += this.length;
+    }
+
+    for (let i = relativeStart; i < relativeEnd; i++) {
+        this[i] = value;
+    }
+
+    return this;
+}
diff --git a/src/transformation/builtins/array.ts b/src/transformation/builtins/array.ts
@@ -94,6 +94,8 @@ export function transformArrayPrototypeCall(
             return transformLuaLibFunction(context, LuaLibFeature.ArrayConcat, node, caller, ...params);
         case "entries":
             return transformLuaLibFunction(context, LuaLibFeature.ArrayEntries, node, caller);
+        case "fill":
+            return transformLuaLibFunction(context, LuaLibFeature.ArrayFill, node, caller, ...params);
         case "push":
             if (node.arguments.length === 1) {
                 const param = params[0] ?? lua.createNilLiteral();
diff --git a/test/unit/builtins/array.spec.ts b/test/unit/builtins/array.spec.ts
@@ -788,6 +788,33 @@ test.each([
     util.testExpression(literal).expectToHaveNoDiagnostics();
 });
 
+describe("array.fill", () => {
+    test.each(["[]", "[1]", "[1,2,3,4]"])("Fills full length of array without other parameters (%p)", arr => {
+        util.testExpression`${arr}.fill(5)`.expectToMatchJsResult();
+    });
+
+    test.each(["[1,2,3]", "[1,2,3,4,5,6]"])("Fills starting from start parameter (%p)", arr => {
+        util.testExpression`${arr}.fill(5, 3)`.expectToMatchJsResult();
+    });
+
+    test("handles negative start parameter", () => {
+        util.testExpression`[1,2,3,4,5,6,7].fill(8, -3)`.expectToMatchJsResult();
+    });
+
+    test("handles negative end parameter", () => {
+        util.testExpression`[1,2,3,4,5,6,7].fill(8, -5, -2)`.expectToMatchJsResult();
+    });
+
+    test("Fills starting from start parameter, up to ending parameter", () => {
+        util.testExpression`[1,2,3,4,5,6,7,8].fill(5, 2, 6)`.expectToMatchJsResult();
+    });
+
+    // NOTE: This is different from the default ECMAScript specification for the behavior, but for Lua this is much more useful
+    test("Extends size of the array if ending size is larger than array", () => {
+        util.testExpression`[1,2,3].fill(5, 0, 6)`.expectToEqual([5, 5, 5, 5, 5, 5]);
+    });
+});
+
 // Issue #1218: https://github.com/TypeScriptToLua/TypeScriptToLua/issues/1218
 test.each(["[1, 2, 3]", "undefined"])("prototype call on nullable array (%p)", value => {
     util.testFunction`
