ArraySetLength lib function (#521)

tomblind · web-flow · commit 29047b51c48a · 2019-04-13T11:10:15.000-06:00
* added ArrayLengthSet lib function

* Disabled tslint error in ArraySetLength

* Handling NaN, Infinity, and non-integers

* Removed unneeded -Infinity check
diff --git a/src/LuaLib.ts b/src/LuaLib.ts
@@ -19,6 +19,7 @@ export enum LuaLibFeature {
     ArraySplice = "ArraySplice",
     ArrayFlat = "ArrayFlat",
     ArrayFlatMap = "ArrayFlatMap",
+    ArraySetLength = "ArraySetLength",
     ClassIndex = "ClassIndex",
     ClassNewIndex = "ClassNewIndex",
     FunctionApply = "FunctionApply",
diff --git a/src/LuaTransformer.ts b/src/LuaTransformer.ts
@@ -2494,6 +2494,18 @@ export class LuaTransformer {
         const leftType = this.checker.getTypeAtLocation(expression.left);
         this.validateFunctionAssignment(expression.right, rightType, leftType);
 
+        if (tsHelper.isArrayLengthAssignment(expression, this.checker, this.program)) {
+            // array.length = x
+            return tstl.createExpressionStatement(
+                this.transformLuaLibFunction(
+                    LuaLibFeature.ArraySetLength,
+                    expression,
+                    this.transformExpression(expression.left.expression),
+                    this.transformExpression(expression.right)
+                )
+            );
+        }
+
         if (ts.isArrayLiteralExpression(expression.left)) {
             // Destructuring assignment
             const left = expression.left.elements.length > 0
@@ -2528,6 +2540,16 @@ export class LuaTransformer {
         const leftType = this.checker.getTypeAtLocation(expression.left);
         this.validateFunctionAssignment(expression.right, rightType, leftType);
 
+        if (tsHelper.isArrayLengthAssignment(expression, this.checker, this.program)) {
+            // array.length = x
+            return this.transformLuaLibFunction(
+                LuaLibFeature.ArraySetLength,
+                expression,
+                this.transformExpression(expression.left.expression),
+                this.transformExpression(expression.right)
+            );
+        }
+
         if (ts.isArrayLiteralExpression(expression.left)) {
             // Destructuring assignment
             // (function() local ${tmps} = ${right}; ${left} = ${tmps}; return {${tmps}} end)()
diff --git a/src/TSHelper.ts b/src/TSHelper.ts
@@ -752,4 +752,30 @@ export class TSHelper {
         }
         return false;
     }
+
+    public static isArrayLengthAssignment(
+        expression: ts.BinaryExpression,
+        checker: ts.TypeChecker,
+        program: ts.Program
+    ): expression is ts.BinaryExpression & { left: ts.PropertyAccessExpression | ts.ElementAccessExpression; }
+    {
+        if (expression.operatorToken.kind !== ts.SyntaxKind.EqualsToken) {
+            return false;
+        }
+
+        if (!ts.isPropertyAccessExpression(expression.left) && !ts.isElementAccessExpression(expression.left)) {
+            return false;
+        }
+
+        const type = checker.getTypeAtLocation(expression.left.expression);
+        if (!TSHelper.isArrayType(type, checker, program)) {
+            return false;
+        }
+
+        const name = ts.isPropertyAccessExpression(expression.left)
+            ? expression.left.name.escapedText as string
+            : ts.isStringLiteral(expression.left.argumentExpression) && expression.left.argumentExpression.text;
+
+        return name === "length";
+    }
 }
diff --git a/src/lualib/ArraySetLength.ts b/src/lualib/ArraySetLength.ts
@@ -0,0 +1,14 @@
+function __TS__ArraySetLength<T>(this: void, arr: T[], length: number): number {
+    if (length < 0
+        || length !== length // NaN
+        || length === (1 / 0) // Infinity
+        || Math.floor(length) !== length) // non-integer
+    {
+        // tslint:disable-next-line:no-string-throw
+        throw `invalid array length: ${length}`;
+    }
+    for (let i = arr.length - 1; i >= length; --i) {
+        arr[i] = undefined;
+    }
+    return length;
+}
diff --git a/test/unit/array.spec.ts b/test/unit/array.spec.ts
@@ -136,3 +136,43 @@ test("Array property access", () => {
     `;
     expect(util.transpileAndExecute(code)).toBe("bar123");
 });
+
+test.each([{ length: 0, result: 0 }, { length: 1, result: 1 }, { length: 7, result: 3 }])(
+    "Array length set",
+    ({ length, result }) => {
+        const code = `
+        const arr = [1, 2, 3];
+        arr.length = ${length};
+        return arr.length;
+    `;
+        expect(util.transpileAndExecute(code)).toBe(result);
+    },
+);
+
+test.each([
+    { length: 0, result: "0/0" },
+    { length: 1, result: "1/1" },
+    { length: 7, result: "7/3" },
+])("Array length set as expression", ({ length, result }) => {
+    const code = `
+        const arr = [1, 2, 3];
+        const l = arr.length = ${length};
+        return \`\${l}/\${arr.length}\`;
+    `;
+    expect(util.transpileAndExecute(code)).toBe(result);
+});
+
+test.each([
+    { length: -1, result: -1 },
+    { length: -7, result: -7 },
+    { length: 0.1, result: 0.1 },
+    { length: "0 / 0", result: "NaN" },
+    { length: "1 / 0", result: "Infinity" },
+    { length: "-1 / 0", result: "-Infinity" },
+])("Invalid array length set", ({ length, result }) => {
+    const code = `
+        const arr = [1, 2, 3];
+        arr.length = ${length};
+    `;
+    expect(() => util.transpileAndExecute(code)).toThrowError(`invalid array length: ${result}`);
+});
