Omitted expression support (#643)

hazzard993 · Perryvw · commit 3fa2065ac064 · 2019-06-29T16:10:58.000+02:00
* Omitted expression support

* Add test for result of omitted expression

* Check the contents of the same array

* Neaten up test

* Support OmittedExpressions in array binding assignments

* Make transformOmittedExpression context aware and use transformBindingExpression
diff --git a/src/LuaTransformer.ts b/src/LuaTransformer.ts
@@ -2683,6 +2683,8 @@ export class LuaTransformer {
                 return this.transformArrayLiteral(expression as ts.ArrayLiteralExpression);
             case ts.SyntaxKind.ObjectLiteralExpression:
                 return this.transformObjectLiteral(expression as ts.ObjectLiteralExpression);
+            case ts.SyntaxKind.OmittedExpression:
+                return this.transformOmittedExpression(expression as ts.OmittedExpression);
             case ts.SyntaxKind.DeleteExpression:
                 return this.transformDeleteExpression(expression as ts.DeleteExpression);
             case ts.SyntaxKind.FunctionExpression:
@@ -2909,7 +2911,7 @@ export class LuaTransformer {
             // Destructuring assignment
             const left =
                 expression.left.elements.length > 0
-                    ? expression.left.elements.map(e => this.transformExpression(e))
+                    ? expression.left.elements.map(e => this.transformArrayBindingExpression(e))
                     : [tstl.createAnonymousIdentifier(expression.left)];
             let right: tstl.Expression[];
             if (ts.isArrayLiteralExpression(expression.right)) {
@@ -3466,6 +3468,11 @@ export class LuaTransformer {
         return tstl.createTableExpression(properties, expression);
     }
 
+    public transformOmittedExpression(node: ts.OmittedExpression): ExpressionVisitResult {
+        const isWithinBindingAssignmentStatement = tsHelper.isWithinLiteralAssignmentStatement(node);
+        return isWithinBindingAssignmentStatement ? tstl.createAnonymousIdentifier() : tstl.createNilLiteral(node);
+    }
+
     public transformDeleteExpression(expression: ts.DeleteExpression): ExpressionVisitResult {
         const lhs = this.transformExpression(expression.expression) as tstl.AssignmentLeftHandSideExpression;
         const assignment = tstl.createAssignmentStatement(lhs, tstl.createNilLiteral(), expression);
@@ -4577,14 +4584,18 @@ export class LuaTransformer {
     }
 
     public transformArrayBindingElement(name: ts.ArrayBindingElement): ExpressionVisitResult {
+        return this.transformArrayBindingExpression(name as ts.Expression);
+    }
+
+    public transformArrayBindingExpression(name: ts.Expression): ExpressionVisitResult {
         if (ts.isOmittedExpression(name)) {
-            return tstl.createIdentifier("__", name);
+            return this.transformOmittedExpression(name);
         } else if (ts.isIdentifier(name)) {
             return this.transformIdentifier(name);
         } else if (ts.isBindingElement(name) && ts.isIdentifier(name.name)) {
             return this.transformIdentifier(name.name);
         } else {
-            throw TSTLErrors.UnsupportedKind("array binding element", name.kind, name);
+            throw TSTLErrors.UnsupportedKind("array binding expression", name.kind, name);
         }
     }
 
diff --git a/src/TSHelper.ts b/src/TSHelper.ts
@@ -794,6 +794,19 @@ export function isEnumMember(
     }
 }
 
+export function isWithinLiteralAssignmentStatement(node: ts.Node): boolean {
+    if (!node.parent) {
+        return false;
+    }
+    if (ts.isArrayLiteralExpression(node.parent) || ts.isObjectLiteralExpression(node.parent)) {
+        return isWithinLiteralAssignmentStatement(node.parent);
+    } else if (ts.isBinaryExpression(node.parent) && node.parent.operatorToken.kind === ts.SyntaxKind.EqualsToken) {
+        return true;
+    } else {
+        return false;
+    }
+}
+
 export function moduleHasEmittedBody(
     statement: ts.ModuleDeclaration
 ): statement is ts.ModuleDeclaration & { body: ts.ModuleBlock | ts.ModuleDeclaration } {
diff --git a/test/unit/array.spec.ts b/test/unit/array.spec.ts
@@ -191,3 +191,22 @@ test.each([
     `;
     expect(() => util.transpileAndExecute(code)).toThrowError(`invalid array length: ${result}`);
 });
+
+test.each([0, 1, 2])("Array with OmittedExpression", index => {
+    const result = util.transpileAndExecute(
+        `const myarray = [1, , 2];
+        return myarray[${index}];`
+    );
+
+    expect(result).toBe([1, , 2][index]);
+});
+
+test("OmittedExpression in Array Binding Assignment Statement", () => {
+    const result = util.transpileAndExecute(
+        `let a, c;
+        [a, , c] = [1, 2, 3];
+        return a + c;`
+    );
+
+    expect(result).toBe(4);
+});
