TypeScriptToLua · Perryvw · Jan 21, 2019 · Jan 18, 2019 · Jan 18, 2019 · Jan 18, 2019
diff --git a/src/Errors.ts b/src/Errors.ts
@@ -116,4 +116,9 @@ export class TSTLErrors {
                                   + "the TupleReturn decorator.",
                                   node);
     }
+
+    public static UnsupportedUnionAccessor = (node: ts.Node) => {
+        return new TranspileError(`Unsupported union of accessor with non-accessor types.`,
+                                  node);
+    }
 }
diff --git a/src/TSHelper.ts b/src/TSHelper.ts
@@ -245,11 +245,22 @@ export class TSHelper {
         }
     }
 
-    public static hasGetAccessor(node: ts.Node, checker: ts.TypeChecker): boolean {
+    public static typeHasGetAccessor(type: ts.Type, name: ts.__String, checker: ts.TypeChecker): boolean | undefined {
+        if (type.isUnion()) {
+            if (type.types.some(t => this.typeHasGetAccessor(t, name, checker))) {
+                // undefined if only a subset of types implements the accessor
+                return type.types.every(t => this.typeHasGetAccessor(t, name, checker)) ? true : undefined;
+            }
+            return false;
+        }
+        return this.forTypeOrAnySupertype(type, checker, t => this.hasExplicitGetAccessor(t, name));
+    }
+
+    public static hasGetAccessor(node: ts.Node, checker: ts.TypeChecker): boolean | undefined {
         if (ts.isPropertyAccessExpression(node)) {
             const name = node.name.escapedText;
             const type = checker.getTypeAtLocation(node.expression);
-            return this.forTypeOrAnySupertype(type, checker, t => this.hasExplicitGetAccessor(t, name));
+            return this.typeHasGetAccessor(type, name, checker);
         }
         return false;
     }
@@ -261,11 +272,22 @@ export class TSHelper {
         }
     }
 
+    public static typeHasSetAccessor(type: ts.Type, name: ts.__String, checker: ts.TypeChecker): boolean | undefined {
+        if (type.isUnion()) {
+            if (type.types.some(t => this.typeHasSetAccessor(t, name, checker))) {
+                // undefined if only a subset of types implements the accessor
+                return type.types.every(t => this.typeHasSetAccessor(t, name, checker)) ? true : undefined;
+            }
+            return false;
+        }
+        return this.forTypeOrAnySupertype(type, checker, t => this.hasExplicitSetAccessor(t, name));
+    }
+
     public static hasSetAccessor(node: ts.Node, checker: ts.TypeChecker): boolean {
         if (ts.isPropertyAccessExpression(node)) {
             const name = node.name.escapedText;
             const type = checker.getTypeAtLocation(node.expression);
-            return this.forTypeOrAnySupertype(type, checker, t => this.hasExplicitSetAccessor(t, name));
+            return this.typeHasSetAccessor(type, name, checker);
         }
         return false;
     }

diff --git a/src/Transpiler.ts b/src/Transpiler.ts
@@ -965,8 +965,11 @@ export abstract class LuaTranspiler {
     }
 
     public transpileAssignment(node: ts.BinaryExpression, lhs: string, rhs: string): string {
-        if (tsHelper.hasSetAccessor(node.left, this.checker)) {
+        const hasSetAccessor = tsHelper.hasSetAccessor(node.left, this.checker);
+        if (hasSetAccessor) {
             return this.transpileSetAccessor(node.left as ts.PropertyAccessExpression, rhs);
+        } else if (hasSetAccessor === undefined) {
+            throw TSTLErrors.UnsupportedUnionAccessor(node);
         }
 
         // Validate assignment
@@ -1611,8 +1614,11 @@ export abstract class LuaTranspiler {
     public transpilePropertyAccessExpression(node: ts.PropertyAccessExpression): string {
         const property = node.name.text;
 
-        if (tsHelper.hasGetAccessor(node, this.checker)) {
+        const hasGetAccessor = tsHelper.hasGetAccessor(node, this.checker);
+        if (hasGetAccessor) {
             return this.transpileGetAccessor(node);
+        } else if (hasGetAccessor === undefined) {
+            throw TSTLErrors.UnsupportedUnionAccessor(node);
         }
 
         // Check for primitive types to override

diff --git a/test/unit/expressions.spec.ts b/test/unit/expressions.spec.ts
@@ -317,6 +317,34 @@ export class ExpressionTests {
         Expect(result).toBe(expected);
     }
 
+    @TestCase("return x.value;", 1)
+    @TestCase("x.value = 3; return x.value;", 3)
+    @Test("Union accessors")
+    public unionAccessors(expression: string, expected: any): void {
+        const source = `class A{ get value(){ return this.v || 1; } set value(v){ this.v = v; } v: number; }
+                        class B{ get value(){ return this.v || 2; } set value(v){ this.v = v; } v: number; }
+                        let x: A|B = new A();
+                        ${expression}`;
+
+        const lua = util.transpileString(source);
+        const result = util.executeLua(lua);
+        Expect(result).toBe(expected);
+    }
+
+    @TestCase("x.value = 3;")
+    @TestCase("return x.value;")
+    @Test("Unsupported Union accessors")
+    public unsupportedUnionAccessors(expression: string): void {
+        const source = `class A{ get value(){ return 1; } }
+                        class B{ value:number = 3; }
+                        let x: A|B = new A();
+                        ${expression}`;
+        Expect(() => { util.transpileString(source); }).toThrowError(
+            TranspileError,
+            "Unsupported union of accessor with non-accessor types."
+        );
+    }
+
     @TestCase("i++", 10)
     @TestCase("i--", 10)
     @TestCase("++i", 11)