Handled conditional types (dart-archive#70)

Author: derekxu16

lib/declaration.ts

@@ -636,8 +636,12 @@ export default class DeclarationTranspiler extends base.TranspilerBase {
             this.emit(
                 'Warning: Mapped types are not supported in Dart. Uses of this type will be replaced by dynamic.');
             this.emitNoSpace('\n');
+          } else if (ts.isConditionalTypeNode(alias.type)) {
+            this.emit(
+                'Warning: Conditional types are not supported in Dart. Uses of this type will be replaced by dynamic.');
+            this.emitNoSpace('\n');
           }
-          this.emit(alias.getText());
+          this.emitNoSpace(alias.getText());
           this.emitNoSpace('\n');
           this.exitCodeComment();
           this.emitNoSpace('\n');

lib/facade_converter.ts

@@ -399,11 +399,16 @@ export class FacadeConverter extends base.TranspilerBase {
       const indexTypeName = this.generateDartTypeName(node.indexType, addInsideComment(options));
 
       comment = `${objectTypeName}[${indexTypeName}]`;
-    } else if (ts.isMappedTypeNode(node)) {
+    } else if (ts.isMappedTypeNode(node) || ts.isConditionalTypeNode(node)) {
       name = 'dynamic';
       if (ts.isTypeAliasDeclaration(node.parent)) {
-        // MappedTypeNodes don't contain information about the name or type arguments that were
-        // passed to the alias, so we have to get that information from the parent
+        // Declarations of mapped types and conditional types will be printed in a comment elsewhere
+        // in the file. Upon reaching a node of these kinds, we do not want to re-print the
+        // declaration. We just want to print the alias name and the type arguments that were
+        // passed.
+        // MappedTypeNodes and ConditionalTypeNodes don't contain information about the name or type
+        // arguments that were passed to the alias, so we have to get that information from the
+        // parent.
         const parent = node.parent;
         comment = parent.name.getText();
         if (parent.typeParameters && options.resolvedTypeArguments) {

test/type_test.ts

@@ -166,14 +166,51 @@ abstract class Todo {
 
 /*
  Warning: Mapped types are not supported in Dart. Uses of this type will be replaced by dynamic.
- type ReadonlyTodo = {
+type ReadonlyTodo = {
         readonly[P in keyof Todo]: Todo[P];
       }
 */
 @JS()
 external dynamic /*ReadonlyTodo*/ get todo;`);
     });
   });
+
+  it('should support conditional types', () => {
+    expectTranslate(`
+type TypeName<T> = T extends string ? "string" :
+T extends string ? "string" :
+T extends number ? "number" :
+T extends boolean ? "boolean" :
+T extends undefined ? "undefined" :
+T extends Function ? "function" :
+"object";
+
+declare var x: TypeName<number>;
+declare var y: TypeName<string>;
+declare var z: TypeName<boolean>;`)
+        .to.equal(
+            `/*Warning: Conditional types are not supported in Dart. Uses of this type will be replaced by dynamic.
+type TypeName<T> = T extends string ? "string" :
+T extends string ? "string" :
+T extends number ? "number" :
+T extends boolean ? "boolean" :
+T extends undefined ? "undefined" :
+T extends Function ? "function" :
+"object";
+*/
+@JS()
+external dynamic /*TypeName<num>*/ get x;
+@JS()
+external set x(dynamic /*TypeName<num>*/ v);
+@JS()
+external dynamic /*TypeName<String>*/ get y;
+@JS()
+external set y(dynamic /*TypeName<String>*/ v);
+@JS()
+external dynamic /*TypeName<bool>*/ get z;
+@JS()
+external set z(dynamic /*TypeName<bool>*/ v);`);
+  });
 });
 
 describe('type arguments', () => {