add Target ES2021 mapping in transpilers/swc (#1521)

* add Target ES2021 mapping in transpilers/swc

I was getting error: `jsc.target should be es5 or upper to use getter / setter` 
and after investigation I've isolated issue and here is the "fix"

* fix and add tests

* fix

* lintfix

Co-authored-by: Andrew Bradley <cspotcode@gmail.com>

src/test/transpilers.spec.ts

@@ -0,0 +1,47 @@
+// third-party transpiler and swc transpiler tests
+// TODO: at the time of writing, other transpiler tests have not been moved into this file.
+// Should consolidate them here.
+
+import { context } from './testlib';
+import { contextTsNodeUnderTest, testsDirRequire } from './helpers';
+import * as expect from 'expect';
+
+const test = context(contextTsNodeUnderTest);
+
+test.suite('swc', (test) => {
+  test('verify that TS->SWC target mappings suppport all possible values from both TS and SWC', async (t) => {
+    const swcTranspiler = testsDirRequire(
+      'ts-node/transpilers/swc-experimental'
+    ) as typeof import('../transpilers/swc');
+
+    // Detect when mapping is missing any ts.ScriptTargets
+    const ts = testsDirRequire('typescript') as typeof import('typescript');
+    for (const key of Object.keys(ts.ScriptTarget)) {
+      if (/^\d+$/.test(key)) continue;
+      if (key === 'JSON') continue;
+      expect(
+        swcTranspiler.targetMapping.has(ts.ScriptTarget[key as any] as any)
+      ).toBe(true);
+    }
+
+    // Detect when mapping is missing any swc targets
+    // Assuming that tests/package.json declares @swc/core: latest
+    const swc = testsDirRequire('@swc/core');
+    let msg: string | undefined = undefined;
+    try {
+      swc.transformSync('', { jsc: { target: 'invalid' } });
+    } catch (e) {
+      msg = (e as Error).message;
+    }
+    expect(msg).toBeDefined();
+    // Error looks like:
+    // unknown variant `invalid`, expected one of `es3`, `es5`, `es2015`, `es2016`, `es2017`, `es2018`, `es2019`, `es2020`, `es2021` at line 1 column 28
+    const match = msg!.match(/unknown variant.*, expected one of (.*) at line/);
+    expect(match).toBeDefined();
+    const targets = match![1].split(', ').map((v: string) => v.slice(1, -1));
+
+    for (const target of targets) {
+      expect([...swcTranspiler.targetMapping.values()]).toContain(target);
+    }
+  });
+});

src/transpilers/swc.ts

@@ -56,7 +56,20 @@ export function create(createOptions: SwcTranspilerOptions): Transpiler {
   const nonTsxOptions = createSwcOptions(false);
   const tsxOptions = createSwcOptions(true);
   function createSwcOptions(isTsx: boolean): swcTypes.Options {
-    const swcTarget = targetMapping.get(target!) ?? 'es3';
+    let swcTarget = targetMapping.get(target!) ?? 'es3';
+    // Downgrade to lower target if swc does not support the selected target.
+    // Perhaps project has an older version of swc.
+    // TODO cache the results of this; slightly faster
+    let swcTargetIndex = swcTargets.indexOf(swcTarget);
+    for (; swcTargetIndex >= 0; swcTargetIndex--) {
+      try {
+        swcInstance.transformSync('', {
+          jsc: { target: swcTargets[swcTargetIndex] },
+        });
+        break;
+      } catch (e) {}
+    }
+    swcTarget = swcTargets[swcTargetIndex];
     const keepClassNames = target! >= /* ts.ScriptTarget.ES2016 */ 3;
     const moduleType =
       module === ModuleKind.CommonJS
@@ -119,16 +132,35 @@ export function create(createOptions: SwcTranspilerOptions): Transpiler {
   };
 }
 
-const targetMapping = new Map<ts.ScriptTarget, swcTypes.JscTarget>();
+/** @internal */
+export const targetMapping = new Map<ts.ScriptTarget, SwcTarget>();
 targetMapping.set(/* ts.ScriptTarget.ES3 */ 0, 'es3');
 targetMapping.set(/* ts.ScriptTarget.ES5 */ 1, 'es5');
 targetMapping.set(/* ts.ScriptTarget.ES2015 */ 2, 'es2015');
 targetMapping.set(/* ts.ScriptTarget.ES2016 */ 3, 'es2016');
 targetMapping.set(/* ts.ScriptTarget.ES2017 */ 4, 'es2017');
 targetMapping.set(/* ts.ScriptTarget.ES2018 */ 5, 'es2018');
 targetMapping.set(/* ts.ScriptTarget.ES2019 */ 6, 'es2019');
-targetMapping.set(/* ts.ScriptTarget.ES2020 */ 7, 'es2019');
-targetMapping.set(/* ts.ScriptTarget.ESNext */ 99, 'es2019');
+targetMapping.set(/* ts.ScriptTarget.ES2020 */ 7, 'es2020');
+targetMapping.set(/* ts.ScriptTarget.ES2021 */ 8, 'es2021');
+targetMapping.set(/* ts.ScriptTarget.ESNext */ 99, 'es2021');
+
+type SwcTarget = typeof swcTargets[number];
+/**
+ * @internal
+ * We use this list to downgrade to a prior target when we probe swc to detect if it supports a particular target
+ */
+const swcTargets = [
+  'es3',
+  'es5',
+  'es2015',
+  'es2016',
+  'es2017',
+  'es2018',
+  'es2019',
+  'es2020',
+  'es2021',
+] as const;
 
 const ModuleKind = {
   None: 0,