allow disabling "use strict" emit in SWC when you reeeally want to

src/transpilers/swc.ts

@@ -52,6 +52,9 @@ export function create(createOptions: SwcTranspilerOptions): Transpiler {
     module,
     jsxFactory,
     jsxFragmentFactory,
+    strict,
+    alwaysStrict,
+    noImplicitUseStrict,
   } = compilerOptions;
   const nonTsxOptions = createSwcOptions(false);
   const tsxOptions = createSwcOptions(true);
@@ -71,21 +74,39 @@ export function create(createOptions: SwcTranspilerOptions): Transpiler {
     }
     swcTarget = swcTargets[swcTargetIndex];
     const keepClassNames = target! >= /* ts.ScriptTarget.ES2016 */ 3;
+    // swc only supports these 4x module options
     const moduleType =
       module === ModuleKind.CommonJS
         ? 'commonjs'
         : module === ModuleKind.AMD
         ? 'amd'
         : module === ModuleKind.UMD
         ? 'umd'
-        : undefined;
+        : 'es6';
+    // In swc:
+    //   strictMode means `"use strict"` is *always* emitted for non-ES module, *never* for ES module where it is assumed it can be omitted.
+    //   (this assumption is invalid, but that's the way swc behaves)
+    // tsc is a bit more complex:
+    //   alwaysStrict will force emitting it always unless `import`/`export` syntax is emitted which implies it per the JS spec.
+    //   if not alwaysStrict, will emit implicitly whenever module target is non-ES *and* transformed module syntax is emitted.
+    // For node, best option is to assume that all scripts are modules (commonjs or esm) and thus should get tsc's implicit strict behavior.
+
+    // Always set strictMode, *unless* alwaysStrict is disabled and noImplicitUseStrict is enabled
+    const strictMode =
+      // if `alwaysStrict` is disabled, remembering that `strict` defaults `alwaysStrict` to true
+      (alwaysStrict === false || (alwaysStrict !== true && strict !== true)) &&
+      // if noImplicitUseStrict is enabled
+      noImplicitUseStrict === true
+        ? false
+        : true;
     return {
       sourceMaps: sourceMap,
       // isModule: true,
       module: moduleType
         ? ({
             noInterop: !esModuleInterop,
             type: moduleType,
+            strictMode,
           } as swcTypes.ModuleConfig)
         : undefined,
       swcrc: false,