cli: disable sucrase ES transforms

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

.changeset/mighty-needles-know.md

@@ -0,0 +1,5 @@
+---
+'@backstage/cli': patch
+---
+
+Disabled ECMAScript transforms in app and backend builds in order to reduce bundle size and runtime performance. For the rationale and a full list of syntax that is no longer transformed, see https://github.com/alangpierce/sucrase#transforms. This also enables TypeScripts `useDefineForClassFields` flag by default, which in rare occasions could cause build failures. For instructions on how to mitigate issues due to the flag, see the [TypeScript documentation](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#the-usedefineforclassfields-flag-and-the-declare-property-modifier).

packages/cli/config/tsconfig.json

@@ -33,6 +33,7 @@
     "strictPropertyInitialization": true,
     "stripInternal": true,
     "target": "ES2019",
-    "types": ["node", "jest", "webpack-env"]
+    "types": ["node", "jest", "webpack-env"],
+    "useDefineForClassFields": true
   }
 }

packages/cli/src/lib/bundler/transforms.ts

@@ -39,6 +39,7 @@ export const transforms = (options: TransformOptions): Transforms => {
       loader: require.resolve('@sucrase/webpack-loader'),
       options: {
         transforms: ['typescript', 'jsx', ...extraTransforms],
+        disableESTransforms: true,
         production: !isDev,
       },
     },
@@ -48,6 +49,7 @@ export const transforms = (options: TransformOptions): Transforms => {
       loader: require.resolve('@sucrase/webpack-loader'),
       options: {
         transforms: ['jsx', ...extraTransforms],
+        disableESTransforms: true,
         production: !isDev,
       },
     },
@@ -64,6 +66,7 @@ export const transforms = (options: TransformOptions): Transforms => {
           loader: require.resolve('@sucrase/webpack-loader'),
           options: {
             transforms: ['jsx', ...extraTransforms],
+            disableESTransforms: true,
             production: !isDev,
           },
         },