Merge pull request #8982 from backstage/rugvip/tsbump

Upgrade TypeScript to 4.5 and decouple versioning

.changeset/clever-olives-shake.md

@@ -0,0 +1,40 @@
+---
+'@backstage/cli': minor
+---
+
+Removed the `typescript` dependency from the Backstage CLI in order to decouple the TypeScript version in Backstage projects. To keep using a specific TypeScript version, be sure to add an explicit dependency in your root `package.json`:
+
+```json
+  "dependencies": {
+    ...
+    "typescript": "~4.5.4",
+  }
+```
+
+We recommend using a `~` version range since TypeScript releases do not adhere to semver.
+
+It may be the case that you end up with errors if you upgrade the TypeScript version. This is because there was a change to TypeScript not long ago that defaulted the type of errors caught in `catch` blocks to `unknown`. You can work around this by adding `"useUnknownInCatchVariables": false` to the `"compilerOptions"` in your `tsconfig.json`:
+
+```json
+  "compilerOptions": {
+    ...
+    "useUnknownInCatchVariables": false
+  }
+```
+
+Another option is to use the utilities from `@backstage/errors` to assert the type of errors caught in `catch` blocks:
+
+```ts
+import { assertError, isError } from '@backstage/errors';
+
+try {
+  ...
+} catch (error) {
+  assertError(error);
+  ...
+  // OR
+  if (isError(error)) {
+    ...
+  }
+}
+```

.changeset/stupid-baboons-hug.md

@@ -0,0 +1,42 @@
+---
+'@backstage/create-app': patch
+---
+
+The app template has been updated to add an explicit dependency on `typescript` in the root `package.json`. This is because it was removed as a dependency of `@backstage/cli` in order to decouple the TypeScript versioning in Backstage projects.
+
+To apply this change in an existing app, add a `typescript` dependency to your `package.json` in the project root:
+
+```json
+  "dependencies": {
+    ...
+    "typescript": "~4.5.4",
+  }
+```
+
+We recommend using a `~` version range since TypeScript releases do not adhere to semver.
+
+It may be the case that you end up with errors if you upgrade the TypeScript version. This is because there was a change to TypeScript not long ago that defaulted the type of errors caught in `catch` blocks to `unknown`. You can work around this by adding `"useUnknownInCatchVariables": false` to the `"compilerOptions"` in your `tsconfig.json`:
+
+```json
+  "compilerOptions": {
+    ...
+    "useUnknownInCatchVariables": false
+  }
+```
+
+Another option is to use the utilities from `@backstage/errors` to assert the type of errors caught in `catch` blocks:
+
+```ts
+import { assertError, isError } from '@backstage/errors';
+
+try {
+  ...
+} catch (error) {
+  assertError(error);
+  ...
+  // OR
+  if (isError(error)) {
+    ...
+  }
+}
+```