Migration to Angular 10.1 doesn't update TypeScript version to 4

[destus90]

🐞 Bug report

Command (mark with an x)

• new
• build
• serve
• test
• e2e
• generate
• add
• update
• lint
• xi18n
• run
• config
• help
• version
• doc

Is this a regression?

Not sure if this is a regression or not.

Description

When you update to 10.1 version, your TypeScript version won't be updated. It retains as ~3.9.5". As I know, Angular 10.1 supports TypeScript@4, due to #18319

🔬 Minimal Reproduction

1. clone it https://github.com/destus90/angular-ts-update-issue
2. run npm ci
3. run ng update @angular/core @angular/cli

🔥 Exception or Error

🌍 Your Environment

Anything else relevant?

[alan-agius4]

Hi @destus90,

This is working as intended.

Angular 10.1 still supports TypeScript 3.9.x, and therefore TypeScript 3.9.x is still within the supported range, therefore ng update @angular/core will not update the TypeScript version automatically. If you want to use TypeScript 4.0 in an existing application you'll need to opt-in manually by either running ng update typescript or updating the package.json.

The main reason for this is that TypeScript minor versions are breaking and it's likely that updating the TypeScript 4.0.2 will cause compilation errors, which is not ideal when updating between minor.

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