Compiler CLI typings cannot be processed with typescript 4.2.4

Bug Report

Affected Package

The issue is caused by package @angular/compiler-cli

Is this a regression?

Don’t know

Description

Compiler CLI uses ts.MemberName type, which in typescript 4.2.4 is not present, probable added in typescript 4.3 which reports error:

node_modules/@angular/compiler-cli/src/ngtsc/translator/src/typescript_ast_factory.d.ts:38:73 - error TS2694: Namespace 'ts' has no exported member 'MemberName'.

Minimal Reproduction

Try to compile compiler-cli ts files with ts 4.2.4

Exception or Error

node_modules/@angular/compiler-cli/src/ngtsc/translator/src/typescript_ast_factory.d.ts:38:73 - error TS2694: Namespace 'ts' has no exported member 'MemberName'.

Your Environment

Angular Version:

Angular CLI: 12.1.0

Anything else relevant? Probably compiler-cli should require at last typescript 4.3 or should not use types which were not present in typescript 4.2.4

[alan-agius4]

@ngtools/webpack supports the exact versions of TypeScript versions that the framework support, in terms of which version of TypeScript can be used to compile an application.

Therefore, changing the TypeScript peer dependency to the upper bound version would not be correct here and technically it would be a breaking change.

We can add it to the docs, although from my experience this is the first time that someone experienced this problem and seeing that this issue didn’t receive any community interest. I’d say it doesn’t warrant to do any change from our end and having this issue on GitHub should be sufficient.

We can always revisit this if we see that it impacts the community in a greater manner, but for the time being my suggestion would be to close this issue as also by using @ngtools/webpack directly you are opting to off the “happy path”.

[alan-agius4]

Discussed this with @devversion and we feel that the best course of action here is that if you are using the compiler-cli types/API both directly or transitively via @ngtools/webpack. The better option would be to use the same TypeScript version used to compile the package. This is typically the max version which is supported by the Angular Compiler. If for a reason or another this is not possible using skipLibCheck as an interim solution is a good enough workaround.

The reasoning behind this is that while making @angular/compiler-cli work with TypeScript 4.2 type-wise is straightforward in this case, it sets the precedent for us “caring” about such things which might complicate things in the future.

While we do guarantee the the compiler will compile source files when using TypeScript 4.2, we don’t guarantee that its’ types are compatible with this version.