fix: lock Typescript to 3.6.0

[imnotjames]

Because of a breaking feature in Typescript 3.7.0 we cannot upgrade
past that without marooning users of Typescript 3.5 / 3.6 & 4.0+

this locks typescript to ~3.6.0 explicitly and fixes some small
issues that arise in using that version

fixes #6809
fixes #6805

[imnotjames]

):

It looks like the only safe upgrade path is directly to 4.0 & requiring all users of TypeORM with Typescript to use 4.0+?

[imnotjames]

nestjs ran into this issue as well nestjs/nest#3513

The issue about this in Typescript is microsoft/TypeScript#33939 but was closed as working as intended. Unfortunately, the backwards compat break in a minor release was the intended outcome.

[pleerock]

I guess I need to release a new version?

[imnotjames]

😢 yes, apologies on it being so soon.

[imnotjames]

Ideally we get some folks confirming this as well - I checked against TS 4.0.3 myself and it seemed fine?

[pleerock]

there are many 👍 on that issue, so I guess there is a problem.

[bryantbiggs]

so can typeorm be used with TS v4.0.x or no?

[imnotjames]

It should work for you but it's not officially supported yet. We transpile using 3.6 but it should be compatible with 4.0 - we don't run tests to confirm that.

[bryantbiggs]

perfect, thanks

[pleerock]

yes, of course it does support 4.x. This PR is only about used compiler version for the internal development.

[nebkat]

Could we consider using https://github.com/sandersn/downlevel-dts and "typesVersions" in package.json to fix this? We would benefit a lot from TypeScript 3.7's optional chaining and nullish coalescing to replace the hundreds of options && options.option in the repo, and I'm sure some later features too.

Since it's only a matter of having the .d.ts files correctly parsed we could easily add an extra test for every TS version down to the minimum that is supported, which will prevent accidents like this in the future.