experimental-utils v3.0 requires TS 3.8 compiler and ES2015 target

[adidahiya]

I just upgraded to typescript-eslint 3.0 in a TypeScript project which uses @typescript-eslint/experimental-utils and got a slightly surprising compile error. The usage of ES private field syntax introduced in #2023 requires downstream TypeScript consumers to target ES2015 / ES6 or newer (TS docs).

../../node_modules/@typescript-eslint/experimental-utils/dist/eslint-utils/RuleTester.d.ts:7:5 - error TS18028: Private identifiers are only available when targeting ECMAScript 2015 and higher.
7     #private;
      ~~~~~~~~

This isn't a big problem for me, since I can update my "target" compiler option, but I just wanted to note this slight breaking change.

Versions

package	version
@typescript-eslint/experimental-utils	3.0.1
TypeScript	3.9.3
node	12.16.2

[bradzacher]

Interesting. I didn't realise that the truly private fields would even output in the .d.ts file.

there's no such thing as private field clashes, so it seems weird that they're even output in the .d.ts.

I was leveraging them because there was some stuff that I didn't want to leak, and I've made heavy use of them in the new scope manager #1939.

This means that consumers of the package must be on TS 3.8 or newer as well.
I might have to remove them then? Hmmm... I'll need to think a bit

[Etheryte]

Ran into the same issue unexpectedly when adding experimental utils to an existing project. Downgrading to 2.34.0 worked out well for us for now because we can't upgrade TS on a whim.