BooleanCompilerOptions uses TypeScript@2.9 features

[JoshuaKGoldberg]

See discussion in microsoft/tslint-microsoft-contrib#469 (comment):

Using tsc v2.6.2
node_modules/tsutils/util/util.d.ts(117,73): error TS1005: ';' expected.
node_modules/tsutils/util/util.d.ts(118,1): error TS1128: Declaration or statement expected.
node_modules/tsutils/util/util.d.ts(118,3): error TS1128: Declaration or statement expected.
node_modules/tsutils/util/util.d.ts(119,17): error TS1005: ',' expected.
node_modules/tsutils/util/util.d.ts(119,36): error TS1005: ';' expected.
node_modules/tsutils/util/util.d.ts(119,44): error TS1005: ';' expected.
node_modules/tsutils/util/util.d.ts(120,3): error TS1128: Declaration or statement expected.

tsutils lists its TypeScript dependency as allowing 2.1 and up. Two issues:

• Either this construct should be simplified or that dependency should be upgraded
• Can there be builds added that test with TypeScript at the lowest allowed version?

[ajafff]

tsutils lists its TypeScript dependency as allowing 2.1 and up

Note that the version of TypeScript used to compile your project is not necessarily the version installed in node_modules (at design or run time).

From README.md:

This package is backwards compatible with typescript 2.1.0 at runtime although compiling might need a newer version of typescript installed.

Shipping declaration files for different versions of the compiler is not possible. Especially when adding utilities for newer TypeScript versions.

Compiling with TypeScript@2.8 succeeds. And that's currently the lowest version I'm actively trying to make this library compatible with at compile time.

---

I agree it's a bit surprising this is now a syntax error which cannot be suppressed with skipLibCheck.

Can there be builds added that test with TypeScript at the lowest allowed version?

Sure. Feel free to submit a pull request that ensures the emitted declaration files are compatible with a certain version of TypeScript.

[ajafff]

FWIW, I updated the dependency of TypeScript to >=2.8.0 in v3.0.0 of this library