[NewErrors] 4.3.0-dev.20210307 vs 4.2.3

[typescript-bot]

The following errors were reported by 4.3.0-dev.20210307, but not by 4.2.3

cdr/code-server

10 of 51 projects failed to build with the old tsc

lib/vscode/extensions/html-language-features/server/tsconfig.json

• error TS2367: This condition will always return 'true' since the types 'Promise<import("/mnt/ts_downloads/code-server/lib/vscode/extensions/node_modules/typescript/lib/typescript").LanguageService>' and 'false' have no overlap.
  • lib/vscode/extensions/html-language-features/server/src/modes/javascriptMode.ts#L68

lib/vscode/extensions/typescript-language-features/tsconfig.json

• error TS2367: This condition will always return 'true' since the types 'Promise<import("/mnt/ts_downloads/code-server/lib/vscode/extensions/typescript-language-features/src/typescriptService").ServerResponse.Response<protocol.Response>>' and 'false' have no overlap.
  • lib/vscode/extensions/typescript-language-features/src/tsServer/server.ts#L362

vercel/hyper

1 of 2 projects failed to build with the old tsc

tsconfig.json

• error TS2367: This condition will always return 'true' since the types 'Promise<void>' and 'false' have no overlap.
  • cli/index.ts#L189 in tsconfig.json

ReactiveX/rxjs

7 of 11 projects failed to build with the old tsc

src/tsconfig.cjs.spec.json

• error TS2769: No overload matches this call.
  • src/internal/operators/zipWith.ts#L81

src/tsconfig.esm5.rollup.json

• error TS2769: No overload matches this call.
  • src/internal/operators/zipWith.ts#L81

typeorm/typeorm

tsconfig.json

• error TS2367: This condition will always return 'true' since the types 'Promise<any>' and 'false' have no overlap.
  • src/driver/aurora-data-api-pg/AuroraDataApiPostgresQueryRunner.ts#L71
  • src/driver/cockroachdb/CockroachQueryRunner.ts#L89
  • src/driver/mysql/MysqlQueryRunner.ts#L75
  • src/driver/oracle/OracleQueryRunner.ts#L73
  • src/driver/postgres/PostgresQueryRunner.ts#L79

[DanielRosenwasser]

The cdr/code-server errors seem good - these are unnecessary checks for Promises that will always be present as far as I can tell.

The Vercel one is way more questionable - it looks like we're not checking the narrowed type or something like that on commandPromise.

I already brought up issues around TypeORM last week's #43004 (comment), in that without strictPropertyInitialization and checks against this.yaddaYadda, you really have no way to ensure that the properties were definitely assigned.