Fix #33448 - Filter discriminants of type never

[Jack Williams (jack-williams)]

Fixes#33448

[Jack Williams (jack-williams)]

Here is something that is new with the PR (be it good or bad).

exporttypeRuntimeValue={type: 'number',value: number,}|{type: 'string',value: string,}|{type: boolean,value: boolean,};functionfoo(x: RuntimeValue&({type: 'number'}|{type: 'string'})){if(x.type==="number"){x.value// now number}else{x.value// now string}}

Awkwardly, this does not work.

functionfoo(x: RuntimeValue&{type: 'number'}){if(x.type==="number"){x.value// number | string | boolean}else{x.value// number | string | boolean}}

Is it worth expanding the definition of discriminant properties to fix this?

[Jack Williams (jack-williams)]

TypeScript Bot (@typescript-bot) test this
TypeScript Bot (@typescript-bot) user test this

[TypeScript Bot (typescript-bot)]

Heya Jack Williams (@jack-williams), I've started to run the extended test suite on this PR at 97c5587. You can monitor the build here. It should now contribute to this PR's status checks.

[TypeScript Bot (typescript-bot)]

Heya Jack Williams (@jack-williams), I've started to run the parallelized community code test suite on this PR at 97c5587. You can monitor the build here. It should now contribute to this PR's status checks.

[TypeScript Bot (typescript-bot)]

The user suite test run you requested has finished and failed. I've opened a PR with the baseline diff from master.