TS issues in FR Gatherer Meta #12619
Description
A few days ago, we ran into an issue with distributed conditional types on FRTransitionalContext. This caused unexpected behavior when defining a gatherer with multiple dependencies.
The issues with FRTransitionalContext have been resolved by #12565 but this popped up again with GathererMeta.
lighthouse/types/gatherer.d.ts
Lines 98 to 101 in 761e47e
Multiple dependencies doesn't produce any errors, but the type is too lenient. For example, these are both valid according to our type definition:
/**
* @type {LH.Gatherer.GathererMeta<'DevtoolsLog'|'Trace'>}
*/
this.meta = {
supportedModes: ['timespan', 'navigation'],
dependencies: {DevtoolsLog: DevtoolsLog.symbol, Trace: Trace.symbol},
}/**
* @type {LH.Gatherer.GathererMeta<'DevtoolsLog'|'Trace'>}
*/
this.meta = {
supportedModes: ['timespan', 'navigation'],
dependencies: {DevtoolsLog: DevtoolsLog.symbol},
}Enforcing the expected behavior with square brackets fixes this, but it also opens pandora's box of other type violations. I haven't found a silver bullet to resolve these issues other than to keep the type definition of GathererMeta. Are these type violations valid, or can we stick with the weaker definition for GathererMeta?