Cannot read property 'kind' of undefined at Object.parenthesizeArrayTypeMember

[victorwelling]

TypeScript Version: 3.1.0-dev.20180802

Search Terms:

• Cannot read property 'kind' of undefined
• Optional element in tuple
• ReadonlyArray
• Strict mode

Code

type Foo = [object, object?];

const bar: ReadonlyArray<Foo> = [{}, {}];

Expected behavior:
An error along the lines of:

Type '{}[]' is not assignable to type '[object, (object | undefined)?][]

Actual behavior:

./node_modules/typescript/lib/tsc.js:67968
                throw e;
                ^

TypeError: Cannot read property 'kind' of undefined
    at Object.parenthesizeArrayTypeMember (./node_modules/typescript/lib/tsc.js:50576:24)
    at Object.createOptionalTypeNode (./node_modules/typescript/lib/tsc.js:47850:24)
    at typeReferenceToTypeNode (./node_modules/typescript/lib/tsc.js:26572:44)
    at typeToTypeNodeHelper (./node_modules/typescript/lib/tsc.js:26383:28)
    at typeReferenceToTypeNode (./node_modules/typescript/lib/tsc.js:26560:43)
    at typeToTypeNodeHelper (./node_modules/typescript/lib/tsc.js:26383:28)
    at signatureToSignatureDeclarationHelper (./node_modules/typescript/lib/tsc.js:26827:52)
    at createTypeNodesFromResolvedType (./node_modules/typescript/lib/tsc.js:26666:43)
    at createTypeNodeFromObjectType (./node_modules/typescript/lib/tsc.js:26547:35)
    at createAnonymousTypeNode (./node_modules/typescript/lib/tsc.js:26502:42)

Conditions
It seems this bug is only triggered if:

• a ReadonlyArray is used – Array doesn't seem to trigger it
• strict mode is enabled
• the last element of the tuple is optional

Playground Link:
Playground. Be sure to enable strictNullChecks to replicate.

[timkendrick]

FYI I am experiencing this error in the current release version (3.0.3).

Any idea whether it is likely to be fixed any time soon, or should I refactor my code to work around it?

[jonaskello]

I'm using using tsc 3.0.3 and I got this error when doing a rather large merge I'm not sure how to find which file is causing it. Are there any tricks to find the offending file?

[yortus]

I just hit this too. My repro is quite different to OP's, but the PR at #26433 fixes it. Hope it gets merged soon.