Crash involving union of function types

[tomblind]

TypeScript Version: 3.5.0-dev.20190518

Search Terms:
Cannot read property 'flags' of undefined
createSymbolWithType

Code

interface A {
    (this: void, a: string, b: number, c?: string): void;
    (this: void, b: number, c?: string): void;
}
interface B {
    (i: number): number;
}
declare const fn: A | B;
fn(0);

Expected behavior:
Should not crash.

Actual behavior:
tsc crashes with the following output:

node_modules\typescript\lib\tsc.js:72973
                throw e;
                ^

TypeError: Cannot read property 'flags' of undefined
    at createSymbolWithType (node_modules\typescript\lib\tsc.js:36787:46)
    at getUnionSignatures (node_modules\typescript\lib\tsc.js:30929:53)
    at resolveUnionTypeMembers (node_modules\typescript\lib\tsc.js:31021:34)
    at resolveStructuredTypeMembers (node_modules\typescript\lib\tsc.js:31330:21)
    at getSignaturesOfStructuredType (node_modules\typescript\lib\tsc.js:31782:32)
    at getSignaturesOfType (node_modules\typescript\lib\tsc.js:31788:20)
    at resolveCallExpression (node_modules\typescript\lib\tsc.js:42223:34)
    at resolveSignature (node_modules\typescript\lib\tsc.js:42494:28)
    at getResolvedSignature (node_modules\typescript\lib\tsc.js:42514:26)
    at checkCallExpression (node_modules\typescript\lib\tsc.js:42585:29)

Playground Link:

Related Issues:
#29884 may be related, as there's an example with a similar callstack, but it's closed as fixed already.

[andrewbranch]

Hah, that second stack frame:

// TODO: GH#18217 We tested that *some* has thisParameter and now act as if *all* do
const thisType = getUnionType(map(unionSignatures, sig => sig.thisParameter ? getTypeOfSymbol(sig.thisParameter) : anyType), UnionReduction.Subtype);
thisParameter = createSymbolWithType(signature.thisParameter!, thisType);

🙃

(#18217)