Cannot read property 'flags' of undefined in JS class

[mjbvz]

From microsoft/vscode#53250

TypeScript Version: 3.0.0-dev.20180630

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Code
In a js file:

class Child extends Namespace.Parent {

}

Request completions inside the class

Bug

[Error  - 18:12:36] 'completions' request failed with error.
Error processing request. Cannot read property 'flags' of undefined
TypeError: Cannot read property 'flags' of undefined
    at getApparentType (/Users/matb/projects/san/node_modules/typescript/lib/tsserver.js:35388:25)
    at Object.getPropertiesOfType (/Users/matb/projects/san/node_modules/typescript/lib/tsserver.js:35133:20)
    at /Users/matb/projects/san/node_modules/typescript/lib/tsserver.js:91759:44
    at Object.flatMap (/Users/matb/projects/san/node_modules/typescript/lib/tsserver.js:471:25)
    at tryGetClassLikeCompletionSymbols (/Users/matb/projects/san/node_modules/typescript/lib/tsserver.js:91757:42)
    at tryGetGlobalSymbols (/Users/matb/projects/san/node_modules/typescript/lib/tsserver.js:91302:24)
    at getCompletionData (/Users/matb/projects/san/node_modules/typescript/lib/tsserver.js:91191:22)
    at Object.getCompletionsAtPosition (/Users/matb/projects/san/node_modules/typescript/lib/tsserver.js:90410:34)
    at Object.getCompletionsAtPosition (/Users/matb/projects/san/node_modules/typescript/lib/tsserver.js:110196:35)
    at IOSession.Session.getCompletions (/Users/matb/projects/san/node_modules/typescript/lib/tsserver.js:117787:64)
    at Session.handlers.ts.createMapFromTemplate._a.(anonymous function) (/Users/matb/projects/san/node_modules/typescript/lib/tsserver.js:116820:61)
    at /Users/matb/projects/san/node_modules/typescript/lib/tsserver.js:118299:88
    at IOSession.Session.executeWithRequestId (/Users/matb/projects/san/node_modules/typescript/lib/tsserver.js:118290:28)
    at IOSession.Session.executeCommand (/Users/matb/projects/san/node_modules/typescript/lib/tsserver.js:118299:33)
    at IOSession.Session.onMessage (/Users/matb/projects/san/node_modules/typescript/lib/tsserver.js:118319:35)
    at Interface.<anonymous> (/Users/matb/projects/san/node_modules/typescript/lib/tsserver.js:119574:27)
    at emitOne (events.js:96:13)
    at Interface.emit (events.js:191:7)
    at Interface._onLine (readline.js:241:10)
    at Interface._normalWrite (readline.js:384:12)
    at Socket.ondata (readline.js:101:10)
    at emitOne (events.js:96:13)
    at Socket.emit (events.js:191:7)
    at readableAddChunk (_stream_readable.js:178:18)
    at Socket.Readable.push (_stream_readable.js:136:10)
    at Pipe.onread (net.js:560:20)

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Related Issues:

• Bug: tsc crash TypeError: Cannot read property 'flags' of undefined #25264