TypeError: Cannot read property 'parent' of undefined at getAssignedJSPrototype

[minestarks]

TypeScript Version: 3.1.0-dev.20180925

git clone --depth=1 https://github.com/TeamFleet/WhoCallsTheFleet
cd WhoCallsTheFleet
tsc --init
tsc --allowJs --checkJs

Compiler crashes with the callstack:

TypeError: Cannot read property 'parent' of undefined
    at getAssignedJSPrototype (node_modules\typescript\lib\tsc.js:40752:23)
    at getAssignedClassType (node_modules\typescript\lib\tsc.js:40748:37)
    at getJSClassType (node_modules\typescript\lib\tsc.js:40732:28)
    at checkCallExpression (node_modules\typescript\lib\tsc.js:40794:46)
    at checkExpressionWorker (node_modules\typescript\lib\tsc.js:42392:28)
    at checkExpression (node_modules\typescript\lib\tsc.js:42334:42)
    at checkNonNullExpression (node_modules\typescript\lib\tsc.js:39352:37)
    at checkPropertyAccessExpressionOrQualifiedName (node_modules\typescript\lib\tsc.js:39378:28)
    at checkPropertyAccessExpression (node_modules\typescript\lib\tsc.js:39371:20)
    at checkExpressionWorker (node_modules\typescript\lib\tsc.js:42384:28)

[RyanCavanaugh]

Confirmed call stack on master; regression from 3.0

[RyanCavanaugh]

Repro requires two files in this order:

var SomeClass = function () {
    this.otherProp = 0;
};

new SomeClass();

class SomeClass { }
SomeClass.prop = 0

[sandersn]

The check for prototype assignment on constructor functions assumes that the prototype property, if present, comes from an assignment declaration, such as:

SomeClass.prototype = { /* methods go here */ }

In this case, however, when class SomeClass and var SomeClass merge (because this is allowed), prototype is the synthetic property from class SomeClass, which has no valueDeclaration.

The fix is to check that prototype has a valueDeclaration before checking whether the valueDeclaration is in fact a prototype-assignment declaration.