==== tests/cases/compiler/collisionThisExpressionAndAmbientVarInGlobal.ts (1 errors) ====
    declare var _this: number; // no error as no code gen
    var f = () => this;
    _this = 10; // Error
    ~~~~~
!!! collisionThisExpressionAndAmbientVarInGlobal.ts(3,1): error TS2206: Expression resolves to variable declaration '_this' that compiler uses to capture 'this' reference.