=== tests/cases/compiler/bestCommonTypeWithOptionalProperties.ts ===
interface X { foo: string }
>X : Symbol(X, Decl(bestCommonTypeWithOptionalProperties.ts, 0, 0))
>foo : Symbol(foo, Decl(bestCommonTypeWithOptionalProperties.ts, 0, 13))

interface Y extends X { bar?: number }
>Y : Symbol(Y, Decl(bestCommonTypeWithOptionalProperties.ts, 0, 27))
>X : Symbol(X, Decl(bestCommonTypeWithOptionalProperties.ts, 0, 0))
>bar : Symbol(bar, Decl(bestCommonTypeWithOptionalProperties.ts, 1, 23))

interface Z extends X { bar: string }
>Z : Symbol(Z, Decl(bestCommonTypeWithOptionalProperties.ts, 1, 38))
>X : Symbol(X, Decl(bestCommonTypeWithOptionalProperties.ts, 0, 0))
>bar : Symbol(bar, Decl(bestCommonTypeWithOptionalProperties.ts, 2, 23))

var x: X;
>x : Symbol(x, Decl(bestCommonTypeWithOptionalProperties.ts, 4, 3))
>X : Symbol(X, Decl(bestCommonTypeWithOptionalProperties.ts, 0, 0))

var y: Y;
>y : Symbol(y, Decl(bestCommonTypeWithOptionalProperties.ts, 5, 3))
>Y : Symbol(Y, Decl(bestCommonTypeWithOptionalProperties.ts, 0, 27))

var z: Z;
>z : Symbol(z, Decl(bestCommonTypeWithOptionalProperties.ts, 6, 3))
>Z : Symbol(Z, Decl(bestCommonTypeWithOptionalProperties.ts, 1, 38))

// All these arrays should be X[]
var b1 = [x, y, z];
>b1 : Symbol(b1, Decl(bestCommonTypeWithOptionalProperties.ts, 9, 3))
>x : Symbol(x, Decl(bestCommonTypeWithOptionalProperties.ts, 4, 3))
>y : Symbol(y, Decl(bestCommonTypeWithOptionalProperties.ts, 5, 3))
>z : Symbol(z, Decl(bestCommonTypeWithOptionalProperties.ts, 6, 3))

var b2 = [x, z, y];
>b2 : Symbol(b2, Decl(bestCommonTypeWithOptionalProperties.ts, 10, 3))
>x : Symbol(x, Decl(bestCommonTypeWithOptionalProperties.ts, 4, 3))
>z : Symbol(z, Decl(bestCommonTypeWithOptionalProperties.ts, 6, 3))
>y : Symbol(y, Decl(bestCommonTypeWithOptionalProperties.ts, 5, 3))

var b3 = [y, x, z];
>b3 : Symbol(b3, Decl(bestCommonTypeWithOptionalProperties.ts, 11, 3))
>y : Symbol(y, Decl(bestCommonTypeWithOptionalProperties.ts, 5, 3))
>x : Symbol(x, Decl(bestCommonTypeWithOptionalProperties.ts, 4, 3))
>z : Symbol(z, Decl(bestCommonTypeWithOptionalProperties.ts, 6, 3))

var b4 = [y, z, x];
>b4 : Symbol(b4, Decl(bestCommonTypeWithOptionalProperties.ts, 12, 3))
>y : Symbol(y, Decl(bestCommonTypeWithOptionalProperties.ts, 5, 3))
>z : Symbol(z, Decl(bestCommonTypeWithOptionalProperties.ts, 6, 3))
>x : Symbol(x, Decl(bestCommonTypeWithOptionalProperties.ts, 4, 3))

var b5 = [z, x, y];
>b5 : Symbol(b5, Decl(bestCommonTypeWithOptionalProperties.ts, 13, 3))
>z : Symbol(z, Decl(bestCommonTypeWithOptionalProperties.ts, 6, 3))
>x : Symbol(x, Decl(bestCommonTypeWithOptionalProperties.ts, 4, 3))
>y : Symbol(y, Decl(bestCommonTypeWithOptionalProperties.ts, 5, 3))

var b6 = [z, y, x];
>b6 : Symbol(b6, Decl(bestCommonTypeWithOptionalProperties.ts, 14, 3))
>z : Symbol(z, Decl(bestCommonTypeWithOptionalProperties.ts, 6, 3))
>y : Symbol(y, Decl(bestCommonTypeWithOptionalProperties.ts, 5, 3))
>x : Symbol(x, Decl(bestCommonTypeWithOptionalProperties.ts, 4, 3))