The root cause is that we're calling `printComments` with an empty string, meaning that the leading/trailing comments are not correctly inserted at the right location.
So, the way to fix it is to call `p => concat(parts)` but because we're mutating the array in place, it doesn't work. We need to mutate it and create a copy. But, the root call is actually checking the shape of the parts array which our code is now breaking...
```js
// Don't include the initial expression in the indentation
// level. The first item is guaranteed to be the first
// left-most expression.
parts.length > 0 ? parts[0] : "",
```
The consequence is that binary expressions are no longer indented if the first expression has a comment (but now it places the comment properly!), which seems like a good trade-off.
I'm not sure if we should merge this one or instead refactor this code such that it doesn't rely on mutation and looking at the shape of the printed tree. `printMemberChain` is a good thing to reference for inspiration.
Fixes#946
JounQin