Comment inconsistency with file-lines option

[jsgf]

Given this source:

extern crate ascii;
#[allow(unused_imports)] // workaround for macro_use
#[macro_use]
extern crate lazy_static;

If you format the whole file, then it works fine. However if you use --file-lines on a range that just covers lines 1 and 2, it drops the space before the comment:

$ rustfmt --unstable-features --emit-stdout -q --file-lines '[{"file": "t.rs", "range" : [2,2]}]' t.rs
extern crate ascii;
#[allow(unused_imports)]// workaround for macro_use
#[macro_use]
extern crate lazy_static;

Extending the range to the next line works correctly:

$ rustfmt --unstable-features --emit-stdout -q --file-lines '[{"file": "t.rs", "range" : [2,3]}]' t.rs
extern crate ascii;
#[allow(unused_imports)] // workaround for macro_use
#[macro_use]
extern crate lazy_static;

This is rustfmt 1.0.3-nightly (d6829d6 2019-02-14)

[scampi]

I am having a look at this