When config file shrinks it breaks syntax

Confy seems to work fine as long as you're adding information to the config file, but as soon as you remove anything from the config, confy breaks. For example, consider the following code:

extern crate confy;
#[macro_use] extern crate serde_derive;
use std::default::{Default};

#[derive(Serialize, Deserialize)]
struct Config {
    lines: Vec<i32>
}

impl Default for Config {
    fn default() -> Self {
        Self {
            lines: vec![1, 2, 3]
        }
    }
}

fn main() -> Result<(), std::io::Error> {
    let mut config: Config = confy::load("confy-bug")?;
    confy::store("confy-bug", config)
}

If you run the above code you will produce the following output as expected:

lines = [
    1,
    2,
    3,
]

however if you add the following:

 fn main() -> Result<(), std::io::Error> {
     let mut config: Config = confy::load("confy-bug")?;
+    config.lines.clear();
     confy::store("confy-bug", config)
 }

You will instead end up with this syntactically incorrect file:

lines = []
   1,
    2,
    3,
]

It seems that confy is just writing on top of the old file without cleaning up any excess lines left over from the last write.

I was able to fix the issue locally by making the following changes:

diff --git a/src/lib.rs b/src/lib.rs
index f468e89..cb3e03b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -143,7 +143,7 @@ pub fn store<T: Serialize>(name: &str, cfg: T) -> Result<(), IoError> {
     ].iter()
         .collect();

-    let mut f = OpenOptions::new().write(true).create(true).open(path)?;
+    let mut f = OpenOptions::new().write(true).create(true).truncate(true).open(path)?;
     let s = toml::to_string_pretty(&cfg).unwrap();
     f.write_all(s.as_bytes())?;
     Ok(())

rust-cli / confy

When config file shrinks it breaks syntax #9