`Cargo init` creates duplicates in .gitignore

[collin5]

Doing cargo init in an existing git repository will either create a new .gitignore or append to an existing one. However if we already have a .gitignore file with both /target and **/*.rs.bk ignored, cargo init will still add these to the existing file.

Steps

$ mkdir foo && cd foo 
$ git init
$ echo "/target\n**/*.rs.bk" > .gitignore
$ cargo init

The new .gitignore will now contain

/target
**/*.rs.bk

/target
**/*.rs.bk

Possible Solution(s)

Before creating or adding to the existing .gitignore, we could perhaps check the contents and only add what is missing. Looks like the code handling this is

cargo/src/cargo/ops/cargo_new.rs

Lines 460 to 465 in 485670b

	let ignore = if path.join(".gitignore").exists() {
	format!("\n{}", ignore)
	} else {
	ignore
	};
	paths::append(&path.join(".gitignore"), ignore.as_bytes())?;

,

cargo/src/cargo/ops/cargo_new.rs

Lines 471 to 476 in 485670b

	let hgignore = if path.join(".hgignore").exists() {
	format!("\n{}", hgignore)
	} else {
	hgignore
	};
	paths::append(&path.join(".hgignore"), hgignore.as_bytes())?;

and

cargo/src/cargo/ops/cargo_new.rs

Lines 482 to 487 in 485670b

	let ignore = if path.join(".ignore").exists() {
	format!("\n{}", ignore)
	} else {
	ignore
	};
	paths::append(&path.join(".ignore"), ignore.as_bytes())?;

Version: cargo 1.31.0-nightly (2d0863f 2018-10-20)

[starsheriff]

I'd happily start working on that one as a first contribution. Seems to be quite straight forward.

[collin5]

Great! Go for it.

[Lucretiel]

I'd like to reopen this issue; I'm still seeing this behavior on git when I run cargo init --lib .

[dwijnand]

@Lucretiel That's because this fix hasn't made it way into stable Rust yet. It's in nightly and beta (try cargo +nightly init or cargo +beta init) and stable is releasing in next week Friday 1 March.

[Lucretiel]

Oh, sorry, I didn't see the dates that this was so recent. Thank you!