Add fs::read_to_string

[brson]

Every time I want to load the contents of a file to a String I think this same thing: "there should be a fs::read_to_string".

It looks like to me the most convenient way to do this once ? is stable (which doesn't seem to be near) might be File::open(path)?.read_to_string()?, assuming you've got the Read trait imported. It's just not as nice.

We as @rust-lang/libs can be more aggressive about identifying and adding simple ergonomic improvements like this.

[retep998]

What if we had a read_to_vec instead and then you convert that into String?

Oh also, there is already a read_to_string method that takes a &mut String, so you'll need a better name.

[Stebalien]

Alternatively, we could make it generic:

// Call as `fs::read::<String>("my_file")`. Alternatively, we could try landing default type arguments :)
mod fs {
    fn read<T: SomeTrait, P: AsRef<Path>>(path: P) -> T { /* ... */ }
}

SomeTrait could just be Write but that would be a bit inefficient (it would require an intermediate buffer).

[gkoz]

An fs::read_to_string would encourage trying to slurp files regardless of their size. Going through Read you can use take (but it won't tell you if the input is too big 😞).

BTW is trying to read the whole file into memory an anti-pattern? Apparently toml-rs only parses &str but not T: Read. If it did take any reader would you still need to read_to_string so often?

[Stebalien]

@gkoz I think this is one of those "pay for what you use" things. If you want to do things efficiently, manually read the file one chunk at a time; if you just need to read the file into memory and know it isn't malicious (e.g., a config file), you can use the helper function. However, your two caveats should definitely be mentioned in the documentation.

[brson]

Libs team discussed and is amenable to a convenience, though the design may need some consideration still. Some concrete points brought up:

• Taking &mut String like Read::read_to_string probably the wrong choice for the convenience method - should return String
• If it doesn't take &mut String then the name read_to_string may not be right because it doesn't look like Read::read_to_string.
• Maybe it should be a method on Path.

[kvark]

Can we just impl<R: Read> Into<String> for R {...}?

[joshtriplett]

@kvark That would work for files, but would conflict with instances of Into for other implementations of Read, notably the implementation for String.

[matklad]

There's a crate for that: https://github.com/pornel/rust-file

[binarybana]

For naming, how about read_as_str to indicate that it is allocating a new String for you?

[Mark-Simulacrum]

The questions that were already brought up by the libs team and general uncertainty I can see about this lead me to believe it requires an RFC. As such, I'm closing -- if someone wants to pursue this, please follow the process outlined here: https://github.com/rust-lang/rfcs#before-creating-an-rfc.