Implement Extend and FromIterator for OsString

[lopopolo]

Add the following trait impls:

• impl Extend<OsString> for OsString
• impl<'a> Extend<&'a OsStr> for OsString
• impl FromIterator<OsString> for OsString
• impl<'a> FromIterator<&'a OsStr> for OsString

Because OsString is a platform string with no particular semantics, concatenating them together seems acceptable.

I came across a use case for these trait impls in artichoke/artichoke#1089:

Artichoke is a Ruby interpreter. Its CLI accepts multiple -e switches for executing inline Ruby code, like:

$ cargo -q run --bin artichoke -- -e '2.times {' -e 'puts "foo: #{__LINE__}"' -e '}'
foo: 2
foo: 2

I use clap for command line argument parsing, which collects these -e commands into a Vec<OsString>. To pass these commands to the interpreter for Eval, I need to join them together. Combining these impls with Iterator::intersperse #79524 would enable me to build a single bit of Ruby code.

Currently, I'm doing something like:

let mut commands = commands.into_iter();
let mut buf = if let Some(command) = commands.next() {
    command
} else {
    return Ok(Ok(()));
};
for command in commands {
    buf.push("\n");
    buf.push(command);
}

If there's interest, I'd also like to add impls for Cow<'a, OsStr>, which would avoid allocating the "\n" OsString in the concatenate + intersperse use case.

[rust-highfive]

r? @m-ou-se

(rust-highfive has picked a reviewer for you, use r? to override)

[m-ou-se]

@rfcbot merge

[rfcbot]

Team member @m-ou-se has proposed to merge this. The next step is review by the rest of the tagged team members:

• @Amanieu
• @BurntSushi
• @KodrAus
• @dtolnay
• @joshtriplett
• @m-ou-se
• @sfackler

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

[lopopolo]

@m-ou-se can I go ahead and add the impls for Cow<'a, OsStr> as well?

[m-ou-se]

@lopopolo Yes, that seems reasonable, since we also have those for str/String.

cc @dtolnay @Amanieu since you already checked your checkboxes.

[lopopolo]

I added FromIterator and Extend impls for Iterator<Item = Cow<'a, OsStr>>.

These impls can potentially expanded to add impls for Box<OsStr>, Rc<OsStr>, and Arc<OsStr>, but I don't have a need for these so I'm not planning on adding these.

Also for the future, the iterators implemented and not implemented in this PR could also be done for String/str if there was a use case for them, but these can be worked around by mapping with OsStr::new/OsString::from.

[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

The RFC will be merged soon.

[joshtriplett]

@bors r+

[bors]

📌 Commit 05ea200 has been approved by joshtriplett

[pthariensflame]

This is insta-stable and so needs relnotes, yes?