shows (override) in toolchain list

[bestia-dev]

This PR is for issue #2295
The command list now shows the override toolchain for this specific directory):

$ home/bin/rustup toolchain list
stable-x86_64-unknown-linux-gnu (default)
nightly-x86_64-unknown-linux-gnu

$ home/bin/rustup override set stable

$ home/bin/rustup toolchain list
stable-x86_64-unknown-linux-gnu (default) (override)
nightly-x86_64-unknown-linux-gnu

$ home/bin/rustup override set nightly

$ home/bin/rustup toolchain list
stable-x86_64-unknown-linux-gnu (default)
nightly-x86_64-unknown-linux-gnu (override)

[kinnison]

The examples look good, but I'd like to see some tests added to check all the cases (e.g. override by rust-toolchain vs. override by path etc.)

I think the tests probably belong in cli-misc.rs

[bestia-dev]

I found a similar test in cli-rustup.rs: list_default_toolchain()
So there I added 2 tests for list override:

• list_override_toolchain()
• list_default_and_override_toolchain()
  You mentioned "override by path". Those are different kinds of override.
  If I understand correctly, all of them are "overrides" until we don't get deeper into more details.

[bestia-dev]

I think OverrideReason is not needed for the rustup toolchain list command.
The user is informed about the override.
For more details he could find elsewhere maybe in rustup override list?
But if needed I could add the OverrideReason to the string "(override)":

#[derive(Debug)]
pub enum OverrideReason {
    Environment,
    CommandLine,
    OverrideDB(PathBuf),
    ToolchainFile(PathBuf),
}

impl Display for OverrideReason {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> std::result::Result<(), fmt::Error> {
        match self {
            Self::Environment => write!(f, "environment override by RUSTUP_TOOLCHAIN"),
            Self::CommandLine => write!(f, "overridden by +toolchain on the command line"),
            Self::OverrideDB(path) => write!(f, "directory override for '{}'", path.display()),
            Self::ToolchainFile(path) => write!(f, "overridden by '{}'", path.display()),
        }
    }
}

[bestia-dev]

The real command for getting the details about OverrideReason is this:
rustup show active-toolchain
result:
nightly-x86_64-unknown-linux-gnu (directory override for '/mnt/c/Users/Luciano/rustprojects/rustfmt')

[kinnison]

This is looking really good. Could you please rebase to squash everything down to one or two neat commits, rather than the formatting nightmare you appear to have had in the middle, and then we should be good to merge. I'm fine with the hint, rustup show will suffice as you say.

[kinnison]

Approved modulo rebase/squash cleanup of commits and commit messages.

[bestia-dev]

I made the requested changes. Is it now ok to merge?

[kinnison]

Looks good 👍