Improve rustup show, list toolchains, default

1. Change the output format of `rustup show`, to be in a more logical
   order and have more pleasing formatting
2. Update the formatting of `rustup show active-toolchain` and
   `rustup toolchain list` to match the new `rustup show` format.
3. `rustup +nightly show` will no longer install the nightly toolchain
   if it isn't already installed. Ditto for
   `rustup show active-toolchain`.
4. Fix a bug where the RUSTUP_TOOLCHAIN environment variable took
   priority over the +toolchain command line option, and add a test for
   override priority.
5. `rustup default` no longer errors when there is no default toolchain
   configured, it prints a message instead.
6. Update the docs, and fix an issue where they incorrectly stated
   that `rust-toolchain.toml` config files couldn't specify custom
   names. (Text last touched here, see commit message: 7bfbd3b)

doc/user-guide/src/overrides.md

@@ -19,10 +19,7 @@ the directory tree toward the filesystem root, and a `rust-toolchain.toml` file
 that is closer to the current directory will be preferred over a directory
 override that is further away.
 
-To verify which toolchain is active, you can use `rustup show`, 
-which will also try to install the corresponding
-toolchain if the current one has not been installed according to the above rules.
-(Please note that this behavior is subject to change, as detailed in issue [#1397].)
+To verify which toolchain is active, you can use `rustup show`.
 
 [toolchain]: concepts/toolchains.md
 [toolchain override shorthand]: #toolchain-override-shorthand
@@ -123,16 +120,12 @@ The `channel` setting specifies which [toolchain] to use. The value is a
 string in the following form:
 
 ```
-<channel>[-<date>]
+(<channel>[-<date>])|<custom toolchain name>
 
 <channel> = stable|beta|nightly|<major.minor.patch>
 <date> = YYYY-MM-DD
 ```
 
-Note that this is a more restricted form than `rustup` toolchains
-generally, and cannot be used to specify custom toolchains or
-host-specific toolchains.
-
 [toolchain]: concepts/toolchains.md
 
 #### path

src/cli/common.rs

@@ -22,6 +22,7 @@ use crate::currentprocess::{
 };
 use crate::dist::dist::{TargetTriple, ToolchainDesc};
 use crate::install::UpdateStatus;
+use crate::toolchain::names::{LocalToolchainName, ToolchainName};
 use crate::utils::notifications as util_notifications;
 use crate::utils::notify::NotificationLevel;
 use crate::utils::utils;
@@ -461,74 +462,72 @@ pub(crate) fn list_installed_components(distributable: DistributableToolchain<'_
  Ok(())
 }
 
-fn print_toolchain_path(
- cfg: &Cfg,
- toolchain: &str,
- if_default: &str,
- if_override: &str,
- verbose: bool,
-) -> Result<()> {
- let toolchain_path = cfg.toolchains_dir.join(toolchain);
- let toolchain_meta = fs::symlink_metadata(&toolchain_path)?;
- let toolchain_path = if verbose {
- if toolchain_meta.is_dir() {
- format!("\t{}", toolchain_path.display())
- } else {
- format!("\t{}", fs::read_link(toolchain_path)?.display())
- }
- } else {
- String::new()
- };
- writeln!(
- process().stdout().lock(),
- "{}{}{}{}",
- &toolchain,
- if_default,
- if_override,
- toolchain_path
- )?;
- Ok(())
-}
-
 pub(crate) fn list_toolchains(cfg: &Cfg, verbose: bool) -> Result<utils::ExitCode> {
- // Work with LocalToolchainName to accommodate path based overrides
- let toolchains = cfg
- .list_toolchains()?
- .iter()
- .map(Into::into)
- .collect::<Vec<_>>();
+ let toolchains: Vec<ToolchainName> = cfg.list_toolchains()?;
  if toolchains.is_empty() {
  writeln!(process().stdout().lock(), "no installed toolchains")?;
  } else {
- let def_toolchain_name = cfg.get_default()?.map(|t| (&t).into());
+ let default_toolchain_name = cfg.get_default()?;
  let cwd = utils::current_dir()?;
- let ovr_toolchain_name = if let Ok(Some((toolchain, _reason))) = cfg.find_override(&cwd) {
- Some(toolchain)
- } else {
- None
- };
- for toolchain in toolchains {
- let if_default = if def_toolchain_name.as_ref() == Some(&toolchain) {
- " (default)"
+ let active_toolchain_name: Option<ToolchainName> =
+ if let Ok(Some((LocalToolchainName::Named(toolchain), _reason))) =
+ cfg.find_active_toolchain(&cwd)
+ {
+ Some(toolchain)
  } else {
- ""
- };
- let if_override = if ovr_toolchain_name.as_ref() == Some(&toolchain) {
- " (override)"
- } else {
- ""
+ None
  };
 
- print_toolchain_path(
+ for toolchain in toolchains {
+ let is_default_toolchain = default_toolchain_name.as_ref() == Some(&toolchain);
+ let is_active_toolchain = active_toolchain_name.as_ref() == Some(&toolchain);
+
+ print_toolchain(
  cfg,
  &toolchain.to_string(),
- if_default,
- if_override,
+ is_default_toolchain,
+ is_active_toolchain,
  verbose,
  )
  .context("Failed to list toolchains' directories")?;
  }
  }
+
+ fn print_toolchain(
+ cfg: &Cfg,
+ toolchain: &str,
+ is_default: bool,
+ is_active: bool,
+ verbose: bool,
+ ) -> Result<()> {
+ let toolchain_path = cfg.toolchains_dir.join(toolchain);
+ let toolchain_meta = fs::symlink_metadata(&toolchain_path)?;
+ let toolchain_path = if verbose {
+ if toolchain_meta.is_dir() {
+ format!(" {}", toolchain_path.display())
+ } else {
+ format!(" {}", fs::read_link(toolchain_path)?.display())
+ }
+ } else {
+ String::new()
+ };
+ let status_str = match (is_default, is_active) {
+ (true, true) => " (default, active)",
+ (true, false) => " (default)",
+ (false, true) => " (active)",
+ (false, false) => "",
+ };
+
+ writeln!(
+ process().stdout().lock(),
+ "{}{}{}",
+ &toolchain,
+ status_str,
+ toolchain_path
+ )?;
+ Ok(())
+ }
+
  Ok(utils::ExitCode(0))
 }