Teach rustup to override the toolchain from a version file

This adds a .rust-version file similar to rbenv's .ruby-version.

The form of toolchain supported here is limited to channel names,
explicit versions, and optional archive dates.

Author: brson

README.md

@@ -17,8 +17,10 @@ And it runs on all platforms Rust supports, including Windows.
 * [How rustup works](#how-rustup-works)
 * [Keeping Rust up to date](#keeping-rust-up-to-date)
 * [Working with nightly Rust](#working-with-nightly-rust)
-* [Directory overrides](#directory-overrides)
 * [Toolchain specification](#toolchain-specification)
+* [Directory overrides](#directory-overrides)
+* [The version file](#the-version-file)
+* [Toolchain override shorthand](#toolchain-override-shorthand)
 * [Cross-compilation](#cross-compilation)
 * [Working with Rust on Windows](#working-with-rust-on-windows)
 * [Working with custom toolchains](#working-with-custom-toolchains-and-local-builds)
@@ -231,29 +233,6 @@ info: downloading self-updates
 
 ```
 
-## Directory overrides
-
-Directories can be assigned their own Rust toolchain with
-`rustup override`. When a directory has an override then
-any time `rustc` or `cargo` is run inside that directory,
-or one of its child directories, the override toolchain
-will be invoked.
-
-To pin to a specific nightly:
-
-```
-rustup override set nightly-2014-12-18
-```
-
-Or a specific stable release:
-
-```
-rustup override set 1.0.0
-```
-
-To see the active toolchain use `rustup show`. To remove the override
-and use the default toolchain again, `rustup override unset`.
-
 ## Toolchain specification
 
 Many `rustup` commands deal with *toolchains*, a single installation
@@ -299,6 +278,65 @@ Toolchain names that don't name a channel instead can be used to name
 [MSVC-based toolchain]: https://www.rust-lang.org/downloads.html#win-foot
 [custom toolchains]: #working-with-custom-toolchains-and-local-builds
 
+## Toolchain override shorthand
+
+The `rustup` toolchain proxies can be instructed directly to use a
+specific toolchain, a convience for developers who often test
+different toolchains. If the first argument to `cargo`, `rustc` or
+other tools in the toolchain begins with `+`, it will be interpreted
+as a rustup toolchain name, and that toolchain will be preferred,
+as in
+
+```
+cargo +beta test
+```
+
+## Directory overrides
+
+Directories can be assigned their own Rust toolchain with
+`rustup override`. When a directory has an override then
+any time `rustc` or `cargo` is run inside that directory,
+or one of its child directories, the override toolchain
+will be invoked.
+
+To pin to a specific nightly:
+
+```
+rustup override set nightly-2014-12-18
+```
+
+Or a specific stable release:
+
+```
+rustup override set 1.0.0
+```
+
+To see the active toolchain use `rustup show`. To remove the override
+and use the default toolchain again, `rustup override unset`.
+
+## The version file
+
+`rustup` directory overrides are a local configuration, stored in
+`$RUSTUP_HOME`. Some projects though find themselves 'pinned' to a
+specific release of Rust and want this information reflected in their
+source repository. This is most often the case for nightly-only
+software that pins to a revision from the release archives.
+
+In these cases the toolchain can be named in the project's directory
+in a file called `.rust-version`, the content of which is the name of
+a single `rustup` toolchain, and which is suitable to check in to
+source control.
+
+The toolchains named in this file have a more restricted form than
+rustup toolchains generally, and may only contain the names of the
+three release channels, 'stable', 'beta', 'nightly', Rust version
+numbers, like '1.0.0', and optionally an archive date, like
+'nightly-2017-01-01'. They may not name custom toolchains, nor
+host-specific toolchains.
+
+The version file has lower precedence than all other methods of
+specifying the toolchain.
+
 ## Cross-compilation
 
 Rust [supports a great number of platforms][p]. For many of these

src/rustup-dist/src/dist.rs

@@ -302,6 +302,10 @@ impl PartialToolchainDesc {
             target: TargetTriple(trip),
         }
     }
+
+    pub fn has_triple(&self) -> bool {
+        self.target.arch.is_some() || self.target.os.is_some() || self.target.env.is_some()
+    }
 }
 
 impl ToolchainDesc {
@@ -376,6 +380,16 @@ impl ToolchainDesc {
     }
 }
 
+// A little convenience for just parsing a channel name or archived channel name
+pub fn validate_channel_name(name: &str) -> Result<()> {
+    let toolchain = PartialToolchainDesc::from_str(&name)?;
+    if toolchain.has_triple() {
+        Err(format!("target triple in channel name '{}'", name).into())
+    } else {
+        Ok(())
+    }
+}
+
 #[derive(Debug)]
 pub struct Manifest<'a>(temp::File<'a>, String);
 

src/rustup-mock/src/clitools.rs

@@ -34,6 +34,8 @@ pub struct Config {
     pub homedir: PathBuf,
     /// An empty directory. Tests should not write to this.
     pub emptydir: PathBuf,
+    /// This is cwd for the test
+    pub workdir: PathBuf,
 }
 
 // Describes all the features of the mock dist server.
@@ -72,6 +74,7 @@ pub fn setup(s: Scenario, f: &Fn(&Config)) {
     let cargodir = TempDir::new("rustup-cargo").unwrap();
     let homedir = TempDir::new("rustup-home").unwrap();
     let emptydir = TempDir::new("rustup-empty").unwrap();
+    let workdir = TempDir::new("rustup-workdir").unwrap();
 
     // The uninstall process on windows involves using the directory above
     // CARGO_HOME, so make sure it's a subdir of our tempdir
@@ -86,6 +89,7 @@ pub fn setup(s: Scenario, f: &Fn(&Config)) {
         cargodir: cargodir,
         homedir: homedir.path().to_owned(),
         emptydir: emptydir.path().to_owned(),
+        workdir: workdir.path().to_owned(),
     };
 
     create_mock_dist_server(&config.distdir, s);
@@ -139,6 +143,11 @@ pub fn setup(s: Scenario, f: &Fn(&Config)) {
     }
     let _g = LOCK.lock();
 
+    // Change the cwd to a test-specific directory
+    let cwd = env::current_dir().unwrap();
+    env::set_current_dir(&config.workdir).unwrap();
+    let _g = scopeguard::guard(cwd, |d| env::set_current_dir(d).unwrap());
+
     f(config);
 
     // These are the bogus values the test harness sets "HOME" and "CARGO_HOME"

src/rustup/config.rs

@@ -18,17 +18,19 @@ use settings::{TelemetryMode, SettingsFile, DEFAULT_METADATA_VERSION};
 pub enum OverrideReason {
     Environment,
     OverrideDB(PathBuf),
+    VersionFile(PathBuf),
 }
 
-
-
 impl Display for OverrideReason {
     fn fmt(&self, f: &mut fmt::Formatter) -> ::std::result::Result<(), fmt::Error> {
         match *self {
             OverrideReason::Environment => write!(f, "environment override by RUSTUP_TOOLCHAIN"),
             OverrideReason::OverrideDB(ref path) => {
                 write!(f, "directory override for '{}'", path.display())
             }
+            OverrideReason::VersionFile(ref path) => {
+                write!(f, "overridden by '{}'", path.display())
+            }
         }
     }
 }
@@ -223,29 +225,86 @@ impl Cfg {
     }
 
     pub fn find_override(&self, path: &Path) -> Result<Option<(Toolchain, OverrideReason)>> {
+        let mut override_ = None;
+
+        // First check RUSTUP_TOOLCHAIN
         if let Some(ref name) = self.env_override {
-            let toolchain = try!(self.verify_toolchain(name).chain_err(|| ErrorKind::ToolchainNotInstalled(name.to_string())));
+            override_ = Some((name.to_string(), OverrideReason::Environment));
+        }
+
+        // Then look in the override database
+        if override_.is_none() {
+            try!(self.settings_file.with(|s| {
+                let name = s.find_override(path, self.notify_handler.as_ref());
+                override_ = name.map(|(name, reason_path)| (name, OverrideReason::OverrideDB(reason_path)));
+
+                Ok(())
+            }));
+        }
 
-            return Ok(Some((toolchain, OverrideReason::Environment)));
+        // Then check the explicit version file
+        if override_.is_none() {
+            let name_path = self.find_override_version_file(path)?;
+            override_ = name_path.map(|(name, path)| (name, OverrideReason::VersionFile(path)));
         }
 
-        let result = try!(self.settings_file.with(|s| {
-            Ok(s.find_override(path, self.notify_handler.as_ref()))
-        }));
-        if let Some((name, reason_path)) = result {
-            let toolchain = match self.verify_toolchain(&name) {
-                Ok(t) => { t },
+        if let Some((name, reason)) = override_ {
+            // This is hackishly using the error chain to provide a bit of
+            // extra context about what went wrong. The CLI will display it
+            // on a line after the proximate error.
+
+            let reason_err = match reason {
+                OverrideReason::Environment => {
+                    format!("the RUSTUP_TOOLCHAIN environment variable specifies an uninstalled toolchain")
+                }
+                OverrideReason::OverrideDB(ref path) => {
+                    format!("the directory override for '{}' specifies an uninstalled toolchain", path.display())
+                }
+                OverrideReason::VersionFile(ref path) => {
+                    format!("the version file at '{}' specifies an uninstalled toolchain", path.display())
+                }
+            };
+
+            match self.verify_toolchain(&name) {
+                Ok(t) => {
+                    Ok(Some((t, reason)))
+                }
                 Err(Error(ErrorKind::Utils(::rustup_utils::ErrorKind::NotADirectory { .. }), _)) => {
                     // Strip the confusing NotADirectory error and only mention that the override
                     // toolchain is not installed.
-                    return Err(ErrorKind::OverrideToolchainNotInstalled(name.to_string()).into())
+                    Err(Error::from(reason_err))
+                        .chain_err(|| ErrorKind::OverrideToolchainNotInstalled(name.to_string()))
                 },
-                Err(e) => return Err(e).chain_err(|| {
-                    ErrorKind::OverrideToolchainNotInstalled(name.to_string())
-                })
+                Err(e) => {
+                    Err(e)
+                        .chain_err(|| Error::from(reason_err))
+                        .chain_err(|| ErrorKind::OverrideToolchainNotInstalled(name.to_string()))
+                }
+            }
+        } else {
+            Ok(None)
+        }
+    }
 
-            };
-            return Ok(Some((toolchain, OverrideReason::OverrideDB(reason_path))));
+    /// Starting in path walk up the tree looking for .rust-version
+    fn find_override_version_file(&self, path: &Path) -> Result<Option<(String, PathBuf)>> {
+        let mut path = Some(path);
+
+        while let Some(p) = path {
+            let version_file = p.join(".rust-version");
+            if let Ok(s) = utils::read_file("version file", &version_file) {
+                if let Some(s) = s.lines().next() {
+                    let toolchain_name = s.trim();
+                    dist::validate_channel_name(&toolchain_name)
+                        .chain_err(|| format!("invalid channel name '{}' in '{}'",
+                                              toolchain_name,
+                                              version_file.display()))?;
+
+                    return Ok(Some((toolchain_name.to_string(), version_file)));
+                }
+            }
+
+            path = p.parent();
         }
 
         Ok(None)