UX: Report non-installable toolchains

If you pick a default toolchain which is not installable, or if you
try to `rustup toolchain install` something non-installable then we
should report it as such and exit non-zero so scripting can fail.

Signed-off-by: Daniel Silverstone <dsilvers@digital-scurf.org>

src/cli/errors.rs

@@ -37,6 +37,10 @@ error_chain! {
             description("toolchain is not installed")
             display("toolchain '{}' is not installed", t)
         }
+        ToolchainNotInstallable(t: String) {
+            description("toolchain is not installable")
+            display("toolchain '{}' is not installable", t)
+        }
         InvalidToolchainName(t: String) {
             description("invalid toolchain name")
             display("invalid toolchain name: '{}'{}", t, maybe_suggest_toolchain(t))

src/cli/rustup_mode.rs

@@ -977,6 +977,10 @@ fn update(cfg: &mut Cfg, m: &ArgMatches<'_>) -> Result<utils::ExitCode> {
             };
 
             if let Some(status) = status.clone() {
+                let toolchainname = toolchain.name().to_string();
+                if !toolchain.exists() {
+                    return Err(ErrorKind::ToolchainNotInstallable(toolchainname).into());
+                }
                 writeln!(process().stdout())?;
                 common::show_channel_update(cfg, toolchain.name(), Ok(status))?;
             }

src/cli/self_update.rs

@@ -743,6 +743,9 @@ fn maybe_install_rust(
         let distributable = DistributableToolchain::new(&toolchain)?;
         let status = distributable.install_from_dist(true, false, components, targets, None)?;
         let toolchain_str = toolchain.name().to_owned();
+        if !toolchain.exists() {
+            return Err(ErrorKind::ToolchainNotInstallable(toolchain.name().to_string()).into());
+        }
         toolchain.cfg().set_default(&toolchain_str)?;
         writeln!(process().stdout())?;
         common::show_channel_update(&toolchain.cfg(), &toolchain_str, Ok(status))?;

src/errors.rs

@@ -295,6 +295,10 @@ error_chain! {
             description("toolchain is not installed")
             display("toolchain '{}' is not installed", t)
         }
+        ToolchainNotInstallable(t: String) {
+            description("toolchain is not installable")
+            display("toolchain '{}' is not installable", t)
+        }
         ToolchainNotSelected {
             description("toolchain is not selected")
             display("no override and no default toolchain set")

src/install.rs

@@ -5,7 +5,7 @@ use crate::dist::dist;
 use crate::dist::download::DownloadCfg;
 use crate::dist::prefix::InstallPrefix;
 use crate::dist::Notification;
-use crate::errors::Result;
+use crate::errors::{ErrorKind, Result};
 use crate::notifications::Notification as RootNotification;
 use crate::toolchain::{CustomToolchain, DistributableToolchain, Toolchain, UpdateStatus};
 use crate::utils::utils;
@@ -76,7 +76,12 @@ impl<'a> InstallMethod<'a> {
             (false, _) => UpdateStatus::Unchanged,
         };
 
-        Ok(status)
+        // Final check, to ensure we're installed
+        if !toolchain.exists() {
+            Err(ErrorKind::ToolchainNotInstallable(toolchain.name().to_string()).into())
+        } else {
+            Ok(status)
+        }
     }
 
     pub fn run(self, path: &Path, notify_handler: &dyn Fn(Notification<'_>)) -> Result<bool> {

tests/cli-misc.rs

@@ -685,6 +685,26 @@ fn update_unavailable_rustc() {
     });
 }
 
+// issue 2562
+#[test]
+fn install_unavailable_platform() {
+    clitools::setup(Scenario::Unavailable, &|config| {
+        set_current_dist_date(config, "2015-01-02");
+        // explicit attempt to install should fail
+        expect_err(
+            config,
+            &["rustup", "toolchain", "install", "nightly"],
+            "is not installable",
+        );
+        // implicit attempt to install should fail
+        expect_err(
+            config,
+            &["rustup", "default", "nightly"],
+            "is not installable",
+        );
+    });
+}
+
 #[test]
 fn update_nightly_even_with_incompat() {
     clitools::setup(Scenario::MissingComponent, &|config| {