feat(config): warn user if auto-install is enabled

src/cli/rustup_mode.rs

@@ -689,34 +689,40 @@ pub async fn main(
             toolchain,
             force_non_host,
         } => default_(cfg, toolchain, force_non_host).await,
-        RustupSubcmd::Target { subcmd } => match subcmd {
-            TargetSubcmd::List {
-                toolchain,
-                installed,
-                quiet,
-            } => handle_epipe(target_list(cfg, toolchain, installed, quiet).await),
-            TargetSubcmd::Add { target, toolchain } => target_add(cfg, target, toolchain).await,
-            TargetSubcmd::Remove { target, toolchain } => {
-                target_remove(cfg, target, toolchain).await
+        RustupSubcmd::Target { subcmd } => {
+            cfg.skip_auto_install = true;
+            match subcmd {
+                TargetSubcmd::List {
+                    toolchain,
+                    installed,
+                    quiet,
+                } => handle_epipe(target_list(cfg, toolchain, installed, quiet).await),
+                TargetSubcmd::Add { target, toolchain } => target_add(cfg, target, toolchain).await,
+                TargetSubcmd::Remove { target, toolchain } => {
+                    target_remove(cfg, target, toolchain).await
+                }
             }
-        },
-        RustupSubcmd::Component { subcmd } => match subcmd {
-            ComponentSubcmd::List {
-                toolchain,
-                installed,
-                quiet,
-            } => handle_epipe(component_list(cfg, toolchain, installed, quiet).await),
-            ComponentSubcmd::Add {
-                component,
-                toolchain,
-                target,
-            } => component_add(cfg, component, toolchain, target).await,
-            ComponentSubcmd::Remove {
-                component,
-                toolchain,
-                target,
-            } => component_remove(cfg, component, toolchain, target).await,
-        },
+        }
+        RustupSubcmd::Component { subcmd } => {
+            cfg.skip_auto_install = true;
+            match subcmd {
+                ComponentSubcmd::List {
+                    toolchain,
+                    installed,
+                    quiet,
+                } => handle_epipe(component_list(cfg, toolchain, installed, quiet).await),
+                ComponentSubcmd::Add {
+                    component,
+                    toolchain,
+                    target,
+                } => component_add(cfg, component, toolchain, target).await,
+                ComponentSubcmd::Remove {
+                    component,
+                    toolchain,
+                    target,
+                } => component_remove(cfg, component, toolchain, target).await,
+            }
+        }
         RustupSubcmd::Override { subcmd } => match subcmd {
             OverrideSubcmd::List => handle_epipe(common::list_overrides(cfg)),
             OverrideSubcmd::Set { toolchain, path } => {
@@ -1061,7 +1067,7 @@ async fn run(
     install: bool,
 ) -> Result<ExitStatus> {
     let toolchain = toolchain.resolve(&cfg.get_default_host_triple()?)?;
-    let toolchain = Toolchain::from_local(toolchain, install, cfg).await?;
+    let toolchain = Toolchain::from_local(toolchain, || Ok(install), cfg).await?;
     let cmd = toolchain.command(&command[0])?;
     command::run_command_for_dir(cmd, &command[0], &command[1..])
 }

src/config.rs

@@ -246,6 +246,12 @@ pub(crate) struct Cfg<'a> {
     pub quiet: bool,
     pub current_dir: PathBuf,
     pub process: &'a Process,
+
+    /// If this flag is set to `true`, it can stop `rustup` from automatically installing the active
+    /// toolchain in certain undesired cases, such as under `rustup component` and `rustup target`
+    /// subcommands. This effect has higher precedence than the `RUSTUP_AUTO_INSTALL` environment
+    /// variable and the `rustup set auto-install` setting.
+    pub skip_auto_install: bool,
 }
 
 impl<'a> Cfg<'a> {
@@ -317,6 +323,7 @@ impl<'a> Cfg<'a> {
             quiet,
             current_dir,
             process,
+            skip_auto_install: false,
         };
 
         // Run some basic checks against the constructed configuration
@@ -373,12 +380,30 @@ impl<'a> Cfg<'a> {
     }
 
     pub(crate) fn should_auto_install(&self) -> Result<bool> {
-        if let Ok(mode) = self.process.var("RUSTUP_AUTO_INSTALL") {
-            Ok(mode != "0")
-        } else {
-            self.settings_file
-                .with(|s| Ok(s.auto_install != Some(AutoInstallMode::Disable)))
+        if self.skip_auto_install {
+            return Ok(false);
+        }
+
+        let should_auto = match self.process.var("RUSTUP_AUTO_INSTALL") {
+            Ok(mode) => mode != "0",
+            Err(_) => self
+                .settings_file
+                .with(|s| Ok(s.auto_install != Some(AutoInstallMode::Disable)))?,
+        };
+        if !should_auto {
+            return Ok(false);
         }
+
+        // We also need to suppress this warning if we're deep inside a recursive call.
+        let recursions = self.process.var("RUST_RECURSION_COUNT");
+        if recursions.is_ok_and(|it| it != "0") {
+            return Ok(true);
+        }
+
+        warn!("auto-install is enabled, active toolchain will be installed if absent");
+        warn!("this might cause rustup commands to take longer time to finish than expected");
+        info!("you may opt out with `RUSTUP_AUTO_INSTALL=0` or `rustup set auto-install disable`");
+        Ok(true)
     }
 
     // Returns a profile, if one exists in the settings file.
@@ -706,13 +731,10 @@ impl<'a> Cfg<'a> {
         name: Option<(LocalToolchainName, ActiveSource)>,
     ) -> Result<(Toolchain<'_>, ActiveSource)> {
         match name {
-            Some((tc, source)) => {
-                let install_if_missing = self.should_auto_install()?;
-                Ok((
-                    Toolchain::from_local(tc, install_if_missing, self).await?,
-                    source,
-                ))
-            }
+            Some((tc, src)) => Ok((
+                Toolchain::from_local(tc, || self.should_auto_install(), self).await?,
+                src,
+            )),
             None => {
                 let (tc, source) = self
                     .maybe_ensure_active_toolchain(None)
@@ -959,6 +981,7 @@ impl Debug for Cfg<'_> {
             dist_root_url,
             quiet,
             current_dir,
+            skip_auto_install,
             process: _,
         } = self;
 
@@ -976,6 +999,7 @@ impl Debug for Cfg<'_> {
             .field("dist_root_url", dist_root_url)
             .field("quiet", quiet)
             .field("current_dir", current_dir)
+            .field("skip_auto_install", skip_auto_install)
             .finish()
     }
 }

src/test/clitools.rs

@@ -314,6 +314,12 @@ impl Config {
             "/bogus-config-file.toml",
         );
 
+        // Clear current recursion count to avoid messing up related logic
+        cmd.env("RUST_RECURSION_COUNT", "");
+
+        // Clear override for auto installation of active toolchain unless explicitly requested
+        cmd.env("RUSTUP_AUTO_INSTALL", "");
+
         // Pass `RUSTUP_CI` over to the test process in case it is required downstream
         if let Some(ci) = env::var_os("RUSTUP_CI") {
             cmd.env("RUSTUP_CI", ci);

src/toolchain.rs

@@ -52,15 +52,15 @@ pub(crate) struct Toolchain<'a> {
 impl<'a> Toolchain<'a> {
     pub(crate) async fn from_local(
         name: LocalToolchainName,
-        install_if_missing: bool,
+        install_if_missing: impl Fn() -> anyhow::Result<bool>,
         cfg: &'a Cfg<'a>,
     ) -> anyhow::Result<Toolchain<'a>> {
         match Self::new(cfg, name) {
             Ok(tc) => Ok(tc),
             Err(RustupError::ToolchainNotInstalled {
                 name: ToolchainName::Official(desc),
                 ..
-            }) if install_if_missing => {
+            }) if install_if_missing()? => {
                 let options = DistOptions::new(&[], &[], &desc, cfg.get_profile()?, true, cfg)?;
                 Ok(DistributableToolchain::install(options).await?.1.toolchain)
             }

tests/suite/cli_misc.rs

@@ -64,7 +64,7 @@ async fn rustc_with_bad_rustup_toolchain_env_var() {
         .expect_with_env(["rustc"], [("RUSTUP_TOOLCHAIN", "bogus")])
         .await
         .with_stderr(snapbox::str![[r#"
-error: override toolchain 'bogus' is not installed[..]
+error:[..] toolchain 'bogus' is not installed[..]
 
 "#]])
         .is_err();
@@ -1381,7 +1381,10 @@ async fn which_asking_uninstalled_toolchain() {
 "#]])
         .is_ok();
     cx.config
-        .expect(["rustup", "which", "--toolchain=nightly", "rustc"])
+        .expect_with_env(
+            ["rustup", "which", "--toolchain=nightly", "rustc"],
+            [("RUSTUP_AUTO_INSTALL", "1")],
+        )
         .await
         .with_stdout(snapbox::str![[r#"
 [..]/toolchains/nightly-[HOST_TUPLE]/bin/rustc[EXE]
@@ -1512,7 +1515,7 @@ active because: overridden by +toolchain on the command line
         .expect(["rustup", "+foo", "which", "rustc"])
         .await
         .with_stderr(snapbox::str![[r#"
-error: override toolchain 'foo' is not installed: the +toolchain on the command line specifies an uninstalled toolchain
+error:[..] toolchain 'foo' is not installed[..]
 
 "#]])
         .is_err();
@@ -1746,3 +1749,26 @@ info: falling back to "[EXTERN_PATH]"
 "#]])
         .is_ok();
 }
+
+#[tokio::test]
+async fn warn_auto_install() {
+    let cx = CliTestContext::new(Scenario::SimpleV2).await;
+    cx.config
+        .expect_with_env(
+            ["rustc", "--version"],
+            [("RUSTUP_TOOLCHAIN", "stable"), ("RUSTUP_AUTO_INSTALL", "1")],
+        )
+        .await
+        .with_stdout(snapbox::str![[r#"
+1.1.0 (hash-stable-1.1.0)
+
+"#]])
+        .with_stderr(snapbox::str![[r#"
+...
+warn: auto-install is enabled, active toolchain will be installed if absent
+warn: this might cause rustup commands to take longer time to finish than expected
+info: you may opt out with `RUSTUP_AUTO_INSTALL=0` or `rustup set auto-install disable`
+...
+"#]])
+        .is_ok();
+}

tests/suite/cli_rustup.rs

@@ -1240,7 +1240,7 @@ async fn show_toolchain_override_not_installed() {
         .await
         .is_ok();
     cx.config
-        .expect(["rustup", "show"])
+        .expect_with_env(["rustup", "show"], [("RUSTUP_AUTO_INSTALL", "1")])
         .await
         .extend_redactions([("[RUSTUP_DIR]", &cx.config.rustupdir.to_string())])
         .with_stdout(snapbox::str![[r#"
@@ -1355,7 +1355,13 @@ installed targets:
 async fn show_toolchain_env_not_installed() {
     let cx = CliTestContext::new(Scenario::SimpleV2).await;
     cx.config
-        .expect_with_env(["rustup", "show"], [("RUSTUP_TOOLCHAIN", "nightly")])
+        .expect_with_env(
+            ["rustup", "show"],
+            [
+                ("RUSTUP_TOOLCHAIN", "nightly"),
+                ("RUSTUP_AUTO_INSTALL", "1"),
+            ],
+        )
         .await
         .extend_redactions([("[RUSTUP_DIR]", &cx.config.rustupdir.to_string())])
         .is_ok()

tests/suite/cli_v1.rs

@@ -271,7 +271,7 @@ async fn remove_override_toolchain_err_handling() {
         .await
         .is_ok();
     cx.config
-        .expect(["rustc", "--version"])
+        .expect_with_env(["rustc", "--version"], [("RUSTUP_AUTO_INSTALL", "1")])
         .await
         .with_stdout(snapbox::str![[r#"
 1.2.0 (hash-beta-1.2.0)

tests/suite/cli_v2.rs

@@ -478,7 +478,7 @@ async fn remove_override_toolchain_err_handling() {
         .await
         .is_ok();
     cx.config
-        .expect(["rustc", "--version"])
+        .expect_with_env(["rustc", "--version"], [("RUSTUP_AUTO_INSTALL", "1")])
         .await
         .with_stdout(snapbox::str![[r#"
 1.2.0 (hash-beta-1.2.0)
@@ -511,7 +511,7 @@ async fn file_override_toolchain_err_handling() {
     let toolchain_file = cwd.join("rust-toolchain");
     rustup::utils::raw::write_file(&toolchain_file, "beta").unwrap();
     cx.config
-        .expect(["rustc", "--version"])
+        .expect_with_env(["rustc", "--version"], [("RUSTUP_AUTO_INSTALL", "1")])
         .await
         .with_stdout(snapbox::str![[r#"
 1.2.0 (hash-beta-1.2.0)
@@ -553,7 +553,10 @@ error: toolchain 'beta-[HOST_TUPLE]' is not installed
 "#]])
         .is_err();
     cx.config
-        .expect(["rustc", "+beta", "--version"])
+        .expect_with_env(
+            ["rustc", "+beta", "--version"],
+            [("RUSTUP_AUTO_INSTALL", "1")],
+        )
         .await
         .with_stdout(snapbox::str![[r#"
 1.2.0 (hash-beta-1.2.0)