Suggest alternative toolchains for unavailable targets

src/errors.rs

@@ -22,6 +22,21 @@ use crate::{
 
 pub(crate) const DEFAULT_STABLE_HINT: &str = "help: run 'rustup default stable' to download the latest stable release of Rust and set it as your default toolchain.";
 
+#[derive(Debug, Clone)]
+pub enum TargetSuggestion {
+    Toolchain(String),
+    Component(String),
+}
+
+impl std::fmt::Display for TargetSuggestion {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::Toolchain(command) => write!(f, "; try `{command}`"),
+            Self::Component(name) => write!(f, "; did you mean '{name}'?"),
+        }
+    }
+}
+
 /// A type erasing thunk for the retry crate to permit use with anyhow. See <https://github.com/dtolnay/anyhow/issues/149>
 #[derive(Debug, ThisError)]
 #[error(transparent)]
@@ -162,11 +177,11 @@ pub enum RustupError {
         suggestion: Option<String>,
     },
     #[error("toolchain '{}' does not have target '{}' installed{}\n", .desc, .target,
-    suggest_message(.suggestion))]
+    .suggestion.as_ref().map_or_else(String::new, ToString::to_string))]
     TargetNotInstalled {
         desc: Box<ToolchainDesc>,
         target: TargetTuple,
-        suggestion: Option<String>,
+        suggestion: Option<TargetSuggestion>,
     },
     #[error(
         "rustup executable proxies don't seem to work\n\

src/toolchain/distributable.rs

@@ -15,14 +15,14 @@ use crate::{
     RustupError, component_for_bin,
     config::{ActiveSource, Cfg, EnsureInstalled},
     dist::{
-        DistOptions, PartialToolchainDesc, ToolchainDesc,
+        DistOptions, PartialToolchainDesc, TargetTuple, ToolchainDesc,
         config::Config,
         download::DownloadCfg,
         manifest::{Component, ComponentStatus, Manifest, ManifestWithHash},
         manifestation::{Changes, Manifestation},
         prefix::InstallPrefix,
     },
-    errors::UnknownComponentInfo,
+    errors::{TargetSuggestion, UnknownComponentInfo},
     install::InstallMethod,
 };
 
@@ -385,6 +385,27 @@ impl<'a> DistributableToolchain<'a> {
         }
     }
 
+    fn find_toolchain_with_target(&self, target: &TargetTuple) -> Option<String> {
+        let toolchains = self.toolchain.cfg.list_toolchains(true).ok()?;
+
+        for toolchain_name in toolchains {
+            if let ToolchainName::Official(desc) = &toolchain_name
+                && desc == &self.desc
+            {
+                continue;
+            }
+
+            if let Ok(toolchain) = Toolchain::new(self.toolchain.cfg, toolchain_name.clone().into())
+                && let Ok(installed_targets) = toolchain.installed_targets()
+                && installed_targets.contains(target)
+            {
+                return Some(format!("+{toolchain_name}"));
+            }
+        }
+
+        None
+    }
+
     pub(crate) async fn remove_components(
         &self,
         components: impl IntoIterator<Item = anyhow::Result<Component>>,
@@ -413,19 +434,31 @@ impl<'a> DistributableToolchain<'a> {
             }
 
             let suggestion = self.get_component_suggestion(&component, &config, &manifest, true);
-            // Check if the target is installed.
             if !config
                 .components
                 .iter()
                 .any(|c| c.target() == component.target())
             {
+                let target = component
+                    .target
+                    .as_ref()
+                    .expect("component target should be known");
+                let suggestion = self
+                    .find_toolchain_with_target(target)
+                    .map(|toolchain| {
+                        TargetSuggestion::Toolchain(format!(
+                            "rustup {toolchain} target remove {target}"
+                        ))
+                    })
+                    .or_else(|| suggestion.map(TargetSuggestion::Component));
                 return Err(RustupError::TargetNotInstalled {
                     desc: Box::new(self.desc.clone()),
-                    target: component.target.expect("component target should be known"),
+                    target: target.clone(),
                     suggestion,
                 }
                 .into());
             }
+
             unknown_components.push(UnknownComponentInfo {
                 name: manifest.short_name(&component).to_string(),
                 description: manifest.description(&component),

tests/suite/cli_v2.rs

@@ -1795,6 +1795,72 @@ error: toolchain 'nightly-[HOST_TUPLE]' does not have target '[CROSS_ARCH_I]' in
         .is_err();
 }
 
+#[tokio::test]
+async fn remove_target_not_installed_with_suggestion() {
+    let cx = CliTestContext::new(Scenario::SimpleV2).await;
+    cx.config
+        .expect(["rustup", "toolchain", "install", "stable"])
+        .await
+        .is_ok();
+    cx.config
+        .expect(["rustup", "toolchain", "install", "nightly"])
+        .await
+        .is_ok();
+    cx.config
+        .expect(["rustup", "default", "stable"])
+        .await
+        .is_ok();
+    cx.config
+        .expect([
+            "rustup",
+            "target",
+            "add",
+            CROSS_ARCH1,
+            "--toolchain=nightly",
+        ])
+        .await
+        .is_ok();
+    cx.config
+        .expect(["rustup", "target", "remove", CROSS_ARCH1])
+        .await
+        .extend_redactions([
+            ("[HOST_TUPLE]", this_host_tuple()),
+            ("[CROSS_ARCH_I]", CROSS_ARCH1.to_string()),
+        ])
+        .with_stderr(snapbox::str![[r#"
+...
+error: toolchain 'stable-[HOST_TUPLE]' does not have target '[CROSS_ARCH_I]' installed; try `rustup +nightly-[HOST_TUPLE] target remove [CROSS_ARCH_I]`
+...
+"#]])
+        .is_err();
+}
+
+#[tokio::test]
+async fn remove_target_not_installed_no_alternative() {
+    let cx = CliTestContext::new(Scenario::SimpleV2).await;
+    cx.config
+        .expect(["rustup", "toolchain", "install", "stable"])
+        .await
+        .is_ok();
+    cx.config
+        .expect(["rustup", "default", "stable"])
+        .await
+        .is_ok();
+    cx.config
+        .expect(["rustup", "target", "remove", CROSS_ARCH1])
+        .await
+        .extend_redactions([
+            ("[HOST_TUPLE]", this_host_tuple()),
+            ("[CROSS_ARCH_I]", CROSS_ARCH1.to_string()),
+        ])
+        .with_stderr(snapbox::str![[r#"
+...
+error: toolchain 'stable-[HOST_TUPLE]' does not have target '[CROSS_ARCH_I]' installed
+...
+"#]])
+        .is_err();
+}
+
 #[tokio::test]
 async fn remove_target_no_toolchain() {
     let cx = CliTestContext::new(Scenario::SimpleV2).await;