Better error message for missing binary

src/rustup/errors.rs

@@ -26,9 +26,9 @@ error_chain! {
             description("override toolchain is not installed")
             display("override toolchain '{}' is not installed", t)
         }
-        BinaryNotFound(t: String, bin: String) {
+        BinaryNotFound(bin: String, t: String, is_default: bool) {
             description("toolchain does not contain binary")
-            display("'{}' is not installed for the toolchain '{}'{}", bin, t, install_msg(bin))
+            display("'{}' is not installed for the toolchain '{}'{}", bin, t, install_msg(bin, t, *is_default))
         }
         NeedMetadataUpgrade {
             description("rustup's metadata is out of date. run `rustup self upgrade-data`")
@@ -73,9 +73,15 @@ error_chain! {
     }
 }
 
-fn install_msg(bin: &str) -> String {
+fn install_msg(bin: &str, toolchain: &str, is_default: bool) -> String {
     match component_for_bin(bin) {
-        Some(c) => format!("\nTo install, run `rustup component add {}`", c),
+        Some(c) => format!("\nTo install, run `rustup component add {}{}`", c, {
+            if is_default {
+                String::new()
+            } else {
+                format!(" --toolchain {}", toolchain)
+            }
+        }),
         None => String::new(),
     }
 }

src/rustup/toolchain.rs

@@ -344,8 +344,9 @@ impl<'a> Toolchain<'a> {
                 .unwrap_or(0);
             if recursion_count > env_var::RUST_RECURSION_COUNT_MAX - 1 {
                 return Err(ErrorKind::BinaryNotFound(
-                    self.name.clone(),
                     binary.to_string_lossy().into(),
+                    self.name.clone(),
+                    Some(&self.name) == self.cfg.get_default().ok().as_ref(),
                 )
                 .into());
             }

tests/cli-misc.rs

@@ -380,6 +380,9 @@ fn rustup_failed_path_search() {
                 &config.customdir.join("custom-1").to_string_lossy(),
             ],
         );
+
+        expect_ok(config, &["rustup", "default", "custom"]);
+
         let broken = &["rustup", "run", "custom", "fake_proxy"];
         expect_err(
             config,
@@ -394,6 +397,54 @@ fn rustup_failed_path_search() {
     });
 }
 
+#[test]
+fn rustup_failed_path_search_toolchain() {
+    setup(&|config| {
+        use std::env::consts::EXE_SUFFIX;
+
+        let ref rustup_path = config.exedir.join(&format!("rustup{}", EXE_SUFFIX));
+        let ref tool_path = config.exedir.join(&format!("cargo-miri{}", EXE_SUFFIX));
+        utils::hardlink_file(rustup_path, tool_path)
+            .expect("Failed to create fake cargo-miri for test");
+
+        expect_ok(
+            config,
+            &[
+                "rustup",
+                "toolchain",
+                "link",
+                "custom-1",
+                &config.customdir.join("custom-1").to_string_lossy(),
+            ],
+        );
+
+        expect_ok(
+            config,
+            &[
+                "rustup",
+                "toolchain",
+                "link",
+                "custom-2",
+                &config.customdir.join("custom-2").to_string_lossy(),
+            ],
+        );
+
+        expect_ok(config, &["rustup", "default", "custom-2"]);
+
+        let broken = &["rustup", "run", "custom-1", "cargo-miri"];
+        expect_err(
+            config,
+            broken,
+            "rustup component add miri --toolchain custom-1",
+        );
+
+        let broken = &["rustup", "run", "custom-2", "cargo-miri"];
+        expect_err(config, broken, "rustup component add miri");
+
+        // Hardlink will be automatically cleaned up by test setup code
+    });
+}
+
 #[test]
 fn rustup_run_not_installed() {
     setup(&|config| {