Improve error message when default components are unavailable on a new toolchain

src/dist/mod.rs

@@ -84,6 +84,12 @@ fn components_missing_msg(cs: &[Component], manifest: &ManifestV2, toolchain: &s
         }
     }
 
+    let from_complete_profile = manifest
+        .profiles
+        .get(&Profile::Complete)
+        .map(|profile| cs.iter().all(|c| profile.contains(&c.pkg)))
+        .unwrap_or(false);
+
     if toolchain.starts_with("nightly") {
         let _ = write!(
             buf,
@@ -97,6 +103,13 @@ fn components_missing_msg(cs: &[Component], manifest: &ManifestV2, toolchain: &s
         help: then you can use the toolchain with commands such as:\n\
         help:     cargo +nightly-2018-12-27 build"
         );
+    } else if from_complete_profile {
+        let _ = write!(
+            buf,
+            "\
+note: these were added as default components on another toolchain
+help: run `rustup set profile minimal` to stop new toolchains from inheriting extra components"
+        );
     } else if ["beta", "stable"].iter().any(|&p| toolchain.starts_with(p)) {
         let _ = write!(
             buf,

src/errors.rs

@@ -12,7 +12,7 @@ use url::Url;
 
 use crate::{
     dist::{
-        Channel, TargetTuple, ToolchainDesc,
+        Channel, Profile, TargetTuple, ToolchainDesc,
         manifest::{Component, Manifest},
     },
     toolchain::{PathBasedToolchainName, ToolchainName},
@@ -217,6 +217,8 @@ fn component_unavailable_msg(cs: &[Component], manifest: &Manifest, toolchain: &
 
             if toolchain.starts_with("nightly") {
                 let _ = write!(buf, "{NIGHTLY_COMPONENT_NOTE}");
+            } else {
+                write_nightly_profile_hint(&mut buf, cs, manifest);
             }
         }
         cs => {
@@ -244,13 +246,31 @@ fn component_unavailable_msg(cs: &[Component], manifest: &Manifest, toolchain: &
 
             if toolchain.starts_with("nightly") {
                 let _ = write!(buf, "{NIGHTLY_COMPONENT_NOTE}");
+            } else {
+                write_nightly_profile_hint(&mut buf, cs, manifest);
             }
         }
     }
 
     String::from_utf8(buf).unwrap()
 }
 
+fn write_nightly_profile_hint(buf: &mut Vec<u8>, cs: &[Component], manifest: &Manifest) {
+    let from_complete_profile = manifest
+        .profiles
+        .get(&Profile::Complete)
+        .map(|profile| cs.iter().all(|c| profile.contains(&c.pkg)))
+        .unwrap_or(false);
+    if from_complete_profile {
+        let _ = write!(
+            buf,
+            "\
+note: these were added as default components on another toolchain
+help: run `rustup set profile minimal` to stop new toolchains from inheriting extra components"
+        );
+    }
+}
+
 fn unknown_components_msg(desc: &ToolchainDesc, components: &[UnknownComponentInfo]) -> String {
     let mut buf = String::new();