Refactor components_missing_msg and add a Panics section to its d…

…ocstring

src/dist/dist.rs

@@ -42,46 +42,56 @@ static TOOLCHAIN_CHANNELS: &[&str] = &[
  r"\d{1}\.\d{1,3}(?:\.\d{1,2})?",
 ];
 
+/// Returns a error message indicating that certain [`Component`]s are missing in a toolchain distribution.
+/// This message is currently used exclusively in toolchain-wide operations,
+/// otherwise [`component_unavailable_msg`](`crate::errors::component_unavailable_msg`) will be used.
+///
+/// # Panics
+/// This function will panic when the collection of unavailable components `cs` is empty.
 fn components_missing_msg(cs: &[Component], manifest: &ManifestV2, toolchain: &str) -> String {
- assert!(!cs.is_empty());
  let mut buf = vec![];
  let suggestion = format!(" rustup toolchain add {toolchain} --profile minimal");
  let nightly_tips = "Sometimes not all components are available in any given nightly. ";
 
- if cs.len() == 1 {
- let _ = writeln!(
- buf,
- "component {} is unavailable for download for channel '{}'",
- &cs[0].description(manifest),
- toolchain,
- );
+ match cs {
+ [] => panic!("`components_missing_msg` should not be called with an empty collection of unavailable components"),
+ [c] => {
+ _ = writeln!(
+ buf,
+ "component {} is unavailable for download for channel '{}'",
+ c.description(manifest),
+ toolchain,
+ );
+
+ if toolchain.starts_with("nightly") {
+ _ = write!(buf, "{nightly_tips}");
+ }
 
- if toolchain.starts_with("nightly") {
- let _ = write!(buf, "{nightly_tips}");
+ _ = write!(
+ buf,
+ "If you don't need the component, you could try a minimal installation with:\n\n{suggestion}"
+ );
  }
+ cs => {
+ let cs_str = cs
+ .iter()
+ .map(|c| c.description(manifest))
+ .collect::<Vec<_>>()
+ .join(", ");
+ _ = write!(
+ buf,
+ "some components unavailable for download for channel '{toolchain}': {cs_str}"
+ );
 
- let _ = write!(
- buf,
- "If you don't need the component, you could try a minimal installation with:\n\n{suggestion}"
- );
- } else {
- let cs_str = cs
- .iter()
- .map(|c| c.description(manifest))
- .collect::<Vec<_>>()
- .join(", ");
- let _ = write!(
- buf,
- "some components unavailable for download for channel '{toolchain}': {cs_str}"
- );
+ if toolchain.starts_with("nightly") {
+ let _ = write!(buf, "{nightly_tips}");
+ }
 
- if toolchain.starts_with("nightly") {
- let _ = write!(buf, "{nightly_tips}");
+ _ = write!(
+ buf,
+ "If you don't need the components, you could try a minimal installation with:\n\n{suggestion}"
+ );
  }
- let _ = write!(
- buf,
- "If you don't need the components, you could try a minimal installation with:\n\n{suggestion}"
- );
  }
 
  String::from_utf8(buf).unwrap()