Show the command summary when running cargo --list

src/bin/cargo/cli.rs

@@ -70,8 +70,9 @@ Run with 'cargo -Z [FLAG] [SUBCOMMAND]'"
         println!("Installed Commands:");
         for command in list_commands(config) {
             match command {
-                CommandInfo::BuiltIn { name } => {
-                    println!("    {:<20} {}", name)
+                CommandInfo::BuiltIn { name, about } => {
+                    let summary = about.unwrap_or_default();
+                    println!("    {:<20} {}", name, summary)
                 }
                 CommandInfo::External { name, path } => {
                     if is_verbose {

src/bin/cargo/command_prelude.rs

@@ -414,7 +414,7 @@ pub fn values(args: &ArgMatches, name: &str) -> Vec<String> {
 
 #[derive(PartialEq, PartialOrd, Eq, Ord)]
 pub enum CommandInfo {
-    BuiltIn { name: String },
+    BuiltIn { name: String, about: Option<String>, },
     External { name: String, path: PathBuf },
 }
 

src/bin/cargo/main.rs

@@ -114,6 +114,7 @@ fn list_commands(config: &Config) -> BTreeSet<CommandInfo> {
     for cmd in commands::builtin() {
         commands.insert(CommandInfo::BuiltIn {
             name: cmd.get_name().to_string(),
+            about: cmd.p.meta.about.map(|s| s.to_string()),
         });
     }
 

tests/testsuite/cargo_command.rs

@@ -60,6 +60,18 @@ fn path() -> Vec<PathBuf> {
     env::split_paths(&env::var_os("PATH").unwrap_or_default()).collect()
 }
 
+#[test]
+fn list_commands_with_descriptions() {
+    let p = project().build();
+    let output = p.cargo("--list").exec_with_output().unwrap();
+    let output = str::from_utf8(&output.stdout).unwrap();
+    assert!(
+        output.contains("\n    build                Compile a local package and all of its dependencies"),
+        "missing build, with description: {}",
+        output
+    );
+}
+
 #[test]
 fn list_command_looks_at_path() {
     let proj = project().build();