Display alias target on 'cargo help <alias>`

src/bin/cargo/commands/help.rs

@@ -1,6 +1,6 @@
 use crate::aliased_command;
 use cargo::util::errors::CargoResult;
-use cargo::Config;
+use cargo::{drop_println, Config};
 use cargo_util::paths::resolve_executable;
 use flate2::read::GzDecoder;
 use std::ffi::OsString;
@@ -46,8 +46,16 @@ fn try_help(config: &Config) -> CargoResult<bool> {
         Some(s) => s,
         None => return Ok(false),
     };
-    // Check if this is a built-in command (or alias);
-    let subcommand = match check_alias(config, subcommand) {
+
+    // Check if this is an alias. If so, just display the alias information.
+    if let Some(argv) = check_alias(config, subcommand) {
+        let alias = argv.join(" ");
+        drop_println!(config, "'{}' is aliased to '{}'", subcommand, alias);
+        return Ok(true);
+    }
+
+    // If not an alias, this should be a built-in subcommand.
+    let subcommand = match check_builtin(subcommand) {
         Some(s) => s,
         None => return Ok(false),
     };
@@ -73,26 +81,26 @@ fn try_help(config: &Config) -> CargoResult<bool> {
     Ok(true)
 }
 
-/// Checks if the given subcommand is a built-in command (possibly via an alias).
+/// Checks if the given subcommand is an alias.
 ///
-/// Returns None if it is not a built-in command.
-fn check_alias(config: &Config, subcommand: &str) -> Option<String> {
-    if super::builtin_exec(subcommand).is_some() {
-        return Some(subcommand.to_string());
-    }
+/// Returns None if it is not an alias.
+fn check_alias(config: &Config, subcommand: &str) -> Option<Vec<String>> {
     match aliased_command(config, subcommand) {
-        Ok(Some(alias)) => {
-            let alias = alias.into_iter().next()?;
-            if super::builtin_exec(&alias).is_some() {
-                Some(alias)
-            } else {
-                None
-            }
-        }
+        Ok(Some(alias)) => Some(alias),
         _ => None,
     }
 }
 
+/// Checks if the given subcommand is a built-in command (not via an alias).
+///
+/// Returns None if it is not a built-in command.
+fn check_builtin(subcommand: &str) -> Option<String> {
+    match super::builtin_exec(subcommand) {
+        Some(_) => Some(subcommand.to_string()),
+        None => None,
+    }
+}
+
 /// Extracts the given man page from the compressed archive.
 ///
 /// Returns None if the command wasn't found.

tests/testsuite/help.rs

@@ -110,6 +110,20 @@ fn help_with_man_and_path(
     assert_eq!(stdout, contents);
 }
 
+fn help_with_stdout_and_path(subcommand: &str, path: &Path) -> String {
+    let output = process(&cargo_exe())
+        .arg("help")
+        .arg(subcommand)
+        .env("PATH", path)
+        .exec_with_output()
+        .unwrap();
+    assert!(output.status.success());
+    let stderr = from_utf8(&output.stderr).unwrap();
+    assert_eq!(stderr, "");
+    let stdout = from_utf8(&output.stdout).unwrap();
+    stdout.to_string()
+}
+
 #[cargo_test]
 fn help_man() {
     // Checks that `help command` displays the man page using the given command.
@@ -124,7 +138,8 @@ fn help_man() {
 #[cargo_test]
 fn help_alias() {
     // Check that `help some_alias` will resolve.
-    help_with_man_and_path("", "b", "build", Path::new(""));
+    let out = help_with_stdout_and_path("b", Path::new(""));
+    assert_eq!(out, "'b' is aliased to 'build'\n");
 
     let config = paths::root().join(".cargo/config");
     fs::create_dir_all(config.parent().unwrap()).unwrap();
@@ -136,7 +151,8 @@ fn help_alias() {
         "#,
     )
     .unwrap();
-    help_with_man_and_path("", "my-alias", "build", Path::new(""));
+    let out = help_with_stdout_and_path("my-alias", Path::new(""));
+    assert_eq!(out, "'my-alias' is aliased to 'build --release'\n");
 }
 
 #[cargo_test]