Add Listing of Installed Components

This feature adds the ability to only list installed components
rather than all available components.

src/rustup-cli/common.rs

@@ -339,6 +339,17 @@ pub fn list_components(toolchain: &Toolchain<'_>) -> Result<()> {
     Ok(())
 }
 
+pub fn list_installed_components(toolchain: &Toolchain<'_>) -> Result<()> {
+    let mut t = term2::stdout();
+    for component in toolchain.list_components()? {
+        if component.installed {
+            let name = component.name;
+            let _ = writeln!(t, "{}", name);
+        }
+    }
+    Ok(())
+}
+
 pub fn list_toolchains(cfg: &Cfg) -> Result<()> {
     let toolchains = cfg.list_toolchains()?;
 

src/rustup-cli/rustup_mode.rs

@@ -291,6 +291,11 @@ pub fn cli() -> App<'static, 'static> {
                 .subcommand(
                     SubCommand::with_name("list")
                         .about("List installed and available components")
+                        .arg(
+                            Arg::with_name("installed")
+                                .long("--installed")
+                                .help("List only installed components"),
+                        )
                         .arg(
                             Arg::with_name("toolchain")
                                 .help(TOOLCHAIN_ARG_HELP)
@@ -834,7 +839,11 @@ fn target_remove(cfg: &Cfg, m: &ArgMatches<'_>) -> Result<()> {
 fn component_list(cfg: &Cfg, m: &ArgMatches<'_>) -> Result<()> {
     let toolchain = explicit_or_dir_toolchain(cfg, m)?;
 
-    common::list_components(&toolchain)
+    if m.is_present("installed") {
+        common::list_installed_components(&toolchain)
+    } else {
+        common::list_components(&toolchain)
+    }
 }
 
 fn component_add(cfg: &Cfg, m: &ArgMatches<'_>) -> Result<()> {