feat(cli): enhance help documentation and dynamic applet dispatch

crates/irtt-cli/src/applet.rs

@@ -41,13 +41,15 @@ pub fn dispatch_from_argv(argv: Vec<OsString>) -> Result<AppletDispatch, String>
     let basename = applet_basename(argv0);
     if basename.starts_with("irtt-") && basename != "irtt-rs" {
         return Err(format!(
-            "unknown applet name '{basename}'. Known applet names: irtt-rs, irtt-cli, irtt-tui, irtt-server"
+            "unknown applet name '{basename}'. Known applet names: {}",
+            known_applet_binary_names()
         ));
     }
 
     let Some(command) = argv.get(1).and_then(|arg| arg.to_str()) else {
         return Err(format!(
-            "choose an applet: client, tui, or server\n\n{}",
+            "choose an applet: {}\n\n{}",
+            applet_command_names(),
             dispatcher_help()
         ));
     };
@@ -67,7 +69,8 @@ pub fn dispatch_from_argv(argv: Vec<OsString>) -> Result<AppletDispatch, String>
             argv: applet_argv("irtt-server", &argv[2..]),
         }),
         _ => Err(format!(
-            "unknown applet '{command}'. Choose one of: client, tui, server\n\n{}",
+            "unknown applet '{command}'. Choose one of: {}\n\n{}",
+            applet_command_names(),
             dispatcher_help()
         )),
     }
@@ -76,13 +79,47 @@ pub fn dispatch_from_argv(argv: Vec<OsString>) -> Result<AppletDispatch, String>
 pub fn dispatcher_help() -> String {
     let mut command = Command::new("irtt-rs")
         .about("IRTT-compatible multi-applet dispatcher")
-        .subcommand(Command::new("client").about("Run the stream client applet"))
-        .subcommand(Command::new("tui").about("Run the terminal UI applet"))
-        .subcommand(Command::new("server").about("Run the server applet"))
-        .after_help("Applet binary names: irtt-cli, irtt-tui, irtt-server");
+        .subcommand(Command::new("client").about(client_applet_about()))
+        .subcommand(Command::new("tui").about(tui_applet_about()))
+        .subcommand(Command::new("server").about("Server applet is not available in this build"))
+        .after_help(dispatcher_after_help());
     command.render_help().to_string()
 }
 
+fn client_applet_about() -> &'static str {
+    if cfg!(feature = "client") {
+        "Run the stream client applet"
+    } else {
+        "Stream client applet is not available in this build"
+    }
+}
+
+fn tui_applet_about() -> &'static str {
+    if cfg!(feature = "tui") {
+        "Run the terminal UI applet"
+    } else {
+        "Terminal UI applet is not available in this build"
+    }
+}
+
+fn known_applet_binary_names() -> &'static str {
+    "irtt-rs, irtt-cli, irtt-tui, irtt-server"
+}
+
+fn applet_command_names() -> &'static str {
+    "client, tui, or server"
+}
+
+fn dispatcher_after_help() -> &'static str {
+    if cfg!(feature = "tui") {
+        "Recognized applet binary names: irtt-cli, irtt-tui, irtt-server"
+    } else if cfg!(feature = "client") {
+        "Recognized applet binary names: irtt-cli, irtt-tui, irtt-server\nOptional applet: irtt-tui requires the tui feature"
+    } else {
+        "Recognized applet binary names: irtt-cli, irtt-tui, irtt-server\nOptional applets: irtt-cli requires the client feature; irtt-tui requires the tui feature"
+    }
+}
+
 fn applet_basename(argv0: &str) -> &str {
     Path::new(argv0)
         .file_name()
@@ -127,7 +164,11 @@ mod tests {
         };
         assert!(help.contains("IRTT-compatible multi-applet dispatcher"));
         assert!(help.contains("client"));
-        assert!(help.contains("tui"));
+        if cfg!(feature = "tui") {
+            assert!(help.contains("Run the terminal UI applet"));
+        } else {
+            assert!(help.contains("Terminal UI applet is not available in this build"));
+        }
         assert!(help.contains("server"));
     }
 
@@ -136,7 +177,9 @@ mod tests {
         let err = dispatch_from_argv(vec!["irtt-rs".into()]).unwrap_err();
         assert!(err.contains("choose an applet"));
         assert!(err.contains("client"));
-        assert!(err.contains("tui"));
+        if cfg!(feature = "tui") {
+            assert!(err.contains("tui"));
+        }
         assert!(err.contains("server"));
     }
 
@@ -171,7 +214,9 @@ mod tests {
         let err = dispatch_from_argv(vec!["/usr/bin/irtt-typo".into()]).unwrap_err();
         assert!(err.contains("unknown applet name 'irtt-typo'"));
         assert!(err.contains("irtt-cli"));
-        assert!(err.contains("irtt-tui"));
+        if cfg!(feature = "tui") {
+            assert!(err.contains("irtt-tui"));
+        }
         assert!(err.contains("irtt-server"));
     }
 }