6 files changed, 76 insertions, 23 deletions

diff --git a/src/main.rs b/src/main.rs
index 7143a59bf..16d0e3025 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -10,6 +10,7 @@ mod print;
 mod segment;
 mod utils;
 
+use crate::module::ALL_MODULES;
 use clap::{App, AppSettings, Arg, SubCommand};
 
 fn main() {
@@ -91,7 +92,14 @@ fn main() {
                 .arg(
                     Arg::with_name("name")
                         .help("The name of the module to be printed")
-                        .required(true),
+                        .required(true)
+                        .required_unless("list"),
+                )
+                .arg(
+                    Arg::with_name("list")
+                        .short("l")
+                        .long("list")
+                        .help("List out all supported modules"),
                 )
                 .arg(&status_code_arg)
                 .arg(&path_arg)
@@ -112,8 +120,16 @@ fn main() {
         }
         ("prompt", Some(sub_m)) => print::prompt(sub_m.clone()),
         ("module", Some(sub_m)) => {
-            let module_name = sub_m.value_of("name").expect("Module name missing.");
-            print::module(module_name, sub_m.clone());
+            if sub_m.is_present("list") {
+                println!("Supported modules list");
+                println!("----------------------");
+                for modules in ALL_MODULES {
+                    println!("{}", modules);
+                }
+            }
+            if let Some(module_name) = sub_m.value_of("name") {
+                print::module(module_name, sub_m.clone());
+            }
         }
         _ => {}
     }
diff --git a/src/module.rs b/src/module.rs
index 98f586cb3..fcb1ea361 100644
--- a/src/module.rs
+++ b/src/module.rs
@@ -4,6 +4,25 @@ use ansi_term::Style;
 use ansi_term::{ANSIString, ANSIStrings};
 use std::fmt;
 
+// List of all modules
+pub const ALL_MODULES: &[&str] = &[
+    "battery",
+    "character",
+    "cmd_duration",
+    "directory",
+    "git_branch",
+    "git_status",
+    "golang",
+    "jobs",
+    "line_break",
+    "nodejs",
+    "package",
+    "python",
+    "ruby",
+    "rust",
+    "username",
+];
+
 /// A module is a collection of segments showing data for a single integration
 /// (e.g. The git module shows the current git branch and status)
 pub struct Module<'a> {
diff --git a/src/modules/mod.rs b/src/modules/mod.rs
index 3ab7d8b3f..4aa67108e 100644
--- a/src/modules/mod.rs
+++ b/src/modules/mod.rs
@@ -1,3 +1,4 @@
+// While adding out new module add out module to src/module.rs ALL_MODULES const array also.
 mod battery;
 mod character;
 mod cmd_duration;
@@ -35,6 +36,9 @@ pub fn handle<'a>(module: &str, context: &'a Context) -> Option<Module<'a>> {
         "cmd_duration" => cmd_duration::module(context),
         "jobs" => jobs::module(context),
 
-        _ => panic!("Unknown module: {}", module),
+        _ => {
+            eprintln!("Error: Unknown module {}. Use starship module --list to list out all supported modules.", module);
+            None
+        }
     }
 }
diff --git a/src/print.rs b/src/print.rs
index 0cf495f72..69c56027a 100644
--- a/src/print.rs
+++ b/src/print.rs
@@ -5,27 +5,9 @@ use std::io::{self, Write};
 use crate::config::Config;
 use crate::context::Context;
 use crate::module::Module;
+use crate::module::ALL_MODULES;
 use crate::modules;
 
-// List of all modules
-const ALL_MODULES: &[&str] = &[
-    "battery",
-    "character",
-    "cmd_duration",
-    "directory",
-    "git_branch",
-    "git_status",
-    "golang",
-    "jobs",
-    "line_break",
-    "nodejs",
-    "package",
-    "python",
-    "ruby",
-    "rust",
-    "username",
-];
-
 // List of default prompt order
 // NOTE: If this const value is changed then Default prompt order subheading inside
 // prompt heading of config docs needs to be updated according to changes made here.
diff --git a/tests/testsuite/main.rs b/tests/testsuite/main.rs
index cbb1d9b69..bceb14035 100644
--- a/tests/testsuite/main.rs
+++ b/tests/testsuite/main.rs
@@ -6,6 +6,7 @@ mod directory;
 mod golang;
 mod jobs;
 mod line_break;
+mod modules;
 mod nodejs;
 mod python;
 mod ruby;
diff --git a/tests/testsuite/modules.rs b/tests/testsuite/modules.rs
new file mode 100644
index 000000000..0ffcb5ca3
--- /dev/null
+++ b/tests/testsuite/modules.rs
@@ -0,0 +1,31 @@
+use std::io;
+
+use crate::common;
+
+#[test]
+fn unknown_module_name() -> io::Result<()> {
+    let unknown_module_name = "some_random_name";
+    let output = common::render_module(unknown_module_name).output()?;
+    let actual_stdout = String::from_utf8(output.stdout).unwrap();
+    let actual_stderr = String::from_utf8(output.stderr).unwrap();
+    let expected_stdout = "";
+    let expected_stderr = format!(
+        "Error: Unknown module {}. Use starship module --list to list out all supported modules.\n",
+        unknown_module_name
+    );
+    assert_eq!(expected_stdout, actual_stdout);
+    assert_eq!(expected_stderr, actual_stderr);
+    Ok(())
+}
+
+#[test]
+fn known_module_name() -> io::Result<()> {
+    let output = common::render_module("line_break").output()?;
+    let actual_stdout = String::from_utf8(output.stdout).unwrap();
+    let actual_stderr = String::from_utf8(output.stderr).unwrap();
+    let expected_stdout = "\n";
+    let expected_stderr = "";
+    assert_eq!(expected_stdout, actual_stdout);
+    assert_eq!(expected_stderr, actual_stderr);
+    Ok(())
+}