feat: Implement simplified prompt setup process (#90)

• Add starship init which prints the shell function used to execute starship
• Document the new setup process using starship init
• Remove benchmarks for now (WIP replacement benchmarks in "benchmarking" branch )

src/init.rs

@@ -0,0 +1,40 @@
+pub fn init(shell_name: &str) {
+    log::debug!("Shell name: {}", shell_name);
+    let setup_script = match shell_name {
+        "bash" => {
+            let script = "PS1=\"$(starship prompt --status=$?)\"";
+            Some(script)
+        }
+        "zsh" => {
+            let script = "PROMPT=\"$(starship prompt --status=$?)\"";
+            Some(script)
+        }
+        "fish" => {
+            let script = "function fish_prompt; starship prompt --status=$status; end";
+            Some(script)
+        }
+        _ => {
+            println!(
+                "printf \"\\n{0} is not yet supported by starship.\\n\
+                 For the time being, we support bash, zsh, and fish.\\n\
+                 Please open an issue in the starship repo if you would like to \
+                 see support for {0}:\\nhttps://github.com/starship/starship/issues/new\"\\n\\n",
+                shell_name
+            );
+            None
+        }
+    };
+
+    if setup_script.is_some() {
+        let script = setup_script.unwrap();
+        print!("{}", script);
+    }
+}
+
+#[derive(Debug)]
+enum Shell {
+    Bash,
+    Fish,
+    Zsh,
+    Unsupported(String),
+}

src/main.rs

@@ -3,13 +3,14 @@ extern crate clap;
 
 mod config;
 mod context;
+mod init;
 mod module;
 mod modules;
 mod print;
 mod segment;
 mod utils;
 
-use clap::{App, Arg, SubCommand};
+use clap::{App, AppSettings, Arg, SubCommand};
 
 fn main() {
     pretty_env_logger::init();
@@ -28,13 +29,26 @@ fn main() {
         .help("The path that the prompt should render for")
         .takes_value(true);
 
-    let matches = App::new("Starship")
-        .about("The cross-shell prompt for astronauts. ✨🚀")
+    let shell_arg = Arg::with_name("shell")
+        .value_name("SHELL")
+        .help(
+            "The name of the currently running shell\nCurrently supported options: bash, zsh, fish",
+        )
+        .required(true);
+
+    let matches = App::new("starship")
+        .about("The cross-shell prompt for astronauts. ☄🌌️")
         // pull the version number from Cargo.toml
         .version(crate_version!())
         // pull the authors from Cargo.toml
         .author(crate_authors!())
-        .after_help("https://github.com/matchai/starship")
+        .after_help("https://github.com/starship/starship")
+        .setting(AppSettings::SubcommandRequiredElseHelp)
+        .subcommand(
+            SubCommand::with_name("init")
+                .about("Prints the shell function used to execute starship")
+                .arg(&shell_arg),
+        )
         .subcommand(
             SubCommand::with_name("prompt")
                 .about("Prints the full starship prompt")
@@ -55,6 +69,10 @@ fn main() {
         .get_matches();
 
     match matches.subcommand() {
+        ("init", Some(sub_m)) => {
+            let shell_name = sub_m.value_of("shell").expect("Shell name missing.");
+            init::init(shell_name)
+        }
         ("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.");