Implement argument passing in config

This commit implements the following syntax in the config file:

```yaml
shell:
  program: /bin/bash
  args:
    - --login
    - --norc
```

src/config.rs

@@ -12,6 +12,7 @@ use std::str::FromStr;
 use std::sync::mpsc;
 use std::ops::{Index, IndexMut};
 use std::fs::File;
+use std::borrow::Cow;
 
 use ::Rgb;
 use font::Size;
@@ -166,6 +167,31 @@ impl IndexMut<usize> for ColorList {
     }
 }
 
+#[derive(Debug, Deserialize)]
+pub struct Shell<'a> {
+    program: Cow<'a, str>,
+
+    #[serde(default)]
+    args: Vec<String>,
+}
+
+impl<'a> Shell<'a> {
+    pub fn new(program: &'a str) -> Shell<'a> {
+        Shell {
+            program: Cow::from(program),
+            args: Vec::new(),
+        }
+    }
+
+    pub fn program(&self) -> &str {
+        &*self.program
+    }
+
+    pub fn args(&self) -> &[String] {
+        self.args.as_slice()
+    }
+}
+
 /// Top-level config type
 #[derive(Debug, Deserialize)]
 pub struct Config {
@@ -197,7 +223,8 @@ pub struct Config {
     mouse_bindings: Vec<MouseBinding>,
 
     /// Path to a shell program to run on startup
-    shell: Option<String>,
+    #[serde(default)]
+    shell: Option<Shell<'static>>,
 
     /// Path where config was loaded from
     config_path: Option<PathBuf>,
@@ -902,10 +929,8 @@ impl Config {
             .map(|p| p.as_path())
     }
 
-    pub fn shell(&self) -> Option<&str> {
-        self.shell
-            .as_ref()
-            .map(String::as_str)
+    pub fn shell(&self) -> Option<&Shell> {
+        self.shell.as_ref()
     }
 
     fn load_from<P: Into<PathBuf>>(path: P) -> Result<Config> {

src/tty.rs

@@ -19,13 +19,13 @@ use std::fs::File;
 use std::os::unix::io::FromRawFd;
 use std::os::unix::process::CommandExt;
 use std::ptr;
-use std::process;
+use std::process::{Command, Stdio};
 
 use libc::{self, winsize, c_int, pid_t, WNOHANG, WIFEXITED, WEXITSTATUS, SIGCHLD, TIOCSCTTY};
 
 use term::SizeInfo;
 use display::OnResize;
-use config::Config;
+use config::{Config, Shell};
 
 /// Process ID of child process
 ///
@@ -186,19 +186,23 @@ pub fn new<T: ToWinsize>(config: &Config, size: T) -> Pty {
 
     let (master, slave) = openpty(win.ws_row as _, win.ws_col as _);
 
-    let shell = config.shell().unwrap_or(pw.shell);
+    let default_shell = Shell::new(pw.shell);
+    let shell = config.shell().unwrap_or(&default_shell);
 
-    let mut builder = process::Command::new(shell);
+    let mut builder = Command::new(shell.program());
+    for arg in shell.args() {
+        builder.arg(arg);
+    }
 
     // Setup child stdin/stdout/stderr as slave fd of pty
-    builder.stdin(unsafe { process::Stdio::from_raw_fd(slave) });
-    builder.stderr(unsafe { process::Stdio::from_raw_fd(slave) });
-    builder.stdout(unsafe { process::Stdio::from_raw_fd(slave) });
+    builder.stdin(unsafe { Stdio::from_raw_fd(slave) });
+    builder.stderr(unsafe { Stdio::from_raw_fd(slave) });
+    builder.stdout(unsafe { Stdio::from_raw_fd(slave) });
 
     // Setup environment
     builder.env("LOGNAME", pw.name);
     builder.env("USER", pw.name);
-    builder.env("SHELL", shell);
+    builder.env("SHELL", shell.program());
     builder.env("HOME", pw.dir);
     builder.env("TERM", "xterm-256color"); // sigh