Create platform module (#178)

Moves platform specific functionality into its own module.

Thanks to @Meralis40 for starting this!

This also gets just building on windows \^_^/

Although a lot of tests still fail (✖╭╮✖)

The `PlatformInterface` trait contains functions which abstract
over platform specific functionality, with implementations for
different platforms behind #[cfg(*)] attributes.

- `make_shebang_command()` constructs a command which will execute
  the given script as if by a shebang. On linux this executes the
  file, on windows it runs the interpreter directly.

- `set_execute_permission()` sets the execute permission on a
  file. This is a nop on windows, since all files are executable.

- `signal_from_exit_status()` extracts the signal a process was
  halted by from its exit status, if it was halted by a signal.

src/app.rs

@@ -2,7 +2,6 @@ extern crate ansi_term;
 extern crate atty;
 extern crate clap;
 extern crate libc;
-extern crate regex;
 
 use ::prelude::*;
 use std::{convert, ffi};
@@ -179,7 +178,7 @@ pub fn app() {
     }
   }
 
-  let override_re = regex::Regex::new("^([^=]+)=(.*)$").unwrap();
+  let override_re = Regex::new("^([^=]+)=(.*)$").unwrap();
 
   let raw_arguments = matches.values_of("ARGUMENTS").map(|values| values.collect::<Vec<_>>())
     .unwrap_or_default();

src/lib.rs

@@ -14,12 +14,16 @@ mod unit;
 #[cfg(test)]
 mod integration;
 
+mod platform;
+
 mod app;
 
 mod prelude {
+  pub use std::io::prelude::*;
+  pub use libc::{EXIT_FAILURE, EXIT_SUCCESS};
+  pub use regex::Regex;
   pub use std::path::Path;
   pub use std::{cmp, env, fs, fmt, io, iter, process};
-  pub use libc::{EXIT_FAILURE, EXIT_SUCCESS};
 }
 
 use prelude::*;
@@ -27,13 +31,11 @@ use prelude::*;
 pub use app::app;
 
 use app::UseColor;
-use regex::Regex;
 use std::borrow::Cow;
 use std::collections::{BTreeMap as Map, BTreeSet as Set};
 use std::fmt::Display;
-use std::io::prelude::*;
 use std::ops::Range;
-use std::os::unix::fs::PermissionsExt;
+use platform::{Platform, PlatformInterface};
 
 macro_rules! warn {
   ($($arg:tt)*) => {{
@@ -47,7 +49,7 @@ macro_rules! die {
   ($($arg:tt)*) => {{
     extern crate std;
     warn!($($arg)*);
-    std::process::exit(EXIT_FAILURE)
+    process::exit(EXIT_FAILURE)
   }};
 }
 
@@ -65,6 +67,25 @@ impl Slurp for fs::File {
   }
 }
 
+/// Split a shebang line into a command and an optional argument
+fn split_shebang(shebang: &str) -> Option<(&str, Option<&str>)> {
+  lazy_static! {
+    static ref EMPTY:    Regex = re(r"^#!\s*$");
+    static ref SIMPLE:   Regex = re(r"^#!(\S+)\s*$");
+    static ref ARGUMENT: Regex = re(r"^#!(\S+)\s+(\S.*?)?\s*$");
+  }
+
+  if EMPTY.is_match(shebang) {
+    Some(("", None))
+  } else if let Some(captures) = SIMPLE.captures(shebang) {
+    Some((captures.at(1).unwrap(), None))
+  } else if let Some(captures) = ARGUMENT.captures(shebang) {
+    Some((captures.at(1).unwrap(), Some(captures.at(2).unwrap())))
+  } else {
+    None
+  }
+}
+
 fn re(pattern: &str) -> Regex {
   Regex::new(pattern).unwrap()
 }
@@ -178,48 +199,31 @@ impl<'a> Display for Expression<'a> {
   }
 }
 
-#[cfg(unix)]
+/// Return a RunError::Signal if the process was terminated by a signal,
+/// otherwise return an RunError::UnknownFailure
 fn error_from_signal(
   recipe:      &str,
   line_number: Option<usize>,
   exit_status: process::ExitStatus
 ) -> RunError {
-  use std::os::unix::process::ExitStatusExt;
-  match exit_status.signal() {
+  match Platform::signal_from_exit_status(exit_status) {
     Some(signal) => RunError::Signal{recipe: recipe, line_number: line_number, signal: signal},
     None => RunError::UnknownFailure{recipe: recipe, line_number: line_number},
   }
 }
 
-#[cfg(windows)]
-fn error_from_signal(
-  recipe:      &str,
-  line_number: Option<usize>,
-  exit_status: process::ExitStatus
-) -> RunError {
-  RunError::UnknownFailure{recipe: recipe, line_number: line_number}
-}
-
-#[cfg(unix)]
+/// Return a RunError::BacktickSignal if the process was terminated by signal,
+/// otherwise return a RunError::BacktickUnknownFailure
 fn backtick_error_from_signal<'a>(
   token:       &Token<'a>,
   exit_status: process::ExitStatus
 ) -> RunError<'a> {
-  use std::os::unix::process::ExitStatusExt;
-  match exit_status.signal() {
+  match Platform::signal_from_exit_status(exit_status) {
     Some(signal) => RunError::BacktickSignal{token: token.clone(), signal: signal},
     None => RunError::BacktickUnknownFailure{token: token.clone()},
   }
 }
 
-#[cfg(windows)]
-fn backtick_error_from_signal<'a>(
-  token:       &Token<'a>,
-  exit_status: process::ExitStatus
-) -> RunError<'a> {
-  RunError::BacktickUnknownFailure{token: token.clone()}
-}
-
 fn export_env<'a>(
   command: &mut process::Command,
   scope:   &Map<&'a str, String>,
@@ -237,7 +241,6 @@ fn export_env<'a>(
   Ok(())
 }
 
-
 fn run_backtick<'a>(
   raw:     &str,
   token:   &Token<'a>,
@@ -383,22 +386,27 @@ impl<'a> Recipe<'a> {
          .map_err(|error| RunError::TmpdirIoError{recipe: self.name, io_error: error})?;
       }
 
-      // get current permissions
-      let mut perms = fs::metadata(&path)
-        .map_err(|error| RunError::TmpdirIoError{recipe: self.name, io_error: error})?
-        .permissions();
-
       // make the script executable
-      let current_mode = perms.mode();
-      perms.set_mode(current_mode | 0o100);
-      fs::set_permissions(&path, perms)
+      Platform::set_execute_permission(&path)
         .map_err(|error| RunError::TmpdirIoError{recipe: self.name, io_error: error})?;
 
-      // run it!
-      let mut command = process::Command::new(path);
+      let shebang_line = evaluated_lines.first()
+        .ok_or_else(|| RunError::InternalError {
+          message: "evaluated_lines was empty".to_string()
+        })?;
 
+      let (shebang_command, shebang_argument) = split_shebang(shebang_line)
+        .ok_or_else(|| RunError::InternalError {
+          message: format!("bad shebang line: {}", shebang_line)
+        })?;
+
+      // create a command to run the script
+      let mut command = Platform::make_shebang_command(&path, shebang_command, shebang_argument);
+
+      // export environment variables
       export_env(&mut command, scope, exports)?;
 
+      // run it!
       match command.status() {
         Ok(exit_status) => if let Some(code) = exit_status.code() {
           if code != 0 {

src/platform.rs

@@ -0,0 +1,66 @@
+use ::prelude::*;
+
+pub struct Platform;
+
+pub trait PlatformInterface {
+  /// Construct a command equivelant to running the script at `path` with the
+  /// shebang line `shebang`
+  fn make_shebang_command(path: &Path, command: &str, argument: Option<&str>) -> process::Command;
+
+  /// Set the execute permission on the file pointed to by `path`
+  fn set_execute_permission(path: &Path) -> Result<(), io::Error>;
+
+  /// Extract the signal from a process exit status, if it was terminated by a signal
+  fn signal_from_exit_status(exit_status: process::ExitStatus) -> Option<i32>;
+}
+
+#[cfg(unix)]
+impl PlatformInterface for Platform {
+  fn make_shebang_command(path: &Path, _command: &str, _argument: Option<&str>) -> process::Command {
+    // shebang scripts can be executed directly on unix
+    process::Command::new(path)
+  }
+
+  fn set_execute_permission(path: &Path) -> Result<(), io::Error> {
+    use std::os::unix::fs::PermissionsExt;
+
+    // get current permissions
+    let mut permissions = fs::metadata(&path)?.permissions();
+
+    // set the execute bit
+    let current_mode = permissions.mode();
+    permissions.set_mode(current_mode | 0o100);
+
+    // set the new permissions
+    fs::set_permissions(&path, permissions)
+  }
+
+  fn signal_from_exit_status(exit_status: process::ExitStatus) -> Option<i32> {
+    use std::os::unix::process::ExitStatusExt;
+    exit_status.signal()
+  }
+}
+
+#[cfg(windows)]
+impl PlatformInterface for Platform {
+  fn make_shebang_command(path: &Path, command: &str, argument: Option<&str>) -> process::Command {
+    let mut cmd = process::Command::new(command);
+    if let Some(argument) = argument {
+      cmd.arg(argument);
+    }
+    cmd.arg(path);
+    cmd
+  }
+
+  fn set_execute_permission(_path: &Path) -> Result<(), io::Error> {
+    // it is not necessary to set an execute permission on a script on windows,
+    // so this is a nop
+    Ok(())
+  }
+
+  fn signal_from_exit_status(_exit_status: process::ExitStatus) -> Option<i32> {
+    // The rust standard library does not expose a way to extract a signal
+    // from a process exit status, so just return None
+    None
+  }
+}

src/unit.rs

@@ -1111,3 +1111,23 @@ fn readme_test() {
     parse_success(&justfile);
   }
 }
+
+#[test]
+fn split_shebang() {
+  use ::split_shebang;
+
+  fn check(shebang: &str, expected_split: Option<(&str, Option<&str>)>) {
+    assert_eq!(split_shebang(shebang), expected_split);
+  }
+
+  check("#!    ",                       Some(("",             None              )));
+  check("#!",                           Some(("",             None              )));
+  check("#!/bin/bash",                  Some(("/bin/bash",    None              )));
+  check("#!/bin/bash    ",              Some(("/bin/bash",    None              )));
+  check("#!/usr/bin/env python",        Some(("/usr/bin/env", Some("python"     ))));
+  check("#!/usr/bin/env python   ",     Some(("/usr/bin/env", Some("python"     ))));
+  check("#!/usr/bin/env python -x",     Some(("/usr/bin/env", Some("python -x"  ))));
+  check("#!/usr/bin/env python   -x",   Some(("/usr/bin/env", Some("python   -x"))));
+  check("#!/usr/bin/env python \t-x\t", Some(("/usr/bin/env", Some("python \t-x"))));
+  check("#/usr/bin/env python \t-x\t",  None                                       );
+}