auto merge of #13954 : aturon/rust/issue-11650, r=alexcrichton

## Process API

The existing APIs for spawning processes took strings for the command
and arguments, but the underlying system may not impose utf8 encoding,
so this is overly limiting.

The assumption we actually want to make is just that the command and
arguments are viewable as [u8] slices with no interior NULLs, i.e., as
CStrings. The ToCStr trait is a handy bound for types that meet this
requirement (such as &str and Path).

However, since the commands and arguments are often a mixture of
strings and paths, it would be inconvenient to take a slice with a
single T: ToCStr bound. So this patch revamps the process creation API
to instead use a builder-style interface, called `Command`, allowing
arguments to be added one at a time with differing ToCStr
implementations for each.

The initial cut of the builder API has some drawbacks that can be
addressed once issue #13851 (libstd as a facade) is closed. These are
detailed as FIXMEs.

## Dynamic library API

`std::unstable::dynamic_library::open_external` currently takes a
`Path`, but because `Paths` produce normalized strings, this can
change the semantics of lookups in a given environment. This patch
generalizes the function to take a `ToCStr`-bounded type, which
includes both `Path`s and `str`s.

## ToCStr API

Adds ToCStr impl for &Path and ~str. This is a stopgap until DST (#12938) lands.

Until DST lands, we cannot decompose &str into & and str, so we cannot
usefully take ToCStr arguments by reference (without forcing an
additional & around &str). So we are instead temporarily adding an
instance for &Path and ~str, so that we can take ToCStr as owned. When
DST lands, the &Path instance should be removed, the string instances
should be revisted, and arguments bound by ToCStr should be passed by
reference.

FIXMEs have been added accordingly. 

## Tickets closed

Closes #11650.
Closes #7928.

src/compiletest/procsrv.rs

@@ -10,7 +10,7 @@
 
 use std::os;
 use std::str;
-use std::io::process::{ProcessExit, Process, ProcessConfig, ProcessOutput};
+use std::io::process::{ProcessExit, Command, Process, ProcessOutput};
 
 #[cfg(target_os = "win32")]
 fn target_env(lib_path: &str, prog: &str) -> Vec<(~str, ~str)> {
@@ -68,14 +68,7 @@ pub fn run(lib_path: &str,
            input: Option<~str>) -> Option<Result> {
 
     let env = env.clone().append(target_env(lib_path, prog).as_slice());
-    let opt_process = Process::configure(ProcessConfig {
-        program: prog,
-        args: args,
-        env: Some(env.as_slice()),
-        .. ProcessConfig::new()
-    });
-
-    match opt_process {
+    match Command::new(prog).args(args).env(env.as_slice()).spawn() {
         Ok(mut process) => {
             for input in input.iter() {
                 process.stdin.get_mut_ref().write(input.as_bytes()).unwrap();
@@ -100,14 +93,7 @@ pub fn run_background(lib_path: &str,
            input: Option<~str>) -> Option<Process> {
 
     let env = env.clone().append(target_env(lib_path, prog).as_slice());
-    let opt_process = Process::configure(ProcessConfig {
-        program: prog,
-        args: args,
-        env: Some(env.as_slice()),
-        .. ProcessConfig::new()
-    });
-
-    match opt_process {
+    match Command::new(prog).args(args).env(env.as_slice()).spawn() {
         Ok(mut process) => {
             for input in input.iter() {
                 process.stdin.get_mut_ref().write(input.as_bytes()).unwrap();

src/compiletest/runtest.rs

@@ -420,7 +420,7 @@ fn run_debuginfo_gdb_test(config: &Config, props: &TestProps, testfile: &Path) {
 }
 
 fn run_debuginfo_lldb_test(config: &Config, props: &TestProps, testfile: &Path) {
-    use std::io::process::{Process, ProcessConfig, ProcessOutput};
+    use std::io::process::{Command, ProcessOutput};
 
     if config.lldb_python_dir.is_none() {
         fatal("Can't run LLDB test because LLDB's python path is not set.".to_owned());
@@ -483,25 +483,13 @@ fn run_debuginfo_lldb_test(config: &Config, props: &TestProps, testfile: &Path)
 
     fn run_lldb(config: &Config, test_executable: &Path, debugger_script: &Path) -> ProcRes {
         // Prepare the lldb_batchmode which executes the debugger script
-        let lldb_batchmode_script = "./src/etc/lldb_batchmode.py".to_owned();
-        let test_executable_str = test_executable.as_str().unwrap().to_owned();
-        let debugger_script_str = debugger_script.as_str().unwrap().to_owned();
-        let commandline = format!("python {} {} {}",
-                                  lldb_batchmode_script.as_slice(),
-                                  test_executable_str.as_slice(),
-                                  debugger_script_str.as_slice());
-
-        let args = &[lldb_batchmode_script, test_executable_str, debugger_script_str];
-        let env = &[("PYTHONPATH".to_owned(), config.lldb_python_dir.clone().unwrap())];
-
-        let opt_process = Process::configure(ProcessConfig {
-            program: "python",
-            args: args,
-            env: Some(env),
-            .. ProcessConfig::new()
-        });
-
-        let (status, out, err) = match opt_process {
+        let mut cmd = Command::new("python");
+        cmd.arg("./src/etc/lldb_batchmode.py")
+           .arg(test_executable)
+           .arg(debugger_script)
+           .env([("PYTHONPATH", config.lldb_python_dir.clone().unwrap().as_slice())]);
+
+        let (status, out, err) = match cmd.spawn() {
             Ok(process) => {
                 let ProcessOutput { status, output, error } =
                     process.wait_with_output().unwrap();
@@ -520,7 +508,7 @@ fn run_debuginfo_lldb_test(config: &Config, props: &TestProps, testfile: &Path)
             status: status,
             stdout: out,
             stderr: err,
-            cmdline: commandline
+            cmdline: format!("{}", cmd)
         };
     }
 }

src/libnative/io/mod.rs

@@ -27,13 +27,12 @@ use std::c_str::CString;
 use std::io;
 use std::io::IoError;
 use std::io::net::ip::SocketAddr;
-use std::io::process::ProcessConfig;
 use std::io::signal::Signum;
 use std::os;
 use std::rt::rtio;
 use std::rt::rtio::{RtioTcpStream, RtioTcpListener, RtioUdpSocket};
 use std::rt::rtio::{RtioUnixListener, RtioPipe, RtioFileStream, RtioProcess};
-use std::rt::rtio::{RtioSignal, RtioTTY, CloseBehavior, RtioTimer};
+use std::rt::rtio::{RtioSignal, RtioTTY, CloseBehavior, RtioTimer, ProcessConfig};
 use ai = std::io::net::addrinfo;
 
 // Local re-exports
@@ -258,10 +257,10 @@ impl rtio::IoFactory for IoFactory {
     fn timer_init(&mut self) -> IoResult<Box<RtioTimer:Send>> {
         timer::Timer::new().map(|t| box t as Box<RtioTimer:Send>)
     }
-    fn spawn(&mut self, config: ProcessConfig)
+    fn spawn(&mut self, cfg: ProcessConfig)
             -> IoResult<(Box<RtioProcess:Send>,
                          Vec<Option<Box<RtioPipe:Send>>>)> {
-        process::Process::spawn(config).map(|(p, io)| {
+        process::Process::spawn(cfg).map(|(p, io)| {
             (box p as Box<RtioProcess:Send>,
              io.move_iter().map(|p| p.map(|p| {
                  box p as Box<RtioPipe:Send>