io::process::Command: add fine-grained env builder

This commit changes the `io::process::Command` API to provide
fine-grained control over the environment:

* The `env` method now inserts/updates a key/value pair.
* The `env_remove` method removes a key from the environment.
* The old `env` method, which sets the entire environment in one shot,
  is renamed to `env_set_all`. It can be used in conjunction with the
  finer-grained methods. This renaming is a breaking change.

To support these new methods, the internal `env` representation for
`Command` has been changed to an optional `HashMap` holding owned
`CString`s (to support non-utf8 data). The `HashMap` is only
materialized if the environment is updated. The implementation does not
try hard to avoid allocation, since the cost of launching a process will
dwarf any allocation cost.

This patch also adds `PartialOrd`, `Eq`, and `Hash` implementations for
`CString`.

[breaking-change]

2 files changed, 4 insertions, 14 deletions

diff --git a/src/test/run-pass/backtrace.rs b/src/test/run-pass/backtrace.rs
index 97862844030..c2a1c01b919 100644
--- a/src/test/run-pass/backtrace.rs
+++ b/src/test/run-pass/backtrace.rs
@@ -37,19 +37,8 @@ fn double() {
 }
 
 fn runtest(me: &str) {
-    let mut env = os::env().move_iter()
-                           .map(|(ref k, ref v)| {
-                               (k.to_string(), v.to_string())
-                           }).collect::<Vec<(String,String)>>();
-    match env.iter()
-             .position(|&(ref s, _)| "RUST_BACKTRACE" == s.as_slice()) {
-        Some(i) => { env.remove(i); }
-        None => {}
-    }
-    env.push(("RUST_BACKTRACE".to_string(), "1".to_string()));
-
     // Make sure that the stack trace is printed
-    let mut p = Command::new(me).arg("fail").env(env.as_slice()).spawn().unwrap();
+    let mut p = Command::new(me).arg("fail").env("RUST_BACKTRACE", "1").spawn().unwrap();
     let out = p.wait_with_output().unwrap();
     assert!(!out.status.success());
     let s = str::from_utf8(out.error.as_slice()).unwrap();
@@ -73,7 +62,8 @@ fn runtest(me: &str) {
             "bad output3: {}", s);
 
     // Make sure a stack trace isn't printed too many times
-    let mut p = Command::new(me).arg("double-fail").env(env.as_slice()).spawn().unwrap();
+    let mut p = Command::new(me).arg("double-fail")
+                                .env("RUST_BACKTRACE", "1").spawn().unwrap();
     let out = p.wait_with_output().unwrap();
     assert!(!out.status.success());
     let s = str::from_utf8(out.error.as_slice()).unwrap();
diff --git a/src/test/run-pass/process-spawn-with-unicode-params.rs b/src/test/run-pass/process-spawn-with-unicode-params.rs
index 70839c18847..de86ca179b7 100644
--- a/src/test/run-pass/process-spawn-with-unicode-params.rs
+++ b/src/test/run-pass/process-spawn-with-unicode-params.rs
@@ -58,7 +58,7 @@ fn main() {
         let p = Command::new(&child_path)
                         .arg(arg)
                         .cwd(&cwd)
-                        .env(my_env.append_one(env).as_slice())
+                        .env_set_all(my_env.append_one(env).as_slice())
                         .spawn().unwrap().wait_with_output().unwrap();
 
         // display the output