Overhaul Nix's error types

For many of Nix's consumers it be convenient to easily convert a Nix
error into a std::io::Error.  That's currently not possible because of
the InvalidPath, InvalidUtf8, and UnsupportedOperation types that have
no equivalent in std::io::Error.

However, very few of Nix's public APIs actually return those unusual
errors.  So a more useful API would be for Nix's standard error type to
implement Into<std::io::Error>.

This commit makes Error a simple NewType around Errno.  For most
functions it's a drop-in replacement.  There are only three exceptions:

* clearenv now returns a bespoke error type.  It was the only Nix
  function whose error couldn't be cleanly mapped onto an Errno.

* sys::signal::signal now returns Error(Errno::ENOTSUP) instead of
  Error::UnsupportedOperation when the user passes an incompatible
  argument to `handler`.

* When a NixPath exceeds PATH_MAX, it will now return
  Error(Errno::ENAMETOOLONG) instead of Error::InvalidPath.

In the latter two cases there is now some abiguity about whether the
error code was generated by Nix or by the OS.  But I think the ambiguity
is worth it for the sake of being able to implement Into<io::Error>.

This commit also introduces Error::Sys() as a migration aid.  Previously
that as an enum variant.  Now it's a function, but it will work in many
of the same contexts as the original.

Fixes #1155

1 files changed, 9 insertions, 9 deletions

diff --git a/test/test_mq.rs b/test/test_mq.rs
index 1667a35b..e16103fb 100644
--- a/test/test_mq.rs
+++ b/test/test_mq.rs
@@ -1,8 +1,8 @@
 use std::ffi::CString;
 use std::str;
 
-use nix::errno::Errno::*;
-use nix::Error::Sys;
+use nix::errno::Errno;
+use nix::Error;
 use nix::mqueue::{mq_open, mq_close, mq_send, mq_receive, mq_attr_member_t};
 use nix::mqueue::{MqAttr, MQ_OFlag};
 use nix::sys::stat::Mode;
@@ -16,7 +16,7 @@ fn test_mq_send_and_receive() {
     let oflag0 = MQ_OFlag::O_CREAT | MQ_OFlag::O_WRONLY;
     let mode = Mode::S_IWUSR | Mode::S_IRUSR | Mode::S_IRGRP | Mode::S_IROTH;
     let r0 = mq_open(mq_name, oflag0, mode, Some(&attr));
-    if let Err(Sys(ENOSYS)) = r0 {
+    if let Err(Error(Errno::ENOSYS)) = r0 {
         println!("message queues not supported or module not loaded?");
         return;
     };
@@ -47,7 +47,7 @@ fn test_mq_getattr() {
     let oflag = MQ_OFlag::O_CREAT | MQ_OFlag::O_WRONLY;
     let mode = Mode::S_IWUSR | Mode::S_IRUSR | Mode::S_IRGRP | Mode::S_IROTH;
     let r = mq_open(mq_name, oflag, mode, Some(&initial_attr));
-    if let Err(Sys(ENOSYS)) = r {
+    if let Err(Error(Errno::ENOSYS)) = r {
         println!("message queues not supported or module not loaded?");
         return;
     };
@@ -70,7 +70,7 @@ fn test_mq_setattr() {
     let oflag = MQ_OFlag::O_CREAT | MQ_OFlag::O_WRONLY;
     let mode = Mode::S_IWUSR | Mode::S_IRUSR | Mode::S_IRGRP | Mode::S_IROTH;
     let r = mq_open(mq_name, oflag, mode, Some(&initial_attr));
-    if let Err(Sys(ENOSYS)) = r {
+    if let Err(Error(Errno::ENOSYS)) = r {
         println!("message queues not supported or module not loaded?");
         return;
     };
@@ -107,7 +107,7 @@ fn test_mq_set_nonblocking() {
     let oflag = MQ_OFlag::O_CREAT | MQ_OFlag::O_WRONLY;
     let mode = Mode::S_IWUSR | Mode::S_IRUSR | Mode::S_IRGRP | Mode::S_IROTH;
     let r = mq_open(mq_name, oflag, mode, Some(&initial_attr));
-    if let Err(Sys(ENOSYS)) = r {
+    if let Err(Error(Errno::ENOSYS)) = r {
         println!("message queues not supported or module not loaded?");
         return;
     };
@@ -132,7 +132,7 @@ fn test_mq_unlink() {
     let oflag = MQ_OFlag::O_CREAT | MQ_OFlag::O_WRONLY;
     let mode = Mode::S_IWUSR | Mode::S_IRUSR | Mode::S_IRGRP | Mode::S_IROTH;
     let r = mq_open(mq_name_opened, oflag, mode, Some(&initial_attr));
-    if let Err(Sys(ENOSYS)) = r {
+    if let Err(Error(Errno::ENOSYS)) = r {
         println!("message queues not supported or module not loaded?");
         return;
     };
@@ -142,9 +142,9 @@ fn test_mq_unlink() {
     assert_eq!(res_unlink, Ok(()) );
 
     let res_unlink_not_opened = mq_unlink(mq_name_not_opened);
-    assert_eq!(res_unlink_not_opened, Err(Sys(ENOENT)) );
+    assert_eq!(res_unlink_not_opened, Err(Error(Errno::ENOENT)) );
 
     mq_close(mqd).unwrap();
     let res_unlink_after_close = mq_unlink(mq_name_opened);
-    assert_eq!(res_unlink_after_close, Err(Sys(ENOENT)) );
+    assert_eq!(res_unlink_after_close, Err(Error(Errno::ENOENT)) );
 }