Rollup merge of #34270 - gkoz:error_file_exists, r=alexcrichton

Add ERROR_FILE_EXISTS to ErrorKind conversion on Windows

Bug report: https://users.rust-lang.org/t/detecting-error-kind-for-opening-file/6215
Reference: https://msdn.microsoft.com/en-us/library/windows/desktop/ms681382(v=vs.85).aspx#error_file_exists

Author: Manishearth

src/libstd/fs.rs

@@ -512,7 +512,7 @@ impl OpenOptions {
     /// No file is allowed to exist at the target location, also no (dangling)
     /// symlink.
     ///
-    /// This option is useful because it as atomic. Otherwise between checking
+    /// This option is useful because it is atomic. Otherwise between checking
     /// whether a file exists and creating a new one, the file may have been
     /// created by another process (a TOCTOU race condition / attack).
     ///
@@ -1770,6 +1770,15 @@ mod tests {
         check!(fs::remove_dir(dir));
     }
 
+    #[test]
+    fn file_create_new_already_exists_error() {
+        let tmpdir = tmpdir();
+        let file = &tmpdir.join("file_create_new_error_exists");
+        check!(fs::File::create(file));
+        let e = fs::OpenOptions::new().write(true).create_new(true).open(file).unwrap_err();
+        assert_eq!(e.kind(), ErrorKind::AlreadyExists);
+    }
+
     #[test]
     fn mkdir_path_already_exists_error() {
         let tmpdir = tmpdir();

src/libstd/sys/windows/c.rs

@@ -181,6 +181,7 @@ pub const ERROR_ACCESS_DENIED: DWORD = 5;
 pub const ERROR_INVALID_HANDLE: DWORD = 6;
 pub const ERROR_NO_MORE_FILES: DWORD = 18;
 pub const ERROR_HANDLE_EOF: DWORD = 38;
+pub const ERROR_FILE_EXISTS: DWORD = 80;
 pub const ERROR_BROKEN_PIPE: DWORD = 109;
 pub const ERROR_CALL_NOT_IMPLEMENTED: DWORD = 120;
 pub const ERROR_INSUFFICIENT_BUFFER: DWORD = 122;

src/libstd/sys/windows/mod.rs

@@ -68,6 +68,7 @@ pub fn decode_error_kind(errno: i32) -> ErrorKind {
     match errno as c::DWORD {
         c::ERROR_ACCESS_DENIED => return ErrorKind::PermissionDenied,
         c::ERROR_ALREADY_EXISTS => return ErrorKind::AlreadyExists,
+        c::ERROR_FILE_EXISTS => return ErrorKind::AlreadyExists,
         c::ERROR_BROKEN_PIPE => return ErrorKind::BrokenPipe,
         c::ERROR_FILE_NOT_FOUND => return ErrorKind::NotFound,
         c::ERROR_PATH_NOT_FOUND => return ErrorKind::NotFound,