add support of the unikernel RustyHermit

- use the crate hermit-abi as interface to the kernel

Cargo.toml

@@ -17,6 +17,9 @@ travis-ci = { repository = "softprops/atty" }
 [target.'cfg(unix)'.dependencies]
 libc = { version = "0.2", default-features = false }
 
+[target.'cfg(target_os = "hermit")'.dependencies]
+hermit-abi = "0.1.6"
+
 [target.'cfg(windows)'.dependencies.winapi]
 version = "0.3"
 features = ["consoleapi", "processenv", "minwinbase", "minwindef", "winbase"]

src/lib.rs

@@ -48,6 +48,19 @@ pub fn is(stream: Stream) -> bool {
     unsafe { libc::isatty(fd) != 0 }
 }
 
+/// returns true if this is a tty
+#[cfg(target_os = "hermit")]
+pub fn is(stream: Stream) -> bool {
+    extern crate hermit_abi;
+
+    let fd = match stream {
+        Stream::Stdout => hermit_abi::STDOUT_FILENO,
+        Stream::Stderr => hermit_abi::STDERR_FILENO,
+        Stream::Stdin => hermit_abi::STDIN_FILENO,
+    };
+    hermit_abi::isatty(fd)
+}
+
 /// returns true if this is a tty
 #[cfg(windows)]
 pub fn is(stream: Stream) -> bool {