mv compiler to compiler/

compiler/rustc_driver/src/args.rs

@@ -0,0 +1,38 @@
+use std::error;
+use std::fmt;
+use std::fs;
+use std::io;
+
+pub fn arg_expand(arg: String) -> Result<Vec<String>, Error> {
+    if arg.starts_with('@') {
+        let path = &arg[1..];
+        let file = match fs::read_to_string(path) {
+            Ok(file) => file,
+            Err(ref err) if err.kind() == io::ErrorKind::InvalidData => {
+                return Err(Error::Utf8Error(Some(path.to_string())));
+            }
+            Err(err) => return Err(Error::IOError(path.to_string(), err)),
+        };
+        Ok(file.lines().map(ToString::to_string).collect())
+    } else {
+        Ok(vec![arg])
+    }
+}
+
+#[derive(Debug)]
+pub enum Error {
+    Utf8Error(Option<String>),
+    IOError(String, io::Error),
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Error::Utf8Error(None) => write!(fmt, "Utf8 error"),
+            Error::Utf8Error(Some(path)) => write!(fmt, "Utf8 error in {}", path),
+            Error::IOError(path, err) => write!(fmt, "IO Error: {}: {}", path, err),
+        }
+    }
+}
+
+impl error::Error for Error {}