fix slice of Result into slice of u8

Author: Oneirical

src/tools/run-make-support/src/run.rs

@@ -40,6 +40,12 @@ fn run_common(name: &str) -> (Command, Output) {
     (cmd, output)
 }
 
+fn read_bytes<R: Read>(mut reader: R) -> Result<Vec<u8>, std::io::Error> {
+    let mut buffer = Vec::new();
+    reader.read_to_end(&mut buffer)?;
+    Ok(buffer)
+}
+
 /// Run a command taking in standard input from a file, and passing an argument
 /// referring to a different file.
 pub fn stdin_command<P>(command: &str, stdin: P, argument: P)
@@ -58,7 +64,8 @@ pub fn stdin_command<P>(command: &str, stdin: P, argument: P)
        .unwrap();
 
     let mut child_stdin = child.stdin.take().unwrap();
-    child_stdin.write_all(reader.bytes().collect::<Vec<_>>().as_slice()).unwrap();
+    let byte_slice = read_bytes(reader).expect("failed to read bytes of standard input").as_slice();
+    child_stdin.write_all(byte_slice).unwrap();
     child_stdin.flush().unwrap();
 
     child.wait_with_output().unwrap();