Add `dkeprintln` macro

This macro functions exactly like `eprintln` while prepending the string
"dome-key: error: " to all messages. Allows us to give a uniform prefix
to printed rerrors.

Used the `println` macro as a reference:
https://doc.rust-lang.org/src/std/macros.rs.html#157-162

2 files changed, 22 insertions, 0 deletions

diff --git a/src/lib.rs b/src/lib.rs
index 92399dc..6a08e4b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -37,6 +37,7 @@ mod config;
 mod errors;
 mod key_code;
 mod parser;
+mod prefix_println;
 mod trial;
 
 use parser::{Action, HeadphoneButton, MapAction, MapGroup, MapKind};
diff --git a/src/prefix_println.rs b/src/prefix_println.rs
new file mode 100644
index 0000000..d1a8949
--- /dev/null
+++ b/src/prefix_println.rs
@@ -0,0 +1,21 @@
+#[macro_export]
+macro_rules! dkeprintln {
+    () => (eprint!("\n"));
+    ($($arg:tt)*) => {
+        eprintln!(
+            "dome-key: error: {}",
+            format!($($arg)*),
+        );
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    #[ignore]
+    fn dkprintln_macro() {
+        dkeprintln!();
+        dkeprintln!("test");
+        dkeprintln!("multiple arguments {}, {}", 5, 50 / 2);
+    }
+}