support trailing commas in macros (#273)

Author: ExpHP

src/macros.rs

@@ -11,8 +11,8 @@ macro_rules! bail {
     ($e:expr) => {
         return Err($crate::err_msg($e));
     };
-    ($fmt:expr, $($arg:tt)+) => {
-        return Err($crate::err_msg(format!($fmt, $($arg)+)));
+    ($fmt:expr, $($arg:tt)*) => {
+        return Err($crate::err_msg(format!($fmt, $($arg)*)));
     };
 }
 
@@ -28,9 +28,9 @@ macro_rules! ensure {
             bail!($e);
         }
     };
-    ($cond:expr, $fmt:expr, $($arg:tt)+) => {
+    ($cond:expr, $fmt:expr, $($arg:tt)*) => {
         if !($cond) {
-            bail!($fmt, $($arg)+);
+            bail!($fmt, $($arg)*);
         }
     };
 }

tests/macro_trailing_comma.rs

@@ -0,0 +1,54 @@
+#[macro_use]
+extern crate failure;
+
+// NOTE:
+//
+// This test is in a separate file due to the fact that ensure! cannot be used
+// from within failure.
+//
+// (you get: 'macro-expanded `macro_export` macros from the current crate cannot
+//           be referred to by absolute paths')
+
+// Encloses an early-returning macro in an IIFE so that we
+// can treat it as a Result-returning function.
+macro_rules! wrap_early_return {
+    ($expr:expr) => {{
+        fn func() -> Result<(), failure::Error> {
+            let _ = $expr;
+
+            #[allow(unreachable_code)]
+            Ok(())
+        }
+        func().map_err(|e| e.to_string())
+    }};
+}
+
+#[test]
+fn bail() {
+    assert_eq!(
+        wrap_early_return!(bail!("test")),
+        wrap_early_return!(bail!("test",)));
+    assert_eq!(
+        wrap_early_return!(bail!("test {}", 4)),
+        wrap_early_return!(bail!("test {}", 4,)));
+}
+
+#[test]
+fn ensure() {
+    assert_eq!(
+        wrap_early_return!(ensure!(false, "test")),
+        wrap_early_return!(ensure!(false, "test",)));
+    assert_eq!(
+        wrap_early_return!(ensure!(false, "test {}", 4)),
+        wrap_early_return!(ensure!(false, "test {}", 4,)));
+}
+
+#[test]
+fn format_err() {
+    assert_eq!(
+        format_err!("test").to_string(),
+        format_err!("test",).to_string());
+    assert_eq!(
+        format_err!("test {}", 4).to_string(),
+        format_err!("test {}", 4,).to_string());
+}