From c69948d3915c4d7cc56daed043d3b15c190396ac Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Sat, 9 Mar 2019 15:51:43 -0800
Subject: [PATCH] Improve error when missing macro argument

The log! macro matches part of its arguments as $($arg:tt)+, but the other
macros match it as $($arg:tt)*. That means if a user calls error!() or any of
the other macros with an empty argument, it successfully matches the macro rules
of the first macro they called but then turns into an invalid call to log!,
leading to a confusing error message.

This PR uses $($arg:tt)+ consistently to match arguments.

Example:

    use log::error;

    fn main() {
        error!();
    }

Before:

    error: expected identifier, found `,`
     --> src/main.rs:4:5
      |
    4 |     error!();
      |     ^^^^^^^^^
      |     |
      |     expected identifier
      |     help: remove this comma
      |
      = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

After:

    error: unexpected end of macro invocation
     --> src/main.rs:4:5
      |
    4 |     error!();
      |     ^^^^^^^^^ missing tokens in macro arguments
---
 src/macros.rs | 40 ++++++++++++++++++++--------------------
 1 file changed, 20 insertions(+), 20 deletions(-)

diff --git a/src/macros.rs b/src/macros.rs
index 06ce65a..a77d56a 100644
--- a/src/macros.rs
+++ b/src/macros.rs
@@ -60,11 +60,11 @@ macro_rules! log {
 /// ```
 #[macro_export(local_inner_macros)]
 macro_rules! error {
-    (target: $target:expr, $($arg:tt)*) => (
-        log!(target: $target, $crate::Level::Error, $($arg)*);
+    (target: $target:expr, $($arg:tt)+) => (
+        log!(target: $target, $crate::Level::Error, $($arg)+);
     );
-    ($($arg:tt)*) => (
-        log!($crate::Level::Error, $($arg)*);
+    ($($arg:tt)+) => (
+        log!($crate::Level::Error, $($arg)+);
     )
 }
 
@@ -84,11 +84,11 @@ macro_rules! error {
 /// ```
 #[macro_export(local_inner_macros)]
 macro_rules! warn {
-    (target: $target:expr, $($arg:tt)*) => (
-        log!(target: $target, $crate::Level::Warn, $($arg)*);
+    (target: $target:expr, $($arg:tt)+) => (
+        log!(target: $target, $crate::Level::Warn, $($arg)+);
     );
-    ($($arg:tt)*) => (
-        log!($crate::Level::Warn, $($arg)*);
+    ($($arg:tt)+) => (
+        log!($crate::Level::Warn, $($arg)+);
     )
 }
 
@@ -110,11 +110,11 @@ macro_rules! warn {
 /// ```
 #[macro_export(local_inner_macros)]
 macro_rules! info {
-    (target: $target:expr, $($arg:tt)*) => (
-        log!(target: $target, $crate::Level::Info, $($arg)*);
+    (target: $target:expr, $($arg:tt)+) => (
+        log!(target: $target, $crate::Level::Info, $($arg)+);
     );
-    ($($arg:tt)*) => (
-        log!($crate::Level::Info, $($arg)*);
+    ($($arg:tt)+) => (
+        log!($crate::Level::Info, $($arg)+);
     )
 }
 
@@ -135,11 +135,11 @@ macro_rules! info {
 /// ```
 #[macro_export(local_inner_macros)]
 macro_rules! debug {
-    (target: $target:expr, $($arg:tt)*) => (
-        log!(target: $target, $crate::Level::Debug, $($arg)*);
+    (target: $target:expr, $($arg:tt)+) => (
+        log!(target: $target, $crate::Level::Debug, $($arg)+);
     );
-    ($($arg:tt)*) => (
-        log!($crate::Level::Debug, $($arg)*);
+    ($($arg:tt)+) => (
+        log!($crate::Level::Debug, $($arg)+);
     )
 }
 
@@ -162,11 +162,11 @@ macro_rules! debug {
 /// ```
 #[macro_export(local_inner_macros)]
 macro_rules! trace {
-    (target: $target:expr, $($arg:tt)*) => (
-        log!(target: $target, $crate::Level::Trace, $($arg)*);
+    (target: $target:expr, $($arg:tt)+) => (
+        log!(target: $target, $crate::Level::Trace, $($arg)+);
     );
-    ($($arg:tt)*) => (
-        log!($crate::Level::Trace, $($arg)*);
+    ($($arg:tt)+) => (
+        log!($crate::Level::Trace, $($arg)+);
     )
 }