From 3829f52b019ff6124a89648e36b7427cfb3111a8 Mon Sep 17 00:00:00 2001
From: bluss <bluss@users.noreply.github.com>
Date: Mon, 16 Sep 2019 19:51:59 +0200
Subject: [PATCH] FEAT: Add error message for invalid syntax in s![]

Invalid syntax, like for example empty `s![]` or clearly invalid
productions like `s![;;]` etc, end up in this new catch-all branch of
the macro and produce a clearer error message.

    error: Invalid syntax in s![], expected at least one index or range
      --> src/foo.rs:11:13
       |
    11 |     a.slice(s![]);
       |             ^^^^
---
 src/slice.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/slice.rs b/src/slice.rs
index 85abfb8e0..53dbae0a3 100644
--- a/src/slice.rs
+++ b/src/slice.rs
@@ -612,6 +612,8 @@ macro_rules! s(
     (@convert $r:expr, $s:expr) => {
         <$crate::SliceOrIndex as ::std::convert::From<_>>::from($r).step_by($s as isize)
     };
+    // Catch-all clause for syntax errors
+    (@parse $($t:tt)*) => { compile_error!("Invalid syntax in s![], expected at least one index or range") };
     ($($t:tt)*) => {
         // The extra `*&` is a workaround for this compiler bug:
         // https://github.com/rust-lang/rust/issues/23014