fix workaround false positive clippy lint reversed_empty_ranges

[ModProg]

As the rust-clippy issue rust-lang/rust-clippy#5808 doesn't seam to make much progress I propose to just allow the lint for s![] macro invocations for now.

The let = ... is necessary, because attributes are not allowed on expressions
currently (rust-lang/rust#15701).

[ModProg]

@bluss removed the depricated zip

[bluss]

Can we hold off on removing the deprecated zip until it can be replaced by std::iter::zip? That's after all the whole point of it, to use the function version :slightly_smiling_face:

(Function zip is the best 🙂 )

[ModProg]

Yeah no problem, only did so because the ci was failing because of it.

[adamreichold]

Did you try using #![allow(clippy::reversed_empty_ranges)] to allow this for the block and thereby avoiding the temporary binding? (Tail expressions do influence lifetime extension of temporaries and hence I would like to avoid changing this if it can be avoided.)

[ModProg]

attributes on expressions are experimental

Wouldn't work, as it needs a statement to apply the attribute

[adamreichold]

Note the exclamation mark. This is similar to the form used at the beginning of a module to apply a directive to the whole module. So this would apply to everything inside the block, which in this case is just a single expression.

[ModProg]

($($t:tt)*) => {
    {
        #![allow(clippy::reversed_empty_ranges)]
        $crate::s![@parse
            ::core::marker::PhantomData::<$crate::Ix0>,
            ::core::marker::PhantomData::<$crate::Ix0>,
            []
            $($t)*
        ]
    }
};

error[E0658]: attributes on expressions are experimental
   --> /mnt/data-ssd/modprog/Development/Rust/ndarray/src/slice.rs:871:13
    |
775 | macro_rules! s(
    | -------------- in this expansion of `s!`
...
871 |             #![allow(clippy::reversed_empty_ranges)]
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
   ::: tests/array.rs:202:16
    |
202 |     let info = s![1.., 1, NewAxis, ..;2];
    |                ------------------------- in this macro invocation
    |
    = note: see issue #15701 <https://github.com/rust-lang/rust/issues/15701> for more information
    = help: add `#![feature(stmt_expr_attributes)]` to the crate attributes to enable

[adamreichold]

Ok, so this did work. Sorry for that.

Could you give the diff

diff --git a/src/slice.rs b/src/slice.rs
index 0146d6db..53763ae2 100644
--- a/src/slice.rs
+++ b/src/slice.rs
@@ -779,7 +779,7 @@ macro_rules! s(
             r => {
                 let in_dim = $crate::SliceNextDim::next_in_dim(&r, $in_dim);
                 let out_dim = $crate::SliceNextDim::next_out_dim(&r, $out_dim);
-                #[allow(unsafe_code)]
+                #[allow(unsafe_code, clippy::reversed_empty_ranges)]
                 unsafe {
                     $crate::SliceInfo::new_unchecked(
                         [$($stack)* $crate::s!(@convert r, $s)],
@@ -796,7 +796,7 @@ macro_rules! s(
             r => {
                 let in_dim = $crate::SliceNextDim::next_in_dim(&r, $in_dim);
                 let out_dim = $crate::SliceNextDim::next_out_dim(&r, $out_dim);
-                #[allow(unsafe_code)]
+                #[allow(unsafe_code, clippy::reversed_empty_ranges)]
                 unsafe {
                     $crate::SliceInfo::new_unchecked(
                         [$($stack)* $crate::s!(@convert r)],

a try? It does work for me without forcing the slice info into a local binding.

If it does, could use this approach and rebase this on the current master branch?

[ModProg]

That didn't work, but I found a different solution, using two blocks to convince rust to allow an attribute on an expression.