Hello i try to implement fill array macro in Rust! And i have a problem!
My macro code:

macro_rules! fill_tensor {
    ($elem:expr; ($dim:expr, $($dims:expr),+)) => {
        vec![fill_tensor!($elem; ($($dims),+)); $dim]
    };
    ($elem:expr; $dim:expr) => {
        vec![$elem; $dim]
    };
}

When i call my macro like this

fill_tensor!(4; (3_usize, 3_usize))

All works correctly (output is 3 by 3 matrix)

But when i call this macro like this

let shape: (usize, usize) = (3_usize, 3_usize)
fill_tensor!(4; shape)

I got error
rustc: mismatched typesexpected type usize found tuple (usize, usize)
And my question is Why?

Link To Reproduce problem (Rust Playground)

I i try to see hows $dim looks in this block of code

($elem:expr; $dim:expr) => {
    vec![$elem; $dim]
};              

I make tiny change in code

macro_rules! fill_tensor {
    ($elem:expr; ($dim:expr, $($dims:expr),+)) => {
        vec![fill_tensor!($elem; ($($dims),+)); $dim]
    };
    ($elem:expr; $dim:expr) => {
        assert_eq!($shape, (3_usize, 3_usize)) 
    };
}

And i have no error assertion correct

My final question is Why this pattern $elem:expr; ($dim:expr, $($dims:expr),+) match to (3_usize, 3_usize) but not match to this value in variable? And how to fix it?