Added test (fails to compile)

dfdx/tests/issue_tests.rs

@@ -0,0 +1,44 @@
+use dfdx::prelude::*;
+use std::fmt::Debug;
+
+#[test]
+fn test_issue_891() {
+    #[derive(Default, Debug, Clone, Copy, CustomModule)]
+    pub struct Id;
+
+    impl<Input> Module<Input> for Id {
+        type Output = Input;
+        fn try_forward(&self, x: Input) -> Result<Self::Output, Error> {
+            Ok(x)
+        }
+    }
+
+    #[derive(Default, Debug, Clone, Copy, dfdx_derives::CustomModule)]
+    struct ConcatTensorAlong<Ax: Axes<Array = [isize; 1]> + Debug>(pub Ax);
+
+    impl<Input, const AXIS: isize> Module<Input> for ConcatTensorAlong<Axis<AXIS>>
+    where
+        Input: TryConcatAlong<Axis<AXIS>>,
+    {
+        type Output = <Input as TryConcatAlong<Axis<AXIS>>>::Output;
+
+        fn try_forward(&self, x: Input) -> Result<Self::Output, Error> {
+            x.try_concat_along(Axis)
+        }
+    }
+
+    type Arch = (SplitInto<(Id, Id)>, ConcatTensorAlong<Axis<0>>);
+
+    let dev = Cpu::default();
+    let x = dev.tensor([1.]);
+    let m = dev.build_module::<f32>(Arch::default());
+    let y = m.forward(x);
+    /*
+    error[E0275]: overflow evaluating the requirement `((_, _, _, _), (..., ..., ..., ...)): dfdx::prelude::TryConcatAlong<...>`
+      --> dfdx/tests/issue_tests.rs:36:15
+       |
+    36 |     let y = m.forward(x);
+       |               ^^^^^^^
+       |
+        */
+}