compiletests: future-proof issue-46 against MIR optimizations.

Author: eddyb

tests/compiletests/ui/lang/issue-46.rs

@@ -2,7 +2,7 @@
 
 use spirv_std::spirv;
 
-#[derive(Default)]
+#[derive(Copy, Clone, Default)]
 struct Foo {
     bar: bool,
     baz: [[u32; 2]; 1],
@@ -13,3 +13,20 @@ pub fn main() {
     let x = [[1; 2]; 1];
     let y = [Foo::default(); 1];
 }
+
+// HACK(eddyb) future-proofing against `[expr; 1]` -> `[expr]`
+// MIR optimization (https://github.com/rust-lang/rust/pull/135322).
+fn force_repeat_one<const ONE: usize>() -> ([[u32; 2]; ONE], [Foo; ONE]) {
+    ([[1; 2]; ONE], [Foo::default(); ONE])
+}
+
+#[spirv(fragment)]
+pub fn main_future_proof(
+    #[spirv(storage_buffer, descriptor_set = 0, binding = 0)] out: &mut [[u32; 2]; 2],
+) {
+    let (x, y) = force_repeat_one::<1>();
+
+    // NOTE(eddyb) further guard against optimizations by using `x` and `y`.
+    out[0] = x[0];
+    out[1] = y[0].baz[0];
+}