Add a regression test for #96699

Signed-off-by: Yuki Okushi <jtitor@2k36.org>

tests/ui/const-generics/generic_const_exprs/issue-96699.rs

@@ -0,0 +1,87 @@
+// check-pass
+
+#![allow(dead_code, incomplete_features)]
+#![feature(generic_const_exprs)]
+
+const fn min(a: usize, b: usize) -> usize {
+    if a < b {
+        a
+    } else {
+        b
+    }
+}
+
+trait Trait1<Inner1>
+where
+    Self: Sized,
+{
+    fn crash_here()
+    where
+        Inner1: Default,
+    {
+        Inner1::default();
+    }
+}
+
+struct Struct1<T>(T);
+impl<T> Trait1<T> for Struct1<T> {}
+
+trait Trait2<Inner2>
+where
+    Self: Sized,
+{
+    type Assoc: Trait1<Inner2>;
+
+    fn call_crash()
+    where
+        Inner2: Default,
+    {
+        // if Inner2 implements Default, we can call crash_here.
+        Self::Assoc::crash_here();
+    }
+}
+
+struct Struct2<const SIZE1: usize, const SIZE2: usize> {}
+/*
+where
+    [(); min(SIZE1, SIZE2)]:,
+{
+    elem: [i32; min(SIZE1, SIZE2)],
+}
+*/
+
+impl<const SIZE1: usize, const SIZE2: usize> Trait2<[i32; min(SIZE1, SIZE2)]>
+    for Struct2<SIZE1, SIZE2>
+{
+    type Assoc = Struct1<[i32; min(SIZE1, SIZE2)]>;
+    // dose Struct1<[i32; min(SIZE1, SIZE2)]> implement Default?
+}
+
+fn main() {
+    pattern2();
+
+    print_fully_name(<Struct2<1, 2> as Trait2<[i32; min(1, 2)]>>::Assoc::crash_here);
+    // <compiler_bug2::Struct1<[i32; 1]> as compiler_bug2::Trait1<[i32; 1]>>::crash_here
+}
+
+fn pattern1() {
+    // no crash
+    <Struct2<1, 2> as Trait2<[i32; min(1, 2)]>>::Assoc::crash_here();
+    <Struct2<1, 2> as Trait2<[i32; min(1, 2)]>>::call_crash();
+}
+
+fn pattern2() {
+    // crash
+    <Struct2<1, 2> as Trait2<[i32; min(1, 2)]>>::call_crash();
+
+    // undefined reference to `compiler_bug2::Trait1::crash_here'
+}
+
+fn pattern3() {
+    // no crash
+    <Struct2<1, 2> as Trait2<[i32; min(1, 2)]>>::Assoc::crash_here();
+}
+
+fn print_fully_name<T>(_: T) {
+    let _ = std::any::type_name::<T>();
+}