2 files changed, 42 insertions, 0 deletions
diff --git a/src/test/ui/const-generics/defaults/forward-declared.rs b/src/test/ui/const-generics/defaults/forward-declared.rs
new file mode 100644
index 00000000000..09fc105320e
--- /dev/null
+++ b/src/test/ui/const-generics/defaults/forward-declared.rs
@@ -0,0 +1,15 @@
+#![feature(const_generics_defaults)]
+
+struct Foo<const N: usize = M, const M: usize = 10>;
+//~^ ERROR generic parameters with a default cannot use forward declared identifiers
+
+enum Bar<const N: usize = M, const M: usize = 10> {}
+//~^ ERROR generic parameters with a default cannot use forward declared identifiers
+
+struct Foo2<const N: usize = N>;
+//~^ ERROR generic parameters with a default cannot use forward declared identifiers
+
+enum Bar2<const N: usize = N> {}
+//~^ ERROR generic parameters with a default cannot use forward declared identifiers
+
+fn main() {}
diff --git a/src/test/ui/const-generics/defaults/forward-declared.stderr b/src/test/ui/const-generics/defaults/forward-declared.stderr
new file mode 100644
index 00000000000..a6c4a7ae4ef
--- /dev/null
+++ b/src/test/ui/const-generics/defaults/forward-declared.stderr
@@ -0,0 +1,27 @@
+error[E0128]: generic parameters with a default cannot use forward declared identifiers
+  --> $DIR/forward-declared.rs:3:29
+   |
+LL | struct Foo<const N: usize = M, const M: usize = 10>;
+   |                             ^ defaulted generic parameters cannot be forward declared
+
+error[E0128]: generic parameters with a default cannot use forward declared identifiers
+  --> $DIR/forward-declared.rs:6:27
+   |
+LL | enum Bar<const N: usize = M, const M: usize = 10> {}
+   |                           ^ defaulted generic parameters cannot be forward declared
+
+error[E0128]: generic parameters with a default cannot use forward declared identifiers
+  --> $DIR/forward-declared.rs:9:30
+   |
+LL | struct Foo2<const N: usize = N>;
+   |                              ^ defaulted generic parameters cannot be forward declared
+
+error[E0128]: generic parameters with a default cannot use forward declared identifiers
+  --> $DIR/forward-declared.rs:12:28
+   |
+LL | enum Bar2<const N: usize = N> {}
+   |                            ^ defaulted generic parameters cannot be forward declared
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0128`.