add min_adt_const_params gate tests

tests/ui/const-generics/min_adt_const_params/const_param_ty-on-adt-without-adt-gate.rs

@@ -0,0 +1,17 @@
+//! Ensure we enforce `min_adt_const_params` rules on any adt `ConstParamTy_`
+//! implementation unless `adt_const_params` feature is used.
+#![allow(incomplete_features)]
+#![feature(const_param_ty_trait)]
+
+use std::marker::ConstParamTy_;
+
+#[derive(PartialEq, Eq)]
+pub struct Fumo {
+    cirno: i32,
+    pub(crate) reimu: i32
+}
+
+impl ConstParamTy_ for Fumo {}
+                    //~^ ERROR: the trait `ConstParamTy` may not be implemented for this struct
+
+fn main() {}

tests/ui/const-generics/min_adt_const_params/const_param_ty-on-adt-without-adt-gate.stderr

@@ -0,0 +1,8 @@
+error: the trait `ConstParamTy` may not be implemented for this struct
+  --> $DIR/const_param_ty-on-adt-without-adt-gate.rs:14:24
+   |
+LL | impl ConstParamTy_ for Fumo {}
+   |                        ^^^^ struct fields are less visible than the struct
+
+error: aborting due to 1 previous error
+

tests/ui/const-generics/min_adt_const_params/min_adt_const_params-gate-fail.rs

@@ -0,0 +1,35 @@
+//! Ensure min_adt_const_params enforce
+//! struct's visibility on its fields
+#![allow(incomplete_features)]
+#![feature(min_adt_const_params)]
+#![feature(const_param_ty_trait)]
+
+use std::marker::ConstParamTy_;
+
+#[derive(PartialEq, Eq)]
+pub struct Meowl {
+    pub public: i32,
+    private: i32
+}
+
+#[derive(PartialEq, Eq)]
+pub struct Meowl2 {
+    pub a: i32,
+    pub b: i32
+}
+
+#[derive(PartialEq, Eq)]
+pub(crate) struct Meowl3 {
+    pub(crate) a: i32,
+    pub b: i32
+}
+
+impl ConstParamTy_ for Meowl {}
+                    //~^ ERROR the trait `ConstParamTy` may not be implemented for this struct
+impl ConstParamTy_ for Meowl2 {}
+impl ConstParamTy_ for Meowl3 {}
+
+fn something<const N: Meowl2>() {}
+fn something2<const N: Meowl3>() {}
+
+fn main() {}

tests/ui/const-generics/min_adt_const_params/min_adt_const_params-gate-fail.stderr

@@ -0,0 +1,8 @@
+error: the trait `ConstParamTy` may not be implemented for this struct
+  --> $DIR/min_adt_const_params-gate-fail.rs:27:24
+   |
+LL | impl ConstParamTy_ for Meowl {}
+   |                        ^^^^^ struct fields are less visible than the struct
+
+error: aborting due to 1 previous error
+

tests/ui/const-generics/min_adt_const_params/min_adt_const_params-gate.rs

@@ -0,0 +1,18 @@
+// gate-test-min_adt_const_params
+//@run-pass
+#![feature(min_adt_const_params, const_param_ty_trait)]
+#![allow(incomplete_features, dead_code)]
+
+use std::marker::ConstParamTy_;
+
+#[derive(PartialEq, Eq)]
+pub struct Meowl {
+    pub public: i32,
+    pub also_public: i32
+}
+
+impl ConstParamTy_ for Meowl {}
+
+fn meoow<const N: Meowl>() {}
+
+fn main() {}

tests/ui/const-generics/min_adt_const_params/type-field-more-visible-than-type.rs

@@ -0,0 +1,12 @@
+//@run-pass
+#![feature(min_adt_const_params)]
+
+use std::marker::ConstParamTy;
+
+#[derive(ConstParamTy, Eq, PartialEq)]
+#[allow(dead_code)]
+struct Foo {
+    pub field: u32,
+}
+
+fn main() {}