add tests

src/test/ui/const_evaluatable/function-call.rs

@@ -0,0 +1,17 @@
+// check-pass
+
+const fn foo<T>() -> usize {
+    if std::mem::size_of::<*mut T>() < 8 { // size of *mut T does not depend on T
+        std::mem::size_of::<T>()
+    } else {
+        8
+    }
+}
+
+fn test<T>() {
+    let _ = [0; foo::<T>()];
+    //~^ WARN cannot use constants which depend on generic parameters in types
+    //~| WARN this was previously accepted by the compiler but is being phased out
+}
+
+fn main() {}

src/test/ui/const_evaluatable/function-call.stderr

@@ -0,0 +1,12 @@
+warning: cannot use constants which depend on generic parameters in types
+  --> $DIR/function-call.rs:12:17
+   |
+LL |     let _ = [0; foo::<T>()];
+   |                 ^^^^^^^^^^
+   |
+   = note: `#[warn(const_evaluatable_unchecked)]` on by default
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see TODO
+
+warning: 1 warning emitted
+