Add a test for the 878 and a to-be-supported one

prusti-tests/tests/verify_overflow/pass/issues/issue-878.rs

@@ -0,0 +1,18 @@
+use prusti_contracts::*;
+use std::cmp::{Ord, Ordering};
+fn main() {}
+
+#[extern_spec]
+trait Ord {
+    #[pure]
+    fn cmp(&self, other: &Self) -> Ordering;
+}
+
+#[pure]
+pub fn eq<T: Ord>(a: &T, b: &T) -> bool {
+    match a.cmp(b) {
+        Ordering::Equal => true,
+        Ordering::Less => false,
+        Ordering::Greater => false,
+    }
+}

prusti-tests/tests/verify_overflow/pass/quantifiers/generics.rs

@@ -0,0 +1,41 @@
+// The client code still causes crashes:
+// ignore-test
+use prusti_contracts::*;
+use std::cmp::{Ord, Ordering::{self, Equal, Less}};
+fn main() {
+    let mut v = 42;
+    client(&mut v, true);
+}
+
+#[pure]
+fn tautology<T>(_arg: &T, _arg2: &T) -> bool { true }
+
+#[requires(forall(|other: &T| tautology(&x, other)))]
+#[ensures(forall(|other: T| tautology(&other, &result)))]
+fn foo<T>(x: T) -> T { x }
+
+#[extern_spec]
+trait Ord {
+    #[pure]
+    fn cmp(&self, other: &Self) -> Ordering;
+}
+
+#[requires(forall(|other: &T|
+    matches!(_lower.cmp(other), Less)
+    && matches!(other.cmp(_upper), Less)
+        ==> matches!(_only_middle.cmp(other), Equal)))]
+fn bar<T: Ord>(_lower: &T, _only_middle: &T, _upper: &T) { }
+
+fn client<U: Ord, T: Ord + Copy>(x1: U, y1: T) {
+    let x2 = foo(x1);
+    bar(&x2, &x2, &x2);
+
+    let y2 = foo(y1);
+    let y3 = y2;
+    bar(&y2, &y1, &y3);
+
+    let val1 = 10;
+    let val2 = foo(val1);
+    let val3 = val1;
+    bar(&val1, &val3, &val2);
+}