Rust: Add type inference tests for impl trait types

rust/ql/test/library-tests/type-inference/main.rs

@@ -1873,8 +1873,10 @@ mod async_ {
 }
 
 mod impl_trait {
+    #[derive(Copy, Clone)]
     struct S1;
     struct S2;
+    struct S3<T3>(T3);
 
     trait Trait1 {
         fn f1(&self) {} // Trait1f1
@@ -1906,6 +1908,13 @@ mod impl_trait {
         }
     }
 
+    impl<T: Clone> MyTrait<T> for S3<T> {
+        fn get_a(&self) -> T {
+            let S3(t) = self;
+            t.clone()
+        }
+    }
+
     fn get_a_my_trait() -> impl MyTrait<S2> {
         S1
     }
@@ -1914,6 +1923,14 @@ mod impl_trait {
         t.get_a() // $ target=MyTrait::get_a
     }
 
+    fn get_a_my_trait2<T: Clone>(x: T) -> impl MyTrait<T> {
+        S3(x)
+    }
+
+    fn get_a_my_trait3<T: Clone>(x: T) -> Option<impl MyTrait<T>> {
+        Some(S3(x))
+    }
+
     fn uses_my_trait2<A>(t: impl MyTrait<A>) -> A {
         t.get_a() // $ target=MyTrait::get_a
     }
@@ -1927,6 +1944,9 @@ mod impl_trait {
         let a = get_a_my_trait(); // $ target=get_a_my_trait
         let c = uses_my_trait2(a); // $ type=c:S2 target=uses_my_trait2
         let d = uses_my_trait2(S1); // $ type=d:S2 target=uses_my_trait2
+        let e = get_a_my_trait2(S1).get_a(); // $ target=get_a_my_trait2 target=MyTrait::get_a MISSING: type=e:S1
+        // For this function the `impl` type does not appear in the root of the return type
+        let f = get_a_my_trait3(S1).unwrap().get_a(); // $ target=get_a_my_trait3 target=unwrap MISSING: target=MyTrait::get_a type=f:S1
     }
 }
 
@@ -2385,7 +2405,7 @@ mod tuples {
 
         let pair = [1, 1].into(); // $ type=pair:(T_2) type=pair:0(2).i32 type=pair:1(2).i32 MISSING: target=into
         match pair {
-            (0,0) => print!("unexpected"),
+            (0, 0) => print!("unexpected"),
             _ => print!("expected"),
         }
         let x = pair.0; // $ type=x:i32