Rust: Add CFG test for early return in async block

Also made the test comply with `cargo check`.

rust/ql/test/library-tests/controlflow-unstable/Cfg.expected

@@ -0,0 +1,53 @@
+edges
+| test.rs:5:5:11:5 | enter test_and_if_let | test.rs:5:24:5:24 | a |  |
+| test.rs:5:5:11:5 | exit test_and_if_let (normal) | test.rs:5:5:11:5 | exit test_and_if_let |  |
+| test.rs:5:24:5:24 | a | test.rs:5:24:5:30 | Param | match |
+| test.rs:5:24:5:30 | Param | test.rs:5:33:5:33 | b |  |
+| test.rs:5:33:5:33 | b | test.rs:5:33:5:47 | Param | match |
+| test.rs:5:33:5:47 | Param | test.rs:5:50:5:50 | c |  |
+| test.rs:5:50:5:50 | c | test.rs:5:50:5:56 | Param | match |
+| test.rs:5:50:5:56 | Param | test.rs:6:12:6:12 | a |  |
+| test.rs:5:67:11:5 | BlockExpr | test.rs:5:5:11:5 | exit test_and_if_let (normal) |  |
+| test.rs:6:9:10:9 | IfExpr | test.rs:5:67:11:5 | BlockExpr |  |
+| test.rs:6:12:6:12 | a | test.rs:6:12:6:31 | [boolean(false)] ... && ... | false |
+| test.rs:6:12:6:12 | a | test.rs:6:17:6:31 | LetExpr | true |
+| test.rs:6:12:6:31 | [boolean(false)] ... && ... | test.rs:9:13:9:17 | false | false |
+| test.rs:6:12:6:31 | [boolean(true)] ... && ... | test.rs:7:13:7:13 | d | true |
+| test.rs:6:17:6:31 | LetExpr | test.rs:6:31:6:31 | b |  |
+| test.rs:6:21:6:27 | TupleStructPat | test.rs:6:12:6:31 | [boolean(false)] ... && ... | no-match |
+| test.rs:6:21:6:27 | TupleStructPat | test.rs:6:26:6:26 | d | match |
+| test.rs:6:26:6:26 | d | test.rs:6:12:6:31 | [boolean(true)] ... && ... | match |
+| test.rs:6:31:6:31 | b | test.rs:6:21:6:27 | TupleStructPat |  |
+| test.rs:6:33:8:9 | BlockExpr | test.rs:6:9:10:9 | IfExpr |  |
+| test.rs:7:13:7:13 | d | test.rs:6:33:8:9 | BlockExpr |  |
+| test.rs:8:16:10:9 | BlockExpr | test.rs:6:9:10:9 | IfExpr |  |
+| test.rs:9:13:9:17 | false | test.rs:8:16:10:9 | BlockExpr |  |
+| test.rs:13:5:21:5 | enter test_and_if_let2 | test.rs:13:25:13:25 | a |  |
+| test.rs:13:5:21:5 | exit test_and_if_let2 (normal) | test.rs:13:5:21:5 | exit test_and_if_let2 |  |
+| test.rs:13:25:13:25 | a | test.rs:13:25:13:31 | Param | match |
+| test.rs:13:25:13:31 | Param | test.rs:13:34:13:34 | b |  |
+| test.rs:13:34:13:34 | b | test.rs:13:34:13:39 | Param | match |
+| test.rs:13:34:13:39 | Param | test.rs:13:42:13:42 | c |  |
+| test.rs:13:42:13:42 | c | test.rs:13:42:13:48 | Param | match |
+| test.rs:13:42:13:48 | Param | test.rs:14:12:14:12 | a |  |
+| test.rs:13:59:21:5 | BlockExpr | test.rs:13:5:21:5 | exit test_and_if_let2 (normal) |  |
+| test.rs:14:9:20:9 | IfExpr | test.rs:13:59:21:5 | BlockExpr |  |
+| test.rs:14:12:14:12 | a | test.rs:14:12:14:25 | [boolean(false)] ... && ... | false |
+| test.rs:14:12:14:12 | a | test.rs:14:17:14:25 | LetExpr | true |
+| test.rs:14:12:14:25 | [boolean(false)] ... && ... | test.rs:14:12:15:16 | [boolean(false)] ... && ... | false |
+| test.rs:14:12:14:25 | [boolean(true)] ... && ... | test.rs:15:16:15:16 | c | true |
+| test.rs:14:12:15:16 | [boolean(false)] ... && ... | test.rs:19:13:19:17 | false | false |
+| test.rs:14:12:15:16 | [boolean(true)] ... && ... | test.rs:17:13:17:13 | d | true |
+| test.rs:14:17:14:25 | LetExpr | test.rs:14:25:14:25 | b |  |
+| test.rs:14:21:14:21 | d | test.rs:14:12:14:25 | [boolean(true)] ... && ... | match |
+| test.rs:14:25:14:25 | b | test.rs:14:21:14:21 | d |  |
+| test.rs:15:16:15:16 | c | test.rs:14:12:15:16 | [boolean(false)] ... && ... | false |
+| test.rs:15:16:15:16 | c | test.rs:14:12:15:16 | [boolean(true)] ... && ... | true |
+| test.rs:16:9:18:9 | BlockExpr | test.rs:14:9:20:9 | IfExpr |  |
+| test.rs:17:13:17:13 | d | test.rs:17:17:17:17 | 0 |  |
+| test.rs:17:13:17:17 | ... > ... | test.rs:16:9:18:9 | BlockExpr |  |
+| test.rs:17:17:17:17 | 0 | test.rs:17:13:17:17 | ... > ... |  |
+| test.rs:18:16:20:9 | BlockExpr | test.rs:14:9:20:9 | IfExpr |  |
+| test.rs:19:13:19:17 | false | test.rs:18:16:20:9 | BlockExpr |  |
+breakTarget
+continueTarget

rust/ql/test/library-tests/controlflow-unstable/Cfg.qlref

@@ -0,0 +1 @@
+query: utils/Cfg.ql

rust/ql/test/library-tests/controlflow-unstable/test.rs

@@ -0,0 +1,22 @@
+// TODO: Move these tests into `controlflow` when they become stable features
+
+mod if_expression {
+
+    fn test_and_if_let(a: bool, b: Option<bool>, c: bool) -> bool {
+        if a && let Some(d) = b {
+            d
+        } else {
+            false
+        }
+    }
+
+    fn test_and_if_let2(a: bool, b: i64, c: bool) -> bool {
+        if a && let d = b
+            && c
+        {
+            d > 0
+        } else {
+            false
+        }
+    }
+}