Rust: Handle early returns in async blocks in CFG

Author: hvitved

rust/ql/lib/codeql/rust/controlflow/internal/Scope.qll

@@ -22,6 +22,9 @@ final class AsyncBlockScope extends CfgScopeImpl, AsyncBlockExpr instanceof Expr
 
   override predicate scopeLast(AstNode last, Completion c) {
     last(super.getLastChildElement(), last, c)
+    or
+    last(super.getChildNode(_), last, c) and
+    not c instanceof NormalCompletion
   }
 }
 

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

@@ -892,6 +892,7 @@ edges
 | test.rs:403:13:405:14 | ExprStmt | test.rs:403:16:403:16 | b |  |
 | test.rs:403:16:403:16 | b | test.rs:403:13:405:13 | IfExpr | false |
 | test.rs:403:16:403:16 | b | test.rs:404:17:404:41 | ExprStmt | true |
+| test.rs:404:17:404:40 | ReturnExpr | test.rs:402:28:407:9 | exit BlockExpr (normal) | return |
 | test.rs:404:17:404:41 | ExprStmt | test.rs:404:24:404:34 | async_block |  |
 | test.rs:404:24:404:34 | async_block | test.rs:404:36:404:39 | true |  |
 | test.rs:404:24:404:40 | CallExpr | test.rs:404:17:404:40 | ReturnExpr |  |