Scope: Extend getParentScope for lambda expressions

Lambda functions are tied into the parent statement of their
declaring lambda expression, which enables Scope's hiding
predicates to calculate hiding behaviour for lambda expressions.

Author: lcartey

cpp/common/src/codingstandards/cpp/Scope.qll

@@ -57,11 +57,22 @@ module Internal {
     // A catch-block `Handler`, whose parent is the `TryStmt`
     e.(Handler).getParent() = result
     or
+    // The parent scope of a lambda is the scope in which the lambda expression is defined.
+    //
+    // Lambda functions are defined in a generated `Closure` class, as the `operator()` function. We choose the
+    // enclosing statement of the lambda expression as the parent scope of the lambda function. This is so we can
+    // determine the order of definition if a variable is defined in the same scope as the lambda expression.
+    exists(Closure lambdaClosure |
+      lambdaClosure.getLambdaFunction() = e and
+      lambdaClosure.getLambdaExpression().getEnclosingStmt() = result
+    )
+    or
     not exists(Loop loop | loop.getAChild() = e) and
     not exists(IfStmt ifStmt | ifStmt.getThen() = e or ifStmt.getElse() = e) and
     not exists(SwitchStmt switchStmt | switchStmt.getStmt() = e) and
     not exists(CatchBlock c | c.getParameter() = e) and
     not e instanceof Handler and
+    not exists(Closure lambdaClosure | lambdaClosure.getLambdaFunction() = e) and
     if exists(e.getParentScope())
     then result = e.getParentScope()
     else (

cpp/common/test/library/codingstandards/cpp/scope/ParentScope.expected

@@ -77,7 +77,7 @@
 | test.cpp:27:28:27:28 | operator= | file://:0:0:0:0 | decltype([...](...){...}) |
 | test.cpp:27:29:27:29 | id1 | file://:0:0:0:0 | decltype([...](...){...}) |
 | test.cpp:27:29:27:31 | id1 | test.cpp:26:15:28:11 | { ... } |
-| test.cpp:27:33:27:33 | operator() | file://:0:0:0:0 | decltype([...](...){...}) |
+| test.cpp:27:33:27:33 | operator() | test.cpp:27:13:27:53 | declaration |
 | test.cpp:27:36:27:52 | { ... } | test.cpp:27:33:27:33 | operator() |
 | test.cpp:27:38:27:50 | declaration | test.cpp:27:36:27:52 | { ... } |
 | test.cpp:27:42:27:44 | id1 | test.cpp:27:36:27:52 | { ... } |