GH-734: Improve handling of lambdas that escape enclosing frame

src/Frame.cc

@@ -128,6 +128,20 @@ const zeek::ValPtr& Frame::GetElementByID(const zeek::detail::ID* id) const
 
 void Frame::Reset(int startIdx)
 	{
+	if ( functions_with_closure_frame_reference )
+		{
+		for ( auto& func : *functions_with_closure_frame_reference )
+			{
+			// A lambda could be escaping its enclosing Frame at this point so
+			// it needs to claim some ownership (or copy) of the Frame in
+			// order to be of any further use.
+			func->StrengthenClosureReference(this);
+			Unref(func);
+			}
+
+		functions_with_closure_frame_reference.reset();
+		}
+
 	for ( int i = startIdx; i < size; ++i )
 		ClearElement(i);
 	}

testing/btest/Baseline/language.lambda-escaping/out

@@ -0,0 +1,4 @@
+101
+101
+101
+101

testing/btest/Baseline/language.lambda-zeek-init/out

@@ -0,0 +1 @@
+103

testing/btest/language/lambda-escaping.zeek

@@ -0,0 +1,31 @@
+# @TEST-EXEC: zeek -b %INPUT >out
+# @TEST-EXEC: btest-diff out
+
+global my_func: function();
+
+event other_event()
+	{
+	local baz = 42;
+	my_func();
+	}
+
+event zeek_init() &priority=+10
+	{
+	local outer = 101;
+
+	local lambda = function()
+		{ print outer; };
+
+	lambda();
+
+	my_func = lambda;
+	my_func();
+
+	event other_event();
+	}
+
+event zeek_init() &priority=-10
+	{
+	local qux = 13;
+	my_func();
+	}

testing/btest/language/lambda-zeek-init.zeek

@@ -0,0 +1,12 @@
+# @TEST-EXEC: zeek -b %INPUT >out
+# @TEST-EXEC: btest-diff out
+
+event zeek_init() &priority=+10
+	{
+	local outer = 101;
+
+	local lambda = function()
+		{ print outer + 2; };
+
+	lambda();
+	}