python: add test for capturing by value

python/ql/test/experimental/dataflow/validTest.py

@@ -71,6 +71,7 @@ if __name__ == "__main__":
     check_tests_valid("variable-capture.global")
     check_tests_valid("variable-capture.dict")
     check_tests_valid("variable-capture.test_collections")
+    check_tests_valid("variable-capture.by_value")
     check_tests_valid("module-initialization.multiphase")
     check_tests_valid("fieldflow.test")
     check_tests_valid_after_version("match.test", (3, 10))

python/ql/test/experimental/dataflow/variable-capture/by_value.py

@@ -0,0 +1,54 @@
+# Here we test writing to a captured variable via the `nonlocal` keyword (see `out`).
+# We also test reading one captured variable and writing the value to another (see `through`).
+
+# All functions starting with "test_" should run and execute `print("OK")` exactly once.
+# This can be checked by running validTest.py.
+
+import sys
+import os
+
+sys.path.append(os.path.dirname(os.path.dirname((__file__))))
+from testlib import expects
+
+# These are defined so that we can evaluate the test code.
+NONSOURCE = "not a source"
+SOURCE = "source"
+
+def is_source(x):
+    return x == "source" or x == b"source" or x == 42 or x == 42.0 or x == 42j
+
+
+def SINK(x):
+    if is_source(x):
+        print("OK")
+    else:
+        print("Unexpected flow", x)
+
+
+def SINK_F(x):
+    if is_source(x):
+        print("Unexpected flow", x)
+    else:
+        print("OK")
+
+
+def by_value1():
+    a = SOURCE
+    def inner(a_val=a):
+        SINK(a_val) #$ captured
+        SINK_F(a)
+    a = NONSOURCE
+    inner()
+
+def by_value2():
+    a = NONSOURCE
+    def inner(a_val=a):
+        SINK(a) #$ MISSING:captured
+        SINK_F(a_val)
+    a = SOURCE
+    inner()
+
+@expects(4)
+def test_by_value():
+    by_value1()
+    by_value2()