Python: Add barrier test to import resolution

Just like the one added for `py/insecure-protocol` in fb425b7, but
instead added in the import-resolution tests, such that we don't have to
remember it's in a completely different directory.

Author: RasmusWL

python/ql/test/experimental/import-resolution/ModuleExport.expected

@@ -11,6 +11,9 @@
 | baz | __file__ | baz.py:2:7:2:14 | ControlFlowNode for __file__ |
 | baz | __file__ | baz.py:6:6:6:13 | ControlFlowNode for __file__ |
 | baz | baz_attr | baz.py:4:12:4:21 | ControlFlowNode for Str |
+| block_flow_check | SOURCE | block_flow_check.py:4:1:4:21 | ControlFlowNode for ClassExpr |
+| block_flow_check | __file__ | block_flow_check.py:2:7:2:14 | ControlFlowNode for __file__ |
+| block_flow_check | __file__ | block_flow_check.py:14:6:14:13 | ControlFlowNode for __file__ |
 | foo | __file__ | foo.py:2:7:2:14 | ControlFlowNode for __file__ |
 | foo | __file__ | foo.py:14:6:14:13 | ControlFlowNode for __file__ |
 | foo | __private_foo_attr | foo.py:8:22:8:41 | ControlFlowNode for Str |

python/ql/test/experimental/import-resolution/block_flow_check.py

@@ -0,0 +1,14 @@
+from trace import *
+enter(__file__)
+
+class SOURCE(object):
+    @staticmethod
+    def block_flow(): pass
+
+check("SOURCE", SOURCE, SOURCE, globals()) #$ prints=SOURCE
+
+SOURCE.block_flow()
+
+check("SOURCE", SOURCE, SOURCE, globals())
+
+exit(__file__)

python/ql/test/experimental/import-resolution/importflow.ql

@@ -66,6 +66,10 @@ private class ImportConfiguration extends DataFlow::Configuration {
   override predicate isSink(DataFlow::Node sink) {
     sink = API::moduleImport("trace").getMember("check").getACall().getArg(1)
   }
+
+  override predicate isBarrier(DataFlow::Node node) {
+    exists(DataFlow::MethodCallNode call | call.calls(node, "block_flow"))
+  }
 }
 
 class ResolutionTest extends InlineExpectationsTest {

python/ql/test/experimental/import-resolution/main.py

@@ -146,6 +146,10 @@ def local_import():
 check("simplistic_reexport.bar_attr", simplistic_reexport.bar_attr, "overwritten", globals()) #$ prints=overwritten SPURIOUS: prints=bar_attr
 check("simplistic_reexport.baz_attr", simplistic_reexport.baz_attr, "overwritten", globals()) #$ prints=overwritten SPURIOUS: prints=baz_attr
 
+# check that we don't treat all assignments as being exports
+import block_flow_check #$ imports=block_flow_check as=block_flow_check
+check("block_flow_check.SOURCE", block_flow_check.SOURCE, block_flow_check.SOURCE, globals()) #$ SPURIOUS: prints=SOURCE
+
 exit(__file__)
 
 print()