Python: Add test for "hidden" import * flow

TL;DR: We were missing out on flow in the following situation:

`mod1.py`:
```python
foo = SOURCE
```

`mod2.py`:
```python
from mod1 import *
```

`test.py`:
```python
from mod2 import foo
SINK(foo)
```

This is because there's no node at which a read of `foo` takes place
within `test.py`, and so the added reads make no difference.

Unfortunately, this means the previous test was a bit too simplistic,
since it only looks for module variable reads and writes. Because of
this, we change the test to be a more traditional "all flow" style
(though restricted to `CfgNode`s).

Author: tausbn

python/ql/test/experimental/dataflow/import-star/global.expected

@@ -1,11 +1,9 @@
-moduleVariables
-| three.py:0:0:0:0 | ModuleVariableNode for three.foo |
-| trois.py:0:0:0:0 | ModuleVariableNode for trois.foo |
-reads
-| three.py:0:0:0:0 | ModuleVariableNode for three.foo | test1.py:2:7:2:9 | ControlFlowNode for foo |
-| three.py:0:0:0:0 | ModuleVariableNode for three.foo | two.py:2:7:2:9 | ControlFlowNode for foo |
-| trois.py:0:0:0:0 | ModuleVariableNode for trois.foo | deux.py:2:7:2:9 | ControlFlowNode for foo |
-| trois.py:0:0:0:0 | ModuleVariableNode for trois.foo | test2.py:2:7:2:9 | ControlFlowNode for foo |
-writes
-| three.py:1:1:1:3 | GSSA Variable foo | three.py:0:0:0:0 | ModuleVariableNode for three.foo |
-| trois.py:1:1:1:3 | GSSA Variable foo | trois.py:0:0:0:0 | ModuleVariableNode for trois.foo |
+| test3.py:1:17:1:19 | ControlFlowNode for ImportMember | test3.py:2:7:2:9 | ControlFlowNode for foo |
+| three.py:1:1:1:3 | ControlFlowNode for foo | test1.py:2:7:2:9 | ControlFlowNode for foo |
+| three.py:1:1:1:3 | ControlFlowNode for foo | two.py:2:7:2:9 | ControlFlowNode for foo |
+| three.py:1:7:1:7 | ControlFlowNode for IntegerLiteral | test1.py:2:7:2:9 | ControlFlowNode for foo |
+| three.py:1:7:1:7 | ControlFlowNode for IntegerLiteral | two.py:2:7:2:9 | ControlFlowNode for foo |
+| trois.py:1:1:1:3 | ControlFlowNode for foo | deux.py:2:7:2:9 | ControlFlowNode for foo |
+| trois.py:1:1:1:3 | ControlFlowNode for foo | test2.py:2:7:2:9 | ControlFlowNode for foo |
+| trois.py:1:7:1:7 | ControlFlowNode for IntegerLiteral | deux.py:2:7:2:9 | ControlFlowNode for foo |
+| trois.py:1:7:1:7 | ControlFlowNode for IntegerLiteral | test2.py:2:7:2:9 | ControlFlowNode for foo |

python/ql/test/experimental/dataflow/import-star/global.ql

@@ -1,12 +1,19 @@
-import python
 import semmle.python.dataflow.new.DataFlow
 
-query DataFlow::Node moduleVariables() { result instanceof DataFlow::ModuleVariableNode }
+/**
+ * A configuration to find all flows.
+ * To be used on tiny programs.
+ */
+class AllFlowsConfig extends DataFlow::Configuration {
+  AllFlowsConfig() { this = "AllFlowsConfig" }
 
-query predicate reads(DataFlow::Node fromNode, DataFlow::Node toNode) {
-  fromNode.(DataFlow::ModuleVariableNode).getARead() = toNode
-}
+  override predicate isSource(DataFlow::Node node) { any() }
 
-query predicate writes(DataFlow::Node fromNode, DataFlow::Node toNode) {
-  fromNode = toNode.(DataFlow::ModuleVariableNode).getAWrite()
+  override predicate isSink(DataFlow::Node node) { any() }
 }
+
+from DataFlow::CfgNode source, DataFlow::CfgNode sink
+where
+  source != sink and
+  exists(AllFlowsConfig cfg | cfg.hasFlow(source, sink))
+select source, sink

python/ql/test/experimental/dataflow/import-star/test3.py

@@ -0,0 +1,2 @@
+from one import foo
+print(foo)