Python: Fix missing module resolution

This was due to bad manual magic: restricting the attribute name makes
sense when we're talking about submodules of a package, but it doesn't
when we're talking about reexported modules.

Also (hopefully) fixes the tests so that the Python 3-specific bits are
ignored under Python 2.

python/ql/lib/semmle/python/dataflow/new/internal/ImportResolution.qll

@@ -235,9 +235,12 @@ module ImportResolution {
       result = ar
     |
       isPreferredModuleForName(m.getFile(), p.getPackageName() + "." + attr_name + ["", ".__init__"])
-      or
-      // This is also true for attributes that come from reexports.
-      module_reexport(p, attr_name, m)
+    )
+    or
+    // This is also true for attributes that come from reexports.
+    exists(Module reexporter, string attr_name |
+      result.(DataFlow::AttrRead).accesses(getModuleReference(reexporter), attr_name) and
+      module_reexport(reexporter, attr_name, m)
     )
     or
     // Submodules that are implicitly defined with relative imports of the form `from .foo import ...`.

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

@@ -74,7 +74,7 @@ class ResolutionTest extends InlineExpectationsTest {
     (
       exists(DataFlow::PathNode source, DataFlow::PathNode sink, ImportConfiguration config |
         config.hasFlowPath(source, sink) and
-        correct_version(sink.getNode()) and
+        not sink.getNode() instanceof VersionGuardedNode and
         tag = "prints" and
         location = sink.getNode().getLocation() and
         value = source.getNode().(SourceString).getContents() and
@@ -82,7 +82,7 @@ class ResolutionTest extends InlineExpectationsTest {
       )
       or
       exists(ModuleRef ref |
-        correct_version(ref) and
+        not ref instanceof VersionGuardedNode and
         ref instanceof CheckArgument and
         tag = "prints" and
         location = ref.getLocation() and
@@ -93,7 +93,30 @@ class ResolutionTest extends InlineExpectationsTest {
   }
 }
 
-private predicate correct_version(DataFlow::Node n) {
-  not n instanceof VersionGuardedNode or
-  n.(VersionGuardedNode).getVersion() = major_version()
+class ResolutionTest3 extends InlineExpectationsTest {
+  ResolutionTest3() { this = "ResolutionTest3" }
+
+  override string getARelevantTag() { result = "prints3" }
+
+  override predicate hasActualResult(Location location, string element, string tag, string value) {
+    (
+      exists(DataFlow::PathNode source, DataFlow::PathNode sink, ImportConfiguration config |
+        config.hasFlowPath(source, sink) and
+        sink.getNode().(VersionGuardedNode).getVersion() = 3 and
+        tag = "prints3" and
+        location = sink.getNode().getLocation() and
+        value = source.getNode().(SourceString).getContents() and
+        element = sink.getNode().toString()
+      )
+      or
+      exists(ModuleRef ref |
+        ref.(VersionGuardedNode).getVersion() = 3 and
+        ref instanceof CheckArgument and
+        tag = "prints3" and
+        location = ref.getLocation() and
+        value = "\"<module " + ref.getName() + ">\"" and
+        element = ref.toString()
+      )
+    )
+  }
 }

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

@@ -35,7 +35,8 @@ import foo as foo_alias #$ imports=foo as=foo_alias
 check("foo_alias.foo_attr", foo_alias.foo_attr, "foo_attr", globals()) #$ prints=foo_attr
 
 # A reference to a reexported module
-check("foo.bar_reexported.bar_attr", foo.bar_reexported.bar_attr, "bar_attr", globals()) #$ MISSING: prints=bar_attr
+check("foo.bar_reexported", foo.bar_reexported, "<module bar>", globals()) #$ prints="<module bar>"
+check("foo.bar_reexported.bar_attr", foo.bar_reexported.bar_attr, "bar_attr", globals()) #$ prints=bar_attr
 
 # A simple "import from" statement.
 from bar import bar_attr
@@ -71,7 +72,7 @@ check("package.package_attr", package.package_attr, "package_attr", globals()) #
 if sys.version_info[0] == 3:
     # Importing from a namespace module.
     from namespace_package.namespace_module import namespace_module_attr
-    check("namespace_module_attr", namespace_module_attr, "namespace_module_attr", globals()) #$ prints=namespace_module_attr
+    check("namespace_module_attr", namespace_module_attr, "namespace_module_attr", globals()) #$ prints3=namespace_module_attr
 
 
 from attr_clash import clashing_attr, non_clashing_submodule #$ imports=attr_clash.clashing_attr as=clashing_attr imports=attr_clash.non_clashing_submodule as=non_clashing_submodule