Python: preserve phi uses at module exit

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: yoff

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

@@ -546,7 +546,7 @@ class EssaVariable extends Ssa::SsaDefinition {
    */
   Cfg::ControlFlowNode getAUse() {
     exists(CfgImpl::BasicBlock bb, int i |
-      Impl::ssaDefReachesRead(this.getSourceVariable(), this.(Ssa::SsaWriteDefinition), bb, i) and
+      Impl::ssaDefReachesRead(this.getSourceVariable(), this, bb, i) and
       bb.getNode(i) = result
     )
   }

python/ql/test/library-tests/dataflow-new-ssa/SsaTest.ql

@@ -64,6 +64,7 @@ module SsaTest implements TestSig {
       phi.definesAt(_, bb, _) and
       variable.getAUse() = exit and
       exit.isNormalExit() and
+      exit.getScope() instanceof Module and
       tag = "exit-use" and
       location = bb.getNode(0).getLocation() and
       element = bb.toString() and

python/ql/test/library-tests/dataflow-new-ssa/test.py

@@ -16,7 +16,7 @@
 # on its `def` line.
 
 
-if object():  # $ phi=conditional_factory MISSING: exit-use=conditional_factory
+if object():  # $ phi=conditional_factory exit-use=conditional_factory
     from primary_backend import Factory as conditional_factory  # $ def=conditional_factory
 else:
     from fallback_backend import Factory as conditional_factory  # $ def=conditional_factory