Python: Ignore synthetic CFG nodes

We can only annotate the ones that correspond directly to AST nodes
anyway.

Co-authored-by: yoff <yoff@github.com>

python/ql/test/library-tests/ControlFlow/evaluation-order/NewCfgImpl.qll

@@ -14,6 +14,10 @@ private class NewBasicBlock = CfgImpl::BasicBlock;
 /** New (shared) CFG implementation of the evaluation-order signature. */
 module NewCfg implements EvalOrderCfgSig {
   class CfgNode instanceof NewControlFlowNode {
+    // Only include the unique representative node for each AST node,
+    // filtering out synthetic before/after/entry/exit/additional nodes.
+    CfgNode() { NewControlFlowNode.super.injects(_) }
+
     string toString() { result = NewControlFlowNode.super.toString() }
 
     Py::Location getLocation() { result = NewControlFlowNode.super.getLocation() }
@@ -22,17 +26,42 @@ module NewCfg implements EvalOrderCfgSig {
       result = CfgImpl::astNodeToPyNode(NewControlFlowNode.super.getAstNode())
     }
 
-    CfgNode getASuccessor() { result = NewControlFlowNode.super.getASuccessor() }
+    CfgNode getASuccessor() { nextCfgNode(this, result) }
 
     CfgNode getAnExceptionalSuccessor() {
-      result = NewControlFlowNode.super.getAnExceptionSuccessor()
+      exists(NewControlFlowNode mid |
+        mid = NewControlFlowNode.super.getAnExceptionSuccessor() and
+        nextCfgNodeFrom(mid, result)
+      )
     }
 
     Py::Scope getScope() { result = NewControlFlowNode.super.getEnclosingCallable().asScope() }
 
-    BasicBlock getBasicBlock() { result = NewControlFlowNode.super.getBasicBlock() }
+    BasicBlock getBasicBlock() {
+      exists(NewBasicBlock bb, int i | bb.getNode(i) = this and result = bb)
+    }
   }
 
+  /**
+   * Holds if `next` is the nearest CfgNode reachable from `n` via
+   * one or more raw CFG successor edges, skipping non-CfgNode intermediaries.
+   */
+  private predicate nextCfgNodeFrom(NewControlFlowNode n, CfgNode next) {
+    next = n.getASuccessor()
+    or
+    exists(NewControlFlowNode mid |
+      mid = n.getASuccessor() and
+      not mid instanceof CfgNode and
+      nextCfgNodeFrom(mid, next)
+    )
+  }
+
+  /**
+   * Holds if `next` is the nearest CfgNode successor of `n`,
+   * skipping synthetic intermediate nodes.
+   */
+  private predicate nextCfgNode(CfgNode n, CfgNode next) { nextCfgNodeFrom(n, next) }
+
   class BasicBlock instanceof NewBasicBlock {
     string toString() { result = NewBasicBlock.super.toString() }
 
@@ -46,7 +75,9 @@ module NewCfg implements EvalOrderCfgSig {
   }
 
   CfgNode scopeGetEntryNode(Py::Scope s) {
-    result instanceof CfgImpl::ControlFlow::EntryNode and
-    result.getScope() = s
+    exists(CfgImpl::ControlFlow::EntryNode entry |
+      entry.getEnclosingCallable().asScope() = s and
+      nextCfgNodeFrom(entry, result)
+    )
   }
 }