From 2492236839830aea561d75ed2d3de2c393bc8422 Mon Sep 17 00:00:00 2001
From: Markus Lottmann <markus.lottmann@mlbox.net>
Date: Mon, 8 Dec 2025 18:42:42 +0100
Subject: [PATCH] [pysrc2cpg] Avoid tmp variable creation in for non complex
 receivers.

So far the python frontend emitted tmp variables in the context of call
site lowering if the `<x>` in a `<x>.y()` call was anything other than
an identifier/name. Now we also avoid emitting tmp variables if `<x>` is
a member access chain. E.g. `x.y.z()`. This leads to less clutter and
better alias handling.
---
 .../io/joern/pysrc2cpg/PythonAstVisitor.scala | 15 ++++++-
 .../io/joern/pysrc2cpg/cpg/CallCpgTests.scala | 43 ++++++++++++++++++-
 2 files changed, 56 insertions(+), 2 deletions(-)

diff --git a/joern-cli/frontends/pysrc2cpg/src/main/scala/io/joern/pysrc2cpg/PythonAstVisitor.scala b/joern-cli/frontends/pysrc2cpg/src/main/scala/io/joern/pysrc2cpg/PythonAstVisitor.scala
index 5477c1626a5a..eb910326aaab 100644
--- a/joern-cli/frontends/pysrc2cpg/src/main/scala/io/joern/pysrc2cpg/PythonAstVisitor.scala
+++ b/joern-cli/frontends/pysrc2cpg/src/main/scala/io/joern/pysrc2cpg/PythonAstVisitor.scala
@@ -12,6 +12,7 @@ import io.shiftleft.codepropertygraph.generated.nodes.{NewCall, NewIdentifier, N
 import org.slf4j.LoggerFactory
 import io.shiftleft.codepropertygraph.generated.DiffGraphBuilder
 
+import scala.annotation.tailrec
 import scala.collection.mutable
 
 object MethodParameters {
@@ -1836,6 +1837,18 @@ class PythonAstVisitor(
     ("and", Operators.logicalAnd)
   }
 
+  @tailrec
+  private def mayHaveSideEffects(expr: ast.iexpr): Boolean = {
+    expr match {
+      case attr: ast.Attribute =>
+        mayHaveSideEffects(attr.value)
+      case attr: ast.Name =>
+        false
+      case _ =>
+        true
+    }
+  }
+
   /** TODO For now this function compromises on the correctness of the lowering in order to get some data flow tracking
     * going.
     *   1. For constructs like x.func() we assume x to be the instance which is passed into func. This is not true since
@@ -1862,7 +1875,7 @@ class PythonAstVisitor(
         createXDotYCall(
           () => convert(attribute.value),
           attribute.attr,
-          xMayHaveSideEffects = !attribute.value.isInstanceOf[ast.Name],
+          xMayHaveSideEffects = mayHaveSideEffects(attribute.value),
           lineAndColOf(call),
           argumentNodes,
           keywordArgNodes,
diff --git a/joern-cli/frontends/pysrc2cpg/src/test/scala/io/joern/pysrc2cpg/cpg/CallCpgTests.scala b/joern-cli/frontends/pysrc2cpg/src/test/scala/io/joern/pysrc2cpg/cpg/CallCpgTests.scala
index 7e649ebf5a89..5871be73f77d 100644
--- a/joern-cli/frontends/pysrc2cpg/src/test/scala/io/joern/pysrc2cpg/cpg/CallCpgTests.scala
+++ b/joern-cli/frontends/pysrc2cpg/src/test/scala/io/joern/pysrc2cpg/cpg/CallCpgTests.scala
@@ -7,7 +7,6 @@ import io.shiftleft.semanticcpg.language.*
 import java.io.File
 
 class CallCpgTests extends PySrc2CpgFixture(withOssDataflow = false) {
-
   "call on identifier" should {
     lazy val cpg = code("""func(a, b)""".stripMargin, "test.py")
 
@@ -173,6 +172,48 @@ class CallCpgTests extends PySrc2CpgFixture(withOssDataflow = false) {
     }
   }
 
+  "call on member chain" should {
+    lazy val cpg = code("""x.y.func(a, b)""".stripMargin, "test.py")
+
+    "test call node properties" in {
+      val callNode = cpg.call.codeExact("x.y.func(a, b)").head
+      callNode.name shouldBe "func"
+      callNode.signature shouldBe ""
+      callNode.dispatchType shouldBe DispatchTypes.DYNAMIC_DISPATCH
+      callNode.lineNumber shouldBe Some(1)
+    }
+
+    "test call receiver" in {
+      val callNode     = cpg.call.codeExact("x.y.func(a, b)").head
+      val callReceiver = callNode.receiver.head
+      callReceiver.code shouldBe "x.y.func"
+
+      callNode.astChildren.order(0).head shouldBe callReceiver
+      callNode.start.argument.b should not contain callReceiver
+    }
+
+    "test call instance param" in {
+      val callNode    = cpg.call.codeExact("x.y.func(a, b)").head
+      val instanceArg = callNode.argument(0)
+      instanceArg.code shouldBe "x.y"
+
+      callNode.astChildren.order(1).head shouldBe instanceArg
+    }
+
+    "test call arguments" in {
+      val callNode = cpg.call.codeExact("x.y.func(a, b)").head
+      val arg1     = callNode.argument(1)
+      arg1.code shouldBe "a"
+
+      callNode.astChildren.order(2).head shouldBe arg1
+
+      val arg2 = callNode.argument(2)
+      arg2.code shouldBe "b"
+
+      callNode.astChildren.order(3).head shouldBe arg2
+    }
+  }
+
   "call following a definition within the same module" should {
     lazy val cpg = code(
       """