Python: deprecate Function.getAReturnValueFlowNode() and rewrite internal callers

Follow-up to the getAFlowNode deprecation in the same PR: same AST→legacy-CFG
bridge pattern. The 11 internal call sites (across objects/, types/,
frameworks/, and TypeTrackingImpl) are rewritten to bind a `Return ret`
explicitly, then constrain via `ret.getScope() = f and n.getNode() = ret.getValue()`.

The predicate itself is preserved with a deprecation note so external
users do not experience churn.

Semantic noop.

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

Author: yoff

python/ql/lib/change-notes/2026-06-01-deprecate-getAReturnValueFlowNode.md

@@ -0,0 +1,4 @@
+---
+category: deprecated
+---
+* The `Function.getAReturnValueFlowNode()` predicate has been deprecated. Bind a `Return` node explicitly instead — `exists(Return ret | ret.getScope() = f and n.getNode() = ret.getValue())`. This is a preparatory step towards migrating the dataflow library off the legacy CFG; it has no semantic effect.

python/ql/lib/semmle/python/Function.qll

@@ -153,8 +153,16 @@ class Function extends Function_, Scope, AstNode {
 
   override predicate contains(AstNode inner) { Scope.super.contains(inner) }
 
-  /** Gets a control flow node for a return value of this function */
-  ControlFlowNode getAReturnValueFlowNode() {
+  /**
+   * DEPRECATED: bind a `Return` node explicitly instead, e.g.
+   * `exists(Return ret | ret.getScope() = this and n.getNode() = ret.getValue())`.
+   * This API is being phased out together with `AstNode.getAFlowNode()` to
+   * untangle the AST and CFG hierarchies in preparation for migrating the
+   * dataflow library off the legacy CFG.
+   *
+   * Gets a control flow node for a return value of this function.
+   */
+  deprecated ControlFlowNode getAReturnValueFlowNode() {
     exists(Return ret |
       ret.getScope() = this and
       ret.getValue() = result.getNode()

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

@@ -94,8 +94,10 @@ private module SummaryTypeTrackerInput implements SummaryTypeTracker::Input {
   Node returnOf(Node callable, SummaryComponent return) {
     return = FlowSummaryImpl::Private::SummaryComponent::return() and
     // `result` should be the return value of a callable expression (lambda or function) referenced by `callable`
-    result.asCfgNode() =
-      callable.getALocalSource().asExpr().(CallableExpr).getInnerScope().getAReturnValueFlowNode()
+    exists(Return ret |
+      ret.getScope() = callable.getALocalSource().asExpr().(CallableExpr).getInnerScope() and
+      result.asCfgNode().getNode() = ret.getValue()
+    )
   }
 
   // Relating callables to nodes

python/ql/lib/semmle/python/frameworks/Bottle.qll

@@ -73,7 +73,10 @@ module Bottle {
       /** A response returned by a view callable. */
       class BottleReturnResponse extends Http::Server::HttpResponse::Range {
         BottleReturnResponse() {
-          this.asCfgNode() = any(View::ViewCallable vc).getAReturnValueFlowNode()
+          exists(Return ret |
+            ret.getScope() = any(View::ViewCallable vc) and
+            this.asCfgNode().getNode() = ret.getValue()
+          )
         }
 
         override DataFlow::Node getBody() { result = this }

python/ql/lib/semmle/python/frameworks/Django.qll

@@ -2872,7 +2872,10 @@ module PrivateDjango {
     DataFlow::CfgNode
   {
     DjangoRedirectViewGetRedirectUrlReturn() {
-      node = any(GetRedirectUrlFunction f).getAReturnValueFlowNode()
+      exists(Return ret |
+        ret.getScope() = any(GetRedirectUrlFunction f) and
+        node.getNode() = ret.getValue()
+      )
     }
 
     override DataFlow::Node getRedirectLocation() { result = this }

python/ql/lib/semmle/python/frameworks/FastApi.qll

@@ -309,7 +309,10 @@ module FastApi {
       FastApiRouteSetup routeSetup;
 
       FastApiRequestHandlerReturn() {
-        node = routeSetup.getARequestHandler().getAReturnValueFlowNode()
+        exists(Return ret |
+          ret.getScope() = routeSetup.getARequestHandler() and
+          node.getNode() = ret.getValue()
+        )
       }
 
       override DataFlow::Node getBody() { result = this }

python/ql/lib/semmle/python/frameworks/Pyramid.qll

@@ -166,7 +166,10 @@ module Pyramid {
     /** A response returned by a view callable. */
     private class PyramidReturnResponse extends Http::Server::HttpResponse::Range {
       PyramidReturnResponse() {
-        this.asCfgNode() = any(View::ViewCallable vc).getAReturnValueFlowNode() and
+        exists(Return ret |
+          ret.getScope() = any(View::ViewCallable vc) and
+          this.asCfgNode().getNode() = ret.getValue()
+        ) and
         not this = instance()
       }
 

python/ql/lib/semmle/python/frameworks/Stdlib.qll

@@ -2254,8 +2254,9 @@ module StdlibPrivate {
       DataFlow::CfgNode
     {
       WsgirefSimpleServerApplicationReturn() {
-        exists(WsgirefSimpleServerApplication requestHandler |
-          node = requestHandler.getAReturnValueFlowNode()
+        exists(WsgirefSimpleServerApplication requestHandler, Return ret |
+          ret.getScope() = requestHandler and
+          node.getNode() = ret.getValue()
         )
       }
 

python/ql/lib/semmle/python/frameworks/Twisted.qll

@@ -182,7 +182,10 @@ private module Twisted {
     DataFlow::CfgNode
   {
     TwistedResourceRenderMethodReturn() {
-      this.asCfgNode() = any(TwistedResourceRenderMethod meth).getAReturnValueFlowNode()
+      exists(Return ret |
+        ret.getScope() = any(TwistedResourceRenderMethod meth) and
+        this.asCfgNode().getNode() = ret.getValue()
+      )
     }
 
     override DataFlow::Node getBody() { result = this }

python/ql/lib/semmle/python/objects/Callables.qll

@@ -81,11 +81,12 @@ class PythonFunctionObjectInternal extends CallableObjectInternal, TPythonFuncti
 
   pragma[nomagic]
   override predicate callResult(PointsToContext callee, ObjectInternal obj, CfgOrigin origin) {
-    exists(Function func, ControlFlowNode rval, ControlFlowNode forigin |
+    exists(Function func, Return ret, ControlFlowNode rval, ControlFlowNode forigin |
       func = this.getScope() and
       callee.appliesToScope(func)
     |
-      rval = func.getAReturnValueFlowNode() and
+      ret.getScope() = func and
+      rval.getNode() = ret.getValue() and
       PointsToInternal::pointsTo(rval, callee, obj, forigin) and
       origin = CfgOrigin::fromCfgNode(forigin)
     )