# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1693866459 -7200
# Node ID cdd61ff46fb7a9da7b580d69c27ee820a7ff04ef
# Parent  8ce9d7c0a3180f8b61a3368baa9db45a044fdeaf
Prevent inadvertent mutation of function/method arguments.

diff -r 8ce9d7c0a318 -r cdd61ff46fb7 tests/values.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/values.py	Tue Sep 05 00:27:39 2023 +0200
@@ -0,0 +1,7 @@
+def test(a):
+    a = a - 1.0
+    return a
+
+x = 2.0
+print test(x)               # 1.0
+print x                     # 2.0
diff -r 8ce9d7c0a318 -r cdd61ff46fb7 translator.py
--- a/translator.py	Mon Sep 04 17:55:26 2023 +0200
+++ b/translator.py	Tue Sep 05 00:27:39 2023 +0200
@@ -1765,9 +1765,17 @@
         # objects, with only floats supporting replaceable values.
 
         if expr:
-            target_ref = TrResolvedNameRef(n.name, ref, is_global=is_global,
-                                           location=location)
-            self.result_target_name = str(target_ref)
+            # Prevent parameters from becoming result targets. Otherwise, they
+            # may inadvertently cause the modification of the supplied object.
+
+            parameters = self.importer.function_parameters.get(path)
+
+            if not parameters or n.name not in parameters:
+                target_ref = TrResolvedNameRef(n.name, ref, is_global=is_global,
+                                               location=location)
+                self.result_target_name = str(target_ref)
+            else:
+                self.result_target_name = None
 
         # Expression processing is deferred until after any result target has
         # been set.