From e12d57e893882c1603778018139ed9060579c8a7 Mon Sep 17 00:00:00 2001
From: Karl Wette <karl.wette@ligo.org>
Date: Thu, 24 Oct 2024 21:37:48 +1100
Subject: [PATCH] lal/swig/SWIGCommon.i: refactor SWIGLAL_MAYBE_RETURN_INT
 typemap

- New behaviour of SWIG_Python_AppendOutput() makes it more difficult
  to not add XLAL error code at start of output argument list
- Instead, always add XLAL error code at start of output argument list,
  them remove it later in "newfree" typemap
---
 lal/swig/SWIGCommon.i | 23 +++++------------------
 lal/swig/SWIGOctave.i |  6 ++++--
 lal/swig/SWIGPython.i | 16 +++++++++++++---
 3 files changed, 22 insertions(+), 23 deletions(-)

diff --git a/lal/swig/SWIGCommon.i b/lal/swig/SWIGCommon.i
index bb6dc62e6e..3ce595e232 100644
--- a/lal/swig/SWIGCommon.i
+++ b/lal/swig/SWIGCommon.i
@@ -1650,24 +1650,11 @@ if (strides[I-1] == 0) {
 /// ignored in the wrappings. Functions which fit this criteria but do return a useful <tt>int</tt> can
 /// use <b>SWIGLAL(RETURN_VALUE(int, ...))</b> to disable this behaviour.
 ///
-/// For functions, since <tt>%feature("new")</tt> is set, the <tt>out</tt> typemap will have <tt>$owner=1</tt>,
-/// and the <tt>newfree</tt> typemap is also applied. The <tt>out</tt> typemap ignores the <tt>int</tt> return value
-/// by setting the output argument list to <tt>VOID_Object</tt>; the wrapping function them proceeds to
-/// add other output arguments to the list, if any. After this, the <tt>newfree</tt> typemap is triggered,
-/// which appends the <tt>int</tt> return if the output argument list is empty, using the
-/// scripting-language-specific macro \b swiglal_append_output_if_empty(). For structs,
-/// <tt>$owner=0</tt>, so the int return is set straight away, and the <tt>newfree</tt> typemap is never
-/// applied.
-///
-%typemap(out, noblock=1, fragment=SWIG_From_frag(int)) int SWIGLAL_MAYBE_RETURN_INT {
-%#if $owner
-  %set_output(VOID_Object);
-%#else
-  %set_output(SWIG_From(int)($1));
-%#endif
-}
-%typemap(newfree, noblock=1, fragment=SWIG_From_frag(int)) int SWIGLAL_MAYBE_RETURN_INT {
-  swiglal_append_output_if_empty(SWIG_From(int)($1));
+/// For functions, the <tt>newfree</tt> typemap is applied, which calls the scripting-language-specific macro
+/// \b swiglal_maybe_return_int(). For structs, the <tt>newfree</tt> typemap is never applied.
+///
+%typemap(newfree, noblock=1) int SWIGLAL_MAYBE_RETURN_INT {
+  swiglal_maybe_return_int();
 }
 
 ///
diff --git a/lal/swig/SWIGOctave.i b/lal/swig/SWIGOctave.i
index d2ef3cbdbc..8c0ea50da4 100644
--- a/lal/swig/SWIGOctave.i
+++ b/lal/swig/SWIGOctave.i
@@ -65,9 +65,11 @@ extern "C++" {
 #define swiglal_get_reference(v) (v)
 %}
 
-// Append an argument to the output argument list of an Octave SWIG-wrapped function, if the list is empty.
+// Remove the first argument (i.e. the XLAL error code) from the output argument list of an
+// Octave SWIG-wrapped function, if the list has more than one output argument.
 %header %{
-#define swiglal_append_output_if_empty(v) if (_outp->length() == 0) _outp = SWIG_Octave_AppendOutput(_outp, v)
+#define swiglal_maybe_return_int() \
+  if (_out.length() > 1) _out = _out.slice(1, _out.length() - 1)
 %}
 
 // Evaluates true if an octave_value represents a null pointer, false otherwise.
diff --git a/lal/swig/SWIGPython.i b/lal/swig/SWIGPython.i
index 2482a8580f..8f332822d1 100644
--- a/lal/swig/SWIGPython.i
+++ b/lal/swig/SWIGPython.i
@@ -86,10 +86,20 @@ import_array();
 SWIGINTERNINLINE PyObject* swiglal_get_reference(PyObject* v) { Py_XINCREF(v); return v; }
 %}
 
-// Append an argument to the output argument list of an Python SWIG-wrapped function, if the list is
-// empty.
+// Remove the first argument (i.e. the XLAL error code) from the output argument list of a
+// Python SWIG-wrapped function, if the list has more than one output argument.
 %header %{
-#define swiglal_append_output_if_empty(v) if (resultobj == Py_None) resultobj = SWIG_Python_AppendOutput(resultobj, v)
+SWIGINTERN PyObject* swiglal_py_remove_first_output(PyObject *result) {
+  PySequence_DelItem(result, 0);
+  if (PySequence_Size(result) == 1) {
+    PyObject *obj = result;
+    result = PySequence_GetItem(obj, 0);
+    Py_DECREF(obj);
+  }
+  return result;
+}
+#define swiglal_maybe_return_int() \
+  if (PySequence_Check(resultobj) && PySequence_Size(resultobj) > 1) resultobj = swiglal_py_remove_first_output(resultobj)
 %}
 
 // Evaluates true if a PyObject represents a null pointer, false otherwise.
-- 
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