gh-125063: Emit slices as constants in the bytecode compiler (#125064)

* Make slices marshallable

* Emit slices as constants

* Update Python/marshal.c

Co-authored-by: Peter Bierma <zintensitydev@gmail.com>

* Refactor codegen_slice into two functions so it
always has the same net effect

* Fix for free-threaded builds

* Simplify marshal loading of slices

* Only return SUCCESS/ERROR from codegen_slice

---------

Co-authored-by: Mark Shannon <mark@hotpy.org>
Co-authored-by: Peter Bierma <zintensitydev@gmail.com>

1 files changed, 34 insertions, 0 deletions

diff --git a/Python/marshal.c b/Python/marshal.c
index b1708a7..3d127b4 100644
--- a/Python/marshal.c
+++ b/Python/marshal.c
@@ -76,6 +76,7 @@ module marshal
 #define TYPE_UNKNOWN            '?'
 #define TYPE_SET                '<'
 #define TYPE_FROZENSET          '>'
+#define TYPE_SLICE              ':'
 #define FLAG_REF                '\x80' /* with a type, add obj to index */
 
 #define TYPE_ASCII              'a'
@@ -613,6 +614,13 @@ w_complex_object(PyObject *v, char flag, WFILE *p)
         w_pstring(view.buf, view.len, p);
         PyBuffer_Release(&view);
     }
+    else if (PySlice_Check(v)) {
+        PySliceObject *slice = (PySliceObject *)v;
+        W_TYPE(TYPE_SLICE, p);
+        w_object(slice->start, p);
+        w_object(slice->stop, p);
+        w_object(slice->step, p);
+    }
     else {
         W_TYPE(TYPE_UNKNOWN, p);
         p->error = WFERR_UNMARSHALLABLE;
@@ -1534,6 +1542,32 @@ r_object(RFILE *p)
         retval = Py_NewRef(v);
         break;
 
+    case TYPE_SLICE:
+    {
+        Py_ssize_t idx = r_ref_reserve(flag, p);
+        PyObject *stop = NULL;
+        PyObject *step = NULL;
+        PyObject *start = r_object(p);
+        if (start == NULL) {
+            goto cleanup;
+        }
+        stop = r_object(p);
+        if (stop == NULL) {
+            goto cleanup;
+        }
+        step = r_object(p);
+        if (step == NULL) {
+            goto cleanup;
+        }
+        retval = PySlice_New(start, stop, step);
+        r_ref_insert(retval, idx, flag, p);
+    cleanup:
+        Py_XDECREF(start);
+        Py_XDECREF(stop);
+        Py_XDECREF(step);
+        break;
+    }
+
     default:
         /* Bogus data got written, which isn't ideal.
            This will let you keep working and recover. */