Fix memory leak creating new istr objects (#1133)

Fixes leak 1 from
#1131 (comment)
(`IStr_New` path)

see
#1131 (comment)
#1131 (comment)
#1131 (comment)

This also seems to fix the perf regression in popitem from
#1097 (comment)
https://codspeed.io/aio-libs/multidict/branches/istr-keys

introduced #1097
fixes #1131

---------

Co-authored-by: Andrew Svetlov <andrew.svetlov@gmail.com>

Author: bdraco

CHANGES/1133.bugfix.rst

@@ -0,0 +1,3 @@
+Fixed a memory leak creating new :class:`~multidict.istr` objects -- by :user:`bdraco`.
+
+The leak was introduced in 6.3.0

multidict/_multilib/istr.h

@@ -27,31 +27,20 @@ istr_dealloc(istrobject *self)
 }
 
 static inline PyObject *
-istr_new_with_state(PyTypeObject *type, PyObject *args, PyObject *kwds,
-                    mod_state *state)
+istr_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 {
-    if (state == NULL) {
-        PyObject *mod = PyType_GetModuleByDef(type, &multidict_module);
-        if (mod == NULL) {
-            return NULL;
-        }
-        state = get_mod_state(mod);
+    PyObject *mod = PyType_GetModuleByDef(type, &multidict_module);
+    if (mod == NULL) {
+        return NULL;
     }
+    mod_state *state = get_mod_state(mod);
 
     PyObject *x = NULL;
     static char *kwlist[] = {"object", "encoding", "errors", 0};
     PyObject *encoding = NULL;
     PyObject *errors = NULL;
     PyObject *canonical = NULL;
-    PyObject * ret = NULL;
-    if (kwds != NULL) {
-        int cmp = PyDict_Pop(kwds, state->str_canonical, &canonical);
-        if (cmp < 0) {
-            return NULL;
-        } else if (cmp > 0) {
-            Py_INCREF(canonical);
-        }
-    }
+    PyObject *ret = NULL;
 
     if (!PyArg_ParseTupleAndKeywords(args, kwds, "|OOO:str",
                                      kwlist, &x, &encoding, &errors)) {
@@ -65,20 +54,9 @@ istr_new_with_state(PyTypeObject *type, PyObject *args, PyObject *kwds,
     if (!ret) {
         goto fail;
     }
-
-    if (canonical == NULL) {
-        canonical = PyObject_CallMethodNoArgs(ret, state->str_lower);
-        if (!canonical) {
-            goto fail;
-        }
-    }
-    if (!PyUnicode_CheckExact(canonical)) {
-        PyObject *tmp = PyUnicode_FromObject(canonical);
-        Py_CLEAR(canonical);
-        if (tmp == NULL) {
-            goto fail;
-        }
-        canonical = tmp;
+    canonical = PyObject_CallMethodNoArgs(ret, state->str_lower);
+    if (!canonical) {
+        goto fail;
     }
     ((istrobject*)ret)->canonical = canonical;
     ((istrobject*)ret)->state = state;
@@ -88,12 +66,6 @@ istr_new_with_state(PyTypeObject *type, PyObject *args, PyObject *kwds,
     return NULL;
 }
 
-static inline PyObject *
-istr_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
-{
-    return istr_new_with_state(type, args, kwds, NULL);
-}
-
 static inline PyObject *
 istr_reduce(PyObject *self)
 {
@@ -147,33 +119,20 @@ static inline PyObject *
 IStr_New(mod_state *state, PyObject *str, PyObject *canonical)
 {
     PyObject *args = NULL;
-    PyObject *kwds = NULL;
     PyObject *res = NULL;
-
     args = PyTuple_Pack(1, str);
     if (args == NULL) {
         goto ret;
     }
-
-    if (canonical != NULL) {
-        kwds = PyDict_New();
-        if (kwds == NULL) {
-            goto ret;
-        }
-        if (!PyUnicode_CheckExact(canonical)) {
-            PyErr_SetString(PyExc_TypeError,
-                            "'canonical' argument should be exactly str");
-            goto ret;
-        }
-        if (PyDict_SetItem(kwds, state->str_canonical, canonical) < 0) {
-            goto ret;
-        }
+    res = PyUnicode_Type.tp_new(state->IStrType, args, NULL);
+    if (!res) {
+        goto ret;
     }
-
-    res = istr_new_with_state(state->IStrType, args, kwds, state);
+    Py_INCREF(canonical);
+    ((istrobject*)res)->canonical = canonical;
+    ((istrobject*)res)->state = state;
 ret:
     Py_CLEAR(args);
-    Py_CLEAR(kwds);
     return res;
 }