BUG: Fix issues (mainly) found using pytest-leaks (#20583)

* BUG: Fix issues (mainly) found using pytest-leaks

This fixes mainly simple reference counting issues found with pytest-leaks.
However, two of them are more complicated (will comment on them in the PR).

This may not be the full picture yet, leak-test still running and to be
sure I may need to restart it once more by now (it takes more than 1 day
to complete).

* Undo setitem changes to see if they trip windows tests

The do seem a bit fishy, may be better to remove any special casing
(even if that may require copying the "nbytes logic" from ctors.c

4 files changed, 17 insertions, 10 deletions

diff --git a/numpy/core/src/multiarray/conversion_utils.c b/numpy/core/src/multiarray/conversion_utils.c
index ef101a78b..a1de580d9 100644
--- a/numpy/core/src/multiarray/conversion_utils.c
+++ b/numpy/core/src/multiarray/conversion_utils.c
@@ -172,7 +172,7 @@ PyArray_CopyConverter(PyObject *obj, _PyArray_CopyMode *copymode) {
     }
 
     int int_copymode;
-    PyObject* numpy_CopyMode = NULL;
+    static PyObject* numpy_CopyMode = NULL;
     npy_cache_import("numpy", "_CopyMode", &numpy_CopyMode);
 
     if (numpy_CopyMode != NULL && (PyObject *)Py_TYPE(obj) == numpy_CopyMode) {
@@ -182,6 +182,7 @@ PyArray_CopyConverter(PyObject *obj, _PyArray_CopyMode *copymode) {
         }
 
         int_copymode = (int)PyLong_AsLong(mode_value);
+        Py_DECREF(mode_value);
         if (error_converting(int_copymode)) {
             return NPY_FAIL;
         }
diff --git a/numpy/core/src/multiarray/ctors.c b/numpy/core/src/multiarray/ctors.c
index 487f0d4a9..5ece33e8c 100644
--- a/numpy/core/src/multiarray/ctors.c
+++ b/numpy/core/src/multiarray/ctors.c
@@ -1964,6 +1964,7 @@ PyArray_FromArray(PyArrayObject *arr, PyArray_Descr *newtype, int flags)
         if (flags & NPY_ARRAY_ENSURENOCOPY ) {
             PyErr_SetString(PyExc_ValueError,
                     "Unable to avoid copy while creating an array from given array.");
+            Py_DECREF(newtype);
             return NULL;
         }
 
diff --git a/numpy/core/src/umath/dispatching.c b/numpy/core/src/umath/dispatching.c
index 7bfc0a442..cfeb0b17a 100644
--- a/numpy/core/src/umath/dispatching.c
+++ b/numpy/core/src/umath/dispatching.c
@@ -742,14 +742,15 @@ promote_and_get_info_and_ufuncimpl(PyUFuncObject *ufunc,
     }
     info = promote_and_get_info_and_ufuncimpl(ufunc,
             ops, signature, new_op_dtypes, NPY_FALSE);
+    for (int i = 0; i < ufunc->nargs; i++) {
+        Py_XDECREF(new_op_dtypes[i]);
+    }
+
     /* Add this to the cache using the original types: */
     if (cacheable && PyArrayIdentityHash_SetItem(ufunc->_dispatch_cache,
             (PyObject **)op_dtypes, info, 0) < 0) {
         return NULL;
     }
-    for (int i = 0; i < ufunc->nargs; i++) {
-        Py_XDECREF(new_op_dtypes);
-    }
     return info;
 }
 
diff --git a/numpy/core/src/umath/ufunc_object.c b/numpy/core/src/umath/ufunc_object.c
index 1b310b471..78f6f4b5a 100644
--- a/numpy/core/src/umath/ufunc_object.c
+++ b/numpy/core/src/umath/ufunc_object.c
@@ -2738,12 +2738,10 @@ reducelike_promote_and_resolve(PyUFuncObject *ufunc,
 
     PyArrayMethodObject *ufuncimpl = promote_and_get_ufuncimpl(ufunc,
             ops, signature, operation_DTypes, NPY_FALSE, NPY_TRUE, NPY_TRUE);
-    /* Output can currently get cleared, others XDECREF in case of error */
+    /* DTypes may currently get filled in fallbacks and XDECREF for error: */
+    Py_XDECREF(operation_DTypes[0]);
     Py_XDECREF(operation_DTypes[1]);
-    if (out != NULL) {
-        Py_XDECREF(operation_DTypes[0]);
-        Py_XDECREF(operation_DTypes[2]);
-    }
+    Py_XDECREF(operation_DTypes[2]);
     if (ufuncimpl == NULL) {
         return NULL;
     }
@@ -4892,6 +4890,7 @@ ufunc_generic_fastcall(PyUFuncObject *ufunc,
      */
     Py_XDECREF(wheremask);
     for (int i = 0; i < nop; i++) {
+        Py_DECREF(signature[i]);
         Py_XDECREF(operand_DTypes[i]);
         Py_DECREF(operation_descrs[i]);
         if (i < nin) {
@@ -4915,6 +4914,7 @@ fail:
     Py_XDECREF(wheremask);
     for (int i = 0; i < ufunc->nargs; i++) {
         Py_XDECREF(operands[i]);
+        Py_XDECREF(signature[i]);
         Py_XDECREF(operand_DTypes[i]);
         Py_XDECREF(operation_descrs[i]);
         if (i < nout) {
@@ -6154,7 +6154,9 @@ ufunc_at(PyUFuncObject *ufunc, PyObject *args)
     Py_XDECREF(op2_array);
     Py_XDECREF(iter);
     Py_XDECREF(iter2);
-    for (int i = 0; i < 3; i++) {
+    for (int i = 0; i < nop; i++) {
+        Py_DECREF(signature[i]);
+        Py_XDECREF(operand_DTypes[i]);
         Py_XDECREF(operation_descrs[i]);
         Py_XDECREF(array_operands[i]);
     }
@@ -6180,6 +6182,8 @@ fail:
     Py_XDECREF(iter);
     Py_XDECREF(iter2);
     for (int i = 0; i < 3; i++) {
+        Py_XDECREF(signature[i]);
+        Py_XDECREF(operand_DTypes[i]);
         Py_XDECREF(operation_descrs[i]);
         Py_XDECREF(array_operands[i]);
     }