Slightly rewrite internal C API to reflect the modern dict API (#1187)

1. `md_get_one()`, `md_get_all()`, `md_pop_one()`, `md_pop_all()` now
return `1` if key exists in multidict, `0` otherwise.
2. `md_set_default()` now also returns `1` if key exists in multidict,
`0` if key doesn't exist and the default was iserted into the object.
3. All functions return `-1` in case of error.

The PR doesn't affect any public API; it is a preparation step for
introducing multidict's public C API.

Author: asvetlov

multidict/_multidict.c

@@ -621,6 +621,7 @@ multidict_setdefault(MultiDictObject *self, PyObject *const *args,
     PyObject *key = NULL;
     PyObject *_default = NULL;
     bool decref_default = false;
+    PyObject *ret = NULL;
 
     if (parse2("setdefault",
                args,
@@ -641,7 +642,9 @@ multidict_setdefault(MultiDictObject *self, PyObject *const *args,
         decref_default = true;
     }
     ASSERT_CONSISTENT(self, false);
-    PyObject *ret = md_set_default(self, key, _default);
+    if (md_set_default(self, key, _default, &ret) < 0) {
+        return NULL;
+    }
     if (decref_default) {
         Py_CLEAR(_default);
     }

multidict/_multilib/hashtable.h

@@ -814,7 +814,7 @@ md_get_one(MultiDictObject *md, PyObject *key, PyObject **ret)
         if (tmp > 0) {
             Py_DECREF(identity);
             *ret = Py_NewRef(entry->value);
-            return 0;
+            return 1;
         } else if (tmp < 0) {
             goto fail;
         }
@@ -868,7 +868,7 @@ md_get_all(MultiDictObject *md, PyObject *key, PyObject **ret)
 
     md_finder_cleanup(&finder);
     Py_DECREF(identity);
-    return 0;
+    return ret != NULL;
 fail:
     md_finder_cleanup(&finder);
     Py_XDECREF(identity);
@@ -877,9 +877,11 @@ md_get_all(MultiDictObject *md, PyObject *key, PyObject **ret)
     return -1;
 }
 
-static inline PyObject *
-md_set_default(MultiDictObject *md, PyObject *key, PyObject *value)
+static inline int
+md_set_default(MultiDictObject *md, PyObject *key, PyObject *value,
+               PyObject **result)
 {
+    *result = NULL;
     PyObject *identity = md_calc_identity(md, key);
     if (identity == NULL) {
         goto fail;
@@ -907,7 +909,8 @@ md_set_default(MultiDictObject *md, PyObject *key, PyObject *value)
         if (tmp > 0) {
             Py_DECREF(identity);
             ASSERT_CONSISTENT(md, false);
-            return Py_NewRef(entry->value);
+            *result = Py_NewRef(entry->value);
+            return 1;
         } else if (tmp < 0) {
             goto fail;
         }
@@ -919,10 +922,11 @@ md_set_default(MultiDictObject *md, PyObject *key, PyObject *value)
 
     Py_DECREF(identity);
     ASSERT_CONSISTENT(md, false);
-    return Py_NewRef(value);
+    *result = Py_NewRef(value);
+    return 0;
 fail:
     Py_XDECREF(identity);
-    return NULL;
+    return -1;
 }
 
 static inline int
@@ -963,7 +967,7 @@ md_pop_one(MultiDictObject *md, PyObject *key, PyObject **ret)
             *ret = value;
             md->version = NEXT_VERSION(md->state);
             ASSERT_CONSISTENT(md, false);
-            return 0;
+            return 1;
         } else if (tmp < 0) {
             goto fail;
         }
@@ -1035,7 +1039,7 @@ md_pop_all(MultiDictObject *md, PyObject *key, PyObject **ret)
     *ret = lst;
     Py_DECREF(identity);
     ASSERT_CONSISTENT(md, false);
-    return 0;
+    return lst != NULL;
 fail:
     Py_XDECREF(identity);
     Py_XDECREF(lst);