Fix JSON encoder to handle indentation with skipkeys option in dumps

Author: roeibenartzi

Lib/json/encoder.py

@@ -348,7 +348,6 @@ def _iterencode_dict(dct, _current_indent_level):
             _current_indent_level += 1
             newline_indent = '\n' + _indent * _current_indent_level
             item_separator = _item_separator + newline_indent
-            yield newline_indent
         else:
             newline_indent = None
             item_separator = _item_separator
@@ -381,6 +380,8 @@ def _iterencode_dict(dct, _current_indent_level):
                                 f'not {key.__class__.__name__}')
             if first:
                 first = False
+                if newline_indent is not None:
+                    yield newline_indent
             else:
                 yield item_separator
             yield _encoder(key)
@@ -413,7 +414,7 @@ def _iterencode_dict(dct, _current_indent_level):
             except BaseException as exc:
                 exc.add_note(f'when serializing {type(dct).__name__} item {key!r}')
                 raise
-        if newline_indent is not None:
+        if not first and newline_indent is not None:
             _current_indent_level -= 1
             yield '\n' + _indent * _current_indent_level
         yield '}'

Modules/_json.c

@@ -1616,6 +1616,12 @@ encoder_encode_key_value(PyEncoderObject *s, PyUnicodeWriter *writer, bool *firs
 
     if (*first) {
         *first = false;
+        if (s->indent != Py_None) {
+            if (write_newline_indent(writer, indent_level, indent_cache) < 0) {
+                Py_DECREF(keystr);
+                return -1;
+            }
+        }
     }
     else {
         if (PyUnicodeWriter_WriteStr(writer, item_separator) < 0) {
@@ -1683,11 +1689,8 @@ encoder_listencode_dict(PyEncoderObject *s, PyUnicodeWriter *writer,
     if (s->indent != Py_None) {
         indent_level++;
         separator = get_item_separator(s, indent_level, indent_cache);
-        if (separator == NULL ||
-            write_newline_indent(writer, indent_level, indent_cache) < 0)
-        {
+        if (separator == NULL)
             goto bail;
-        }
     }
 
     if (s->sort_keys || !PyDict_CheckExact(dct)) {
@@ -1727,7 +1730,7 @@ encoder_listencode_dict(PyEncoderObject *s, PyUnicodeWriter *writer,
             goto bail;
         Py_CLEAR(ident);
     }
-    if (s->indent != Py_None) {
+    if (s->indent != Py_None && !first) {
         indent_level--;
         if (write_newline_indent(writer, indent_level, indent_cache) < 0) {
             goto bail;