feat(parse_query_string): change the default value of csv to False (

#2200)

* feat(parse_query_string): change the default value of `csv` to `False`

* docs(parse_query_string): improve docstring in the light of the new default

* test(parse_query_string): resurrect some older tests for `csv=True`

docs/_newsfragments/1999.breakingchange.rst

@@ -0,0 +1,6 @@
+The default value of the ``csv`` parameter in
+:func:`~falcon.uri.parse_query_string` was changed to ``False``, matching the
+default behavior of other parts of the framework (such as
+:attr:`req.params <falcon.Request.params>`, the test client, etc).
+If the old behavior fits your use case better, pass the ``csv=True`` keyword
+argument explicitly.

falcon/cyutil/uri.pyx

@@ -251,7 +251,7 @@ cdef cy_parse_query_string(unsigned char* data, Py_ssize_t length,
 
 
 def parse_query_string(unicode query_string not None, bint keep_blank=False,
-                       bint csv=True):
+                       bint csv=False):
     cdef bytes byte_string = query_string.encode('utf-8')
     cdef unsigned char* data = byte_string
     return cy_parse_query_string(data, len(byte_string), keep_blank, csv)

falcon/util/uri.py

@@ -337,20 +337,22 @@ def decode(encoded_uri: str, unquote_plus: bool = True) -> str:
 
 
 def parse_query_string(
-    query_string: str, keep_blank: bool = False, csv: bool = True
+    query_string: str, keep_blank: bool = False, csv: bool = False
 ) -> Dict[str, Union[str, List[str]]]:
     """Parse a query string into a dict.
 
     Query string parameters are assumed to use standard form-encoding. Only
     parameters with values are returned. For example, given 'foo=bar&flag',
-    this function would ignore 'flag' unless the `keep_blank_qs_values` option
+    this function would ignore 'flag' unless the `keep_blank` option
     is set.
 
     Note:
         In addition to the standard HTML form-based method for specifying
         lists by repeating a given param multiple times, Falcon supports
         a more compact form in which the param may be given a single time
         but set to a ``list`` of comma-separated elements (e.g., 'foo=a,b,c').
+        This comma-separated format can be enabled by setting the `csv`
+        option (see below) to ``True``.
 
         When using this format, all commas uri-encoded will not be treated by
         Falcon as a delimiter. If the client wants to send a value as a list,
@@ -365,12 +367,13 @@ def parse_query_string(
             they do not have a value (default ``False``). For comma-separated
             values, this option also determines whether or not empty elements
             in the parsed list are retained.
-        csv: Set to ``False`` in order to disable splitting query
-            parameters on ``,`` (default ``True``). Depending on the user agent,
-            encoding lists as multiple occurrences of the same parameter might
-            be preferable. In this case, setting `parse_qs_csv` to ``False``
-            will cause the framework to treat commas as literal characters in
-            each occurring parameter value.
+        csv: Set to ``True`` in order to enable splitting query
+            parameters on ``,`` (default ``False``).
+            Depending on the user agent, encoding lists as multiple occurrences
+            of the same parameter might be preferable. In this case, keeping
+            `parse_qs_csv` at its default value (``False``) will cause the
+            framework to treat commas as literal characters in each occurring
+            parameter value.
 
     Returns:
         dict: A dictionary of (*name*, *value*) pairs, one per query

tests/test_utils.py

@@ -380,13 +380,13 @@ def test_parse_query_string(self):
         result = uri.parse_query_string(query_string)
         assert result['a'] == decoded_url
         assert result['b'] == decoded_json
-        assert result['c'] == ['1', '2', '3']
+        assert result['c'] == '1,2,3'
         assert result['d'] == 'test'
-        assert result['e'] == ['a', '&=,']
+        assert result['e'] == 'a,,&=,'
         assert result['f'] == ['a', 'a=b']
         assert result['é'] == 'a=b'
 
-        result = uri.parse_query_string(query_string, True)
+        result = uri.parse_query_string(query_string, True, True)
         assert result['a'] == decoded_url
         assert result['b'] == decoded_json
         assert result['c'] == ['1', '2', '3']
@@ -395,6 +395,15 @@ def test_parse_query_string(self):
         assert result['f'] == ['a', 'a=b']
         assert result['é'] == 'a=b'
 
+        result = uri.parse_query_string(query_string, csv=True)
+        assert result['a'] == decoded_url
+        assert result['b'] == decoded_json
+        assert result['c'] == ['1', '2', '3']
+        assert result['d'] == 'test'
+        assert result['e'] == ['a', '&=,']
+        assert result['f'] == ['a', 'a=b']
+        assert result['é'] == 'a=b'
+
     @pytest.mark.parametrize(
         'query_string,keep_blank,expected',
         [