Use better heuristic for select list elision

Instead of only eliding select lists longer than 12 characters, now only
elide select lists that contain a dot (from a column expression like
`table_name`.`column_name`).  The motivation for this is that as of
Django 1.10, using .count() on a queryset generates
    SELECT COUNT(*) AS `__count` FROM ...
instead of
    SELECT COUNT(*) FROM ...
queries.  This change prevents the new form from being elided.

Author: living180

debug_toolbar/panels/sql/utils.py

@@ -18,25 +18,28 @@ def process(self, stream):
 
     @staticmethod
     def elide_until_from(stream):
-        select_list_characters = 0
-        select_list_tokens = []
+        has_dot = False
+        saved_tokens = []
         for token_type, value in stream:
             if token_type in T.Keyword and value.upper() == "FROM":
-                # Do not elide a select list of 12 characters or fewer to preserve
-                #    SELECT COUNT(*) FROM ...
+                # Do not elide a select lists that do not contain dots (used to separate
+                # table names from column names) in order to preserve
+                #    SELECT COUNT(*) AS `__count` FROM ...
                 # and
                 #    SELECT (1) AS `a` FROM ...
                 # queries.
-                if select_list_characters <= 12:
-                    yield from select_list_tokens
+                if not has_dot:
+                    yield from saved_tokens
                 else:
                     # U+2022: Unicode character 'BULLET'
                     yield T.Other, " \u2022\u2022\u2022 "
                 yield token_type, value
                 break
-            if select_list_characters <= 12:
-                select_list_characters += len(value)
-                select_list_tokens.append((token_type, value))
+            if not has_dot:
+                if token_type in T.Punctuation and value == ".":
+                    has_dot = True
+                else:
+                    saved_tokens.append((token_type, value))
 
 
 class BoldKeywordFilter:

tests/panels/test_sql.py

@@ -495,6 +495,21 @@ def test_prettify_sql(self):
         self.assertEqual(len(self.panel._queries), 1)
         self.assertEqual(pretty_sql, self.panel._queries[-1]["sql"])
 
+    def test_simplification(self):
+        """
+        Test case to validate that select lists for .count() and .exist() queries do not
+        get elided, but other select lists do.
+        """
+        User.objects.count()
+        User.objects.exists()
+        list(User.objects.values_list("id"))
+        response = self.panel.process_request(self.request)
+        self.panel.generate_stats(self.request, response)
+        self.assertEqual(len(self.panel._queries), 3)
+        self.assertNotIn("\u2022", self.panel._queries[0]["sql"])
+        self.assertNotIn("\u2022", self.panel._queries[1]["sql"])
+        self.assertIn("\u2022", self.panel._queries[2]["sql"])
+
     @override_settings(
         DEBUG=True,
     )