fix: allow filter() and isnull() with no space (#644)

* fix: allow filter() and isnull() with no space

* fix: format

src/sqlfmt/rules/__init__.py

@@ -44,6 +44,24 @@
             ),
         ),
     ),
+    Rule(
+        # There are some function names in some dialects that are the same as
+        # word operators in other dialects. Here we lex those as function
+        # names IFF the name is immediately followed by a `(` (with no space
+        # after the name. Otherwise they are lexed as word_operators by the
+        # next rule.
+        name="functions_that_overlap_with_word_operators",
+        priority=1099,
+        pattern=group(
+            r"filter",
+            r"isnull",
+        )
+        + group(r"\("),
+        action=partial(
+            actions.handle_reserved_keyword,
+            action=partial(actions.add_node_to_buffer, token_type=TokenType.NAME),
+        ),
+    ),
     Rule(
         name="word_operator",
         priority=1100,

tests/unit_tests/test_rule.py

@@ -419,6 +419,13 @@ def test_regex_anti_match(
         (MAIN, "frame_clause", "range 1 following", "range "),
         (MAIN, "frame_clause", "range current row", "range "),
         (MAIN, "frame_clause", "groups between 1 preceding", "groups "),
+        (MAIN, "functions_that_overlap_with_word_operators", "filter(foo)", "filter"),
+        (
+            MAIN,
+            "functions_that_overlap_with_word_operators",
+            "isnull(bar, baz)",
+            "isnull",
+        ),
     ],
 )
 def test_regex_partial_match(