Implement error handling for 'format' mode in Style50 and ensure SQL formatter returns newline consistently. Add tests for new behavior.

Author: rongxin-liu

style50/_api.py

@@ -62,6 +62,9 @@ def format_file(self, path):
 
     def run(self, *args, **kwargs):
         """Wraps Style50.check and renders the results using the renderer determined by self.output"""
+        if self.output == "format":
+            raise Error("format mode does not support run(); use format_file() instead")
+
         results = self.check(*args, **kwargs)
 
         if self.output == "html":

style50/languages.py

@@ -112,7 +112,8 @@ class Html(StyleCheck):
     magic_names = ["HTML document"]
 
     def style(self, code):
-        # djhtml reads from stdin when path is '-'
+        # djhtml returns exit 1 when it reformats (same convention as diff/black),
+        # so exit=None is required to avoid treating successful reformats as errors.
         return self.run(["djhtml", "-"], input=code, exit=None)
 
 
@@ -132,5 +133,7 @@ class Sql(StyleCheck):
     magic_names = []
 
     def style(self, code):
-        # Keep this lightweight and dependency-minimal while producing stable formatting.
-        return sqlparse.format(code, reindent=True, keyword_case="upper", indent_width=4) + ("\n" if not code.endswith("\n") else "")
+        formatted = sqlparse.format(code, reindent=True, keyword_case="upper", indent_width=4)
+        if not formatted.endswith("\n"):
+            formatted += "\n"
+        return formatted

tests/test_languages.py

@@ -35,6 +35,7 @@ def test_sql_formatter_runs():
     formatted = Sql(original).styled
     assert isinstance(formatted, str)
     assert "FROM" in formatted
+    assert formatted.endswith("\n")
 
 
 def test_html_formatter_invokes_djhtml(monkeypatch):
@@ -93,3 +94,11 @@ def fake_run(command, input=None, exit=0, shell=False):
 
     assert seen["cmd"] == C.clangFormat
 
+
+def test_format_mode_run_raises_error():
+    from style50._api import Style50, Error
+
+    s = Style50("format")
+    with pytest.raises(Error, match="format mode does not support run"):
+        s.run(["nonexistent_file.py"])
+