feat: ensure trailing newline with comment-only queries

CHANGELOG.md

@@ -7,6 +7,7 @@ All notable changes to this project will be documented in this file.
 ### Formatting Changes and Bug Fixes
 
 - sqlfmt now lexes and formats BigQuery hexadecimal literals as numbers, and no longer adds a space between `0` and `x` ([#696](https://github.com/tconbeer/sqlfmt/issues/696) - thank you [@KMontag42](https://github.com/KMontag42) and [@snrsw](https://github.com/snrsw)!).
+- sqlfmt no longer adds a second blank newline to the end of a query that only contains a comment (with no sql code) ([#686](https://github.com/tconbeer/sqlfmt/issues/686) - thank you [@nevdelap](https://github.com/nevdelap) and [@snrsw](https://github.com/snrsw)!).
 
 ## [0.27.0] - 2025-07-28
 

Makefile

@@ -1,9 +1,9 @@
 .PHONY: check
 check:
-	ruff format .
-	ruff check . --fix
-	pytest
-	mypy
+	poetry run ruff format .
+	poetry run ruff check . --fix
+	poetry run pytest
+	poetry run mypy
 
 .PHONY: unit
 unit:

src/sqlfmt/line.py

@@ -105,7 +105,10 @@ def render_with_comments(self, max_length: int) -> str:
 
         if inline_comments:
             rendered_lines.append(f"{content}{''.join(inline_comments)}\n")
-        else:
+        # if content is empty AND we've already rendered a standalone or multiline
+        # comment, skip rendering the line itself, since that just adds a duplicate
+        # newline.
+        elif content or not self.comments:
             rendered_lines.append(f"{self}")
 
         return "".join(rendered_lines)

src/sqlfmt_primer/primer.py

@@ -30,7 +30,7 @@ def get_projects() -> List[SQLProject]:
         SQLProject(
             name="gitlab",
             git_url="https://github.com/tconbeer/gitlab-analytics-sqlfmt.git",
-            git_ref="5cd49f6",  # sqlfmt aed0f39
+            git_ref="f859b79",  # sqlfmt bc43911
             expected_changed=1,
             expected_unchanged=2416,
             expected_errored=0,
@@ -39,7 +39,7 @@ def get_projects() -> List[SQLProject]:
         SQLProject(
             name="rittman",
             git_url="https://github.com/tconbeer/rittman_ra_data_warehouse.git",
-            git_ref="418af64",  # sqlfmt cd38a6c
+            git_ref="5fe702b",  # sqlfmt bc43911
             expected_changed=0,
             expected_unchanged=307,
             expected_errored=4,  # true mismatching brackets
@@ -48,7 +48,7 @@ def get_projects() -> List[SQLProject]:
         SQLProject(
             name="http_archive",
             git_url="https://github.com/tconbeer/http_archive_almanac.git",
-            git_ref="414b535",  # sqlfmt faaf71b
+            git_ref="37302f3",  # sqlfmt bc43911
             expected_changed=0,
             expected_unchanged=1729,
             expected_errored=0,

tests/data/preformatted/010_comment_only.sql

@@ -0,0 +1 @@
+-- a comment

tests/functional_tests/test_general_formatting.py

@@ -16,6 +16,8 @@
         "preformatted/006_fmt_off_447.sql",
         "preformatted/007_fmt_off_comments.sql",
         "preformatted/008_reserved_names.sql",
+        "preformatted/009_empty.sql",
+        "preformatted/010_comment_only.sql",
         "preformatted/301_multiline_jinjafmt.sql",
         "preformatted/302_jinjafmt_multiline_str.sql",
         "preformatted/303_jinjafmt_more_mutliline_str.sql",

tests/unit_tests/test_query.py

@@ -1,3 +1,5 @@
+import pytest
+
 from sqlfmt.analyzer import Analyzer
 
 
@@ -6,3 +8,17 @@ def test_whitespace_formatting(default_analyzer: Analyzer) -> None:
     expected_string = "select 1\nfrom my_table\nwhere true\n"
     q = default_analyzer.parse_query(source_string=source_string)
     assert str(q) == expected_string
+
+
+def test_only_comment_formatting(default_analyzer: Analyzer) -> None:
+    source_string = "-- a comment"
+    expected_string = "-- a comment\n"
+    q = default_analyzer.parse_query(source_string=source_string)
+    assert str(q) == expected_string
+
+
+@pytest.mark.parametrize("source_string", ["", "\n"])
+def test_empty_formatting(default_analyzer: Analyzer, source_string: str) -> None:
+    expected_string = ""
+    q = default_analyzer.parse_query(source_string=source_string)
+    assert str(q) == expected_string