fix: open files read-only during format --check

format --check only reads files to compare content but opened them
with r+, which requires write permission and fails on read-only
filesystems in certain CI setups. Use r for check mode and keep r+
for normal format runs that write back to disk.

Signed-off-by: Amir Vakili <AVakili@Voleon.com>

Author: avakili-voleon

sqlmesh/core/context.py

@@ -1270,7 +1270,8 @@ def format(
             ):  # introduced to satisfy type checker as still want to pull filter out as many targets as possible before loop
                 continue
 
-            with open(target._path, "r+", encoding="utf-8") as file:
+            mode = "r" if check else "r+"
+            with open(target._path, mode, encoding="utf-8") as file:
                 before = file.read()
 
                 after = self._format(

tests/core/test_format.py

@@ -1,4 +1,6 @@
+import os
 import pathlib
+import stat
 
 from pytest_mock.plugin import MockerFixture
 from sqlmesh.core.config import Config
@@ -146,6 +148,25 @@ def test_ignore_formating_files(tmp_path: pathlib.Path):
     )
 
 
+def test_format_check_read_only_files(tmp_path: pathlib.Path, mocker: MockerFixture):
+    models_dir = pathlib.Path("models")
+
+    model_text = "MODEL(name this.model, dialect 'duckdb'); SELECT 1 AS col"
+    model = create_temp_file(
+        tmp_path,
+        pathlib.Path(models_dir, "model.sql"),
+        model_text,
+    )
+    os.chmod(model, stat.S_IRUSR | stat.S_IRGRP | stat.S_IROTH)
+
+    context = Context(paths=tmp_path, config=Config())
+    context.console = mocker.Mock()
+    context.load()
+
+    assert not context.format(check=True)
+    assert model.read_text(encoding="utf-8") == model_text
+
+
 def test_format_without_state_load(tmp_path: pathlib.Path, mocker: MockerFixture):
     mock = mocker.patch(
         "sqlmesh.core.state_sync.db.facade.EngineAdapterStateSync.get_versions",