Add ruff.toml with Python lint configuration

.ruff.toml

@@ -0,0 +1,25 @@
+target-version = "py312"
+
+[lint]
+select = [
+  "B0",     # bugbear (all B0* checks enabled by default)
+  "B904",   # bugbear (Within an except clause, raise exceptions with raise ... from err)
+  "B905",   # bugbear (zip() without an explicit strict= parameter set.)
+  "E",      # pycodestyles
+  "W",      # pycodestyles
+  "F",      # pyflakes
+  "I",      # isort
+  "PGH",    # pygrep-hooks
+  "PLC",    # pylint conventions
+  "PLE",    # pylint errors
+  "UP",     # pyupgrade
+]
+ignore = [
+  "E402",  # module import not at top of file
+  "UP038",  # Use X | Y in isinstance check instead of (X, Y)
+]
+
+[lint.per-file-ignores]
+# Want to preserve compatibility for old Python versions in tools directory so
+# disable pyupgrade. Oldest supported version is currently 3.9.
+"tools/*" = ["UP"]

tools/cross/format.py

@@ -118,7 +118,9 @@ def buildifier(files: list[Path], check: bool = False) -> bool:
 
 
 def ruff(files: list[Path], check: bool = False) -> bool:
-    if files and not shutil.which(RUFF):
+    if not files:
+        return True
+    if not shutil.which(RUFF):
         msg = "Cannot find ruff, will not format Python"
         if check:
             # In ci, fail.
@@ -129,10 +131,18 @@ def ruff(files: list[Path], check: bool = False) -> bool:
             # formatting they can install ruff and run again.
             logging.warning(msg)
             return True
+    # Format
     cmd = [RUFF, "format"]
     if check:
         cmd.append("--diff")
     result = subprocess.run(cmd + files)
+    if result.returncode != 0:
+        return False
+    # lint
+    cmd = [RUFF, "check"]
+    if not check:
+        cmd.append("--fix")
+    result = subprocess.run(cmd + files)
     return result.returncode == 0