Drop the preview-only lint rule, gate the pre-commit hook too, tolerate a BOM in the Claude config

maxisbey · maxisbey · commit dbf7dca8c209 · 2026-08-14T10:49:24.000Z
- pyproject.toml: remove PLW1514 and lint.preview. Preview mode also changes
  stable rules on ruff upgrades (0.15.x flags a load-bearing `import mcp` as
  a fixable F401), which costs more than an incomplete edit-time check buys;
  the EncodingWarning gate is the enforcement.
- .pre-commit-config.yaml: run the README snippet check with the same
  -X warn_default_encoding -W error::EncodingWarning flags as CI.
- mcp install: read claude_desktop_config.json as utf-8-sig so a BOM written
  by Windows tooling doesn't make a valid config unreadable; the rewrite stays
  plain UTF-8. The existing test seeds a BOM.
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
@@ -56,7 +56,7 @@ repos:
         pass_filenames: false
       - id: readme-snippets
         name: Check README snippets are up to date
-        entry: uv run --frozen python scripts/update_readme_snippets.py --check
+        entry: uv run --frozen python -X warn_default_encoding -W error::EncodingWarning scripts/update_readme_snippets.py --check
         language: system
         files: ^(README\.md|docs_src/.*\.py|scripts/update_readme_snippets\.py)$
         pass_filenames: false
diff --git a/AGENTS.md b/AGENTS.md
@@ -48,8 +48,8 @@
   tests that re-import a module).
 - Always pass `encoding=` (normally `"utf-8"`) to text-mode `open()`,
   `Path.read_text()`/`write_text()`, `tempfile` and `subprocess` text pipes: the
-  default is the process locale, not UTF-8. CI enforces this via
-  `PYTHONWARNDEFAULTENCODING=1` (PEP 597) under pytest's `error` filter, plus ruff `PLW1514`.
+  default is the process locale, not UTF-8. CI enforces this by running pytest with
+  `PYTHONWARNDEFAULTENCODING=1` (PEP 597), which makes any omission an error under the `error` filter.
 
 ## Testing
 
diff --git a/pyproject.toml b/pyproject.toml
@@ -195,11 +195,6 @@ line-length = 120
 target-version = "py310"
 
 [tool.ruff.lint]
-# lint.preview is required to select PLW1514 (text I/O without encoding=); it also opts the stable rules into their
-# preview behaviours and fixes. explicit-preview-rules only stops the prefixes below pulling in other preview rules.
-preview = true
-explicit-preview-rules = true
-extend-select = ["PLW1514"]
 select = [
     "C4",     # flake8-comprehensions
     "C90",    # mccabe
diff --git a/src/mcp/cli/claude.py b/src/mcp/cli/claude.py
@@ -103,7 +103,7 @@ def update_claude_config(
             return False
 
     try:
-        config = json.loads(config_file.read_text(encoding="utf-8"))
+        config = json.loads(config_file.read_text(encoding="utf-8-sig"))
         if "mcpServers" not in config:
             config["mcpServers"] = {}
 
diff --git a/tests/cli/test_claude.py b/tests/cli/test_claude.py
@@ -141,10 +141,10 @@ def test_existing_env_vars_preserved_without_new(config_dir: Path):
 
 
 def test_other_servers_preserved(config_dir: Path):
-    """Installing a new server must not clobber existing entries, non-ASCII text included (the file is UTF-8)."""
+    """Installing a new server must not clobber existing entries, non-ASCII text included (UTF-8, BOM tolerated)."""
     other = {"command": "C:\\Users\\张伟\\uv.exe", "env": {"CITY": "Zürich"}}
     config_file = config_dir / "claude_desktop_config.json"
-    config_file.write_text(json.dumps({"mcpServers": {"文件": other}}, ensure_ascii=False), encoding="utf-8")
+    config_file.write_text(json.dumps({"mcpServers": {"文件": other}}, ensure_ascii=False), encoding="utf-8-sig")
 
     assert update_claude_config(file_spec="s.py:app", server_name="s")
 
