174 lines
6.3 KiB
Markdown
174 lines
6.3 KiB
Markdown
# Development Guidelines
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This document contains critical information about working with this codebase. Follow these guidelines precisely.
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## Core Development Rules
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1. Package Management
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- ONLY use uv, NEVER pip
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- Installation: `uv add <package>`
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- Running tools: `uv run <tool>`
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- Upgrading: `uv lock --upgrade-package <package>`
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- FORBIDDEN: `uv pip install`, `@latest` syntax
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2. Code Quality
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- Type hints required for all code
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- Public APIs must have docstrings
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- Functions must be focused and small
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- Follow existing patterns exactly
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- Line length: 120 chars maximum
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- FORBIDDEN: imports inside functions. THEY SHOULD BE AT THE TOP OF THE FILE.
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3. Testing Requirements
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- Framework: `uv run --frozen pytest`
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- Async testing: use anyio, not asyncio
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- Do not use `Test` prefixed classes, use functions
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- Coverage: test edge cases and errors
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- New features require tests
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- Bug fixes require regression tests
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- IMPORTANT: The `tests/client/test_client.py` is the most well designed test file. Follow its patterns.
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- IMPORTANT: Be minimal, and focus on E2E tests: Use the `mcp.client.Client` whenever possible.
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- Coverage: CI requires 100% (`fail_under = 100`, `branch = true`).
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- Full check: `./scripts/test` (~23s). Runs coverage + `strict-no-cover` on the
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default Python. Not identical to CI: CI also runs 3.10–3.14 × {ubuntu, windows},
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and some branch-coverage quirks only surface on specific matrix entries.
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- Targeted check while iterating (~4s, deterministic):
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```bash
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uv run --frozen coverage erase
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uv run --frozen coverage run -m pytest tests/path/test_foo.py
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uv run --frozen coverage combine
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uv run --frozen coverage report --include='src/mcp/path/foo.py' --fail-under=0
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UV_FROZEN=1 uv run --frozen strict-no-cover
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```
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Partial runs can't hit 100% (coverage tracks `tests/` too), so `--fail-under=0`
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and `--include` scope the report. `strict-no-cover` has no false positives on
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partial runs — if your new test executes a line marked `# pragma: no cover`,
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even a single-file run catches it.
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- Coverage pragmas:
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- `# pragma: no cover` — line is never executed. CI's `strict-no-cover` fails if
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it IS executed. When your test starts covering such a line, remove the pragma.
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- `# pragma: lax no cover` — excluded from coverage but not checked by
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`strict-no-cover`. Use for lines covered on some platforms/versions but not
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others.
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- `# pragma: no branch` — excludes branch arcs only. coverage.py misreports the
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`->exit` arc for nested `async with` on Python 3.11+ (worse on 3.14/Windows).
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- Avoid `anyio.sleep()` with a fixed duration to wait for async operations. Instead:
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- Use `anyio.Event` — set it in the callback/handler, `await event.wait()` in the test
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- For stream messages, use `await stream.receive()` instead of `sleep()` + `receive_nowait()`
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- Exception: `sleep()` is appropriate when testing time-based features (e.g., timeouts)
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- Wrap indefinite waits (`event.wait()`, `stream.receive()`) in `anyio.fail_after(5)` to prevent hangs
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Test files mirror the source tree: `src/mcp/client/streamable_http.py` → `tests/client/test_streamable_http.py`
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Add tests to the existing file for that module.
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- For commits fixing bugs or adding features based on user reports add:
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```bash
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git commit --trailer "Reported-by:<name>"
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```
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Where `<name>` is the name of the user.
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- For commits related to a Github issue, add
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```bash
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git commit --trailer "Github-Issue:#<number>"
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```
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- NEVER ever mention a `co-authored-by` or similar aspects. In particular, never
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mention the tool used to create the commit message or PR.
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## Pull Requests
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- Create a detailed message of what changed. Focus on the high level description of
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the problem it tries to solve, and how it is solved. Don't go into the specifics of the
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code unless it adds clarity.
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- NEVER ever mention a `co-authored-by` or similar aspects. In particular, never
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mention the tool used to create the commit message or PR.
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## Breaking Changes
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When making breaking changes, document them in `docs/migration.md`. Include:
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- What changed
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- Why it changed
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- How to migrate existing code
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Search for related sections in the migration guide and group related changes together
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rather than adding new standalone sections.
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## Python Tools
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## Code Formatting
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1. Ruff
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- Format: `uv run --frozen ruff format .`
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- Check: `uv run --frozen ruff check .`
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- Fix: `uv run --frozen ruff check . --fix`
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- Critical issues:
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- Line length (88 chars)
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- Import sorting (I001)
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- Unused imports
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- Line wrapping:
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- Strings: use parentheses
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- Function calls: multi-line with proper indent
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- Imports: try to use a single line
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2. Type Checking
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- Tool: `uv run --frozen pyright`
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- Requirements:
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- Type narrowing for strings
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- Version warnings can be ignored if checks pass
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3. Pre-commit
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- Config: `.pre-commit-config.yaml`
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- Runs: on git commit
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- Tools: Prettier (YAML/JSON), Ruff (Python)
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- Ruff updates:
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- Check PyPI versions
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- Update config rev
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- Commit config first
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## Error Resolution
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1. CI Failures
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- Fix order:
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1. Formatting
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2. Type errors
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3. Linting
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- Type errors:
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- Get full line context
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- Check Optional types
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- Add type narrowing
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- Verify function signatures
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2. Common Issues
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- Line length:
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- Break strings with parentheses
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- Multi-line function calls
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- Split imports
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- Types:
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- Add None checks
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- Narrow string types
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- Match existing patterns
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3. Best Practices
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- Check git status before commits
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- Run formatters before type checks
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- Keep changes minimal
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- Follow existing patterns
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- Document public APIs
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- Test thoroughly
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## Exception Handling
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- **Always use `logger.exception()` instead of `logger.error()` when catching exceptions**
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- Don't include the exception in the message: `logger.exception("Failed")` not `logger.exception(f"Failed: {e}")`
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- **Catch specific exceptions** where possible:
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- File ops: `except (OSError, PermissionError):`
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- JSON: `except json.JSONDecodeError:`
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- Network: `except (ConnectionError, TimeoutError):`
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- **FORBIDDEN** `except Exception:` - unless in top-level handlers
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