[CI/Build] Add bc-linter to vLLM CI (#21234)

Signed-off-by: zhewenli <zhewenli@meta.com>

.github/.bc-linter.yml

+# doc: https://github.com/pytorch/test-infra/blob/main/tools/stronghold/docs/bc_linter_config.md
+version: 1
+paths:
+# We temporarily disable globally, and will only enable with `annotations.include`
+# include:
+#   - "vllm/v1/attetion/*.py"
+#   - "vllm/v1/core/*.py"
+exclude:
+  - "**/*.py"
+
+scan:
+  functions: true        # check free functions and methods
+  classes: true          # check classes/dataclasses
+  public_only: true      # ignore names starting with "_" at any level
+
+annotations:
+  include:               # decorators that force‑include a symbol
+    - name: "bc_linter_include"  # matched by simple name or dotted suffix
+      propagate_to_members: false # for classes, include methods/inner classes
+  exclude:               # decorators that force‑exclude a symbol
+    - name: "bc_linter_skip"     # matched by simple name or dotted suffix
+      propagate_to_members: true  # for classes, exclude methods/inner classes
+
+excluded_violations: []  # e.g. ["ParameterRenamed", "FieldTypeChanged"]

.github/workflows/bc-lint.yml

+name: BC Lint
+
+on:
+  pull_request:
+    types:
+      - opened
+      - synchronize
+      - reopened
+
+jobs:
+  bc_lint:
+    if: github.repository_owner == 'vllm-project'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Run BC Lint Action
+        uses: pytorch/test-infra/.github/actions/bc-lint@main
+        with:
+          repo: ${{ github.event.pull_request.head.repo.full_name }}
+          base_sha: ${{ github.event.pull_request.base.sha }}
+          head_sha: ${{ github.event.pull_request.head.sha }}
+          suppression: ${{ contains(github.event.pull_request.labels.*.name, 'suppress-bc-linter') }}
+          docs_link: 'https://github.com/pytorch/test-infra/wiki/BC-Linter'
+          config_dir: .github
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.sha }}
+  cancel-in-progress: true

vllm/__init__.py

@@ -14,6 +14,8 @@ import typing
 import vllm.env_override  # noqa: F401
 
 MODULE_ATTRS = {
+    "bc_linter_skip": "._bc_linter:bc_linter_skip",
+    "bc_linter_include": "._bc_linter:bc_linter_include",
     "AsyncEngineArgs": ".engine.arg_utils:AsyncEngineArgs",
     "EngineArgs": ".engine.arg_utils:EngineArgs",
     "AsyncLLMEngine": ".engine.async_llm_engine:AsyncLLMEngine",
@@ -54,6 +56,8 @@ if typing.TYPE_CHECKING:
                               ScoringRequestOutput)
     from vllm.pooling_params import PoolingParams
     from vllm.sampling_params import SamplingParams
+
+    from ._bc_linter import bc_linter_include, bc_linter_skip
 else:
 
     def __getattr__(name: str) -> typing.Any:
@@ -70,6 +74,8 @@ else:
 
 __all__ = [
     "__version__",
+    "bc_linter_skip",
+    "bc_linter_include",
     "__version_tuple__",
     "LLM",
     "ModelRegistry",

vllm/_bc_linter.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# vllm/_bc_linter.py
+from __future__ import annotations
+
+from typing import Any, Callable, TypeVar, overload
+
+T = TypeVar("T")
+
+
+@overload
+def bc_linter_skip(obj: T) -> T:
+    ...
+
+
+@overload
+def bc_linter_skip(*, reason: str | None = ...) -> Callable[[T], T]:
+    ...
+
+
+def bc_linter_skip(obj: Any = None, *, reason: str | None = None):
+    """
+    No-op decorator to mark symbols/files for BC-linter suppression.
+
+    Usage:
+        @bc_linter_skip
+        def legacy_api(...): ...
+    """
+
+    def _wrap(x: T) -> T:
+        return x
+
+    return _wrap if obj is None else obj
+
+
+@overload
+def bc_linter_include(obj: T) -> T:
+    ...
+
+
+@overload
+def bc_linter_include(*, reason: str | None = ...) -> Callable[[T], T]:
+    ...
+
+
+def bc_linter_include(obj: Any = None, *, reason: str | None = None):
+    """
+    Usage:
+        @bc_linter_include
+        def public_api(...): ...
+    """
+
+    def _wrap(x: T) -> T:
+        return x
+
+    return _wrap if obj is None else obj
+
+
+__all__ = ["bc_linter_skip", "bc_linter_include"]

vllm/v1/core/sched/output.py

@@ -6,6 +6,8 @@ from __future__ import annotations
 from dataclasses import dataclass
 from typing import TYPE_CHECKING, Optional
 
+from vllm import bc_linter_include
+
 if TYPE_CHECKING:
     import numpy as np
     import numpy.typing as npt
@@ -19,6 +21,7 @@ if TYPE_CHECKING:
     from vllm.v1.request import Request
 
 
+@bc_linter_include
 @dataclass
 class NewRequestData:
 
@@ -80,6 +83,7 @@ class NewRequestData:
                 ")")
 
 
+@bc_linter_include
 @dataclass
 class CachedRequestData:
 
@@ -109,6 +113,7 @@ class CachedRequestData:
         )
 
 
+@bc_linter_include
 @dataclass
 class SchedulerOutput: