diff --git a/.github/skills/bazel/SKILL.md b/.github/skills/bazel/SKILL.md new file mode 100644 index 000000000000..dc30ce30c57f --- /dev/null +++ b/.github/skills/bazel/SKILL.md @@ -0,0 +1,175 @@ +--- +name: bazel +description: Conventions for editing Bazel files in the github/codeql repository: the shared `misc/bazel` helpers, `codeql_platform_select` and the `{CODEQL_PLATFORM}` packaging placeholder, adding `MODULE.bazel` dependencies, and the `semmle_code` stub that keeps the standalone build working. Use when editing any `BUILD.bazel`, `*.bzl`, `MODULE.bazel` or `.bazelrc` here, and before validating such an edit. +--- + +# Bazel in the codeql repository + +A bzlmod module named `ql`, repo name `@codeql` ([`MODULE.bazel`](../../../MODULE.bazel)). It builds standalone, and is +also consumed by an internal module; standalone builds replace that module with a stub. + +## Traps + +Things that will waste your time or produce a wrong edit here. Read this section even if you skip the rest. + +* **`//...` does not work.** `bazel build //...`, and even `bazel query //...`, fail at the repo root: the patched + modules under [`misc/bazel/registry`](../../../misc/bazel/registry) are real packages referencing repos that are not + visible from the main repo, and [`.bazelrc`](../../../.bazelrc) notes separately that transitions break `...` builds. + The error names a registry directory unrelated to your edit, so it is easy to misdiagnose. **Validate the specific + target or package you changed**, not a recursive pattern. +* **There is no `MODULE.bazel.lock`, deliberately.** [`.bazelrc`](../../../.bazelrc) sets `--lockfile_mode=off` because + the workspace-relative module override makes a lockfile unstable. Do not add one, and do not "fix" its absence. +* **`linux_arm64` vs `linux-arm64`.** The keyword argument and config setting use an underscore; the platform *string* + substituted into paths and zip names uses a hyphen. They are not interchangeable. +* **Do not stub your way out of a missing internal dependency.** See [Building standalone](#building-standalone) for the + one narrow case where extending the stub is correct. + +## Conventions + +* **Copy a neighboring target rather than inventing a shape.** Packaging is not uniform: some packages use the + `codeql_*` wrappers, others still use `pkg_files` directly. Copy the closest *working* neighbor, and prefer the + wrapper for new code. +* **Pin anything fetched over the network** with `sha256` or `integrity`. Bazel only *warns* on an unpinned download, so + nothing fails loudly, but the build stops being reproducible and a retagged upstream release silently changes what you + build. `lfs_archive` is the exception: content is pinned by git object. +* **Format with `bazel run //misc/bazel/buildifier`.** It rewrites in place, so do not hand-tune formatting. Also wired + as a `pre-commit` hook ([`.pre-commit-config.yaml`](../../../.pre-commit-config.yaml)). + +## Where new code goes + +Bazel's own macro / rule / repository-rule distinction applies as usual. What is repo-specific: + +| Adding | Goes in | +| --- | --- | +| a new packaging shape | extend [`misc/bazel/pkg.bzl`](../../../misc/bazel/pkg.bzl), do not fork `pkg_files` | +| a new OS or arch split | [`misc/bazel/os.bzl`](../../../misc/bazel/os.bzl), do not hand-roll a `select()` over `@platforms//` | +| a fetch of something external | a repository rule ([`lfs.bzl`](../../../misc/bazel/lfs.bzl), [`ripunzip.bzl`](../../../misc/ripunzip/ripunzip.bzl)), not a `genrule` | +| a wrapper used by one language | next to that language ([`swift/rules.bzl`](../../../swift/rules.bzl)) | +| a wrapper used across languages | `misc/bazel/` | + +Prefer inline rules in `BUILD.bazel`. A `.bzl` file earns its `load()` only when the shape repeats across packages or a +value must be computed: [`rust.bzl`](../../../misc/bazel/rust.bzl) is worth it because every Rust binary that ships in a +pack must get the same universal-binary wrapper and symbols test, and forgetting either is a release bug. A local +debugging aid opts out and declares a plain `rust_binary`; see `swift-syntax-parse` in +[`unified/swift-syntax-rs/BUILD.bazel`](../../../unified/swift-syntax-rs/BUILD.bazel). The `_gen_binaries` list in +[`go/BUILD.bazel`](../../../go/BUILD.bazel) does not earn a `.bzl`, because it is shared within a single file, where a +local variable does the job. + +Macros here are typically a thin public wrapper around a private rule (`codeql_csharp_binary`, `swift_cc_binary`). Keep +the rule narrow and the ergonomics in the macro. Each macro decorates the caller's `name` to mint its helper targets, +for example `internal/` or `single_arch/`. Their visibility is that macro's choice (private, package +default, or the caller's own), so read the macro instead of assuming. When an error names a target you cannot find in +any source file, a macro minted it: grep the suffix under `misc/bazel/`. + +## Shared helpers + +Frequently-used pieces, so you load the existing one instead of rewriting it. Read the file for its actual exports. + +| `load()` path | Covers | +| --- | --- | +| `//misc/bazel:pkg.bzl` | CodeQL packs and packaging | +| `//misc/bazel:os.bzl` | platform and architecture selection | +| `//misc/bazel:lfs.bzl` | on-demand git-LFS repositories | +| `//misc/bazel:rust.bzl` | Rust binary wrapper | +| `//misc/bazel:csharp.bzl` | C# binary/library/test wrappers | +| `//misc/bazel:utils.bzl` | `select_os`; prefer `os.bzl`'s `os_select` in new code | + +[`defs.bzl`](../../../defs.bzl) at the root exports `codeql_platform` for *dependent* modules. It is not the way to get +the platform string here; use `os.bzl`. + +## Platform selection + +[`codeql_platform_select`](../../../misc/bazel/os.bzl) takes one keyword argument per CodeQL platform: `linux64`, +`linux_arm64`, `osx64` and `win64`. `otherwise` supplies the value for whichever of those you leave unset; it is **not** +a `//conditions:default`. **There is deliberately no fallback from `linux_arm64` to `linux64`.** If you only care about +the OS, use `os_select`, which gives Linux the same value on both architectures and has a `posix` shorthand for the +shared Linux/macOS value. + +In a macro (no `ctx`) it returns a `select()`: + +```python +load("//misc/bazel:os.bzl", "codeql_platform_select") +load("//misc/bazel:pkg.bzl", "codeql_pkg_files") + +codeql_pkg_files( + name = "extractor-arch", + exes = codeql_platform_select( + otherwise = ["//unified/extractor"], + win64 = ["//unified/extractor-unsupported-os:extractor"], + ), + prefix = "tools/{CODEQL_PLATFORM}", +) +``` + +If implementation code needs to *branch* on the value rather than pass it through, pass `ctx` and add +`OS_DETECTION_ATTRS` to the rule's attributes. The value is then resolved eagerly instead of being an opaque `select()`: + +```python +load("//misc/bazel:os.bzl", "OS_DETECTION_ATTRS", "os_select") + +def _impl(ctx): + ext = os_select(ctx, windows = ".exe", posix = "") + ... + +my_rule = rule( + implementation = _impl, + attrs = {"src": attr.label()} | OS_DETECTION_ATTRS, +) +``` + +## Packs + +`codeql_pack` assembles the files that become an extractor pack. See [`unified/BUILD.bazel`](../../../unified/BUILD.bazel) +for a minimal complete example and [`pkg.bzl`](../../../misc/bazel/pkg.bzl) for the arguments. The non-obvious parts: + +* **`{CODEQL_PLATFORM}` in a destination path is the routing mechanism**, not just a substitution. A path containing it + is *arch-specific* and lands in the per-architecture zip; every other path is *common*. So `prefix = + "tools/{CODEQL_PLATFORM}"` both places the file and marks it arch-specific. `arch_overrides` forces named + destinations into the arch-specific part without a placeholder. +* **`codeql_pkg_files` splits `srcs` (plain) from `exes` (mode 755)** and **rejects `attributes =`** with an explicit + error. Use `exes` rather than hand-rolling `pkg_attributes(mode = "755")`. +* **`pkg_dirs` and `pkg_symlinks` are unsupported** and fail at analysis time. +* `codeql_pack` also generates an installer and an `install` alias, hence `bazel run //unified:install`. Pass + `installer_alias = None` if one package defines several packs. +* `codeql_pack_group` exists for bundling packs into distribution zips, but nothing in this repo instantiates it. + +## Adding a dependency + +In order of preference: + +1. **A [Bazel Central Registry](https://registry.bazel.build/) module.** Add a `bazel_dep` in + [`MODULE.bazel`](../../../MODULE.bazel). +2. **A patched upstream module.** Add it under [`misc/bazel/registry`](../../../misc/bazel/registry), which `.bazelrc` + puts ahead of the BCR. Put patches in `modules///patches`, rename the version with a `-codeql.N` + suffix, and run [`fix.py`](../../../misc/bazel/registry/fix.py) to realign the metadata. +3. **A raw archive.** Use `http_archive` via `use_repo_rule`, or a repository rule. Copy an adjacent declaration and + keep its checksum field populated. + +Vendored Rust crates under [`misc/bazel/3rdparty`](../../../misc/bazel/3rdparty) are generated. Regenerate with +[`update_cargo_deps.sh`](../../../misc/bazel/3rdparty/update_cargo_deps.sh) rather than editing, and keep the +`use_repo` lists in sync, which `bazel mod tidy` does for module extensions. + +## Building standalone + +[`MODULE.bazel`](../../../MODULE.bazel) declares `semmle_code` with a `local_path_override` pointing at `..`, which +resolves when this repo is checked out inside the internal module. [`.bazelrc`](../../../.bazelrc), which Bazel reads +when invoked in *this* workspace, overrides that with a stub. This line is the whole reason a standalone build resolves: + +``` +common --override_module=semmle_code=%workspace%/misc/bazel/semmle_code_stub +``` + +Do not change either the override path or the `local_path_override`; they work as a pair. + +[`misc/bazel/semmle_code_stub`](../../../misc/bazel/semmle_code_stub) is an otherwise empty module supplying no-op +versions of the internal helpers that shared `.bzl` files load *unconditionally*. That is its only job, and it is small +enough to read. + +**Extend the stub only when a `.bzl` file every standalone target loads gains a new internal `load()`**, which breaks +package loading outright, for everyone. Prefer not needing one. **Never add a stub so that an internal-only target +appears to build**: some targets depend on internal libraries (`grep -rl @semmle_code --include=*.bazel` finds them) and +are correctly unbuildable here. Unlike a `load()`, such a dependency only fails when that target is actually requested. + +[`.bazelrc.internal`](../../../.bazelrc.internal) is **not** read here; it carries settings for the internal build. A +setting needed by both has to be written in both files, with paths differing because this repo sits at a different depth +there.