Cover top-level BUILD.bazel + MODULE.bazel in mdbook Bazel chapter.

[anforowicz]

PTAL?

The mdbook {{#include ...}} syntax is based on what I found in https://rust-lang.github.io/mdBook/format/mdbook.html#including-portions-of-a-file. I tested manually by running DISPLAY=:20 mdbook build -o under book/ and looking at the Bazel chapter.

I don't really use Bazel often, but I hope that including a more complete example helps. Not sure if a more canonical/reusable example is possible - I hope that Bazel experts if any can chime in with additional/future PRs if needed.

I understand that this PR probably doesn't directly help the reporter of #1676 (since they have more of a custom setup with an ad-hoc rust_binary target for cxxbridge-cmd and with cxxbridge-macro defined somewhere else (hopefully with a matching version).

[sayrer]

I understand that this PR probably doesn't directly help the reporter of #1676 (since they have more of a custom setup with an ad-hoc rust_binary target for cxxbridge-cmd and with cxxbridge-macro defined somewhere else (hopefully with a matching version).

It all matches, but the Bazel CXX docs leave this part unexplained:

        tool = "//:codegen",

I wish the cxxbridge command came as a separate target alongside "cxx" and "cxx_cc", which all works fine. Then, the version numbers would always match.

[anforowicz]

[...] the Bazel CXX docs leave this part unexplained:

        tool = "//:codegen",

Ack. After this PR the docs will cover //:codegen target which is defined in the top-level BUILD.bazel file - see

cxx/BUILD.bazel

Lines 23 to 27 in 2901aa8

	alias(
	name = "codegen",
	actual = ":cxxbridge",
	visibility = ["//visibility:public"],
	)