feat: patch includes in MODULE.bazel when publishing

[jjmaestro]

MODULE.bazel can use include to organize dependencies but, per the docs:

Only the root module may use include(); it is an error if a bazel_dep's MODULE file uses include().

In Slack Thread @fmeum suggested that

combining all the [include] segments into a single MODULE.bazel file could be a feature of a tool based on the buildozer API
(...)
the tool needs to rename top-level variables that conflict. Or use a pattern such as IIFE (immediately invoked function expression).
(...)
It could even be combined with the Publish to BCR app to automatically patch in the full module file content

It would be great to have such a tool and/or automation in the BCR tools!

[fmeum]

I'll bring this up at the next Rules Authors SIG meeting.

[jjmaestro]

Here's a couple more things I thought about:

"pattern"

Maybe a "pattern" that could work nicely would be to invoke such a tool from a tools/bazel wrapper. Something like:

• move MODULE.bazel to includes.MODULE.bazel at the root
• add MODULE.bazel to .gitignore
• have a wrapper in tools/bazel that invokes the tool which parses include.MODULE.bazel and materializes the MODULE.bazel

IMHO it would be ideal if buildozer had an expand_include command that would perform the recursive expansion.

renaming variables

For the renaming of the variables, the tool could probably use the path to the include file plus the MODULE prefix, e.g.:

# includes.MODULE.bazel at the root
include("//dir1/dir2/foo.MODULE.bazel")

bar = use_extension("//other/path:extension.bzl", "bar")

# dir1/dir2/foo.MODULE.bazel

bar = use_extension("//1/2/3:extension.bzl", "bar")

These would expand to:

# MODULE.bazel at the root

# include("//dir1/dir2/foo.MODULE.bazel")
dir1_dir2_foo_bar = use_extension("//1/2/3:extension.bzl", "bar")

bar = use_extension("//other/path:extension.bzl", "bar")

[fmeum]

We discussed this in the Rules Authors SIG meeting and would consider funding the development of a standalone tool (e.g. in Go or Rust) that consumes a segmented module file and combines it into a single module file that can be submitted to the BCR.

Before the SIG commits to funding this tool, we would like to make sure that it will be reasonably popular. If you would like to see this implemented, please upvote! If you would consider working on this, please speak up.