Monorepo: is it possible to read dependencies from package.json?

[spion]

I read through the docs but I couldn't figure out how to set up bazel for a classic lerna / yarn monorepo. Specifically, I can't figure out if its possible to read the dependencies for a bazel rule from another file i.e. package.json

What I like is to avoid duplication of specifying the dependencies twice, once in package.json for npm/yarn publishing and consumption/installation by other users, and once in Bazel for building via TypeScript in the right order.

Ideally I would have deps be generated from reading the toplevel package.json workspaces entry globs, filtered through the individual package's own dependencies and devDependencies as specified in package.json

[pierreis]

I believe what you could do is to write a Bazel macro that takes dependencies as parameters, and based on these dependencies:

• instantiates the ts_library rule
• populates the replacements parameters of npm_package accordingly, so that a placeholder in your package.json is replaced by the actual dependencies.

Something along these lines:

def _format_dep(name, version):
    name = "@prefix/" + name[11:]
    return "\"{}\": \"^{}\"".format(name, version)

def my_ts_library(name, deps = [], dev_deps = [], **kwargs):

    ts_library(
        name = name,
        deps = deps + dev_deps,
        **kwargs
    )

    replacements = {
        "\"DEPS_PLACEHOLDER\": \"\"": ",\n    ".join(
            [
                _format_dep(dep, "0.0.1") for dep in deps 
                if dep.startswith("//packages/")
            ]
        ),
        "\"DEV_DEPS_PLACEHOLDER\": \"\"": ",\n    ".join(
            [
                _format_dep(dep, "0.0.1") for dep in dev_deps
                if dep.startswith("//packages/")
            ]
        ),
    }

    npm_package(
        name = name + "-package",
        srcs = [":package.json"],
        deps = [":" + name] + deps,
        replacements = replacements,
    )

With a package.json formatted as:

{
  "name": "@prefix/mypackage",
  "version": "0.0.0-PLACEHOLDER",
  "dependencies": {
    "DEPS_PLACEHOLDER": ""
  },
  "devDependencies": {
    "DEV_DEPS_PLACEHOLDER": ""
  }
}

Alternatively, I would write a genfile rule generating the package.json file based on your dependencies

[alexeagle]

You're right, the deps are repeated right now.
In google, we don't use package.json files at all, so we accidentally brought that idiom with us. I think the best thing is for you to write package.json files in each package, and something like Gazelle generates BUILD files so that Bazel understands the package too.

[gregmagolan]

No longer in scope for rules_nodejs