WORKSPACE.bazel

load("//support/bazel:python.bzl", "setup_venv")
load("//support/bazel:conan.bzl", "conan_install")

# We setup `venv` in which to install `conan`.
#
# This internally uses a `repository_rule()` to execute `pip install`
# inside the `venv` and expose `conan`.
#
# Ideally we would like to use `rules_python`, but that has two problems:
# 1) currently it does not generate a `py_binary()` for the entry points of a
# python dependency (https://github.com/bazelbuild/rules_python/issues/341) and
# 2) even if it would, we need a file that is available during the loading
# phase to be used in the `conan_install()` invocation below. A binary generated
# via `py_binary()` during  the build phase will not be usable.
setup_venv(
    name = "venv",
    quiet = False,
)

# Generate a `conanbuildinfo.json` and translate it into `variables.bzl`
# file that can be loaded.
#
# This internally uses a `repository_rule()` to install the `conan`
# dependencies. A python script is called to parse the `conanbuildinfo.json`
# and translate it into a `variables.bzl` file. This is the easiest approach
# instead of setting up a custom `bazel` generator for `conan` as the JSON
# already contains everything we need.
#
# We only need the `setup_venv()` call to get a `conan` executable. If
# we were to run in an environment where one is available, we could omit
# the previous step and pass `conan_binary` here instead of
# `conan_binary_target`.
#
# `conan.bzl` also exposes a `conan_repository()` for users that already have
# a `conanbuildinfo.json` available and don't want to run a `conan install`.
conan_install(
    name = "conan-generated",
    conan_binary_target = "@venv//:conan",
    conanfile = "//support/conan:conanfile.txt",
    lockfile = "//support/conan:conan.lock",
    quiet = False,
)

load("@conan-generated//:variables.bzl", conan_root_path = "ROOTPATH")

# The `conan_install()` does not setup `cc_library()` and `cc_binary()`
# targets for us. This might be an avenue for future improvments.
# Instead we generated the `variables.bzl` file from the `conanbuildinfo.json`
# which can be used to setup a `local_repository()` pointing to the `conan`
# cache / data directory via the `ROOTPATH` variable and requires a custom
# `build_file` where the user writes out the `cc_library()` and `cc_binary()`
# targets.
# Note: this will of course not work with the Windows `short_path` hack.
new_local_repository(
    name = "conan",
    build_file = "support/conan/CONAN_BUILD.bazel",
    path = conan_root_path,
)