Bazel - How to use platforms? - bazel

Question

I am trying to run a module with the platforms flag:
--platforms=//:gpu_server
If it is specified, it needs to load the following chunk of code in the WORKSPACE:
pip_parse(
name = "python_perception_libs",
requirements_lock = "//third_party:python_requirements_lock_perception.txt",
python_interpreter_target = "#python//:bin/python3",
)
load("#python_perception_libs//:requirements.bzl", "install_deps")
install_deps()
if it is not specified then it should load
pip_parse(
name = "python_libs",
requirements_lock = "//third_party:python_requirements_lock.txt",
python_interpreter_target = "#python//:bin/python3",
)
load("#python_libs//:requirements.bzl", "install_deps")
install_deps()
I have no clue how to actually approach this, and various experiments with select have yielded no results: For example:
# Define GPU constraint values
constraint_setting(name = "gpu")
constraint_value(name = "turing", constraint_setting = "gpu")
constraint_value(name = "ampere", constraint_setting = "gpu")
constraint_value(name = "none", constraint_setting = "gpu")
# Platform
platform(
name = "gpu_server",
constraint_values = [
"#platforms//os:linux",
"#platforms//cpu:x86_64",
":gpu",
],
)
select({
"#platforms//os:linux": {
pip_parse(
name = "python_perception_libs",
requirements_lock = "//third_party:python_requirements_lock_perception.txt",
python_interpreter_target = "#python//:bin/python3",
)
load("#python_perception_libs//:requirements.bzl", "install_deps")
install_deps()
},
"//conditions:default": {
pip_parse(
name = "python_libs",
requirements_lock = "//third_party:python_requirements_lock.txt",
python_interpreter_target = "#python//:bin/python3",
)
load("#python_libs//:requirements.bzl", "install_deps")
install_deps()
},
})
This does not work at all

Answer 1

WORKSPACE and BUILD files are more declarative than imperative (bzl files are imperative). select() isn't really like an if statement, it's more declaring the possible values an attribute can take, depending on what conditions are true at the the time the target is evaluated.
Similar to https://stackoverflow.com/a/71916582/6327445, declare both (using keyword arguments to disambiguate the symbols in the load() calls), and then elsewhere (e.g. in BUILD files) use one or the other, or use them in select():
pip_parse(
name = "python_perception_libs",
requirements_lock = "//third_party:python_requirements_lock_perception.txt",
python_interpreter_target = "#python//:bin/python3",
)
load("#python_perception_libs//:requirements.bzl", python_perception_libs_install_deps = "install_deps")
python_perception_libs_install_deps()
pip_parse(
name = "python_libs",
requirements_lock = "//third_party:python_requirements_lock.txt",
python_interpreter_target = "#python//:bin/python3",
)
load("#python_libs//:requirements.bzl", python_libs_install_deps = "install_deps")
python_libs_install_deps()
then in a BUILD file, could be something like this:
your_rule(
...
some_attribute = select({
":some_condition": "#python_perception_libs//package:target",
":other_condition": "#python_libs//package:target",
})
...
)
Your actual usage depends on what you're trying to do overall.