Erlang Hello World using Bazel as a build system - erlang

Question

I want to build an Erlang hello world example using rules_erlang on Ubuntu 22.04.
My setup looks like this:
BUILD.bazel
load("#rules_erlang//:erlang_app.bzl", "erlang_app", "test_erlang_app")
load("#rules_erlang//:xref.bzl", "xref")
load("#rules_erlang//:dialyze.bzl", "dialyze", "plt")
load("#rules_erlang//:ct.bzl", "ct_suite", "assert_suites")
APP_NAME = "hello_world"
APP_VERSION = "0.1.0"
erlang_app(
app_name = APP_NAME,
app_version = APP_VERSION,
)
src/hello_world.erl
-module(hello_world).
-compile(export_all).
hello() ->
io:format("hello world~n").
WORKSPACE.bazel
load("#bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
http_archive(
name = "bazel_skylib",
sha256 = "af87959afe497dc8dfd4c6cb66e1279cb98ccc84284619ebfec27d9c09a903de",
urls = [
"https://mirror.bazel.build/github.com/bazelbuild/bazel-skylib/releases/download/1.2.0/bazel-skylib-1.2.0.tar.gz",
"https://github.com/bazelbuild/bazel-skylib/releases/download/1.2.0/bazel-skylib-1.2.0.tar.gz",
],
)
load("#bazel_skylib//:workspace.bzl", "bazel_skylib_workspace")
bazel_skylib_workspace()
http_archive(
name = "rules_erlang",
sha256 = "5e59800ecc786d5375951028c959c6e6275c94eff2a52f5d53ccb1ad8b2ea20a",
strip_prefix = "rules_erlang-3.8.4",
urls = ["https://github.com/rabbitmq/rules_erlang/archive/refs/tags/3.8.4.zip"],
)
load(
"#rules_erlang//:rules_erlang.bzl",
"erlang_config",
"rules_erlang_dependencies",
)
erlang_config()
rules_erlang_dependencies()
load("#erlang_config//:defaults.bzl", "register_defaults")
register_defaults()
The code can also found here.
When I execute bazel build //... I get
ERROR:
/home/vertexwahn/.cache/bazel/_bazel_vertexwahn/b5f945f94177a8ffa6ac0f7108dfc1cd/external/erlang_config/external/BUILD.bazel:12:16:
Validating otp at /usr failed: (Exit 1): bash failed: error executing
command /bin/bash -c ... (remaining 1 argument skipped)
Use --sandbox_debug to see verbose messages from the sandbox and
retain the sandbox build root for debugging Erlang version mismatch
(Expected UNKNOWN, found 24.2.1)
Any hints to get this working are welcome!

Answer 1

To run it, you can declare a shell rule in your BUILD.bazel, for instance:
load("#rules_erlang//:shell.bzl", "shell")
shell(
name = "repl",
deps = [":erlang_app"],
extra_erl_args = ["-eval", "'hello_world:hello()'"],
)
and then you could bazel run :repl.
Or, you could use an escript rule if you change hello_world.erl so that it exports main/1 instead of hello:
load("#rules_erlang//:escript.bzl", "escript_archive")
escript_archive(
name = "hello_world",
app = ":erlang_app",
)
hello_world.erl:
-module(hello_world).
-export([main/1]).
main(_) ->
io:format("hello world~n").
and run with bazel run :hello_world

Answer 2

bazel build //... --sandbox_debug
gave me
compile: warnings being treated as errors
hello_world.erl:2:2: export_all flag enabled - all functions will be exported
With -export([hello/0]). instead of -compile(export_all). it works
-module(hello_world).
-export([hello/0]).
hello() ->
io:format("hello world~n").
❯ bazel build //...
INFO: Analyzed 3 targets (0 packages loaded, 0 targets configured).
INFO: Found 3 targets...
INFO: Elapsed time: 0,326s, Critical Path: 0,25s
INFO: 2 processes: 1 internal, 1 darwin-sandbox.
INFO: Build completed successfully, 2 total actions