obazl_hello

Table of Contents

• Getting started
• Exercising the OCaml compilers

A Minimal Working Example demonstrating the use of

• rules_ocaml

• tools_opam

Getting started

Install Bazel. Then:

git clone https://github.com/obazl/obazl_hello.git
cd obazl_hello
bazel test //... --build_tests_only

You’ll see some messages the first time you build, while the extension configures a local opam switch; for example:

 Fetching module extension @@tools_opam+//extensions:opam.bzl%opam; Building @tools_opam//extensions/config
 Fetching ... @@tools_opam+//extensions:opam.bzl%opam; Creating local switch for compiler 5.3.0 at /path/to/obazl_hello 54s
Fetching module extension @@tools_opam+//extensions:opam.bzl%opam; Installing pkg ounit2 (0 of 1) 15s

You can run the tests individually:

bazel test src/hello:test
bazel test src/goodbye:test

Note

This is an alpha version. There is still some flakiness in some situations involving opam commands (like creating a switch) that I haven’t worked out. If you see error messages, try running the build again. You may need to run bazel clean --expunge. Once your switch is properly configured (which you can do manually if you prefer), you should not see such errors. If you do, please file an issue.

The tools_opam module extension opam supports three different toolchain strategies, local, global, and xdg. See tools_opam for more information and instructions on how to use them.

Exercising the OCaml compilers

The standard OCaml distribution comes with four basic compilers (ocamlopt.opt`, `+ocamlc.byte, ocamlopt.byte`, and `+ocamlc.opt`) plus a profiling frontend (`+ocamlcp). Furthermore, the compilers may be configured in a variety of ways: with a debug-runtime, or the flambda optimizer, and so forth.

The OBazl rules (rules_ocaml) support the four basic compilers out of the box. In this demo you can see how they are configured in ./config/toolchains.bazelrc. To select one, pass --config=<compiler> on the command line; e.g.

$ bazel build src/hello:test --config=ocamlc.byte

Warning

The implementation and syntax of this feature will change in the near future, but the concept will remain the same.

By default, Bazel reads a variety of bazelrc files, such as $HOME/.bazelrc and <projroot>/.bazelrc. (See Write bazelrc configuration files for more information.) This may induce a dependency on the local system, so to prepare a project for release you need to build and test everything without depending on such files. That is the purpose of such start-up options as --nohome_rc, --nosystem_rc, etc. (Run $ bazel startup_options help to see a list of all startup options.)

As an example of one way to do this, see tools/release_build and tools/release_test.

Note that:

• $ bazel test //... will build all targets and run all tests

• $ bazel test //... --build_tests_only will run all tests but only build targets required by the tests