rust

Basic Rust example with Bazel

Goal

Show how to build and execute a binary, how to build a crate, and how to build and run a test.

About the example

In this example we have declared 3 targets. A library crate, an executable, and a test. The binary and the test depends on the library crate.

• //:my_lib: A library crate with a single rs file containing unit tests in the same file. It can be defined in Bazel as follows:

  rust_library(
      name = "my_lib",
      srcs = ["my_lib.rs"],
  )

  name is the name for the target, it will also be used to create the library file in the form of lib<name>-<hash>.rlib.

  srcs is the list of source files needed to generate the create. If more than one file is provided, at least one must be called lib.rs or the parameter crate_root must be provided specifying the root of the crate.

• //:hello_world: A binary that depends on the library mentioned above. It can be defined in Bazel as follows:

  rust_binary(
      name = "hello_world",
      srcs = ["hello_world.rs"],
      deps = [":my_lib"],
  )

  name is the name for the target, it will also be used to create the executable file in the form of <name> in Unix systems or <name>.exe in Windows systems.

  srcs is the list of source files needed to generate the executable.

  deps is the list of libraries that your binary depends on. In this case we specify the target :my_lib that is the library that we want to use in this binary.

• //:my_test: A test for target for the tests inside the my_lib target. In the end it is an executable also but Bazel will treat it different in several aspects. It can be defined in Bazel as follows:

  rust_test(
      name = "my_test",
      crate = ":my_lib",
  )

  name is the name for the target, it will also be used to create the executable file for the test in the form of <name> in Unix systems or <name>.exe in Windows systems.

  crate is the name of the target crate that contains the tests. Typically the crate being tested.

How to try it out

To run the executable you call:

bazel run //:hello_world

It will run the executable and display the output on the terminal.

To run the test you call:

bazel test //:my_test

It will run the test without showing any output from the test but a Bazel output indicating if the test succeeded or failed.

//:my_test                    PASSED in 0.0s

A test, compared to a binary executed with bazel run will not be allways executed. If Bazel detects that nothing changed it will cache the result of th test and show it in the report.

//:my_test           (cached) PASSED in 0.0s

If you want to build the executable without running it you call:

bazel build //:hello_world

And if you want to build only the library you can do the same with the target of the library:

bazel build //:my_lib