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gomock for Bazel

This skylark code allows you to generate code with mockgen (from golang/mock) and use that code as a dependency in your bazel projects. It handles all the GOPATH stuff for you.

Setup

bazel_gomock requires a rules_go external to be set up in your WORKSPACE as well as a go_repository call for com_github_golang_mock.

Then in your WORKSPACE, add

# This commit is tagged as v1.3
bazel_gomock_commit = "fde78c91cf1783cc1e33ba278922ba67a6ee2a84"
http_archive(
    name = "bazel_gomock",
    sha256 = "692421b0c5e04ae4bc0bfff42fb1ce8671fe68daee2b8d8ea94657bb1fcddc0a",
    strip_prefix = "bazel_gomock-{v}".format(v = bazel_gomock_commit),
    urls = [
        "https://github.com/jmhodges/bazel_gomock/archive/{v}.tar.gz".format(v = bazel_gomock_commit),
    ],
)

An example of a com_github_golang_mock you'd need:

go_repository(
    name = "com_github_golang_mock",
    importpath = "github.com/golang/mock",
    sum = "h1:l75CXGRSwbaYNpl/Z2X1XIIAMSCquvXgpVZDhwEIJsc=",
    version = "v1.4.4",
)

Use

Once your WORKSPACE is set up, you can call gomock in your BUILD files like:

load("@bazel_gomock//:gomock.bzl", "gomock")

gomock(
    name = "mock_sess",
    out = "mock_sess_test.go",
    interfaces = ["SessionsClient"],
    library = "//proto/sessions/sessproto:go_default_library",
    package = "main",
)

where library is a go_library target, interfaces is the list of names of the Go interfaces you'd like mockgen to generate mocks of, package is the name of the Go package at the top of the generated file (in this example, package "main"), and out is the path of generated source file that will be made.

There is also a source parameter described below.

You use this target's out file directly in the srcs parameter in go_test, go_library, and so on. So, when the above example gomock call is used in the same BUILD file, you put mock_sess_test.go in the srcs parameter like so:

go_test(
    name = "go_default_test",
    srcs = [
         "cool_test.go",
         "mock_sess_test.go",
    ],
    embed = [":go_default_library"]
    ...
)

If you need to generate mocks from a specific Go file instead of a import path (say, because the go_library you have is a main package and is therefore unreflectable by Go tools and specifically unimportable by mockgen), add the source parameter with the location of source file. E.g. source = "//fancy/path:foo.go" or just source = "foo.go" if the file is in the same directory). The library parameter must still be set to the library that source file lives in so that any referenced dependencies can be pulled into the Go path.

Also, gazelle will remove the generated source file from a go_test target's srcs unless you end the generated file name with _test.go.

As a likely unused feature, you can pass in an alternative external for where to find the mockgen tool target using the mockgen_tool parameter. The only rule for the target is that must be a binary. The current default is "@com_github_golang_mock//mockgen".

If you try to use gomock on a go_library that is in the package main (and so probably being immediately used as an embed target for a go_binary), you'll get an annoying error like:

prog.go:13:2: import "your/main/package/deal" is a program, not an importable package

You can resolve that by setting the source parameter to the location of the file with the interfaces you want in it.

gomock arguments:

Name Default value Type Documentation
name string The name of the target. (Required.)
library Label The go_library to find the interfaces in. (Required.)
interfaces list of string The names of interfaces in library to generate mocks for. (Required if source is not set, and ignored if source is set.)
source string Prefer using library only, instead of using this argument. The Go source file to generate interfaces from. If this is set, interfaces is ignored because mockgen will always generate code for all interfaces. See the gomock documentation on -source for more information.
out string The file name to give the generated output. (Required.)
package string The package name to use in the generated output. See the gomock documentation on -package for more information.
imports string_dict Dictionary of keys of package names and values of import paths to use the keys as the identifier to use when the generated output uses the given import path. See the gomock documentation on -imports for more information.
self_package string The full import path for the generated code. See the gomock documentation on -self_package for more information.
mock_names string_dict Dictionary of interface name to mock name pairs to change the output names of the mock objects. Mock names default to 'Mock' prepended to the name of the interface. See the gomock documentation on -mock_names for more information.
copyright_file Label The file containing the copyright to prepend to the generated output. See the gomock documentation on -copyright_file for more information.
aux_files string_list_dict A map from packages to auxilliary Go source files to load for those packages. Currently, assumes that the file (the value) is a path relative to the directory of library in the GOPATH. See the gomock documentation on -aux_files for more information.