Skip to content

Latest commit

 

History

History
335 lines (274 loc) · 14.1 KB

README.rst

File metadata and controls

335 lines (274 loc) · 14.1 KB
Raw

Gazelle build file generator

Gazelle is a build file generator for Go projects. It can create new BUILD.bazel files for a project that follows "go build" conventions, and it can update existing build files to include new files and options. Gazelle can be invoked directly in a project workspace, or it can be run on an external repository during the build as part of the go_repository rule.

Gazelle is under active development. Its interface and the rules it generates may change.

Contents

Setup

Running Gazelle with Bazel

To use Gazelle in a new project, add the following to the BUILD or BUILD.bazel file in the root directory of your repository:

load("@io_bazel_rules_go//go:def.bzl", "gazelle")

gazelle(
    name = "gazelle",
    prefix = "github.com/example/project",
)

Replace the string in prefix with the portion of your import path that corresponds to your repository.

After adding those rules, run the command below:

bazel run //:gazelle

This will generate new BUILD.bazel files for your project. You can run the same command in the future to update existing BUILD.bazel files to include new source files or options.

Running Gazelle separately

If you have a Go SDK installed, you can install Gazelle in your GOPATH with the command below:

go get -u github.com/bazelbuild/rules_go/go/tools/gazelle/gazelle

Make sure to re-run this command to upgrade Gazelle whenever you upgrade rules_go in your repository.

To generate BUILD.bazel files in a new project, run the command below, replacing the prefix with the portion of your import path that corresponds to your repository.

gazelle -go_prefix github.com/my/project

The prefix only needs to be specified the first time you run Gazelle. To update existing BUILD.bazel files, you can just run gazelle without arguments.

Usage

Command line

gazelle <command> [flags...] [package-dirs...]

The first argument to Gazelle may be one of the commands below. If no command is specified, update is assumed.

Commands
update Gazelle will create new build files and update existing build files. New rules may be created. Files, dependencies, and other options may be added or removed from existing rules.
| from existing rules. |

Gazelle accepts a list Go of package directories to process. If no directories are given, it defaults to the current directory when run on the command line or the repository root when run with Bazel. It recursively traverses subdirectories.

Gazelle accepts the following flags:

Name Default value
-build_file_name file1,file2,... BUILD.bazel,BUILD
Comma-separated list of file names. Gazelle recognizes these files as Bazel build files. New files will use the first name in this list. Use this if your project contains non-Bazel files named BUILD (or build on case-insensitive file systems).
-build_tags tag1,tag2  
List of Go build tags Gazelle will consider to be true. Gazelle applies constraints when generating Go rules. It assumes certain tags are true on certain platforms (for example, amd64,linux). It assumes all Go release tags are true (for example, go1.8). It considers other tags to be false (for example, ignore). This flag overrides that behavior.
-external external|vendored external
Determines how Gazelle resolves import paths. May be external or vendored. Gazelle translates Go import paths to Bazel labels when resolving library dependencies. Import paths that start with the go_prefix are resolved to local labels, but other imports are resolved based on this mode. In external mode, paths are resolved using an external dependency in the WORKSPACE file (Gazelle does not create or maintain these dependencies yet). In vendored mode, paths are resolved to a library in the vendor directory.
-go_prefix example.com/repo  

A prefix of import paths for libraries in the repository that corresponds to the repository root. Gazelle infers this from the go_prefix rule in the root BUILD.bazel file, if it exists. If not, this option is mandatory.

This prefix is used to determine whether an import path refers to a library in the current repository or an external dependency.
-known_import example.com  

Skips import path resolution for a known domain. May be repeated.

When Gazelle resolves an import path to an external dependency, it attempts to discover the remote repository root over HTTP. Gazelle skips this discovery step for a few well-known domains with predictable structure, like golang.org and github.com. This flag specifies additional domains to skip, which is useful in situations where the lookup would fail for some reason.
-mode fix|print|diff fix

Method for emitting merged build files.

In fix mode, Gazelle writes generated and merged files to disk. In print mode, it prints them to stdout. In diff mode, it prints a unified diff.
-proto default|legacy|disable default
Determines how Gazelle should generate rules for .proto files. See details in Directives below.
-repo_root dir  

The root directory of the repository. Gazelle normally infers this to be the directory containing the WORKSPACE file.

Gazelle will not process packages outside this directory.

Bazel rule

When Gazelle is run by Bazel, most of the flags above can be encoded in the gazelle macro. For example:

load("@io_bazel_rules_go//go:def.bzl", "gazelle")

gazelle(
    name = "gazelle",
    command = "fix",
    prefix = "github.com/example/project",
    external = "vendored",
    build_tags = [
        "integration",
        "debug",
    ],
    args = [
        "-build_file_name",
        "BUILD,BUILD.bazel",
    ],
)

Directives

Gazelle supports several directives, written as comments in build files.

  • # gazelle:ignore: may be written at the top level of any build file. Gazelle will not update files with this comment.
  • # gazelle:exclude path: may be written at the top level of any build file. If the path refers to a source file, Gazelle won't include it in any rules. If the path refers to a directory, Gazelle won't recurse into it. The path may refer to something in a subdirectory, for example, a testdata directory somewhere in a vendor tree. This directive may be repeated to exclude multiple paths, one per line.
  • # gazelle:proto <mode>: Tells Gazelle how to generate rules for .proto files. Applies to the current directory and subdirectories. Valid values for mode are:
    • default: proto_library, go_proto_library, go_grpc_library, and go_library rules are generated using @io_bazel_rules_go//proto:def.bzl. This is the default mode.
    • legacy: filegroup rules are generated for use by @io_bazel_rules_go//proto:go_proto_library.bzl. go_proto_library rules must be written by hand. Gazelle will run in this mode automatically if go_proto_library.bzl is loaded to avoid disrupting existing projects, but this can be overridden with a directive.
    • disable: .proto files are ignored. Gazelle will run in this mode automatically if go_proto_library is loaded from any other source, but this can be overridden with a directive.
  • # keep: may be written before a rule to prevent the rule from being updated or after a source file, dependency, or flag to prevent it from being removed.

Example

Suppose you have a library that includes a generated .go file. Gazelle won't know what imports to resolve, so you may need to add dependencies manually with # keep comments.

load("@io_bazel_rules_go//go:def.bzl", "go_library")
load("@com_github_example_gen//:gen.bzl", "gen_go_file")

gen_go_file(
    name = "magic",
    srcs = ["magic.go.in"],
    outs = ["magic.go"],
)

go_library(
    name = "go_default_library",
    srcs = ["magic.go"],
    visibility = ["//visibility:public"],
    deps = [
        "@com_github_example_gen//:go_default_library",  # keep
    ],
)

Fix command transformations

When Gazelle is invoked with the fix command, in addition to updating source files and dependencies of existing rules, Gazelle will remove deprecated usage of the Go rules, analogous to go fix. The following transformations are performed.

Squash cgo libraries: Gazelle will remove cgo_library rules named cgo_default_library and merge their attributes with a go_library rule in the same package named go_default_library. If no such go_library rule exists, a new one will be created. Other cgo_library rules will not be removed.

Remove legacy protos: Gazelle will remove usage of go_proto_library rules loaded from @io_bazel_rules_go//proto:go_proto_library.bzl and filegroup rules named go_default_library_protos. Newly generated proto rules will take their place. Since filegroup isn't needed anymore and go_proto_library has different attributes and was always written by hand, Gazelle will not attempt to merge anything from these rules with the newly generated rules.

This transformation is only applied in the default proto mode. Since Gazelle will run in legacy proto mode if go_proto_library.bzl is loaded, this transformation is not usually applied. You can set the proto mode explicitly using the directive # gazelle:proto default.