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runfiles.go
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runfiles.go
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// Copyright 2020, 2021 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package runfiles provides access to Bazel runfiles. It is an alternative to
// the official Bazel package
// https://pkg.go.dev/github.com/bazelbuild/rules_go/go/tools/bazel.
//
// Installation
//
// To use this package, first set up rules_go as described in
// https://github.com/bazelbuild/rules_go#setup. Then add the following
// snippet to your Bazel WORKSPACE file:
//
// load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
// http_archive(
// name = "com_github_phst_runfiles",
// urls = ["https://github.com/phst/runfiles/archive/f8065aa0cb28b5cc0fffa7d0b5e9ea1a92add4bb.zip"],
// sha256 = "8f0502d14cc35e8857d67ac02a3b8d46a496bb7e3ddf723ebb73ce71c4c0cd6d",
// strip_prefix = "runfiles-f8065aa0cb28b5cc0fffa7d0b5e9ea1a92add4bb",
// )
//
// Usage
//
// This package has two main entry points, the global functions Path and Env,
// and the Runfiles type.
//
// Global functions
//
// For simple use cases that don’t require hermetic behavior, use the Path and
// Env functions to access runfiles. Use Path to find the filesystem location
// of a runfile, and use Env to obtain environmental variables to pass on to
// subprocesses.
//
// Runfiles type
//
// If you need hermetic behavior or want to change the runfiles discovery
// process, use New to create a Runfiles object. New accepts a few options to
// change the discovery process. Runfiles objects have methods Path and Env,
// which correspond to the package-level functions. On Go 1.16, *Runfiles
// implements fs.FS, fs.StatFS, and fs.ReadFileFS.
package runfiles
import (
"errors"
"fmt"
"os"
"path"
"strings"
)
// Runfiles allows access to Bazel runfiles. Use New to create Runfiles
// objects; the zero Runfiles object always returns errors. See
// https://docs.bazel.build/skylark/rules.html#runfiles for some information on
// Bazel runfiles.
type Runfiles struct {
// We don’t need concurrency control since Runfiles objects are
// immutable once created.
impl runfiles
env string
}
// New creates a given Runfiles object. By default, it uses os.Args and the
// RUNFILES_MANIFEST_FILE and RUNFILES_DIR environmental variables to find the
// runfiles location. This can be overwritten by passing some options.
func New(opts ...Option) (*Runfiles, error) {
var o options
for _, a := range opts {
a.apply(&o)
}
if o.program == "" {
o.program = ProgramName(os.Args[0])
}
if o.manifest == "" {
o.manifest = ManifestFile(os.Getenv("RUNFILES_MANIFEST_FILE"))
}
if o.directory == "" {
o.directory = Directory(os.Getenv("RUNFILES_DIR"))
}
// See section “Runfiles discovery” in
// https://docs.google.com/document/d/e/2PACX-1vSDIrFnFvEYhKsCMdGdD40wZRBX3m3aZ5HhVj4CtHPmiXKDCxioTUbYsDydjKtFDAzER5eg7OjJWs3V/pub.
if o.manifest != "" {
return o.manifest.new()
}
if o.directory != "" {
return o.directory.new(), nil
}
manifest := ManifestFile(o.program + ".runfiles_manifest")
if stat, err := os.Stat(string(manifest)); err == nil && stat.Mode().IsRegular() {
return manifest.new()
}
dir := Directory(o.program + ".runfiles")
if stat, err := os.Stat(string(dir)); err == nil && stat.IsDir() {
return dir.new(), nil
}
return nil, errors.New("runfiles: no runfiles found")
}
// Path returns the absolute path name of a runfile. The runfile name must be
// a relative path, using the slash (not backslash) as directory separator. If
// r is the zero Runfiles object, Path always returns an error. If the
// runfiles manifest maps s to an empty name (indicating an empty runfile not
// present in the filesystem), Path returns an error that wraps ErrEmpty.
func (r *Runfiles) Path(s string) (string, error) {
// See section “Library interface” in
// https://docs.google.com/document/d/e/2PACX-1vSDIrFnFvEYhKsCMdGdD40wZRBX3m3aZ5HhVj4CtHPmiXKDCxioTUbYsDydjKtFDAzER5eg7OjJWs3V/pub.
if s == "" {
return "", errors.New("runfiles: name may not be empty")
}
if path.IsAbs(s) {
return "", fmt.Errorf("runfiles: name %q may not be absolute", s)
}
if s != path.Clean(s) {
return "", fmt.Errorf("runfiles: name %q must be canonical", s)
}
if s == ".." || strings.HasPrefix(s, "../") {
return "", fmt.Errorf("runfiles: name %q may not contain a parent directory", s)
}
impl := r.impl
if impl == nil {
return "", errors.New("runfiles: uninitialized Runfiles object")
}
p, err := impl.path(s)
if err != nil {
return "", Error{s, err}
}
return p, nil
}
// Env returns additional environmental variables to pass to subprocesses.
// Each element is of the form “key=value”. Pass these variables to
// Bazel-built binaries so they can find their runfiles as well. See the
// Runfiles example for an illustration of this.
//
// The return value is a newly-allocated slice; you can modify it at will. If
// r is the zero Runfiles object, the return value is nil.
func (r *Runfiles) Env() []string {
if r.env == "" {
return nil
}
return []string{r.env}
}
// Option is an option for the New function to override runfiles discovery.
type Option interface {
apply(*options)
}
// ProgramName is an Option that sets the program name. If not set, New uses
// os.Args[0].
type ProgramName string
// Error represents a failure to look up a runfile.
type Error struct {
// Runfile name that caused the failure.
Name string
// Underlying error.
Err error
}
// Error implements error.Error.
func (e Error) Error() string {
return fmt.Sprintf("runfile %q: %s", e.Name, e.Err.Error())
}
// Unwrap returns the underlying error, for errors.Unwrap.
func (e Error) Unwrap() error { return e.Err }
// ErrEmpty indicates that a runfile isn’t present in the filesystem, but
// should be created as an empty file if necessary.
var ErrEmpty = errors.New("empty runfile")
type options struct {
program ProgramName
manifest ManifestFile
directory Directory
}
func (p ProgramName) apply(o *options) { o.program = p }
func (m ManifestFile) apply(o *options) { o.manifest = m }
func (d Directory) apply(o *options) { o.directory = d }
type runfiles interface {
path(string) (string, error)
}