1 files changed, 167 insertions, 0 deletions
diff --git a/go/tools/builders/replicate.go b/go/tools/builders/replicate.go
new file mode 100644
index 00000000..117f882c
--- /dev/null
+++ b/go/tools/builders/replicate.go
@@ -0,0 +1,167 @@
+// Copyright 2018 The Bazel Authors. All rights reserved.
+//
+// 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
+//
+//    http://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.
+
+// stdlib builds the standard library in the appropriate mode into a new goroot.
+package main
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+)
+
+type replicateMode int
+
+const (
+	copyMode replicateMode = iota
+	hardlinkMode
+	softlinkMode
+)
+
+type replicateOption func(*replicateConfig)
+type replicateConfig struct {
+	removeFirst bool
+	fileMode    replicateMode
+	dirMode     replicateMode
+	paths       []string
+}
+
+func replicatePaths(paths ...string) replicateOption {
+	return func(config *replicateConfig) {
+		config.paths = append(config.paths, paths...)
+	}
+}
+
+// replicatePrepare is the common preparation steps for a replication entry
+func replicatePrepare(dst string, config *replicateConfig) error {
+	dir := filepath.Dir(dst)
+	if err := os.MkdirAll(dir, 0755); err != nil {
+		return fmt.Errorf("Failed to make %s: %v", dir, err)
+	}
+	if config.removeFirst {
+		_ = os.Remove(dst)
+	}
+	return nil
+}
+
+// replicateFile is called internally by replicate to map a single file from src into dst.
+func replicateFile(src, dst string, config *replicateConfig) error {
+	if err := replicatePrepare(dst, config); err != nil {
+		return err
+	}
+	switch config.fileMode {
+	case copyMode:
+		in, err := os.Open(src)
+		if err != nil {
+			return err
+		}
+		defer in.Close()
+		out, err := os.Create(dst)
+		if err != nil {
+			return err
+		}
+		_, err = io.Copy(out, in)
+		closeerr := out.Close()
+		if err != nil {
+			return err
+		}
+		if closeerr != nil {
+			return closeerr
+		}
+		s, err := os.Stat(src)
+		if err != nil {
+			return err
+		}
+		if err := os.Chmod(dst, s.Mode()); err != nil {
+			return err
+		}
+		return nil
+	case hardlinkMode:
+		return os.Link(src, dst)
+	case softlinkMode:
+		return os.Symlink(src, dst)
+	default:
+		return fmt.Errorf("Invalid replication mode %d", config.fileMode)
+	}
+}
+
+// replicateDir makes a tree of files visible in a new location.
+// It is allowed to take any efficient method of doing so.
+func replicateDir(src, dst string, config *replicateConfig) error {
+	if err := replicatePrepare(dst, config); err != nil {
+		return err
+	}
+	switch config.dirMode {
+	case copyMode:
+		return filepath.Walk(src, func(path string, f os.FileInfo, err error) error {
+			if f.IsDir() {
+				return nil
+			}
+			relative, err := filepath.Rel(src, path)
+			if err != nil {
+				return err
+			}
+			return replicateFile(path, filepath.Join(dst, relative), config)
+		})
+	case hardlinkMode:
+		return os.Link(src, dst)
+	case softlinkMode:
+		return os.Symlink(src, dst)
+	default:
+		return fmt.Errorf("Invalid replication mode %d", config.fileMode)
+	}
+}
+
+// replicateTree is called for each single src dst pair.
+func replicateTree(src, dst string, config *replicateConfig) error {
+	if err := os.RemoveAll(dst); err != nil {
+		return fmt.Errorf("Failed to remove file at destination %s: %v", dst, err)
+	}
+	if l, err := filepath.EvalSymlinks(src); err != nil {
+		return err
+	} else {
+		src = l
+	}
+	if s, err := os.Stat(src); err != nil {
+		return err
+	} else if s.IsDir() {
+		return replicateDir(src, dst, config)
+	}
+	return replicateFile(src, dst, config)
+}
+
+// replicate makes a tree of files visible in a new location.
+// You control how it does so using options, by default it presumes the entire tree
+// of files rooted at src must be visible at dst, and that it should do so by copying.
+// src is allowed to be a file, in which case just the one file is copied.
+func replicate(src, dst string, options ...replicateOption) error {
+	config := replicateConfig{
+		removeFirst: true,
+	}
+	for _, option := range options {
+		option(&config)
+	}
+	if len(config.paths) == 0 {
+		return replicateTree(src, dst, &config)
+	}
+	for _, base := range config.paths {
+		from := filepath.Join(src, base)
+		to := filepath.Join(dst, base)
+		if err := replicateTree(from, to, &config); err != nil {
+			return err
+		}
+	}
+	return nil
+}