deploytool: Add README.md, migrate docs to it.

deploytool/cmd/staging.go

-// Copyright 2016 The LUCI Authors. All rights reserved.
-// Use of this source code is governed under the Apache License, Version 2.0
-// that can be found in the LICENSE file.
-
-package main
-
-import (
-        "strings"
-
-        "github.com/luci/luci-go/common/errors"
-        "github.com/luci/luci-go/deploytool/managedfs"
-)
-
-// stageGoPath creates a GOPATH-compatible directory consisting of all of the
-// GOPATHs configured in the supplied components sources. The path begins with
-// "src/", and is rooted in the supplied root.
-func stageGoPath(w *work, comp *layoutDeploymentComponent, root *managedfs.Dir) error {
-        // Build our GoPath sources. To do this, we will build subdirectories under
-        // "src" for the various GoPath components, then symlink the last directory
-        // component to the actual GOPATH root.
-        //
-        // We need to detect path conflicts where one GOPATH checks out into the
-        // parent of another GOPATH, e.g.:
-        // /foo/bar/baz => A
-        // /foo/bar => B
-        //
-        // We do this by checking intermediate Go paths against our deployment plan
-        // incrementally.
-        dirs := make(map[string]struct{})
-        build := make(map[string]string)
-        for _, src := range comp.sources {
-                if src.InitResult == nil {
-                        continue
-                }
-
-                for _, gopath := range src.InitResult.GoPath {
-                        // Make sure our Go package isn't a directory.
-                        if _, ok := dirs[gopath.GoPackage]; ok {
-                                return errors.Reason("GOPATH %(package)q is both a package and directory").
-                                        D("package", gopath.GoPackage).Err()
-                        }
-
-                        // Check intermediate paths to make sure there isn't a deployment
-                        // conflict.
-                        pkgParts := splitGoPackage(gopath.GoPackage)
-                        for _, parentPkg := range pkgParts[:len(pkgParts)-1] {
-                                if _, ok := build[parentPkg]; ok {
-                                        return errors.Reason("GOPATH %(package)q is both a package and directory").
-                                                D("package", parentPkg).Err()
-                                }
-                                dirs[parentPkg] = struct{}{}
-                        }
-
-                        // Everything checks out, add this link.
-                        build[gopath.GoPackage] = src.pathTo(gopath.Path, "")
-                }
-        }
-
-        srcDir, err := root.EnsureDirectory("src")
-        if err != nil {
-                return err
-        }
-
-        for pkg, src := range build {
-                var (
-                        pkgComponents = strings.Split(pkg, "/")
-                        d             = srcDir
-                )
-                for _, comp := range pkgComponents[:len(pkgComponents)-1] {
-                        var err error
-                        d, err = d.EnsureDirectory(comp)
-                        if err != nil {
-                                return errors.Annotate(err).Reason("could not create GOPATH parent directory [%(path)s]").
-                                        D("path", d).Err()
-                        }
-                }
-                link := d.File(pkgComponents[len(pkgComponents)-1])
-                if err := link.SymlinkFrom(src, true); err != nil {
-                        return errors.Annotate(err).Reason("failed to create GOPATH link").Err()
-                }
-        }
-        return nil
-}