go/build: replace FindTree, ScanDir, Tree, DirInfo with Import, Package

This is an API change, but one I have been promising would
happen when it was clear what the go command needed.

This is basically a complete replacement of what used to be here.

build.Tree is gone.

build.DirInfo is expanded and now called build.Package.

build.FindTree is now build.Import(package, srcDir, build.FindOnly).
The returned *Package contains information that FindTree returned,
but applicable only to a single package.

build.ScanDir is now build.ImportDir.

build.FindTree+build.ScanDir is now build.Import.

The new Import API allows specifying the source directory,
in order to resolve local imports (import "./foo") and also allows
scanning of packages outside of $GOPATH.  They will come back
with less information in the Package, but they will still work.

The old go/build API exposed both too much and too little.
This API is much closer to what the go command needs,
and it works well enough in the other places where it is
used.  Path is gone, so it can no longer be misused.  (Fixes issue 2749.)

This CL updates clients of go/build other than the go command.
The go command changes are in a separate CL, to be submitted
at the same time.

R=golang-dev, r, alex.brainman, adg
CC=golang-dev
https://golang.org/cl/5713043

4 files changed, 28 insertions, 32 deletions

diff --git a/src/cmd/api/goapi.go b/src/cmd/api/goapi.go
index ee0f92328e..fe9c862f4f 100644
--- a/src/cmd/api/goapi.go
+++ b/src/cmd/api/goapi.go
@@ -74,16 +74,10 @@ func main() {
 		pkgs = strings.Fields(string(stds))
 	}
 
-	tree, _, err := build.FindTree("os") // some known package
-	if err != nil {
-		log.Fatalf("failed to find tree: %v", err)
-	}
-
 	var featureCtx = make(map[string]map[string]bool) // feature -> context name -> true
 	for _, context := range contexts {
 		w := NewWalker()
 		w.context = context
-		w.tree = tree
 
 		for _, pkg := range pkgs {
 			w.wantedPkg[pkg] = true
@@ -95,7 +89,7 @@ func main() {
 				strings.HasPrefix(pkg, "old/") {
 				continue
 			}
-			if !tree.HasSrc(pkg) {
+			if fi, err := os.Stat(filepath.Join(w.root, pkg)); err != nil || !fi.IsDir() {
 				log.Fatalf("no source in tree for package %q", pkg)
 			}
 			w.WalkPackage(pkg)
@@ -165,7 +159,7 @@ type pkgSymbol struct {
 
 type Walker struct {
 	context         *build.Context
-	tree            *build.Tree
+	root            string
 	fset            *token.FileSet
 	scope           []string
 	features        map[string]bool // set
@@ -191,6 +185,7 @@ func NewWalker() *Walker {
 		selectorFullPkg: make(map[string]string),
 		wantedPkg:       make(map[string]bool),
 		prevConstType:   make(map[pkgSymbol]string),
+		root:            filepath.Join(build.Default.GOROOT, "src/pkg"),
 	}
 }
 
@@ -252,15 +247,13 @@ func (w *Walker) WalkPackage(name string) {
 	defer func() {
 		w.packageState[name] = loaded
 	}()
-	dir := filepath.Join(w.tree.SrcDir(), filepath.FromSlash(name))
+	dir := filepath.Join(w.root, filepath.FromSlash(name))
 
-	var info *build.DirInfo
-	var err error
-	if ctx := w.context; ctx != nil {
-		info, err = ctx.ScanDir(dir)
-	} else {
-		info, err = build.ScanDir(dir)
+	ctxt := w.context
+	if ctxt == nil {
+		ctxt = &build.Default
 	}
+	info, err := ctxt.ImportDir(dir, 0)
 	if err != nil {
 		if strings.Contains(err.Error(), "no Go source files") {
 			return
diff --git a/src/cmd/api/goapi_test.go b/src/cmd/api/goapi_test.go
index dbbec46b0d..c7cc601b1a 100644
--- a/src/cmd/api/goapi_test.go
+++ b/src/cmd/api/goapi_test.go
@@ -7,7 +7,6 @@ package main
 import (
 	"flag"
 	"fmt"
-	"go/build"
 	"io/ioutil"
 	"os"
 	"path/filepath"
@@ -36,7 +35,7 @@ func TestGolden(t *testing.T) {
 		w := NewWalker()
 		w.wantedPkg[fi.Name()] = true
 
-		w.tree = &build.Tree{Path: "testdata", Goroot: true}
+		w.root = "testdata/src/pkg"
 		goldenFile := filepath.Join("testdata", "src", "pkg", fi.Name(), "golden.txt")
 		w.WalkPackage(fi.Name())
 
diff --git a/src/cmd/godoc/godoc.go b/src/cmd/godoc/godoc.go
index 1f212a0bcd..e5f7a73d4f 100644
--- a/src/cmd/godoc/godoc.go
+++ b/src/cmd/godoc/godoc.go
@@ -15,6 +15,7 @@ import (
 	"go/printer"
 	"go/token"
 	"io"
+	"io/ioutil"
 	"log"
 	"net/http"
 	"net/url"
@@ -90,11 +91,11 @@ var (
 
 func initHandlers() {
 	paths := filepath.SplitList(*pkgPath)
-	for _, t := range build.Path {
-		if t.Goroot {
-			continue
+	gorootSrc := filepath.Join(build.Default.GOROOT, "src", "pkg")
+	for _, p := range build.Default.SrcDirs() {
+		if p != gorootSrc {
+			paths = append(paths, p)
 		}
-		paths = append(paths, t.SrcDir())
 	}
 	fsMap.Init(paths)
 
@@ -1002,11 +1003,13 @@ func fsReadDir(dir string) ([]os.FileInfo, error) {
 	return fs.ReadDir(dir)
 }
 
-// fsReadFile implements ReadFile for the go/build package.
-func fsReadFile(dir, name string) (path string, data []byte, err error) {
-	path = filepath.Join(dir, name)
-	data, err = ReadFile(fs, path)
-	return
+// fsOpenFile implements OpenFile for the go/build package.
+func fsOpenFile(name string) (r io.ReadCloser, err error) {
+	data, err := ReadFile(fs, name)
+	if err != nil {
+		return nil, err
+	}
+	return ioutil.NopCloser(bytes.NewReader(data)), nil
 }
 
 func inList(name string, list []string) bool {
@@ -1039,10 +1042,11 @@ func (h *httpHandler) getPageInfo(abspath, relpath, pkgname string, mode PageInf
 		// To use different pair, such as if we allowed the user
 		// to choose, set ctxt.GOOS and ctxt.GOARCH before
 		// calling ctxt.ScanDir.
-		ctxt := build.DefaultContext
+		ctxt := build.Default
+		ctxt.IsAbsPath = path.IsAbs
 		ctxt.ReadDir = fsReadDir
-		ctxt.ReadFile = fsReadFile
-		dir, err := ctxt.ScanDir(abspath)
+		ctxt.OpenFile = fsOpenFile
+		dir, err := ctxt.ImportDir(abspath, 0)
 		if err == nil {
 			pkgFiles = append(dir.GoFiles, dir.CgoFiles...)
 		}
diff --git a/src/cmd/godoc/main.go b/src/cmd/godoc/main.go
index ee905bb7a0..5f42105393 100644
--- a/src/cmd/godoc/main.go
+++ b/src/cmd/godoc/main.go
@@ -388,9 +388,9 @@ func main() {
 	}
 	relpath := path
 	abspath := path
-	if t, pkg, err := build.FindTree(path); err == nil {
-		relpath = pkg
-		abspath = filepath.Join(t.SrcDir(), pkg)
+	if bp, _ := build.Import(path, "", build.FindOnly); bp.Dir != "" && bp.ImportPath != "" {
+		relpath = bp.ImportPath
+		abspath = bp.Dir
 	} else if !filepath.IsAbs(path) {
 		abspath = absolutePath(path, pkgHandler.fsRoot)
 	} else {