cmd/godoc: support automatic vendoring

Fixes golang/go#35429

Change-Id: I060ccfbed4c3975d1ddc94fda4fadea527b29841
Reviewed-on: https://go-review.googlesource.com/c/tools/+/232958
Run-TryBot: Agniva De Sarker <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: agnivade

cmd/godoc/main.go

@@ -19,6 +19,7 @@ package main
 import (
 	"archive/zip"
 	"bytes"
+	"context"
 	"encoding/json"
 	_ "expvar" // to serve /debug/vars
 	"flag"
@@ -44,6 +45,7 @@ import (
 	"golang.org/x/tools/godoc/vfs/gatefs"
 	"golang.org/x/tools/godoc/vfs/mapfs"
 	"golang.org/x/tools/godoc/vfs/zipfs"
+	"golang.org/x/tools/internal/gocommand"
 	"golang.org/x/xerrors"
 )
 
@@ -210,28 +212,48 @@ func main() {
 			usage()
 		}
 
-		// Try to download dependencies that are not in the module cache in order to
-		// to show their documentation.
-		// This may fail if module downloading is disallowed (GOPROXY=off) or due to
-		// limited connectivity, in which case we print errors to stderr and show
-		// documentation only for packages that are available.
-		fillModuleCache(os.Stderr, goModFile)
-
-		// Determine modules in the build list.
-		mods, err := buildList(goModFile)
+		// Detect whether to use vendor mode or not.
+		mainMod, vendorEnabled, err := gocommand.VendorEnabled(context.Background(), gocommand.Invocation{}, &gocommand.Runner{})
 		if err != nil {
-			fmt.Fprintf(os.Stderr, "failed to determine the build list of the main module: %v", err)
+			fmt.Fprintf(os.Stderr, "failed to determine if vendoring is enabled: %v", err)
 			os.Exit(1)
 		}
+		if vendorEnabled {
+			// Bind the root directory of the main module.
+			fs.Bind(path.Join("/src", mainMod.Path), gatefs.New(vfs.OS(mainMod.Dir), fsGate), "/", vfs.BindAfter)
+
+			// Bind the vendor directory.
+			//
+			// Note that in module mode, vendor directories in locations
+			// other than the main module's root directory are ignored.
+			// See https://golang.org/ref/mod#vendoring.
+			vendorDir := filepath.Join(mainMod.Dir, "vendor")
+			fs.Bind("/src", gatefs.New(vfs.OS(vendorDir), fsGate), "/", vfs.BindAfter)
+
+		} else {
+			// Try to download dependencies that are not in the module cache in order to
+			// to show their documentation.
+			// This may fail if module downloading is disallowed (GOPROXY=off) or due to
+			// limited connectivity, in which case we print errors to stderr and show
+			// documentation only for packages that are available.
+			fillModuleCache(os.Stderr, goModFile)
+
+			// Determine modules in the build list.
+			mods, err := buildList(goModFile)
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "failed to determine the build list of the main module: %v", err)
+				os.Exit(1)
+			}
 
-		// Bind module trees into Go root.
-		for _, m := range mods {
-			if m.Dir == "" {
-				// Module is not available in the module cache, skip it.
-				continue
+			// Bind module trees into Go root.
+			for _, m := range mods {
+				if m.Dir == "" {
+					// Module is not available in the module cache, skip it.
+					continue
+				}
+				dst := path.Join("/src", m.Path)
+				fs.Bind(dst, gatefs.New(vfs.OS(m.Dir), fsGate), "/", vfs.BindAfter)
 			}
-			dst := path.Join("/src", m.Path)
-			fs.Bind(dst, gatefs.New(vfs.OS(m.Dir), fsGate), "/", vfs.BindAfter)
 		}
 	} else {
 		fmt.Println("using GOPATH mode")
@@ -395,7 +417,7 @@ func goMod() (string, error) {
 // with all dependencies of the main module in the current directory
 // by invoking the go command. Module download logs are streamed to w.
 // If there are any problems encountered, they are also written to w.
-// It should only be used when operating in module mode.
+// It should only be used in module mode, when vendor mode isn't on.
 //
 // See https://golang.org/cmd/go/#hdr-Download_modules_to_local_cache.
 func fillModuleCache(w io.Writer, goMod string) {
@@ -436,9 +458,14 @@ func fillModuleCache(w io.Writer, goMod string) {
 	}
 }
 
+type mod struct {
+	Path string // Module path.
+	Dir  string // Directory holding files for this module, if any.
+}
+
 // buildList determines the build list in the current directory
-// by invoking the go command. It should only be used when operating
-// in module mode.
+// by invoking the go command. It should only be used in module mode,
+// when vendor mode isn't on.
 //
 // See https://golang.org/cmd/go/#hdr-The_main_module_and_the_build_list.
 func buildList(goMod string) ([]mod, error) {
@@ -467,11 +494,6 @@ func buildList(goMod string) ([]mod, error) {
 	return mods, nil
 }
 
-type mod struct {
-	Path string // Module path.
-	Dir  string // Directory holding files for this module, if any.
-}
-
 // moduleFS is a vfs.FileSystem wrapper used when godoc is running
 // in module mode. It's needed so that packages inside modules are
 // considered to be third party.

internal/gocommand/vendor.go

@@ -0,0 +1,102 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package gocommand
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+
+	"golang.org/x/mod/semver"
+)
+
+// ModuleJSON holds information about a module.
+type ModuleJSON struct {
+	Path      string      // module path
+	Replace   *ModuleJSON // replaced by this module
+	Main      bool        // is this the main module?
+	Indirect  bool        // is this module only an indirect dependency of main module?
+	Dir       string      // directory holding files for this module, if any
+	GoMod     string      // path to go.mod file for this module, if any
+	GoVersion string      // go version used in module
+}
+
+var modFlagRegexp = regexp.MustCompile(`-mod[ =](\w+)`)
+
+// VendorEnabled reports whether vendoring is enabled. It takes a *Runner to execute Go commands
+// with the supplied context.Context and Invocation. The Invocation can contain pre-defined fields,
+// of which only Verb and Args are modified to run the appropriate Go command.
+// Inspired by setDefaultBuildMod in modload/init.go
+func VendorEnabled(ctx context.Context, inv Invocation, r *Runner) (*ModuleJSON, bool, error) {
+	mainMod, go114, err := getMainModuleAnd114(ctx, inv, r)
+	if err != nil {
+		return nil, false, err
+	}
+
+	// We check the GOFLAGS to see if there is anything overridden or not.
+	inv.Verb = "env"
+	inv.Args = []string{"GOFLAGS"}
+	stdout, err := r.Run(ctx, inv)
+	if err != nil {
+		return nil, false, err
+	}
+	goflags := string(bytes.TrimSpace(stdout.Bytes()))
+	matches := modFlagRegexp.FindStringSubmatch(goflags)
+	var modFlag string
+	if len(matches) != 0 {
+		modFlag = matches[1]
+	}
+	if modFlag != "" {
+		// Don't override an explicit '-mod=' argument.
+		return mainMod, modFlag == "vendor", nil
+	}
+	if mainMod == nil || !go114 {
+		return mainMod, false, nil
+	}
+	// Check 1.14's automatic vendor mode.
+	if fi, err := os.Stat(filepath.Join(mainMod.Dir, "vendor")); err == nil && fi.IsDir() {
+		if mainMod.GoVersion != "" && semver.Compare("v"+mainMod.GoVersion, "v1.14") >= 0 {
+			// The Go version is at least 1.14, and a vendor directory exists.
+			// Set -mod=vendor by default.
+			return mainMod, true, nil
+		}
+	}
+	return mainMod, false, nil
+}
+
+// getMainModuleAnd114 gets the main module's information and whether the
+// go command in use is 1.14+. This is the information needed to figure out
+// if vendoring should be enabled.
+func getMainModuleAnd114(ctx context.Context, inv Invocation, r *Runner) (*ModuleJSON, bool, error) {
+	const format = `{{.Path}}
+{{.Dir}}
+{{.GoMod}}
+{{.GoVersion}}
+{{range context.ReleaseTags}}{{if eq . "go1.14"}}{{.}}{{end}}{{end}}
+`
+	inv.Verb = "list"
+	inv.Args = []string{"-m", "-f", format}
+	stdout, err := r.Run(ctx, inv)
+	if err != nil {
+		return nil, false, err
+	}
+
+	lines := strings.Split(stdout.String(), "\n")
+	if len(lines) < 5 {
+		return nil, false, fmt.Errorf("unexpected stdout: %q", stdout.String())
+	}
+	mod := &ModuleJSON{
+		Path:      lines[0],
+		Dir:       lines[1],
+		GoMod:     lines[2],
+		GoVersion: lines[3],
+		Main:      true,
+	}
+	return mod, lines[4] == "go1.14", nil
+}