cmd/go: prevent panic in go work use

Check if paths passed as arguments are existing directories.

Fixes #51841
Fixes #51749

Change-Id: Icfd148627e6f2c4651d6f923a37d413e68c67f6c
GitHub-Last-Rev: 77fffa7
GitHub-Pull-Request: #51845
Reviewed-on: https://go-review.googlesource.com/c/go/+/394154
Trust: Bryan Mills <bcmills@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Trust: Emmanuel Odeke <emmanuel@orijtech.com>
Run-TryBot: Emmanuel Odeke <emmanuel@orijtech.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

Author: Filippo Rossi

src/cmd/go/internal/workcmd/use.go

@@ -12,7 +12,6 @@ import (
 	"cmd/go/internal/modload"
 	"cmd/go/internal/str"
 	"context"
-	"errors"
 	"fmt"
 	"io/fs"
 	"os"
@@ -109,17 +108,33 @@ func runUse(ctx context.Context, cmd *base.Command, args []string) {
 		base.Fatalf("go: 'go work use' requires one or more directory arguments")
 	}
 	for _, useDir := range args {
-		if !*useR {
-			if target, err := fsys.Stat(useDir); err == nil && !target.IsDir() {
-				base.Errorf(`go: argument "%s" is not a directory`, useDir)
+		absArg, _ := pathRel(workDir, useDir)
+
+		info, err := fsys.Stat(absArg)
+		if err != nil {
+			// Errors raised from os.Stat are formatted to be more user-friendly.
+			if os.IsNotExist(err) {
+				base.Errorf("go: directory %v does not exist", absArg)
 			} else {
-				lookDir(useDir)
+				base.Errorf("go: %v", err)
 			}
 			continue
+		} else if !info.IsDir() {
+			base.Errorf("go: %s is not a directory", absArg)
+			continue
+		}
+
+		if !*useR {
+			lookDir(useDir)
+			continue
 		}
 
 		// Add or remove entries for any subdirectories that still exist.
-		err := fsys.Walk(useDir, func(path string, info fs.FileInfo, err error) error {
+		fsys.Walk(useDir, func(path string, info fs.FileInfo, err error) error {
+			if err != nil {
+				return err
+			}
+
 			if !info.IsDir() {
 				if info.Mode()&fs.ModeSymlink != 0 {
 					if target, err := fsys.Stat(path); err == nil && target.IsDir() {
@@ -131,13 +146,9 @@ func runUse(ctx context.Context, cmd *base.Command, args []string) {
 			lookDir(path)
 			return nil
 		})
-		if err != nil && !errors.Is(err, os.ErrNotExist) {
-			base.Errorf("go: %v", err)
-		}
 
 		// Remove entries for subdirectories that no longer exist.
 		// Because they don't exist, they will be skipped by Walk.
-		absArg, _ := pathRel(workDir, useDir)
 		for absDir, _ := range haveDirs {
 			if str.HasFilePathPrefix(absDir, absArg) {
 				if _, ok := keepDirs[absDir]; !ok {

src/cmd/go/testdata/script/work_use_file.txt

@@ -0,0 +1,17 @@
+! go work use foo bar baz
+
+stderr '^go: '$WORK'[/\\]gopath[/\\]src[/\\]foo is not a directory'
+stderr '^go: directory '$WORK'[/\\]gopath[/\\]src[/\\]baz does not exist'
+cmp go.work go.work_want
+
+! go work use -r qux
+stderr '^go: '$WORK'[/\\]gopath[/\\]src[/\\]qux is not a directory'
+
+-- go.work --
+go 1.18
+-- go.work_want --
+go 1.18
+-- foo --
+-- qux --
+-- bar/go.mod --
+module bar