check for error earlier in matchingWalker.Walk to avoid nil deref

internal/bundles/matcher/walker.go

@@ -62,6 +62,14 @@ type matchingWalker struct {
 // for every file and directory that matches the match list.
 func (i *matchingWalker) Walk(base util.AbsolutePath, fn util.AbsoluteWalkFunc) error {
 	return base.Walk(func(path util.AbsolutePath, info fs.FileInfo, err error) error {
+		if errors.Is(err, os.ErrPermission) {
+			i.log.Warn("permission error; skipping", "path", path)
+			return nil
+		}
+		if err != nil {
+			i.log.Warn("Unknown error while accessing file", "path", path, "error", err.Error())
+			return nil
+		}
 		if path != base {
 			m := i.matchList.Match(path)
 			if info.IsDir() {
@@ -84,14 +92,6 @@ func (i *matchingWalker) Walk(base util.AbsolutePath, fn util.AbsoluteWalkFunc)
 				}
 			}
 		}
-		if errors.Is(err, os.ErrPermission) {
-			i.log.Warn("permission error; skipping", "path", path)
-			return nil
-		}
-		if err != nil {
-			i.log.Warn("Unknown error while accessing file", "path", path, "error", err.Error())
-			return nil
-		}
 		return fn(path, info, err)
 	})
 }

internal/bundles/matcher/walker_test.go

@@ -7,15 +7,17 @@ import (
 	"io/fs"
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 
+	"github.com/spf13/afero"
+	"github.com/stretchr/testify/mock"
+	"github.com/stretchr/testify/suite"
+
 	"github.com/posit-dev/publisher/internal/logging"
 	"github.com/posit-dev/publisher/internal/logging/loggingtest"
 	"github.com/posit-dev/publisher/internal/util"
 	"github.com/posit-dev/publisher/internal/util/utiltest"
-	"github.com/spf13/afero"
-	"github.com/stretchr/testify/mock"
-	"github.com/stretchr/testify/suite"
 )
 
 type WalkerSuite struct {
@@ -64,7 +66,7 @@ func (s *WalkerSuite) TestWalk() {
 	s.NoError(err)
 
 	includedFile := includedDir.Join("includeme")
-	err = includedFile.WriteFile([]byte("this is an included file"), 0600)
+	err = includedFile.WriteFile([]byte("this is an included subdir"), 0600)
 	s.NoError(err)
 
 	// This will be excluded by default
@@ -139,6 +141,39 @@ func (s *WalkerSuite) TestWalkPermissionErr() {
 	s.Equal([]string{"."}, seen)
 }
 
+type StatPermissionErrFs struct {
+	afero.Fs
+}
+
+func (m StatPermissionErrFs) Stat(name string) (os.FileInfo, error) {
+	if strings.HasSuffix(name, "foobar") {
+		return nil, fs.ErrPermission
+	}
+	return m.Fs.Stat(name)
+}
+
+func (s *WalkerSuite) TestWalkStatPermissionErr() {
+	afs := StatPermissionErrFs{Fs: s.fs}
+
+	baseDir := s.cwd.WithFs(afs)
+	s.cwd.Join("foobar").Mkdir(0777)
+
+	w, err := NewMatchingWalker([]string{"*"}, s.cwd, logging.New())
+	s.NoError(err)
+	s.NotNil(w)
+
+	seen := []string{}
+	err = w.Walk(baseDir, func(path util.AbsolutePath, info fs.FileInfo, err error) error {
+		s.NoError(err)
+		relPath, err := path.Rel(s.cwd)
+		s.NoError(err)
+		seen = append(seen, relPath.String())
+		return nil
+	})
+	s.NoError(err)
+	s.Equal([]string{"."}, seen)
+}
+
 func (s *WalkerSuite) TestWalkErr_Logged() {
 	// Errors while walking through files are logged but won't halt the current process
 	afs := utiltest.NewMockFs()