cmd/go: do not ignore permission errors when matching patterns

While reviewing CL 228784, I noticed that various filepath.WalkFunc
implementations within cmd/go were dropping non-nil errors.

Those errors turn out to be significant, at least in some cases: for
example, they can cause packages to appear to be missing when any
parent of the directory had the wrong permissions set.

(This also turned up a bug in the existing list_dedup_packages test,
which was accidentally passing a nonexistent directory instead of the
intended duplicate path.)

Change-Id: Ia09a0a33aa7a966d9f132d3747d6c674a5370b2d
Reviewed-on: https://go-review.googlesource.com/c/go/+/232579
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

1 files changed, 9 insertions, 3 deletions

diff --git a/src/cmd/go/internal/search/search.go b/src/cmd/go/internal/search/search.go
index b588c3e467..4efef24152 100644
--- a/src/cmd/go/internal/search/search.go
+++ b/src/cmd/go/internal/search/search.go
@@ -128,8 +128,11 @@ func (m *Match) MatchPackages() {
 			root += "cmd" + string(filepath.Separator)
 		}
 		err := filepath.Walk(root, func(path string, fi os.FileInfo, err error) error {
-			if err != nil || path == src {
-				return nil
+			if err != nil {
+				return err // Likely a permission error, which could interfere with matching.
+			}
+			if path == src {
+				return nil // GOROOT/src and GOPATH/src cannot contain packages.
 			}
 
 			want := true
@@ -261,7 +264,10 @@ func (m *Match) MatchDirs() {
 	}
 
 	err := filepath.Walk(dir, func(path string, fi os.FileInfo, err error) error {
-		if err != nil || !fi.IsDir() {
+		if err != nil {
+			return err // Likely a permission error, which could interfere with matching.
+		}
+		if !fi.IsDir() {
 			return nil
 		}
 		top := false