cmd/go: do not turn list ./nonexist into a network lookup

If you're in a directory corresponding to x/y
and you run go list ./z, we do at some point
want to turn that into x/y/z. But if ./z does
not exist that will make the go command
check the network to see if it can find x/y/z.
That's clearly wrong: ./z means that directory,
nothing else. And it turns a typo into a long delay,
which is even worse.

Fixes #26874.

Change-Id: Iec15fa7b359af11b6a4fc6cb082e593658fb6e41
Reviewed-on: https://go-review.googlesource.com/129061
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/src/cmd/go/internal/modload/load.go b/src/cmd/go/internal/modload/load.go
index b00f81458f..5ca2ed2d10 100644
--- a/src/cmd/go/internal/modload/load.go
+++ b/src/cmd/go/internal/modload/load.go
@@ -116,10 +116,24 @@ func ImportPaths(patterns []string) []*search.Match {
 					} else if path := pathInModuleCache(dir); path != "" {
 						pkg = path
 					} else {
+						pkg = ""
 						if !iterating {
 							base.Errorf("go: directory %s outside available modules", base.ShortPath(dir))
 						}
+					}
+					info, err := os.Stat(dir)
+					if err != nil || !info.IsDir() {
+						// If the directory does not exist,
+						// don't turn it into an import path
+						// that will trigger a lookup.
 						pkg = ""
+						if !iterating {
+							if err != nil {
+								base.Errorf("go: no such directory %v", m.Pattern)
+							} else {
+								base.Errorf("go: %s is not a directory", m.Pattern)
+							}
+						}
 					}
 					m.Pkgs[i] = pkg
 				}