cmd/go: resolve non-standard imports from within GOROOT/src using vendor directories

Updates #30228
Fixes #26924

Change-Id: Ie625c64721559c7633396342320536396cd1fcf5
Reviewed-on: https://go-review.googlesource.com/c/go/+/164621
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, 13 insertions, 17 deletions

diff --git a/src/cmd/go/internal/modload/search.go b/src/cmd/go/internal/modload/search.go
index 45e7ee2674..2e82b92cc5 100644
--- a/src/cmd/go/internal/modload/search.go
+++ b/src/cmd/go/internal/modload/search.go
@@ -35,12 +35,8 @@ func matchPackages(pattern string, tags map[string]bool, useStd bool, modules []
 	}
 	var pkgs []string
 
-	walkPkgs := func(root, importPathRoot string) {
+	walkPkgs := func(root, importPathRoot string, includeVendor bool) {
 		root = filepath.Clean(root)
-		var cmd string
-		if root == cfg.GOROOTsrc {
-			cmd = filepath.Join(root, "cmd")
-		}
 		filepath.Walk(root, func(path string, fi os.FileInfo, err error) error {
 			if err != nil {
 				return nil
@@ -51,14 +47,6 @@ func matchPackages(pattern string, tags map[string]bool, useStd bool, modules []
 				return nil
 			}
 
-			// GOROOT/src/cmd makes use of GOROOT/src/cmd/vendor,
-			// which module mode can't deal with. Eventually we'll stop using
-			// that vendor directory, and then we can remove this exclusion.
-			// golang.org/issue/26924.
-			if path == cmd {
-				return filepath.SkipDir
-			}
-
 			want := true
 			// Avoid .foo, _foo, and testdata directory trees.
 			_, elem := filepath.Split(path)
@@ -86,6 +74,7 @@ func matchPackages(pattern string, tags map[string]bool, useStd bool, modules []
 			if !want {
 				return filepath.SkipDir
 			}
+			// Stop at module boundaries.
 			if path != root {
 				if _, err := os.Stat(filepath.Join(path, "go.mod")); err == nil {
 					return filepath.SkipDir
@@ -101,7 +90,7 @@ func matchPackages(pattern string, tags map[string]bool, useStd bool, modules []
 				}
 			}
 
-			if elem == "vendor" {
+			if elem == "vendor" && !includeVendor {
 				return filepath.SkipDir
 			}
 			return nil
@@ -109,11 +98,14 @@ func matchPackages(pattern string, tags map[string]bool, useStd bool, modules []
 	}
 
 	if useStd {
-		walkPkgs(cfg.GOROOTsrc, "")
+		walkPkgs(cfg.GOROOTsrc, "", true)
+		if treeCanMatch("cmd") {
+			walkPkgs(filepath.Join(cfg.GOROOTsrc, "cmd"), "cmd", true)
+		}
 	}
 
 	if cfg.BuildMod == "vendor" {
-		walkPkgs(filepath.Join(ModRoot(), "vendor"), "")
+		walkPkgs(filepath.Join(ModRoot(), "vendor"), "", false)
 		return pkgs
 	}
 
@@ -135,7 +127,11 @@ func matchPackages(pattern string, tags map[string]bool, useStd bool, modules []
 				continue
 			}
 		}
-		walkPkgs(root, mod.Path)
+		modPrefix := mod.Path
+		if mod.Path == "std" {
+			modPrefix = ""
+		}
+		walkPkgs(root, modPrefix, false)
 	}
 
 	return pkgs