cmd/go: fix module ... pattern to match standard library

The non-module ... pattern always has.

Fixes #26905.

Change-Id: I7b298747fb33b82c58d3e6a6bc6687b6e825e52c
Reviewed-on: https://go-review.googlesource.com/128997
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

src/cmd/go/internal/modload/load.go

@@ -103,7 +103,7 @@ func ImportPaths(args []string) []string {
 			case pkg == "all":
 				loaded.testAll = true
 				// TODO: Don't print warnings multiple times.
-				roots = append(roots, warnPattern("all", matchPackages("...", loaded.tags, []module.Version{Target}))...)
+				roots = append(roots, warnPattern("all", matchPackages("...", loaded.tags, false, []module.Version{Target}))...)
 				paths = append(paths, "all") // will expand after load completes
 
 			case search.IsMetaPackage(pkg): // std, cmd
@@ -113,7 +113,7 @@ func ImportPaths(args []string) []string {
 
 			case strings.Contains(pkg, "..."):
 				// TODO: Don't we need to reevaluate this one last time once the build list stops changing?
-				list := warnPattern(pkg, matchPackages(pkg, loaded.tags, buildList))
+				list := warnPattern(pkg, matchPackages(pkg, loaded.tags, true, buildList))
 				roots = append(roots, list...)
 				paths = append(paths, list...)
 
@@ -286,7 +286,7 @@ var anyTags = map[string]bool{"*": true}
 // TargetPackages returns the list of packages in the target (top-level) module,
 // under all build tag settings.
 func TargetPackages() []string {
-	return matchPackages("...", anyTags, []module.Version{Target})
+	return matchPackages("...", anyTags, false, []module.Version{Target})
 }
 
 // BuildList returns the module build list,

src/cmd/go/internal/modload/search.go

@@ -19,7 +19,7 @@ import (
 
 // matchPackages returns a list of packages in the list of modules
 // matching the pattern. Package loading assumes the given set of tags.
-func matchPackages(pattern string, tags map[string]bool, modules []module.Version) []string {
+func matchPackages(pattern string, tags map[string]bool, useStd bool, modules []module.Version) []string {
 	match := func(string) bool { return true }
 	treeCanMatch := func(string) bool { return true }
 	if !search.IsMetaPackage(pattern) {
@@ -35,28 +35,18 @@ func matchPackages(pattern string, tags map[string]bool, modules []module.Versio
 	}
 	var pkgs []string
 
-	for _, mod := range modules {
-		if !treeCanMatch(mod.Path) {
-			continue
-		}
-		var root string
-		if mod.Version == "" {
-			root = ModRoot
-		} else {
-			var err error
-			root, _, err = fetch(mod)
-			if err != nil {
-				base.Errorf("go: %v", err)
-				continue
-			}
-		}
+	walkPkgs := func(root, importPathRoot string) {
 		root = filepath.Clean(root)
-
 		filepath.Walk(root, func(path string, fi os.FileInfo, err error) error {
 			if err != nil {
 				return nil
 			}
 
+			// Don't use GOROOT/src but do walk down into it.
+			if path == root && importPathRoot == "" {
+				return nil
+			}
+
 			want := true
 			// Avoid .foo, _foo, and testdata directory trees.
 			_, elem := filepath.Split(path)
@@ -64,7 +54,10 @@ func matchPackages(pattern string, tags map[string]bool, modules []module.Versio
 				want = false
 			}
 
-			name := mod.Path + filepath.ToSlash(path[len(root):])
+			name := importPathRoot + filepath.ToSlash(path[len(root):])
+			if importPathRoot == "" {
+				name = name[1:] // cut leading slash
+			}
 			if !treeCanMatch(name) {
 				want = false
 			}
@@ -102,5 +95,28 @@ func matchPackages(pattern string, tags map[string]bool, modules []module.Versio
 			return nil
 		})
 	}
+
+	if useStd {
+		walkPkgs(cfg.GOROOTsrc, "")
+	}
+
+	for _, mod := range modules {
+		if !treeCanMatch(mod.Path) {
+			continue
+		}
+		var root string
+		if mod.Version == "" {
+			root = ModRoot
+		} else {
+			var err error
+			root, _, err = fetch(mod)
+			if err != nil {
+				base.Errorf("go: %v", err)
+				continue
+			}
+		}
+		walkPkgs(root, mod.Path)
+	}
+
 	return pkgs
 }

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

@@ -15,15 +15,14 @@ stdout '^unsafe$'
 ! stdout index/suffixarray
 
 # 'go list ...' should list packages in all active modules and the standard library.
-# BUG: It currently omits the standard library (https://golang.org/issue/26905).
 go list ...
 stdout example.com/unused/useerrors
 stdout example.com/m/useunsafe
 [cgo] stdout example.com/m/useC
 [!cgo] ! stdout example.com/m/useC
-# stdout '^unicode$'
-# stdout '^unsafe$'
-# stdout index/suffixarray
+stdout '^unicode$'
+stdout '^unsafe$'
+stdout index/suffixarray
 
 # 'go list example.com/m/...' should list packages in all modules that begin with
 # "example.com/m/".