cmd/go: allow list of absolute directory path

Relative directory paths have always worked.
This CL makes absolute directory paths be handled the same way.
(It was an oversight that they were excluded.)

It also fixes the case of naming the directory holding source code
for a package in a module dependency.

Fixes #14177.
Fixes #26550.

Change-Id: I29a0ca2795d35eca773121ee91a97628b56947ce
Reviewed-on: https://go-review.googlesource.com/126715
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

src/cmd/go/internal/load/pkg.go

@@ -1755,8 +1755,12 @@ func LoadPackage(arg string, stk *ImportStack) *Package {
 	// This lets you run go test ./ioutil in package io and be
 	// referring to io/ioutil rather than a hypothetical import of
 	// "./ioutil".
-	if build.IsLocalImport(arg) {
-		bp, _ := cfg.BuildContext.ImportDir(filepath.Join(base.Cwd, arg), build.FindOnly)
+	if build.IsLocalImport(arg) || filepath.IsAbs(arg) {
+		dir := arg
+		if !filepath.IsAbs(arg) {
+			dir = filepath.Join(base.Cwd, arg)
+		}
+		bp, _ := cfg.BuildContext.ImportDir(dir, build.FindOnly)
 		if bp.ImportPath != "" && bp.ImportPath != "." {
 			arg = bp.ImportPath
 		}

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

@@ -11,6 +11,7 @@ import (
 	"go/build"
 	"io/ioutil"
 	"os"
+	"path"
 	"path/filepath"
 	"sort"
 	"strings"
@@ -60,17 +61,26 @@ func ImportPaths(args []string) []string {
 		paths = nil
 		for _, pkg := range cleaned {
 			switch {
-			case build.IsLocalImport(pkg):
+			case build.IsLocalImport(pkg) || filepath.IsAbs(pkg):
 				list := []string{pkg}
 				if strings.Contains(pkg, "...") {
 					// TODO: Where is the go.mod cutoff?
 					list = warnPattern(pkg, search.AllPackagesInFS(pkg))
 				}
 				for _, pkg := range list {
-					dir := filepath.Join(cwd, pkg)
+					dir := pkg
+					if !filepath.IsAbs(dir) {
+						dir = filepath.Join(cwd, pkg)
+					} else {
+						dir = filepath.Clean(dir)
+					}
+
+					// Note: The checks for @ here are just to avoid misinterpreting
+					// the module cache directories (formerly GOPATH/src/mod/foo@v1.5.2/bar).
+					// It's not strictly necessary but helpful to keep the checks.
 					if dir == ModRoot {
 						pkg = Target.Path
-					} else if strings.HasPrefix(dir, ModRoot+string(filepath.Separator)) {
+					} else if strings.HasPrefix(dir, ModRoot+string(filepath.Separator)) && !strings.Contains(dir[len(ModRoot):], "@") {
 						suffix := filepath.ToSlash(dir[len(ModRoot):])
 						if strings.HasPrefix(suffix, "/vendor/") {
 							// TODO getmode vendor check
@@ -78,8 +88,12 @@ func ImportPaths(args []string) []string {
 						} else {
 							pkg = Target.Path + suffix
 						}
+					} else if sub := search.InDir(dir, cfg.GOROOTsrc); sub != "" && !strings.Contains(sub, "@") {
+						pkg = filepath.ToSlash(sub)
+					} else if path := pathInModuleCache(dir); path != "" {
+						pkg = path
 					} else {
-						base.Errorf("go: package %s outside module root", pkg)
+						base.Errorf("go: directory %s outside available modules", base.ShortPath(dir))
 						continue
 					}
 					roots = append(roots, pkg)
@@ -156,6 +170,24 @@ func ImportPaths(args []string) []string {
 	return final
 }
 
+// pathInModuleCache returns the import path of the directory dir,
+// if dir is in the module cache copy of a module in our build list.
+func pathInModuleCache(dir string) string {
+	for _, m := range buildList[1:] {
+		root, err := modfetch.DownloadDir(m)
+		if err != nil {
+			continue
+		}
+		if sub := search.InDir(dir, root); sub != "" {
+			sub = filepath.ToSlash(sub)
+			if !strings.Contains(sub, "/vendor/") && !strings.HasPrefix(sub, "vendor/") && !strings.Contains(sub, "@") {
+				return path.Join(m.Path, filepath.ToSlash(sub))
+			}
+		}
+	}
+	return ""
+}
+
 // warnPattern returns list, the result of matching pattern,
 // but if list is empty then first it prints a warning about
 // the pattern not matching any packages.

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

+# go list with path to directory should work
+
+env GO111MODULE=off
+go list -f '{{.ImportPath}}' $GOROOT/src/math
+stdout ^math$
+
+env GO111MODULE=on
+go list -f '{{.ImportPath}}' $GOROOT/src/math
+stdout ^math$
+go list -f '{{.ImportPath}}' .
+stdout ^x$
+go list -f '{{.ImportPath}}' $GOPATH/src/mod/rsc.io/quote@v1.5.2
+stdout '^rsc.io/quote$'
+go list -f '{{.ImportPath}}' $GOPATH/src/mod/rsc.io/sampler@v1.3.0
+stdout '^rsc.io/sampler$'
+go get rsc.io/sampler@v1.3.1
+go list -f '{{.ImportPath}}' $GOPATH/src/mod/rsc.io/sampler@v1.3.1
+stdout '^rsc.io/sampler$'
+! go list -f '{{.ImportPath}}' $GOPATH/src/mod/rsc.io/sampler@v1.3.0
+stderr 'outside available modules'
+
+-- go.mod --
+module x
+require rsc.io/quote v1.5.2
+
+-- x.go --
+package x