go: fix the import path "./..." not matching ".".

Tested manually.

Fixes #3554.

Before:
$ cd $GOROOT/src/pkg
$ go list io
io
$ go list io/...
io
io/ioutil
$ cd $GOROOT/src/pkg/io
$ go list .
io
$ go list ./...
io/ioutil

After:
$ cd $GOROOT/src/pkg
$ go list io
io
$ go list io/...
io
io/ioutil
$ cd $GOROOT/src/pkg/io
$ go list .
io
$ go list ./...
io
io/ioutil
$ go list ././...
io
io/ioutil
$ go list ././.././io/...
io
io/ioutil
$ go list ../image
image
$ go list ../image/...
image
image/color
image/draw
image/gif
image/jpeg
image/png
$ go list ../.../template
html/template
text/template
$ cd $GOROOT/src/pkg
$ go list ./io
io
$ go list ./io/...
io
io/ioutil
$ go list ./.../pprof
net/http/pprof
runtime/pprof
$ go list ./compress
can't load package: package compress: no Go source files in /home/nigeltao/go/src/pkg/compress
$ go list ./compress/...
compress/bzip2
compress/flate
compress/gzip
compress/lzw
compress/zlib
$ cd $GOROOT/src/pkg/code.google.com
$ go list ./p/leveldb-go/...
code.google.com/p/leveldb-go/leveldb
code.google.com/p/leveldb-go/leveldb/crc
code.google.com/p/leveldb-go/leveldb/db
code.google.com/p/leveldb-go/leveldb/memdb
code.google.com/p/leveldb-go/leveldb/memfs
code.google.com/p/leveldb-go/leveldb/record
code.google.com/p/leveldb-go/leveldb/table
code.google.com/p/leveldb-go/manualtest/filelock
$ go list ./p/.../truetype
code.google.com/p/freetype-go/example/truetype
code.google.com/p/freetype-go/freetype/truetype
$ go list ./p/.../example
warning: "./p/.../example" matched no packages
$ go list ./p/.../example/...
code.google.com/p/freetype-go/example/freetype
code.google.com/p/freetype-go/example/gamma
code.google.com/p/freetype-go/example/raster
code.google.com/p/freetype-go/example/round
code.google.com/p/freetype-go/example/truetype
code.google.com/p/x-go-binding/example/imgview
code.google.com/p/x-go-binding/example/xgb

R=rsc
CC=golang-dev
https://golang.org/cl/6194056

src/cmd/go/main.go

@@ -500,13 +500,25 @@ func matchPackagesInFS(pattern string) []string {
 
 	var pkgs []string
 	filepath.Walk(dir, func(path string, fi os.FileInfo, err error) error {
-		if err != nil || !fi.IsDir() || path == dir {
+		if err != nil || !fi.IsDir() {
 			return nil
 		}
+		if path == dir {
+			// filepath.Walk starts at dir and recurses. For the recursive case,
+			// the path is the result of filepath.Join, which calls filepath.Clean.
+			// The initial case is not Cleaned, though, so we do this explicitly.
+			//
+			// This converts a path like "./io/" to "io". Without this step, running
+			// "cd $GOROOT/src/pkg; go list ./io/..." would incorrectly skip the io
+			// package, because prepending the prefix "./" to the unclean path would
+			// result in "././io", and match("././io") returns false.
+			path = filepath.Clean(path)
+		}
 
-		// Avoid .foo, _foo, and testdata directory trees.
+		// Avoid .foo, _foo, and testdata directory trees, but do not avoid "." or "..".
 		_, elem := filepath.Split(path)
-		if strings.HasPrefix(elem, ".") || strings.HasPrefix(elem, "_") || elem == "testdata" {
+		dot := strings.HasPrefix(elem, ".") && elem != "." && elem != ".."
+		if dot || strings.HasPrefix(elem, "_") || elem == "testdata" {
 			return filepath.SkipDir
 		}