path/filepath: fix match of \\?\c:\* on Windows

\\?\c:\ is a "root directory" that is not subject to further matching,
but the ? makes it look like a pattern, which was causing an
infinite recursion. Make sure the code understands the ? is not a pattern.

Fixes #15879.

Change-Id: I3a4310bbc398bcae764b9f8859c875317345e757
Reviewed-on: https://go-review.googlesource.com/31460
Reviewed-by: Quentin Smith <quentin@golang.org>

src/path/filepath/match.go

@@ -240,13 +240,14 @@ func Glob(pattern string) (matches []string, err error) {
 	}
 
 	dir, file := Split(pattern)
+	volumeLen := 0
 	if runtime.GOOS == "windows" {
-		dir = cleanGlobPathWindows(dir)
+		volumeLen, dir = cleanGlobPathWindows(dir)
 	} else {
 		dir = cleanGlobPath(dir)
 	}
 
-	if !hasMeta(dir) {
+	if !hasMeta(dir[volumeLen:]) {
 		return glob(dir, file, nil)
 	}
 
@@ -283,18 +284,21 @@ func cleanGlobPath(path string) string {
 }
 
 // cleanGlobPathWindows is windows version of cleanGlobPath.
-func cleanGlobPathWindows(path string) string {
+func cleanGlobPathWindows(path string) (prefixLen int, cleaned string) {
 	vollen := volumeNameLen(path)
 	switch {
 	case path == "":
-		return "."
+		return 0, "."
 	case vollen+1 == len(path) && os.IsPathSeparator(path[len(path)-1]): // /, \, C:\ and C:/
 		// do nothing to the path
-		return path
+		return vollen + 1, path
 	case vollen == len(path) && len(path) == 2: // C:
-		return path + "." // convert C: into C:.
+		return vollen, path + "." // convert C: into C:.
 	default:
-		return path[0 : len(path)-1] // chop off trailing separator
+		if vollen >= len(path) {
+			vollen = len(path) - 1
+		}
+		return vollen, path[0 : len(path)-1] // chop off trailing separator
 	}
 }
 

src/path/filepath/path_windows.go

@@ -37,7 +37,7 @@ func volumeNameLen(path string) int {
 	if path[1] == ':' && ('a' <= c && c <= 'z' || 'A' <= c && c <= 'Z') {
 		return 2
 	}
-	// is it UNC
+	// is it UNC? https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx
 	if l := len(path); l >= 5 && isSlash(path[0]) && isSlash(path[1]) &&
 		!isSlash(path[2]) && path[2] != '.' {
 		// first, leading `\\` and next shouldn't be `\`. its server name.

src/path/filepath/path_windows_test.go

@@ -12,6 +12,7 @@ import (
 	"os/exec"
 	"path/filepath"
 	"reflect"
+	"runtime/debug"
 	"strings"
 	"testing"
 )
@@ -413,3 +414,10 @@ func TestToNorm(t *testing.T) {
 		}
 	}
 }
+
+func TestUNC(t *testing.T) {
+	// Test that this doesn't go into an infinite recursion.
+	// See golang.org/issue/15879.
+	defer debug.SetMaxStack(debug.SetMaxStack(1e6))
+	filepath.Glob(`\\?\c:\*`)
+}