os: make IsPermission, IsExist, and IsNotExist unwrap SyscallError too

Fixes #12674

Change-Id: I82f53026dd2fc27bd7999d43c27932d683d92af6
Reviewed-on: https://go-review.googlesource.com/15730Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/os/error_plan9.go

@@ -12,6 +12,8 @@ func isExist(err error) bool {
 		err = pe.Err
 	case *LinkError:
 		err = pe.Err
+	case *SyscallError:
+		err = pe.Err
 	}
 	return contains(err.Error(), " exists")
 }
@@ -24,6 +26,8 @@ func isNotExist(err error) bool {
 		err = pe.Err
 	case *LinkError:
 		err = pe.Err
+	case *SyscallError:
+		err = pe.Err
 	}
 	return contains(err.Error(), "does not exist") || contains(err.Error(), "not found") ||
 		contains(err.Error(), "has been removed") || contains(err.Error(), "no parent")
@@ -37,6 +41,8 @@ func isPermission(err error) bool {
 		err = pe.Err
 	case *LinkError:
 		err = pe.Err
+	case *SyscallError:
+		err = pe.Err
 	}
 	return contains(err.Error(), "permission denied")
 }

src/os/error_test.go

@@ -93,6 +93,8 @@ var isExistTests = []struct {
 	{&os.LinkError{Err: os.ErrPermission}, false, false},
 	{&os.LinkError{Err: os.ErrExist}, true, false},
 	{&os.LinkError{Err: os.ErrNotExist}, false, true},
+	{&os.SyscallError{Err: os.ErrNotExist}, false, true},
+	{&os.SyscallError{Err: os.ErrExist}, true, false},
 	{nil, false, false},
 }
 
@@ -107,6 +109,23 @@ func TestIsExist(t *testing.T) {
 	}
 }
 
+var isPermissionTests = []struct {
+	err  error
+	want bool
+}{
+	{nil, false},
+	{&os.PathError{Err: os.ErrPermission}, true},
+	{&os.SyscallError{Err: os.ErrPermission}, true},
+}
+
+func TestIsPermission(t *testing.T) {
+	for _, tt := range isPermissionTests {
+		if got := os.IsPermission(tt.err); got != tt.want {
+			t.Errorf("os.IsPermission(%#v) = %v; want %v", tt.err, got, tt.want)
+		}
+	}
+}
+
 func TestErrPathNUL(t *testing.T) {
 	f, err := ioutil.TempFile("", "_Go_ErrPathNUL\x00")
 	if err == nil {

src/os/error_unix.go

@@ -16,6 +16,8 @@ func isExist(err error) bool {
 		err = pe.Err
 	case *LinkError:
 		err = pe.Err
+	case *SyscallError:
+		err = pe.Err
 	}
 	return err == syscall.EEXIST || err == ErrExist
 }
@@ -28,6 +30,8 @@ func isNotExist(err error) bool {
 		err = pe.Err
 	case *LinkError:
 		err = pe.Err
+	case *SyscallError:
+		err = pe.Err
 	}
 	return err == syscall.ENOENT || err == ErrNotExist
 }
@@ -40,6 +44,8 @@ func isPermission(err error) bool {
 		err = pe.Err
 	case *LinkError:
 		err = pe.Err
+	case *SyscallError:
+		err = pe.Err
 	}
 	return err == syscall.EACCES || err == syscall.EPERM || err == ErrPermission
 }

src/os/error_windows.go

@@ -14,6 +14,8 @@ func isExist(err error) bool {
 		err = pe.Err
 	case *LinkError:
 		err = pe.Err
+	case *SyscallError:
+		err = pe.Err
 	}
 	return err == syscall.ERROR_ALREADY_EXISTS ||
 		err == syscall.ERROR_FILE_EXISTS || err == ErrExist
@@ -29,6 +31,8 @@ func isNotExist(err error) bool {
 		err = pe.Err
 	case *LinkError:
 		err = pe.Err
+	case *SyscallError:
+		err = pe.Err
 	}
 	return err == syscall.ERROR_FILE_NOT_FOUND ||
 		err == _ERROR_BAD_NETPATH ||
@@ -43,6 +47,8 @@ func isPermission(err error) bool {
 		err = pe.Err
 	case *LinkError:
 		err = pe.Err
+	case *SyscallError:
+		err = pe.Err
 	}
 	return err == syscall.ERROR_ACCESS_DENIED || err == ErrPermission
 }