os: test that IsExist and IsNotExist handle PathError and LinkError

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/6442080

src/pkg/os/error_plan9.go

@@ -5,30 +5,36 @@
 package os
 
 func isExist(err error) bool {
-	if err == nil {
+	switch pe := err.(type) {
+	case nil:
 		return false
-	}
-	if pe, ok := err.(*PathError); ok {
+	case *PathError:
+		err = pe.Err
+	case *LinkError:
 		err = pe.Err
 	}
 	return contains(err.Error(), " exists")
 }
 
 func isNotExist(err error) bool {
-	if err == nil {
+	switch pe := err.(type) {
+	case nil:
 		return false
-	}
-	if pe, ok := err.(*PathError); ok {
+	case *PathError:
+		err = pe.Err
+	case *LinkError:
 		err = pe.Err
 	}
 	return contains(err.Error(), "does not exist")
 }
 
 func isPermission(err error) bool {
-	if err == nil {
+	switch pe := err.(type) {
+	case nil:
 		return false
-	}
-	if pe, ok := err.(*PathError); ok {
+	case *PathError:
+		err = pe.Err
+	case *LinkError:
 		err = pe.Err
 	}
 	return contains(err.Error(), "permission denied")

src/pkg/os/error_posix.go

@@ -9,21 +9,36 @@ package os
 import "syscall"
 
 func isExist(err error) bool {
-	if pe, ok := err.(*PathError); ok {
+	switch pe := err.(type) {
+	case nil:
+		return false
+	case *PathError:
+		err = pe.Err
+	case *LinkError:
 		err = pe.Err
 	}
 	return err == syscall.EEXIST || err == ErrExist
 }
 
 func isNotExist(err error) bool {
-	if pe, ok := err.(*PathError); ok {
+	switch pe := err.(type) {
+	case nil:
+		return false
+	case *PathError:
+		err = pe.Err
+	case *LinkError:
 		err = pe.Err
 	}
 	return err == syscall.ENOENT || err == ErrNotExist
 }
 
 func isPermission(err error) bool {
-	if pe, ok := err.(*PathError); ok {
+	switch pe := err.(type) {
+	case nil:
+		return false
+	case *PathError:
+		err = pe.Err
+	case *LinkError:
 		err = pe.Err
 	}
 	return err == syscall.EACCES || err == syscall.EPERM || err == ErrPermission

src/pkg/os/error_test.go

@@ -79,3 +79,30 @@ func checkErrorPredicate(predName string, pred func(error) bool, err error) stri
 	}
 	return ""
 }
+
+var isExistTests = []struct {
+	err   error
+	is    bool
+	isnot bool
+}{
+	{&os.PathError{Err: os.ErrInvalid}, false, false},
+	{&os.PathError{Err: os.ErrPermission}, false, false},
+	{&os.PathError{Err: os.ErrExist}, true, false},
+	{&os.PathError{Err: os.ErrNotExist}, false, true},
+	{&os.LinkError{Err: os.ErrInvalid}, false, false},
+	{&os.LinkError{Err: os.ErrPermission}, false, false},
+	{&os.LinkError{Err: os.ErrExist}, true, false},
+	{&os.LinkError{Err: os.ErrNotExist}, false, true},
+	{nil, false, false},
+}
+
+func TestIsExist(t *testing.T) {
+	for _, tt := range isExistTests {
+		if is := os.IsExist(tt.err); is != tt.is {
+			t.Errorf("os.IsExist(%T %v) = %v, want %v", tt.err, tt.err, is, tt.is)
+		}
+		if isnot := os.IsNotExist(tt.err); isnot != tt.isnot {
+			t.Errorf("os.IsNotExist(%T %v) = %v, want %v", tt.err, tt.err, isnot, tt.isnot)
+		}
+	}
+}

src/pkg/os/error_windows.go

@@ -7,10 +7,12 @@ package os
 import "syscall"
 
 func isExist(err error) bool {
-	if pe, ok := err.(*PathError); ok {
+	switch pe := err.(type) {
+	case nil:
+		return false
+	case *PathError:
 		err = pe.Err
-	}
-	if pe, ok := err.(*LinkError); ok {
+	case *LinkError:
 		err = pe.Err
 	}
 	return err == syscall.ERROR_ALREADY_EXISTS ||
@@ -18,7 +20,12 @@ func isExist(err error) bool {
 }
 
 func isNotExist(err error) bool {
-	if pe, ok := err.(*PathError); ok {
+	switch pe := err.(type) {
+	case nil:
+		return false
+	case *PathError:
+		err = pe.Err
+	case *LinkError:
 		err = pe.Err
 	}
 	return err == syscall.ERROR_FILE_NOT_FOUND ||
@@ -26,7 +33,12 @@ func isNotExist(err error) bool {
 }
 
 func isPermission(err error) bool {
-	if pe, ok := err.(*PathError); ok {
+	switch pe := err.(type) {
+	case nil:
+		return false
+	case *PathError:
+		err = pe.Err
+	case *LinkError:
 		err = pe.Err
 	}
 	return err == syscall.ERROR_ACCESS_DENIED || err == ErrPermission