hst/fs: remove type method

Having a method that returns the canonical string representation of its type seemed like a much better idea for an implementation that never made it to staging. Remove it here and clean up marshal type assertions.

Signed-off-by: Ophestra <cat@gensokyo.uk>

hst/fs.go

@@ -11,8 +11,6 @@ import (
 
 // FilesystemConfig is an abstract representation of a mount point.
 type FilesystemConfig interface {
-	// Type returns the type of this mount point.
-	Type() string
 	// Valid returns whether the configuration is valid.
 	Valid() bool
 	// Target returns the pathname of the mount point in the container.
@@ -34,12 +32,8 @@ type FSTypeError string
 
 func (f FSTypeError) Error() string { return fmt.Sprintf("invalid filesystem type %q", string(f)) }
 
-// FSImplError is returned when the underlying struct of [FilesystemConfig] does not match
-// what [FilesystemConfig.Type] claims to be.
-type FSImplError struct {
-	Type  string
-	Value FilesystemConfig
-}
+// FSImplError is returned for unsupported implementations of [FilesystemConfig].
+type FSImplError struct{ Value FilesystemConfig }
 
 func (f FSImplError) Error() string {
 	implType := reflect.TypeOf(f.Value)
@@ -53,57 +47,49 @@ func (f FSImplError) Error() string {
 	} else {
 		name += "nil"
 	}
-	return fmt.Sprintf("implementation %s is not %s", name, f.Type)
+	return fmt.Sprintf("implementation %s not supported", name)
 }
 
 // FilesystemConfigJSON is the [json] adapter for [FilesystemConfig].
-type FilesystemConfigJSON struct {
-	FilesystemConfig
-}
+type FilesystemConfigJSON struct{ FilesystemConfig }
 
 // Valid returns whether the [FilesystemConfigJSON] is valid.
 func (f *FilesystemConfigJSON) Valid() bool {
 	return f != nil && f.FilesystemConfig != nil && f.FilesystemConfig.Valid()
 }
 
+// fsType holds the string representation of a [FilesystemConfig]'s concrete type.
+type fsType struct {
+	Type string `json:"type"`
+}
+
 func (f *FilesystemConfigJSON) MarshalJSON() ([]byte, error) {
 	if f == nil || f.FilesystemConfig == nil {
 		return nil, ErrFSNull
 	}
 	var v any
-	t := f.Type()
-	switch t {
-	case FilesystemBind:
-		if ct, ok := f.FilesystemConfig.(*FSBind); !ok {
-			return nil, FSImplError{t, f.FilesystemConfig}
-		} else {
+	switch cv := f.FilesystemConfig.(type) {
+	case *FSBind:
 		v = &struct {
-				Type string `json:"type"`
+			fsType
 			*FSBind
-			}{FilesystemBind, ct}
-		}
+		}{fsType{FilesystemBind}, cv}
 
-	case FilesystemEphemeral:
-		if ct, ok := f.FilesystemConfig.(*FSEphemeral); !ok {
-			return nil, FSImplError{t, f.FilesystemConfig}
-		} else {
+	case *FSEphemeral:
 		v = &struct {
-				Type string `json:"type"`
+			fsType
 			*FSEphemeral
-			}{FilesystemEphemeral, ct}
-		}
+		}{fsType{FilesystemEphemeral}, cv}
 
 	default:
-		return nil, FSTypeError(t)
+		return nil, FSImplError{f.FilesystemConfig}
 	}
 
 	return json.Marshal(v)
 }
 
 func (f *FilesystemConfigJSON) UnmarshalJSON(data []byte) error {
-	t := new(struct {
-		Type string `json:"type"`
-	})
+	t := new(fsType)
 	if err := json.Unmarshal(data, &t); err != nil {
 		return err
 	}

hst/fs_test.go

@@ -28,17 +28,11 @@ func TestFilesystemConfigJSON(t *testing.T) {
 			`{"type":"cat","meow":true}`, `{"fs":{"type":"cat","meow":true},"magic":3236757504}`},
 
 		{"bad impl bind", hst.FilesystemConfigJSON{FilesystemConfig: stubFS{"bind"}},
-			hst.FSImplError{
-				Type:  "bind",
-				Value: stubFS{"bind"},
-			},
+			hst.FSImplError{Value: stubFS{"bind"}},
 			"\x00", "\x00"},
 
 		{"bad impl ephemeral", hst.FilesystemConfigJSON{FilesystemConfig: stubFS{"ephemeral"}},
-			hst.FSImplError{
-				Type:  "ephemeral",
-				Value: stubFS{"ephemeral"},
-			},
+			hst.FSImplError{Value: stubFS{"ephemeral"}},
 			"\x00", "\x00"},
 
 		{"bind", hst.FilesystemConfigJSON{
@@ -66,12 +60,18 @@ func TestFilesystemConfigJSON(t *testing.T) {
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Run("marshal", func(t *testing.T) {
+				wantErr := tc.wantErr
+				if errors.As(wantErr, new(hst.FSTypeError)) {
+					// for unsupported implementation tc
+					wantErr = hst.FSImplError{Value: stubFS{"cat"}}
+				}
+
 				{
 					d, err := json.Marshal(&tc.want)
-					if !errors.Is(err, tc.wantErr) {
-						t.Errorf("Marshal: error = %v, want %v", err, tc.wantErr)
+					if !errors.Is(err, wantErr) {
+						t.Errorf("Marshal: error = %v, want %v", err, wantErr)
 					}
-					if tc.wantErr != nil {
+					if wantErr != nil {
 						goto checkSMarshal
 					}
 					if string(d) != tc.data {
@@ -82,10 +82,10 @@ func TestFilesystemConfigJSON(t *testing.T) {
 			checkSMarshal:
 				{
 					d, err := json.Marshal(&sCheck{tc.want, syscall.MS_MGC_VAL})
-					if !errors.Is(err, tc.wantErr) {
-						t.Errorf("Marshal: error = %v, want %v", err, tc.wantErr)
+					if !errors.Is(err, wantErr) {
+						t.Errorf("Marshal: error = %v, want %v", err, wantErr)
 					}
-					if tc.wantErr != nil {
+					if wantErr != nil {
 						return
 					}
 					if string(d) != tc.sData {
@@ -170,15 +170,15 @@ func TestFSErrors(t *testing.T) {
 			val  hst.FilesystemConfig
 			want string
 		}{
-			{"nil", nil, "implementation nil is not cat"},
-			{"stub", stubFS{"cat"}, "implementation stubFS is not cat"},
-			{"*stub", &stubFS{"cat"}, "implementation *stubFS is not cat"},
-			{"(*stub)(nil)", (*stubFS)(nil), "implementation *stubFS is not cat"},
+			{"nil", nil, "implementation nil not supported"},
+			{"stub", stubFS{"cat"}, "implementation stubFS not supported"},
+			{"*stub", &stubFS{"cat"}, "implementation *stubFS not supported"},
+			{"(*stub)(nil)", (*stubFS)(nil), "implementation *stubFS not supported"},
 		}
 
 		for _, tc := range testCases {
 			t.Run(tc.name, func(t *testing.T) {
-				err := hst.FSImplError{Type: "cat", Value: tc.val}
+				err := hst.FSImplError{Value: tc.val}
 				if got := err.Error(); got != tc.want {
 					t.Errorf("Error: %q, want %q", got, tc.want)
 				}
@@ -191,7 +191,6 @@ type stubFS struct {
 	typeName string
 }
 
-func (s stubFS) Type() string                { return s.typeName }
 func (s stubFS) Valid() bool                 { return false }
 func (s stubFS) Target() *container.Absolute { panic("unreachable") }
 func (s stubFS) Host() []*container.Absolute { panic("unreachable") }
@@ -213,15 +212,9 @@ type fsTestCase struct {
 	str    string
 }
 
-func checkFs(t *testing.T, fstype string, testCases []fsTestCase) {
+func checkFs(t *testing.T, testCases []fsTestCase) {
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
-			t.Run("type", func(t *testing.T) {
-				if got := tc.fs.Type(); got != fstype {
-					t.Errorf("Type: %q, want %q", got, fstype)
-				}
-			})
-
 			t.Run("valid", func(t *testing.T) {
 				if got := tc.fs.Valid(); got != tc.valid {
 					t.Errorf("Valid: %v, want %v", got, tc.valid)

hst/fsbind.go

@@ -26,7 +26,6 @@ type FSBind struct {
 	Optional bool `json:"optional,omitempty"`
 }
 
-func (b *FSBind) Type() string { return FilesystemBind }
 func (b *FSBind) Valid() bool { return b != nil && b.Src != nil }
 
 func (b *FSBind) Target() *container.Absolute {

hst/fsbind_test.go

@@ -8,7 +8,7 @@ import (
 )
 
 func TestFSBind(t *testing.T) {
-	checkFs(t, "bind", []fsTestCase{
+	checkFs(t, []fsTestCase{
 		{"nil", (*hst.FSBind)(nil), false, nil, nil, nil, "<invalid>"},
 
 		{"full", &hst.FSBind{

hst/fsephemeral.go

@@ -25,7 +25,6 @@ type FSEphemeral struct {
 	Perm os.FileMode `json:"perm,omitempty"`
 }
 
-func (e *FSEphemeral) Type() string { return FilesystemEphemeral }
 func (e *FSEphemeral) Valid() bool { return e != nil && e.Dst != nil }
 
 func (e *FSEphemeral) Target() *container.Absolute {

hst/fsephemeral_test.go

@@ -9,7 +9,7 @@ import (
 )
 
 func TestFSEphemeral(t *testing.T) {
-	checkFs(t, "ephemeral", []fsTestCase{
+	checkFs(t, []fsTestCase{
 		{"nil", (*hst.FSEphemeral)(nil), false, nil, nil, nil, "<invalid>"},
 
 		{"full", &hst.FSEphemeral{