container/check: return error backed by string type

The struct turned out not necessary during initial implementation but was not unwrapped into its single string field. This change replaces it with the underlying string and removes the indirection.

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

container/check/absolute.go

@@ -13,15 +13,18 @@ import (
 )
 
 // AbsoluteError is returned by [NewAbs] and holds the invalid pathname.
-type AbsoluteError struct{ Pathname string }
+type AbsoluteError string
 
-func (e *AbsoluteError) Error() string { return fmt.Sprintf("path %q is not absolute", e.Pathname) }
-func (e *AbsoluteError) Is(target error) bool {
-	var ce *AbsoluteError
+func (e AbsoluteError) Error() string {
+	return fmt.Sprintf("path %q is not absolute", string(e))
+}
+
+func (e AbsoluteError) Is(target error) bool {
+	var ce AbsoluteError
 	if !errors.As(target, &ce) {
 		return errors.Is(target, syscall.EINVAL)
 	}
-	return *e == *ce
+	return e == ce
 }
 
 // Absolute holds a pathname checked to be absolute.
@@ -59,7 +62,7 @@ func (a *Absolute) Is(v *Absolute) bool {
 // NewAbs checks pathname and returns a new [Absolute] if pathname is absolute.
 func NewAbs(pathname string) (*Absolute, error) {
 	if !path.IsAbs(pathname) {
-		return nil, &AbsoluteError{pathname}
+		return nil, AbsoluteError(pathname)
 	}
 	return unsafeAbs(pathname), nil
 }
@@ -90,7 +93,7 @@ func (a *Absolute) GobEncode() ([]byte, error) {
 func (a *Absolute) GobDecode(data []byte) error {
 	pathname := string(data)
 	if !path.IsAbs(pathname) {
-		return &AbsoluteError{pathname}
+		return AbsoluteError(pathname)
 	}
 	a.pathname = unique.Make(pathname)
 	return nil
@@ -108,7 +111,7 @@ func (a *Absolute) UnmarshalJSON(data []byte) error {
 		return err
 	}
 	if !path.IsAbs(pathname) {
-		return &AbsoluteError{pathname}
+		return AbsoluteError(pathname)
 	}
 	a.pathname = unique.Make(pathname)
 	return nil

container/check/absolute_test.go

@@ -31,8 +31,8 @@ func TestAbsoluteError(t *testing.T) {
 	}{
 		{"EINVAL", new(AbsoluteError), syscall.EINVAL, true},
 		{"not EINVAL", new(AbsoluteError), syscall.EBADE, false},
-		{"ne val", new(AbsoluteError), &AbsoluteError{Pathname: "etc"}, false},
-		{"equals", &AbsoluteError{Pathname: "etc"}, &AbsoluteError{Pathname: "etc"}, true},
+		{"ne val", new(AbsoluteError), AbsoluteError("etc"), false},
+		{"equals", AbsoluteError("etc"), AbsoluteError("etc"), true},
 	}
 
 	for _, tc := range testCases {
@@ -45,7 +45,7 @@ func TestAbsoluteError(t *testing.T) {
 		t.Parallel()
 
 		want := `path "etc" is not absolute`
-		if got := (&AbsoluteError{Pathname: "etc"}).Error(); got != want {
+		if got := (AbsoluteError("etc")).Error(); got != want {
 			t.Errorf("Error: %q, want %q", got, want)
 		}
 	})
@@ -62,8 +62,8 @@ func TestNewAbs(t *testing.T) {
 		wantErr  error
 	}{
 		{"good", "/etc", MustAbs("/etc"), nil},
-		{"not absolute", "etc", nil, &AbsoluteError{Pathname: "etc"}},
-		{"zero", "", nil, &AbsoluteError{Pathname: ""}},
+		{"not absolute", "etc", nil, AbsoluteError("etc")},
+		{"zero", "", nil, AbsoluteError("")},
 	}
 
 	for _, tc := range testCases {
@@ -84,7 +84,7 @@ func TestNewAbs(t *testing.T) {
 		t.Parallel()
 
 		defer func() {
-			wantPanic := &AbsoluteError{Pathname: "etc"}
+			wantPanic := AbsoluteError("etc")
 
 			if r := recover(); !reflect.DeepEqual(r, wantPanic) {
 				t.Errorf("MustAbs: panic = %v; want %v", r, wantPanic)
@@ -175,7 +175,7 @@ func TestCodecAbsolute(t *testing.T) {
 
 			`"/etc"`, `{"val":"/etc","magic":3236757504}`},
 		{"not absolute", nil,
-			&AbsoluteError{Pathname: "etc"},
+			AbsoluteError("etc"),
 			"\t\x7f\x05\x01\x02\xff\x82\x00\x00\x00\a\xff\x80\x00\x03etc",
 			",\xff\x83\x03\x01\x01\x06sCheck\x01\xff\x84\x00\x01\x02\x01\bPathname\x01\xff\x80\x00\x01\x05Magic\x01\x06\x00\x00\x00\t\x7f\x05\x01\x02\xff\x82\x00\x00\x00\x0f\xff\x84\x01\x03etc\x01\xfb\x01\x81\xda\x00\x00\x00",
 

container/errors.go

@@ -18,7 +18,7 @@ func messageFromError(err error) (m string, ok bool) {
 	if m, ok = messagePrefixP[os.PathError]("cannot ", err); ok {
 		return
 	}
-	if m, ok = messagePrefixP[check.AbsoluteError](zeroString, err); ok {
+	if m, ok = messagePrefix[check.AbsoluteError](zeroString, err); ok {
 		return
 	}
 	if m, ok = messagePrefix[OpRepeatError](zeroString, err); ok {

container/errors_test.go

@@ -37,7 +37,7 @@ func TestMessageFromError(t *testing.T) {
 			Err:  stub.UniqueError(0xdeadbeef),
 		}, "cannot mount /sysroot: unique error 3735928559 injected by the test suite", true},
 
-		{"absolute", &check.AbsoluteError{Pathname: "etc/mtab"},
+		{"absolute", check.AbsoluteError("etc/mtab"),
 			`path "etc/mtab" is not absolute`, true},
 
 		{"repeat", OpRepeatError("autoetc"),

container/initoverlay_test.go

@@ -312,7 +312,10 @@ func TestMountOverlayOp(t *testing.T) {
 			},
 		}},
 
-		{"ephemeral", new(Ops).OverlayEphemeral(check.MustAbs("/nix/store"), check.MustAbs("/mnt-root/nix/.ro-store")), Ops{
+		{"ephemeral", new(Ops).OverlayEphemeral(
+			check.MustAbs("/nix/store"),
+			check.MustAbs("/mnt-root/nix/.ro-store"),
+		), Ops{
 			&MountOverlayOp{
 				Target: check.MustAbs("/nix/store"),
 				Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},
@@ -320,7 +323,10 @@ func TestMountOverlayOp(t *testing.T) {
 			},
 		}},
 
-		{"readonly", new(Ops).OverlayReadonly(check.MustAbs("/nix/store"), check.MustAbs("/mnt-root/nix/.ro-store")), Ops{
+		{"readonly", new(Ops).OverlayReadonly(
+			check.MustAbs("/nix/store"),
+			check.MustAbs("/mnt-root/nix/.ro-store"),
+		), Ops{
 			&MountOverlayOp{
 				Target: check.MustAbs("/nix/store"),
 				Lower:  []*check.Absolute{check.MustAbs("/mnt-root/nix/.ro-store")},

container/initsymlink.go

@@ -31,7 +31,7 @@ func (l *SymlinkOp) Valid() bool { return l != nil && l.Target != nil && l.LinkN
 func (l *SymlinkOp) early(_ *setupState, k syscallDispatcher) error {
 	if l.Dereference {
 		if !path.IsAbs(l.LinkName) {
-			return &check.AbsoluteError{Pathname: l.LinkName}
+			return check.AbsoluteError(l.LinkName)
 		}
 		if name, err := k.readlink(l.LinkName); err != nil {
 			return err

container/initsymlink_test.go

@@ -23,7 +23,7 @@ func TestSymlinkOp(t *testing.T) {
 			Target:      check.MustAbs("/etc/mtab"),
 			LinkName:    "etc/mtab",
 			Dereference: true,
-		}, nil, &check.AbsoluteError{Pathname: "etc/mtab"}, nil, nil},
+		}, nil, check.AbsoluteError("etc/mtab"), nil, nil},
 
 		{"readlink", &Params{ParentPerm: 0755}, &SymlinkOp{
 			Target:      check.MustAbs("/etc/mtab"),