cmd/viewer,type/views: add MapSlice for maps of slices

This abstraction provides a nicer way to work with
maps of slices without having to write out three long type
params.

This also allows it to provide an AsMap implementation which
copies the map and the slices at least.

Updates tailscale/corp#20910

Signed-off-by: Maisem Ali <maisem@tailscale.com>

cmd/viewer/tests/tests_view.go

@@ -188,11 +188,7 @@ func (v *MapView) UnmarshalJSON(b []byte) error {
 
 func (v MapView) Int() views.Map[string, int] { return views.MapOf(v.ж.Int) }
 
-func (v MapView) SliceInt() views.MapFn[string, []int, views.Slice[int]] {
-	return views.MapFnOf(v.ж.SliceInt, func(t []int) views.Slice[int] {
-		return views.SliceOf(t)
-	})
-}
+func (v MapView) SliceInt() views.MapSlice[string, int] { return views.MapSliceOf(v.ж.SliceInt) }
 
 func (v MapView) StructPtrWithPtr() views.MapFn[string, *StructWithPtrs, StructWithPtrsView] {
 	return views.MapFnOf(v.ж.StructPtrWithPtr, func(t *StructWithPtrs) StructWithPtrsView {

cmd/viewer/viewer.go

@@ -92,6 +92,9 @@ func(v {{.ViewName}}) {{.FieldName}}() views.MapFn[{{.MapKeyType}},{{.MapValueTy
 	return {{.MapFn}}
 })}
 {{end}}
+{{define "mapSliceField"}}
+func(v {{.ViewName}}) {{.FieldName}}() views.MapSlice[{{.MapKeyType}},{{.MapValueType}}] { return views.MapSliceOf(v.ж.{{.FieldName}}) }
+{{end}}
 {{define "unsupportedField"}}func(v {{.ViewName}}) {{.FieldName}}() {{.FieldType}} {panic("unsupported")}
 {{end}}
 {{define "stringFunc"}}func(v {{.ViewName}}) String() string { return v.ж.String() }
@@ -241,9 +244,8 @@ func genView(buf *bytes.Buffer, it *codegen.ImportTracker, typ *types.Named, thi
 				case *types.Basic, *types.Named:
 					sElem := it.QualifiedName(sElem)
 					args.MapValueView = fmt.Sprintf("views.Slice[%v]", sElem)
-					args.MapValueType = "[]" + sElem
-					args.MapFn = "views.SliceOf(t)"
-					template = "mapFnField"
+					args.MapValueType = sElem
+					template = "mapSliceField"
 				case *types.Pointer:
 					ptr := x
 					pElem := ptr.Elem()

ipn/ipnlocal/local.go

@@ -6565,7 +6565,7 @@ func suggestExitNode(report *netcheck.Report, netMap *netmap.NetworkMap, prevSug
 		if allowList != nil && !allowList.Contains(peer.StableID()) {
 			continue
 		}
-		if peer.CapMap().Has(tailcfg.NodeAttrSuggestExitNode) && tsaddr.ContainsExitRoutes(peer.AllowedIPs()) {
+		if peer.CapMap().Contains(tailcfg.NodeAttrSuggestExitNode) && tsaddr.ContainsExitRoutes(peer.AllowedIPs()) {
 			candidates = append(candidates, peer)
 		}
 	}

ipn/ipnlocal/serve.go

@@ -307,7 +307,7 @@ func (b *LocalBackend) setServeConfigLocked(config *ipn.ServeConfig, etag string
 	if prevConfig.Valid() {
 		has := func(string) bool { return false }
 		if b.serveConfig.Valid() {
-			has = b.serveConfig.Foreground().Has
+			has = b.serveConfig.Foreground().Contains
 		}
 		prevConfig.Foreground().Range(func(k string, v ipn.ServeConfigView) (cont bool) {
 			if !has(k) {
@@ -338,7 +338,7 @@ func (b *LocalBackend) ServeConfig() ipn.ServeConfigView {
 func (b *LocalBackend) DeleteForegroundSession(sessionID string) error {
 	b.mu.Lock()
 	defer b.mu.Unlock()
-	if !b.serveConfig.Valid() || !b.serveConfig.Foreground().Has(sessionID) {
+	if !b.serveConfig.Valid() || !b.serveConfig.Foreground().Contains(sessionID) {
 		return nil
 	}
 	sc := b.serveConfig.AsStruct()

tailcfg/tailcfg_view.go

@@ -168,10 +168,8 @@ func (v NodeView) Online() *bool {
 func (v NodeView) MachineAuthorized() bool                   { return v.ж.MachineAuthorized }
 func (v NodeView) Capabilities() views.Slice[NodeCapability] { return views.SliceOf(v.ж.Capabilities) }
 
-func (v NodeView) CapMap() views.MapFn[NodeCapability, []RawMessage, views.Slice[RawMessage]] {
-	return views.MapFnOf(v.ж.CapMap, func(t []RawMessage) views.Slice[RawMessage] {
-		return views.SliceOf(t)
-	})
+func (v NodeView) CapMap() views.MapSlice[NodeCapability, RawMessage] {
+	return views.MapSliceOf(v.ж.CapMap)
 }
 func (v NodeView) UnsignedPeerAPIOnly() bool    { return v.ж.UnsignedPeerAPIOnly }
 func (v NodeView) ComputedName() string         { return v.ж.ComputedName }

types/views/views.go

@@ -329,13 +329,88 @@ func SliceEqualAnyOrder[T comparable](a, b Slice[T]) bool {
 	return true
 }
 
-// MapOf returns a view over m. It is the caller's responsibility to make sure K
-// and V is immutable, if this is being used to provide a read-only view over m.
-func MapOf[K comparable, V comparable](m map[K]V) Map[K, V] {
-	return Map[K, V]{m}
+// MapSlice is a view over a map whose values are slices.
+type MapSlice[K comparable, V any] struct {
+	// ж is the underlying mutable value, named with a hard-to-type
+	// character that looks pointy like a pointer.
+	// It is named distinctively to make you think of how dangerous it is to escape
+	// to callers. You must not let callers be able to mutate it.
+	ж map[K][]V
 }
 
-// Map is a view over a map whose values are immutable.
+// MapSliceOf returns a MapSlice for the provided map. It is the caller's
+// responsibility to make sure V is immutable.
+func MapSliceOf[K comparable, V any](m map[K][]V) MapSlice[K, V] {
+	return MapSlice[K, V]{m}
+}
+
+// Contains reports whether k has an entry in the map.
+func (m MapSlice[K, V]) Contains(k K) bool {
+	_, ok := m.ж[k]
+	return ok
+}
+
+// IsNil reports whether the underlying map is nil.
+func (m MapSlice[K, V]) IsNil() bool {
+	return m.ж == nil
+}
+
+// Len returns the number of elements in the map.
+func (m MapSlice[K, V]) Len() int { return len(m.ж) }
+
+// Get returns the element with key k.
+func (m MapSlice[K, V]) Get(k K) Slice[V] {
+	return SliceOf(m.ж[k])
+}
+
+// GetOk returns the element with key k and a bool representing whether the key
+// is in map.
+func (m MapSlice[K, V]) GetOk(k K) (Slice[V], bool) {
+	v, ok := m.ж[k]
+	return SliceOf(v), ok
+}
+
+// MarshalJSON implements json.Marshaler.
+func (m MapSlice[K, V]) MarshalJSON() ([]byte, error) {
+	return json.Marshal(m.ж)
+}
+
+// UnmarshalJSON implements json.Unmarshaler.
+// It should only be called on an uninitialized Map.
+func (m *MapSlice[K, V]) UnmarshalJSON(b []byte) error {
+	if m.ж != nil {
+		return errors.New("already initialized")
+	}
+	return json.Unmarshal(b, &m.ж)
+}
+
+// Range calls f for every k,v pair in the underlying map.
+// It stops iteration immediately if f returns false.
+func (m MapSlice[K, V]) Range(f MapRangeFn[K, Slice[V]]) {
+	for k, v := range m.ж {
+		if !f(k, SliceOf(v)) {
+			return
+		}
+	}
+}
+
+// AsMap returns a shallow-clone of the underlying map.
+//
+// If V is a pointer type, it is the caller's responsibility to make sure the
+// values are immutable. The map and slices are cloned, but the values are not.
+func (m MapSlice[K, V]) AsMap() map[K][]V {
+	if m.ж == nil {
+		return nil
+	}
+	out := maps.Clone(m.ж)
+	for k, v := range out {
+		out[k] = slices.Clone(v)
+	}
+	return out
+}
+
+// Map provides a read-only view of a map. It is the caller's responsibility to
+// make sure V is immutable.
 type Map[K comparable, V any] struct {
 	// ж is the underlying mutable value, named with a hard-to-type
 	// character that looks pointy like a pointer.
@@ -344,8 +419,20 @@ type Map[K comparable, V any] struct {
 	ж map[K]V
 }
 
+// MapOf returns a view over m. It is the caller's responsibility to make sure V
+// is immutable.
+func MapOf[K comparable, V any](m map[K]V) Map[K, V] {
+	return Map[K, V]{m}
+}
+
 // Has reports whether k has an entry in the map.
+// Deprecated: use Contains instead.
 func (m Map[K, V]) Has(k K) bool {
+	return m.Contains(k)
+}
+
+// Contains reports whether k has an entry in the map.
+func (m Map[K, V]) Contains(k K) bool {
 	_, ok := m.ж[k]
 	return ok
 }
@@ -428,7 +515,13 @@ type MapFn[K comparable, T any, V any] struct {
 }
 
 // Has reports whether k has an entry in the map.
+// Deprecated: use Contains instead.
 func (m MapFn[K, T, V]) Has(k K) bool {
+	return m.Contains(k)
+}
+
+// Contains reports whether k has an entry in the map.
+func (m MapFn[K, T, V]) Contains(k K) bool {
 	_, ok := m.ж[k]
 	return ok
 }