chore: remove UNOWNED flag

.changeset/four-paths-cheer.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+chore: simplify connection/disconnection logic

.changeset/whole-webs-stick.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: reconnect deriveds to effect tree when time-travelling

packages/svelte/src/internal/client/constants.js

@@ -6,6 +6,13 @@ export const BLOCK_EFFECT = 1 << 4;
 export const BRANCH_EFFECT = 1 << 5;
 export const ROOT_EFFECT = 1 << 6;
 export const BOUNDARY_EFFECT = 1 << 7;
+/**
+ * Indicates that a reaction is connected to an effect root — either it is an effect,
+ * or it is a derived that is depended on by at least one effect. If a derived has
+ * no dependents, we can disconnect it from the graph, allowing it to either be
+ * GC'd or reconnected later if an effect comes to depend on it again
+ */
+export const CONNECTED = 1 << 9;
 export const CLEAN = 1 << 10;
 export const DIRTY = 1 << 11;
 export const MAYBE_DIRTY = 1 << 12;
@@ -26,8 +33,6 @@ export const EFFECT_PRESERVED = 1 << 19;
 export const USER_EFFECT = 1 << 20;
 
 // Flags exclusive to deriveds
-export const UNOWNED = 1 << 8;
-export const DISCONNECTED = 1 << 9;
 /**
  * Tells that we marked this derived and its reactions as visited during the "mark as (maybe) dirty"-phase.
  * Will be lifted during execution of the derived and during checking its dirty state (both are necessary

packages/svelte/src/internal/client/reactivity/deriveds.js

@@ -9,15 +9,14 @@ import {
 	EFFECT_PRESERVED,
 	MAYBE_DIRTY,
 	STALE_REACTION,
-	UNOWNED,
 	ASYNC,
-	WAS_MARKED
+	WAS_MARKED,
+	CONNECTED
 } from '#client/constants';
 import {
 	active_reaction,
 	active_effect,
 	set_signal_status,
-	skip_reaction,
 	update_reaction,
 	increment_write_version,
 	set_active_effect,
@@ -27,7 +26,7 @@ import {
 import { equals, safe_equals } from './equality.js';
 import * as e from '../errors.js';
 import * as w from '../warnings.js';
-import { async_effect, destroy_effect, teardown } from './effects.js';
+import { async_effect, destroy_effect, effect_tracking, teardown } from './effects.js';
 import { eager_effects, internal_set, set_eager_effects, source } from './sources.js';
 import { get_stack } from '../dev/tracing.js';
 import { async_mode_flag, tracing_mode_flag } from '../../flags/index.js';
@@ -61,9 +60,7 @@ export function derived(fn) {
 			? /** @type {Derived} */ (active_reaction)
 			: null;
 
-	if (active_effect === null || (parent_derived !== null && (parent_derived.f & UNOWNED) !== 0)) {
-		flags |= UNOWNED;
-	} else {
+	if (active_effect !== null) {
 		// Since deriveds are evaluated lazily, any effects created inside them are
 		// created too late to ensure that the parent effect is added to the tree
 		active_effect.f |= EFFECT_PRESERVED;
@@ -368,12 +365,16 @@ export function update_derived(derived) {
 		return;
 	}
 
+	// During time traveling we don't want to reset the status so that
+	// traversal of the graph in the other batches still happens
 	if (batch_values !== null) {
-		batch_values.set(derived, derived.v);
+		// only cache the value if we're in a tracking context, otherwise we won't
+		// clear the cache in `mark_reactions` when dependencies are updated
+		if (effect_tracking()) {
+			batch_values.set(derived, derived.v);
+		}
 	} else {
-		var status =
-			(skip_reaction || (derived.f & UNOWNED) !== 0) && derived.deps !== null ? MAYBE_DIRTY : CLEAN;
-
+		var status = (derived.f & CONNECTED) === 0 ? MAYBE_DIRTY : CLEAN;
 		set_signal_status(derived, status);
 	}
 }

packages/svelte/src/internal/client/reactivity/effects.js

@@ -25,15 +25,15 @@ import {
 	ROOT_EFFECT,
 	EFFECT_TRANSPARENT,
 	DERIVED,
-	UNOWNED,
 	CLEAN,
 	EAGER_EFFECT,
 	HEAD_EFFECT,
 	MAYBE_DIRTY,
 	EFFECT_PRESERVED,
 	STALE_REACTION,
 	USER_EFFECT,
-	ASYNC
+	ASYNC,
+	CONNECTED
 } from '#client/constants';
 import * as e from '../errors.js';
 import { DEV } from 'esm-env';
@@ -48,11 +48,11 @@ import { without_reactive_context } from '../dom/elements/bindings/shared.js';
  * @param {'$effect' | '$effect.pre' | '$inspect'} rune
  */
 export function validate_effect(rune) {
-	if (active_effect === null && active_reaction === null) {
-		e.effect_orphan(rune);
-	}
+	if (active_effect === null) {
+		if (active_reaction === null) {
+			e.effect_orphan(rune);
+		}
 
-	if (active_reaction !== null && (active_reaction.f & UNOWNED) !== 0 && active_effect === null) {
 		e.effect_in_unowned_derived();
 	}
 
@@ -103,7 +103,7 @@ function create_effect(type, fn, sync, push = true) {
 		deps: null,
 		nodes_start: null,
 		nodes_end: null,
-		f: type | DIRTY,
+		f: type | DIRTY | CONNECTED,
 		first: null,
 		fn,
 		last: null,

packages/svelte/src/internal/client/reactivity/sources.js

@@ -23,18 +23,18 @@ import {
 	DIRTY,
 	BRANCH_EFFECT,
 	EAGER_EFFECT,
-	UNOWNED,
 	MAYBE_DIRTY,
 	BLOCK_EFFECT,
 	ROOT_EFFECT,
 	ASYNC,
-	WAS_MARKED
+	WAS_MARKED,
+	CONNECTED
 } from '#client/constants';
 import * as e from '../errors.js';
 import { legacy_mode_flag, tracing_mode_flag } from '../../flags/index.js';
 import { get_stack, tag_proxy } from '../dev/tracing.js';
 import { component_context, is_runes } from '../context.js';
-import { Batch, eager_block_effects, schedule_effect } from './batch.js';
+import { Batch, batch_values, eager_block_effects, schedule_effect } from './batch.js';
 import { proxy } from '../proxy.js';
 import { execute_derived } from './deriveds.js';
 
@@ -211,7 +211,8 @@ export function internal_set(source, value) {
 			if ((source.f & DIRTY) !== 0) {
 				execute_derived(/** @type {Derived} */ (source));
 			}
-			set_signal_status(source, (source.f & UNOWNED) === 0 ? CLEAN : MAYBE_DIRTY);
+
+			set_signal_status(source, (source.f & CONNECTED) !== 0 ? CLEAN : MAYBE_DIRTY);
 		}
 
 		source.wv = increment_write_version();
@@ -333,9 +334,17 @@ function mark_reactions(signal, status) {
 		}
 
 		if ((flags & DERIVED) !== 0) {
+			var derived = /** @type {Derived} */ (reaction);
+
+			batch_values?.delete(derived);
+
 			if ((flags & WAS_MARKED) === 0) {
-				reaction.f |= WAS_MARKED;
-				mark_reactions(/** @type {Derived} */ (reaction), MAYBE_DIRTY);
+				// Only connected deriveds can be reliably unmarked right away
+				if (flags & CONNECTED) {
+					reaction.f |= WAS_MARKED;
+				}
+
+				mark_reactions(derived, MAYBE_DIRTY);
 			}
 		} else if (not_dirty) {
 			if ((flags & BLOCK_EFFECT) !== 0) {