make purpose explicit

Author: Rich-Harris

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

@@ -19,7 +19,7 @@ export const EFFECT_TRANSPARENT = 1 << 17;
 export const LEGACY_DERIVED_PROP = 1 << 18;
 export const INSPECT_EFFECT = 1 << 19;
 export const HEAD_EFFECT = 1 << 20;
-export const EFFECT_HAS_DERIVED = 1 << 21;
+export const EFFECT_PRESERVED = 1 << 21; // effects with this flag should not be pruned
 
 // Flags used for async
 export const REACTION_IS_UPDATING = 1 << 22;

packages/svelte/src/internal/client/dom/blocks/boundary.js

@@ -3,6 +3,7 @@
 import {
 	BOUNDARY_EFFECT,
 	BOUNDARY_SUSPENDED,
+	EFFECT_PRESERVED,
 	EFFECT_TRANSPARENT,
 	RENDER_EFFECT
 } from '../../constants.js';
@@ -63,6 +64,8 @@ function with_boundary(boundary, fn) {
 	}
 }
 
+var flags = EFFECT_TRANSPARENT | EFFECT_PRESERVED | BOUNDARY_EFFECT;
+
 /**
  * @param {TemplateNode} node
  * @param {{
@@ -317,7 +320,7 @@ export function boundary(node, props, children) {
 		}
 
 		reset_is_throwing_error();
-	}, EFFECT_TRANSPARENT | BOUNDARY_EFFECT);
+	}, flags);
 
 	if (hydrating) {
 		anchor = hydrate_node;

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

@@ -5,7 +5,7 @@ import {
 	DERIVED,
 	DESTROYED,
 	DIRTY,
-	EFFECT_HAS_DERIVED,
+	EFFECT_PRESERVED,
 	MAYBE_DIRTY,
 	UNOWNED
 } from '../constants.js';
@@ -58,7 +58,7 @@ export function derived(fn) {
 	} else {
 		// 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_HAS_DERIVED;
+		active_effect.f |= EFFECT_PRESERVED;
 	}
 
 	/** @type {Derived<V>} */
@@ -140,7 +140,7 @@ export function async_derived(fn) {
 			// TODO we should probably null out active effect here,
 			// rather than inside `restore()`
 		}
-	}, EFFECT_HAS_DERIVED);
+	}, EFFECT_PRESERVED);
 
 	return Promise.resolve(promise).then(() => value);
 }

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

@@ -34,7 +34,7 @@ import {
 	INSPECT_EFFECT,
 	HEAD_EFFECT,
 	MAYBE_DIRTY,
-	EFFECT_HAS_DERIVED,
+	EFFECT_PRESERVED,
 	BOUNDARY_EFFECT
 } from '../constants.js';
 import { set } from './sources.js';
@@ -147,7 +147,7 @@ function create_effect(type, fn, sync, push = true) {
 		effect.first === null &&
 		effect.nodes_start === null &&
 		effect.teardown === null &&
-		(effect.f & (EFFECT_HAS_DERIVED | BOUNDARY_EFFECT)) === 0;
+		(effect.f & EFFECT_PRESERVED) === 0;
 
 	if (!inert && !is_root && push) {
 		if (parent_effect !== null) {