make things a bit more self-explanatory

Author: Rich-Harris

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

@@ -66,6 +66,8 @@ export function source(v, stack) {
 
 	if (DEV && tracing_mode_flag) {
 		signal.created = stack ?? get_stack('CreatedAt');
+		signal.updated = null;
+		signal.set_during_effect = false;
 	}
 
 	return signal;
@@ -169,10 +171,7 @@ export function internal_set(source, value) {
 			source.updated = get_stack('UpdatedAt');
 
 			if (active_effect !== null) {
-				// Signal that we should increment the write version
-				// after the current effect has run, so that it is
-				// marked dirty if the effect uses `$inspect.trace()`
-				source.trace_need_increase = true;
+				source.set_during_effect = true;
 			}
 		}
 

packages/svelte/src/internal/client/reactivity/types.d.ts

@@ -16,11 +16,19 @@ export interface Value<V = unknown> extends Signal {
 	rv: number;
 	/** The latest value for this signal */
 	v: V;
-	/** Dev only */
+
+	// dev-only
+	/** A label (e.g. the `foo` in `let foo = $state(...)`) used for `$inspect.trace()` */
 	label?: string;
+	/** An error with a stack trace showing when the source was created */
 	created?: Error | null;
+	/** An error with a stack trace showing when the source was last updated */
 	updated?: Error | null;
-	trace_need_increase?: boolean;
+	/**
+	 * Whether or not the source was set while running an effect — if so, we need to
+	 * increment the write version so that it shows up as dirty when the effect re-runs
+	 */
+	set_during_effect?: boolean;
 }
 
 export interface Reaction extends Signal {

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

@@ -442,18 +442,13 @@ export function update_effect(effect) {
 		effect.teardown = typeof teardown === 'function' ? teardown : null;
 		effect.wv = write_version;
 
-		var deps = effect.deps;
-
-		// In DEV, we need to handle a case where $inspect.trace() might
-		// incorrectly state a source dependency has not changed when it has.
-		// That's beacuse that source was changed by the same effect, causing
-		// the versions to match. We can avoid this by incrementing the version
-		if (DEV && tracing_mode_flag && (effect.f & DIRTY) !== 0 && deps !== null) {
-			for (let i = 0; i < deps.length; i++) {
-				var dep = deps[i];
-				if (dep.trace_need_increase) {
+		// In DEV, increment versions of any sources that were written to during the effect,
+		// so that they are correctly marked as dirty when the effect re-runs
+		if (DEV && tracing_mode_flag && (effect.f & DIRTY) !== 0 && effect.deps !== null) {
+			for (var dep of effect.deps) {
+				if (dep.set_during_effect) {
 					dep.wv = increment_write_version();
-					dep.trace_need_increase = undefined;
+					dep.set_during_effect = false;
 				}
 			}
 		}