fix: Unify SyncVar and SyncCollection replay across host visibility, scene re-observation, and pooled respawn by Copilot · Pull Request #4118 · MirrorNetworking/Mirror

Copilot · 2026-07-02T12:26:04Z

SyncVar hooks and SyncCollection callbacks could diverge between host and remote clients when visibility, scene-object reuse, or pooled respawn got involved. This PR brings those paths back into alignment so observation-driven replay behaves consistently across host mode, remote clients, AOI hide/show, and runtime UnSpawn/respawn reuse.

Preserve correct SyncVar baselines
- Weaver-generated hooked SyncVars now capture the real pre-visibility field value, including declaration initializers and non-primitive types.
- Host replay uses that captured baseline so the first visible hook sees the same oldValue a fresh observer would.
Defer host callbacks until actual observation
- Host-mode SyncVar hooks and SyncCollection actions now stay deferred until the host client has a local player and the object is actually observed.
- Re-entering AOI or observing after a delayed player spawn replays state once, instead of firing early or double-firing during host spawn transitions.
Replay re-observation as a fresh observation
- Host and remote clients now treat scene-object hide/show as a new observation for hooked SyncVars.
- SyncCollections replay the current visible state as Add actions again on re-observation, instead of remembering prior observation state.
Handle pooled runtime-object reuse in host mode
- Host-mode NetworkServer.UnSpawn/respawn of pooled runtime objects now marks SyncVar hooks and SyncCollection replays pending before visibility is lost.
- Respawning the same object replays one-time-assigned SyncVars (such as RandomColor) and current SyncCollection contents again, even without AOI.
Preserve server delta queues and avoid duplicate callbacks
- Host visibility replay no longer deserializes the shared server/host SyncObject state or consumes pending remote deltas.
- Replay-pending tracking is now scoped per hooked SyncVar / SyncObject, preventing unrelated members from replaying twice.
- SyncObject callback clearing is limited to reused client scene-object paths so client re-observation does not accumulate handlers and server pooling keeps its subscriptions.
Regression coverage
- Added and corrected focused editor tests for host visibility deferral, AOI leave/re-enter, remote scene-object re-observation, ready-without-player flows, AddPlayer/spawn boundary cases, pooled runtime respawn, and double-fire prevention for both SyncVars and SyncCollections.

Example behavior after this change:

[SyncVar(hook = nameof(OnValueChanged))]
public int value = 42;

// Mutated before the host can observe it
value = 100;
value = 200;

// When the host first observes or re-observes the object:
// OnValueChanged(42, 200)

MrGadget1024 · 2026-07-05T10:55:19Z

@copilot Error: Assets/Mirror/Core/SyncDictionary.cs(371,42): error CS0103: The name 'newItem' does not exist in the current context
Should be TValue capturedNew = item;

Copilot · 2026-07-05T10:59:11Z

@copilot Error: Assets/Mirror/Core/SyncDictionary.cs(371,42): error CS0103: The name 'newItem' does not exist in the current context
Should be TValue capturedNew = item;

Addressed in 485ce90.

MrGadget1024 · 2026-07-06T02:18:18Z

@copilot Fix errors related to failed tests

Copilot · 2026-07-06T02:20:50Z

@copilot Fix errors related to failed tests

Addressed in 7ee058b.

MrGadget1024 · 2026-07-06T10:54:04Z

@copilot Fix failed test
https://github.com/MirrorNetworking/Mirror/actions/runs/28763688725/job/85352608919

Copilot · 2026-07-06T11:00:20Z

@copilot Fix failed test
https://github.com/MirrorNetworking/Mirror/actions/runs/28763688725/job/85352608919

Addressed in 52f22a7.

codecov · 2026-07-06T12:12:51Z

Codecov Report

❌ Patch coverage is 74.94357% with 111 lines in your changes missing coverage. Please review.
✅ Project coverage is 42.84%. Comparing base (31163ab) to head (2ce684a).
⚠️ Report is 9 commits behind head on master.

Files with missing lines	Patch %	Lines
Assets/Mirror/Core/NetworkBehaviour.cs	65.33%	104 Missing ⚠️
Assets/Mirror/Core/SyncObject.cs	75.00%	3 Missing ⚠️
Assets/Mirror/Core/NetworkClient.cs	95.00%	2 Missing ⚠️
Assets/Mirror/Core/SyncDictionary.cs	96.42%	1 Missing ⚠️
Assets/Mirror/Core/SyncSet.cs	96.15%	1 Missing ⚠️

❌ Your patch check has failed because the patch coverage (74.94%) is below the target coverage (90.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4118      +/-   ##
==========================================
+ Coverage   42.22%   42.84%   +0.61%     
==========================================
  Files         156      156              
  Lines       15100    15496     +396     
==========================================
+ Hits         6376     6639     +263     
- Misses       8724     8857     +133

Flag	Coverage Δ
unittests	`42.84% <74.94%> (+0.61%)`	⬆️
unity-6000.5.1f1	`42.84% <74.94%> (+0.61%)`	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
Assets/Mirror/Core/NetworkIdentity.cs	`91.07% <100.00%> (+0.05%)`	⬆️
Assets/Mirror/Core/NetworkServer.cs	`69.00% <100.00%> (+0.53%)`	⬆️
Assets/Mirror/Core/SyncList.cs	`91.91% <100.00%> (+0.77%)`	⬆️
Assets/Mirror/Core/SyncDictionary.cs	`89.83% <96.42%> (+2.09%)`	⬆️
Assets/Mirror/Core/SyncSet.cs	`92.37% <96.15%> (+1.82%)`	⬆️
Assets/Mirror/Core/NetworkClient.cs	`94.14% <95.00%> (+0.34%)`	⬆️
Assets/Mirror/Core/SyncObject.cs	`78.57% <75.00%> (-21.43%)`	⬇️
Assets/Mirror/Core/NetworkBehaviour.cs	`74.37% <65.33%> (-11.35%)`	⬇️

... and 7 files with indirect coverage changes

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

MrGadget1024 · 2026-07-11T11:29:30Z

@copilot Extend the new tests to move host client player out of AOI range, Assert that the test object is no longer observed, change the SyncVar value or make a change to the Sync Collection, Assert no hooks / actions, move host client player into range again, Assert hooks / actions invoked again the same as previously, e.g. same original oldValue as if the host client is seeing it for the first time again.

MrGadget1024 · 2026-07-15T12:19:15Z

@Lymdun We good now?

MrGadget1024 · 2026-07-15T12:57:42Z

@copilot In the Room example, there is a Spawner static class Assets/Mirror/Examples/Room/Scripts/Spawner.cs that uses a Pool Assets/Mirror/Core/Tools/Pool.cs, and a Reward script Assets/Mirror/Examples/Room/Scripts/Reward.cs. The Reward prefab has RandomColor, and the color is set once when the Reward is initially created by the Spawner and never changes. OnTriggerEnter in Reward script recycles the reward item by Unspawning it into the pool to be respawned after a delay at a new position. The host client should fire the SyncVar hook of RandomColor when it's respawned, but it's not firing. There is no AOI in this example. If the reward had a SyncCollection, the Add actions should be invoked again too.

Copilot · 2026-07-15T13:05:17Z

@copilot In the Room example, there is a Spawner static class Assets/Mirror/Examples/Room/Scripts/Spawner.cs that uses a Pool Assets/Mirror/Core/Tools/Pool.cs, and a Reward script `Assets/Mirror/E...

Addressed in 1fab2fc with the test follow-up in 310425d. Host-mode UnSpawn now marks SyncVar and SyncCollection replay pending before the shared object leaves observation, so respawning the same runtime object replays the RandomColor hook again, and SyncCollection Add actions replay again too. I also added focused host/no-AOI regression tests for both runtime-object SyncVar hook replay and SyncCollection replay after unspawn/respawn.

Lymdun · 2026-07-15T15:41:13Z

@Lymdun We good now?

@MrGadget1024 re-ran all evals, all good now ✅

MrGadget1024 · 2026-07-15T17:04:12Z

@copilot Update the Title and Description of this PR reflecting the goals we achieved and describing the work completed.

Copilot · 2026-07-15T17:05:51Z

@copilot Update the Title and Description of this PR reflecting the goals we achieved and describing the work completed.

Use this updated PR metadata:

Title
Unify SyncVar and SyncCollection replay across host visibility, scene re-observation, and pooled respawn

Description
SyncVar hooks and SyncCollection callbacks could diverge between host and remote clients when visibility, scene-object reuse, or pooled respawn got involved. This PR brings those paths back into alignment so observation-driven replay behaves consistently across host mode, remote clients, AOI hide/show, and runtime UnSpawn/respawn reuse.

Preserve correct SyncVar baselines
- Weaver-generated hooked SyncVars now capture the real pre-visibility field value, including declaration initializers and non-primitive types.
- Host replay uses that captured baseline so the first visible hook sees the same oldValue a fresh observer would.
Defer host callbacks until actual observation
- Host-mode SyncVar hooks and SyncCollection actions now stay deferred until the host client has a local player and the object is actually observed.
- Re-entering AOI or observing after a delayed player spawn replays state once, instead of firing early or double-firing during host spawn transitions.
Replay re-observation as a fresh observation
- Host and remote clients now treat scene-object hide/show as a new observation for hooked SyncVars.
- SyncCollections replay the current visible state as Add actions again on re-observation, instead of remembering prior observation state.
Handle pooled runtime-object reuse in host mode
- Host-mode NetworkServer.UnSpawn/respawn of pooled runtime objects now marks SyncVar hooks and SyncCollection replays pending before visibility is lost.
- Respawning the same object replays one-time-assigned SyncVars (such as RandomColor) and current SyncCollection contents again, even without AOI.
Preserve server delta queues and avoid duplicate callbacks
- Host visibility replay no longer deserializes the shared server/host SyncObject state or consumes pending remote deltas.
- Replay-pending tracking is now scoped per hooked SyncVar / SyncObject, preventing unrelated members from replaying twice.
- SyncObject callback clearing is limited to reused client scene-object paths so client re-observation does not accumulate handlers and server pooling keeps its subscriptions.
Regression coverage
- Added and corrected focused editor tests for host visibility deferral, AOI leave/re-enter, remote scene-object re-observation, ready-without-player flows, AddPlayer/spawn boundary cases, pooled runtime respawn, and double-fire prevention for both SyncVars and SyncCollections.

Example behavior after this change:

[SyncVar(hook = nameof(OnValueChanged))]
public int value = 42;

// Mutated before the host can observe it
value = 100;
value = 200;

// When the host first observes or re-observes the object:
// OnValueChanged(42, 200)

That wording matches the behavior covered by the final test set and the host/remote example scenarios fixed in this PR.

GoToNightmare · 2026-09-14T19:30:53Z

~~Suggestion to add FieldAttributes.NotSerialized into SyncVarAttributeProcessor bcs newly generated flag fields would trigger unity error message with unsupported enum type.~~

MrGadget1024 · 2026-09-15T12:55:44Z

Suggestion to add FieldAttributes.NotSerialized into SyncVarAttributeProcessor bcs newly generated flag fields would trigger unity error message with unsupported enum type.

Please provide a more concrete example?

GoToNightmare · 2026-09-15T19:11:28Z

@MrGadget1024 Sorry wasnt able to replicate it, but error message was
Unsupported enum type 'GameData.GameEnums.ModifierStatusEffects' used for field '_Mirror_SyncVarHookOriginal_thisEntityStatusEffects' in class 'CombatEntity'

where CombatEntity is networkbeh and original field is

	[SyncVar(hook = nameof(StatusEffectChangedOnClient))]
	private GameEnums.ModifierStatusEffects thisEntityStatusEffects;

		[Flags]
		public enum ModifierStatusEffects : ulong

Edit: Nvm, might be bad suggestion.

MrGadget1024 · 2026-09-16T13:06:33Z

@GoToNightmare Unity (and Mirror) serialize enums perfectly, even those with non-int bases. We have our own examples that use byte.

GoToNightmare · 2026-09-16T13:15:57Z

@MrGadget1024 I mean unity out of the box doesnt support serialization for enum flags with undeling type long/ulong, and that error I got is exactly that. Mirror generated field Unsupported enum type 'GameData.GameEnums.ModifierStatusEffects' used for field '_Mirror_SyncVarHookOriginal_thisEntityStatusEffects' in class 'CombatEntity' and unity message it as error.

But im not sure if u should care about it on mirrors side.

MrGadget1024 · 2026-09-16T13:40:38Z

@GoToNightmare I can reproduce it with the PlayerTest example. That's a Unity bug and should be reported as such. Annoying, but not a Mirror issue. I notice the inspector still works fine, and the flags work fine, it's erroneous error spam.

EDIT: Apparently Unity isn't going to fix this...long standing issue that I hadn't run into before.
https://docs.unity3d.com/6000.6/Documentation/Manual/script-serialization-analyzer.html#uac1011
Still...not our pasture, not our BS.

Initial plan

5923887

Copilot AI assigned Copilot and MrGadget1024 Jul 2, 2026

Copilot started work on behalf of MrGadget1024 July 2, 2026 12:26 View session

Copilot AI added 3 commits July 2, 2026 12:38

Implement host sync visibility deferral

1ef0fb7

Polish host sync deferral changes

4a4a3ce

Fix host visibility helper access

ebfa5a4

Copilot AI changed the title ~~[WIP] Fix host-client-only bugs in Mirror sync state delivery~~ Fix host-client deferred SyncVar and SyncCollection delivery semantics Jul 2, 2026

Copilot AI requested a review from MrGadget1024 July 2, 2026 12:42

Copilot finished work on behalf of MrGadget1024 July 2, 2026 12:42

Copilot started work on behalf of MrGadget1024 July 5, 2026 10:55 View session

fix deferred SyncDictionary action capture

485ce90

Copilot finished work on behalf of MrGadget1024 July 5, 2026 10:59

Copilot started work on behalf of MrGadget1024 July 6, 2026 02:18 View session

fix host-mode SyncVar test expectations

7ee058b

Copilot finished work on behalf of MrGadget1024 July 6, 2026 02:21

Copilot started work on behalf of MrGadget1024 July 6, 2026 10:54 View session

Copilot AI added 2 commits July 6, 2026 10:58

Flush deferred host sync callbacks after local player setup

efbc424

Document observed callback snapshot copy

52f22a7

Copilot finished work on behalf of MrGadget1024 July 6, 2026 11:00

Copilot started work on behalf of MrGadget1024 July 11, 2026 11:29 View session

Extend host visibility AOI tests

1a04d7d

Copilot finished work on behalf of MrGadget1024 July 14, 2026 15:43

Copilot started work on behalf of MrGadget1024 July 15, 2026 12:58 View session

Copilot AI added 2 commits July 15, 2026 13:01

fix host replay after runtime unspawn respawn

1fab2fc

test clarify host respawn replay regression coverage

310425d

Copilot AI changed the title ~~Fix SyncVar and SyncCollection visibility replay semantics~~ Fix SyncVar and SyncCollection replay semantics across visibility and respawn Jul 15, 2026

Copilot finished work on behalf of MrGadget1024 July 15, 2026 13:05

MrGadget1024 added Awaiting Review and removed work in progress Need more time to decide. Nothing to do here for now. labels Jul 15, 2026

Cleanup from testing

2ce684a

Copilot started work on behalf of MrGadget1024 July 15, 2026 17:04 View session

Copilot finished work on behalf of MrGadget1024 July 15, 2026 17:06

MrGadget1024 changed the title ~~Fix SyncVar and SyncCollection replay semantics across visibility and respawn~~ fix: Unify SyncVar and SyncCollection replay across host visibility, scene re-observation, and pooled respawn Jul 15, 2026

MrGadget1024 approved these changes Jul 15, 2026

View reviewed changes

MrGadget1024 added 4 commits August 6, 2026 15:38

Cleanup: Revert example changes

7795732

Merged master

81cb98a

Merged master

b8bba7d

Merged master

1111251

Chris-Langsenkamp mentioned this pull request Sep 8, 2026

Incorrect SyncVar behaviour in host mode #4126

Open

Uh oh!

Conversation

Copilot AI commented Jul 2, 2026 • edited by MrGadget1024 Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

MrGadget1024 commented Jul 5, 2026

Uh oh!

Copilot AI commented Jul 5, 2026

Uh oh!

MrGadget1024 commented Jul 6, 2026

Uh oh!

Copilot AI commented Jul 6, 2026

Uh oh!

MrGadget1024 commented Jul 6, 2026

Uh oh!

Copilot AI commented Jul 6, 2026

Uh oh!

codecov Bot commented Jul 6, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Codecov Report

Uh oh!

MrGadget1024 commented Jul 11, 2026

Uh oh!

MrGadget1024 commented Jul 15, 2026

Uh oh!

MrGadget1024 commented Jul 15, 2026

Uh oh!

Copilot AI commented Jul 15, 2026

Uh oh!

Lymdun commented Jul 15, 2026

Uh oh!

MrGadget1024 commented Jul 15, 2026

Uh oh!

Copilot AI commented Jul 15, 2026

Uh oh!

GoToNightmare commented Sep 14, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

MrGadget1024 commented Sep 15, 2026

Uh oh!

GoToNightmare commented Sep 15, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

MrGadget1024 commented Sep 16, 2026

Uh oh!

GoToNightmare commented Sep 16, 2026

Uh oh!

MrGadget1024 commented Sep 16, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

5 participants

Copilot AI commented Jul 2, 2026 •

edited by MrGadget1024

Loading

codecov Bot commented Jul 6, 2026 •

edited

Loading

GoToNightmare commented Sep 14, 2026 •

edited

Loading

GoToNightmare commented Sep 15, 2026 •

edited

Loading

MrGadget1024 commented Sep 16, 2026 •

edited

Loading