Fix data-permanent to preserve element attributes, not just descendants by Copilot · Pull Request #64622 · dotnet/aspnetcore

Copilot · 2025-12-03T08:52:28Z

Fix data-permanent to preserve element attributes, not just descendants

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Description

The data-permanent attribute was only preventing child content synchronization during enhanced navigation, but still synchronized attributes on the element itself. This caused JS-modified attributes (like dynamically added classes) to be lost.

<!-- Before: expand class lost after enhanced nav -->
<div id="myelem" data-permanent></div>
<script>document.getElementById('myelem').classList.add('expand')</script>

<!-- Workaround required wrapping in another element -->
<div data-permanent><div id="myelem"></div></div>

Changes:

Move the isDataPermanentElement check in treatAsMatch() to occur before attribute synchronization, skipping both attribute and content sync for permanent elements
Add unit tests for attribute preservation on data-permanent elements, including dynamically added attributes
Add E2E test (ElementsWithDataPermanentAttribute_HavePreservedAttributes) to verify dynamically added CSS classes are preserved after enhanced navigation
Extend PageThatPreservesContent.razor test component to include attribute preservation scenario

Fixes #51021

Original prompt

This section details on the original issue you should resolve

<issue_title>data-permanent doesn't apply to the element with that attribute</issue_title>
<issue_description>I was trying out data-permanent and was confused for a while because it seemed not to work. Then I tried moving it to an ancestor element and it did work.

Repro

Start with <div id='myelem' data-permanent></div>

Use JS to mutate it in some way (e.g., document.getElementById('myelem').classList.toggle('expand'))

Perform an enhanced nav that returns equivalent content (i.e., <div id='myelem' data-permanent></div>)

Expected: The expand class should be retained
Actual: It is not

However if you replace the markup with <div data-permanent><div id='myelem'></div></div> then the class is retained

I guess diffing only uses data-permanent to decide whether to recurse into the element, but I think it should also use it to decide whether to synchronize the attributes on that element.</issue_description>

Comments on the Issue (you are @copilot in this section)
@SteveSandersonMS It is just about entire elements (and all their descendants), i.e., ensuring they are not modified across enhance page loads.
I know that doesn't cover the specific scenario you mention (preserving specific attributes). That would require broader, nontrivial design to give developers ways to express everything possible there. Maybe it would be something more like a callback to let developers intercept the before/after states during DOM merging, so they could use any logic they wanted to capture "before" state and re-apply it to the "after" state. It would be a very reasonable feature request for .NET 9.</comment_new>
<comment_new>@danroth27

I'm confused about this feature in general. Where is the specification?

@marinasundstrom Take a look at #50437 for a description of data-permanent
@ Thanks for contacting us.
We're moving this issue to the .NET 9 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
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<comment_new>@
Thanks for contacting us.

We're moving this issue to the .NET 9 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.</comment_new>
<comment_new>@SteveSandersonMS
Another vote in favour of fixing this: #54658 (need to preserve content in <head> without having multiple heads).</comment_new>

Fixes data-permanent doesn't apply to the element with that attribute #51021

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Co-authored-by: javiercn <6995051+javiercn@users.noreply.github.com>

javiercn · 2025-12-03T09:50:47Z

@copilot Have you followed the steps in src/Components/AGENTS.MD?

Co-authored-by: javiercn <6995051+javiercn@users.noreply.github.com>

Copilot · 2025-12-03T10:06:20Z

@copilot Have you followed the steps in src/Components/AGENTS.MD?

Yes, I've now followed the steps in AGENTS.MD. In commit 68284e42, I:

Extended the existing test component PageThatPreservesContent.razor to include an attribute preservation scenario (adding a dynamically added class to a data-permanent element)
Added an E2E test ElementsWithDataPermanentAttribute_HavePreservedAttributes that verifies dynamically added attributes are preserved after enhanced navigation
Built and ran the E2E tests - all pass including the new test and existing data-permanent tests

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- Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --no-sandbox --ignore-certificate-errors --use-angle=swiftshader-webgl --ignore-certificate-errors --crashpad-handler-pid=9373 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/BrowserFixtureUserProfiles/streaming --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,1075644145285363203,7250468106450785236,262144 --disable-features=IgnoreDuplicateNavs,PaintHolding,Prewarm --variations-seed-version --trace-process-track-uuid=3190708989122997041 --enable-logging=stderr (dns block)
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- Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --no-sandbox --ignore-certificate-errors --use-angle=swiftshader-webgl --ignore-certificate-errors --crashpad-handler-pid=9597 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/BrowserFixtureUserProfiles/streaming --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,3234065746608267733,13207032037754184699,262144 --disable-features=IgnoreDuplicateNavs,PaintHolding,Prewarm --variations-seed-version --trace-process-track-uuid=3190708989122997041 --enable-logging=stderr (dns block)
clients2.google.com
- Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --no-sandbox --ignore-certificate-errors --use-angle=swiftshader-webgl --ignore-certificate-errors --crashpad-handler-pid=9373 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/BrowserFixtureUserProfiles/streaming --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,1075644145285363203,7250468106450785236,262144 --disable-features=IgnoreDuplicateNavs,PaintHolding,Prewarm --variations-seed-version --trace-process-track-uuid=3190708989122997041 --enable-logging=stderr (dns block)
- Triggering command: /opt/google/chrome/chrome /opt/google/chrome/chrome --allow-pre-commit-input --disable-REDACTED-networking --disable-client-side-phishing-detection --disable-default-apps --disable-features=IgnoreDuplicateNavs,Prewarm --disable-hang-monitor --disable-popup-blocking --disable-prompt-on-repost --disable-sync --enable-automation --enable-logging=stderr --headless=new --ignore-certificate-errors --log-level=0 --no-first-run --no-sandbox --no-service-autorun --password-store=basic --remote-debugging-port=0 (dns block)
- Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --no-sandbox --ignore-certificate-errors --use-angle=swiftshader-webgl --ignore-certificate-errors --crashpad-handler-pid=9597 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/BrowserFixtureUserProfiles/streaming --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,3234065746608267733,13207032037754184699,262144 --disable-features=IgnoreDuplicateNavs,PaintHolding,Prewarm --variations-seed-version --trace-process-track-uuid=3190708989122997041 --enable-logging=stderr (dns block)
www.google.com
- Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --no-sandbox --ignore-certificate-errors --use-angle=swiftshader-webgl --ignore-certificate-errors --crashpad-handler-pid=9373 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/BrowserFixtureUserProfiles/streaming --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,1075644145285363203,7250468106450785236,262144 --disable-features=IgnoreDuplicateNavs,PaintHolding,Prewarm --variations-seed-version --trace-process-track-uuid=3190708989122997041 --enable-logging=stderr (dns block)
- Triggering command: /opt/google/chrome/chrome /opt/google/chrome/chrome --allow-pre-commit-input --disable-REDACTED-networking --disable-client-side-phishing-detection --disable-default-apps --disable-features=IgnoreDuplicateNavs,Prewarm --disable-hang-monitor --disable-popup-blocking --disable-prompt-on-repost --disable-sync --enable-automation --enable-logging=stderr --headless=new --ignore-certificate-errors --log-level=0 --no-first-run --no-sandbox --no-service-autorun --password-store=basic --remote-debugging-port=0 (dns block)
- Triggering command: /proc/self/exe /proc/self/exe --type=utility --utility-sub-type=network.mojom.NetworkService --lang=en-US --service-sandbox-type=none --no-sandbox --ignore-certificate-errors --use-angle=swiftshader-webgl --ignore-certificate-errors --crashpad-handler-pid=9597 --enable-crash-reporter=, --noerrdialogs --user-data-dir=/tmp/BrowserFixtureUserProfiles/streaming --change-stack-guard-on-fork=enable --shared-files=v8_context_snapshot_data:100 --field-trial-handle=3,i,3234065746608267733,13207032037754184699,262144 --disable-features=IgnoreDuplicateNavs,PaintHolding,Prewarm --variations-seed-version --trace-process-track-uuid=3190708989122997041 --enable-logging=stderr (dns block)

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Pull request overview

This PR fixes a bug where the data-permanent attribute only prevented child content synchronization during enhanced navigation, but still synchronized attributes on the element itself. The fix moves the isDataPermanentElement check to occur before attribute synchronization, ensuring both attributes and content are preserved for elements marked with data-permanent.

Key Changes:

Modified TypeScript logic to skip all synchronization (attributes and content) for data-permanent elements
Added unit tests verifying attribute preservation on data-permanent elements
Added E2E test confirming dynamically added CSS classes survive enhanced navigation

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
`src/Components/Web.JS/src/Rendering/DomMerging/DomSync.ts`	Moved `isDataPermanentElement` check before attribute synchronization to preserve both attributes and content for permanent elements
`src/Components/Web.JS/test/DomSync.test.ts`	Added two unit tests verifying attributes are preserved: one for existing attributes and one for dynamically added attributes
`src/Components/test/E2ETest/ServerRenderingTests/EnhancedNavigationTest.cs`	Added E2E test verifying dynamically added CSS class is preserved across multiple enhanced navigation events
`src/Components/test/testassets/Components.TestServer/RazorComponents/Pages/EnhancedNav/PageThatPreservesContent.razor`	Extended test page to include element for attribute preservation testing with dynamically added CSS class

javiercn · 2026-01-20T14:19:43Z

/azp run aspnetcore-ci

azure-pipelines · 2026-01-20T14:19:56Z

Azure Pipelines successfully started running 1 pipeline(s).

maraf · 2026-01-20T14:34:49Z

...ssets/Components.TestServer/RazorComponents/Pages/EnhancedNav/PageThatPreservesContent.razor


 <div id="preserved-content" data-permanent></div>
 <div id="non-preserved-content"></div>
+<div id="preserved-attributes" data-permanent></div>


nit: I expect we can reuse the preserved-content element and save two new lines of code in a test :)

ilonatommy · 2026-01-20T11:55:10Z

src/Components/test/E2ETest/ServerRenderingTests/EnhancedNavigationTest.cs

+        Browser.Exists(By.TagName("nav")).FindElement(By.LinkText("Preserve content")).Click();
+        Browser.Equal("Page that preserves content", () => Browser.Exists(By.TagName("h1")).Text);
+
+        // Required until https://github.com/dotnet/aspnetcore/issues/50424 is fixed


But that issue was fixed with #50453 already at the time of posting this PR.

It has just copied from https://github.com/dotnet/aspnetcore/pull/64622/changes#diff-6257fe399feef2288438ea53e07d98e7c4857ef31001680078770686b1477929R487.

I'll leave it like it is for now, but it might be a good task for the AI to look through all these comments in the codebase and react accordingly when the fixes are already done.

ilonatommy · 2026-01-20T14:42:36Z

src/Components/test/E2ETest/ServerRenderingTests/EnhancedNavigationTest.cs

+
+        // Verify the dynamically added class exists before enhanced nav
+        var preservedAttributesElement = Browser.Exists(By.Id("preserved-attributes"));
+        Browser.True(() => preservedAttributesElement.GetAttribute("class")?.Contains("dynamically-added-class") == true);


Should we check the initial state in this test to confirm that the attribute is dynamically added?

I'm not sure what you mean, the attribute isn't in the initial markup, I expect that to be enough (how else would it be there)

if the razor file got changed and the update was not dynamic anymore. But that's maybe too much caution. Ignore

Initial plan

9fb6a51

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Copilot started work on behalf of javiercn December 3, 2025 08:52 View session

Fix data-permanent to preserve element attributes, not just descendants

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Co-authored-by: javiercn <6995051+javiercn@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Fix data-permanent not applying to element with that attribute~~ Fix data-permanent to preserve element attributes, not just descendants Dec 3, 2025

Copilot AI requested a review from javiercn December 3, 2025 09:12

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Copilot started work on behalf of javiercn December 3, 2025 09:51 View session

Add E2E test for data-permanent attribute preservation

68284e4

Co-authored-by: javiercn <6995051+javiercn@users.noreply.github.com>

Copilot finished work on behalf of javiercn December 3, 2025 10:09

javiercn added the area-blazor Includes: Blazor, Razor Components label Dec 3, 2025

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javiercn merged commit 52cf2cf into main Jan 21, 2026
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[main] Source code updates from dotnet/aspnetcore dotnet/dotnet#4350

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Fix data-permanent to preserve element attributes, not just descendants#64622

Fix data-permanent to preserve element attributes, not just descendants#64622
javiercn merged 3 commits intomainfrom
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Fix data-permanent to preserve element attributes, not just descendants

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Copilot AI commented Dec 3, 2025 •

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