feat: Shared Render Tree

[linkdotnet]

Shared Render Tree

This went a bit bigger than initially anticipated. Basically this PR would solve and close:

• Get IRenderedFragment/IRenderedComponent<T> from DOM element (IElement) #153
• When interacting with a child component's html, should it be treated in the whole rendered context? #983
• Enable walking component tree #1180

So it is kind of a heavy-hitter code-wise but also feature-wise.

And has a major breaking behavioural change.

## The state before
Every IRenderedComponent produced its own markup and parsed it into its own AngleSharp document: Markup was Htmlizer.GetHtml(ComponentId, renderer), Nodes was
htmlParser.Parse(Markup), and BunitHtmlParser.Parse opens a fresh IDocument per call.

So parent hat its DOM including all children, but child-elements only have theirs (plus eventually their children). So this PR will allow all 3 attached scenarios / or fix bugs.

The new now

One markup string and one document per render tree, generated by its root.
Htmlizer records the [start, end) character range each component occupies while it
builds the string, in post-order. We had this once on another feature branch. So nothing new.

Markup then is sliced regarding the components position in the overall tree.
Nodes is a view over a run of sibling nodes in the shared document.

Edge cases

Imagine a component hat has only text

<p id="parent-p">Hello <TextOnlyChild /> world</p>

where TextOnlyChild does only contain text, no HTML element. The system then can't really tell what is the child here. The text merged with the parent. So they keep the current behavior more or less, but can't be used with the new GetOwingComponent - there is nothing to latch on here.

Other things

• OnMarkupUpdated triggers now more often - basically because of going up and down the tree
• We should be faster - given less work (hopefully - didn't measure it tbh)

v3?

Now we have a breaking change in behaviour. We might want go ahead with v3 where it is fine to have a breaking change behavioural wise. Breaking change being if a user "clicks" on a child element, it does in fact now bubble up! I do feel that is the better approach and more obvious, but breaks anyway. Depending on how we go ahead, we can make that clear in the docs.

[Copilot]

🟡 Changes recommended

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Pull request overview

This PR reworks bUnit’s rendered-component DOM model so all components under the same render-tree root share a single markup snapshot and AngleSharp document, enabling correct event bubbling across component boundaries and supporting “find owning component” and component-tree navigation APIs.

Changes:

• Introduces a root-owned RootMarkupSnapshot (shared markup + document) and per-component “slice” views for Markup/Nodes.
• Adds public extension APIs for component tree navigation (Parent/Root/GetAncestors/GetChildren) and for mapping DOM nodes back to their rendering component (GetOwningComponent).
• Adds tests, docs, and changelog entries covering shared-document behavior, bubbling behavior changes, and the new APIs.

File summaries

File	Description
tests/bunit.tests/Rendering/SharedDocumentTest.cs	New tests validating shared-document DOM behavior and fallback cases
tests/bunit.tests/Rendering/ComponentTreeNavigationTest.cs	New tests for parent/root/children/ancestor navigation APIs
tests/bunit.tests/Extensions/ElementOwningComponentTest.cs	New tests for INode.GetOwningComponent* resolution
tests/bunit.tests/EventDispatchExtensions/ChildComponentEventBubblingTest.cs	New tests confirming cross-component DOM bubbling behavior
tests/bunit.testassets/SampleComponents/TextOnlyChild.razor	New test asset for text-only child rendering edge case
tests/bunit.testassets/SampleComponents/TableWithChildRows.razor	New test asset for table/row nesting behavior
tests/bunit.testassets/SampleComponents/SiblingChildren.razor	New test asset for sibling re-render scenarios
tests/bunit.testassets/SampleComponents/SelectWithChildOptions.razor	New test asset for <select>/<option> ownership/selection behavior
tests/bunit.testassets/SampleComponents/ParentWithTextOnlyChild.razor	New test asset covering inlined text-only child output
tests/bunit.testassets/SampleComponents/ParentWithLeadingTextChild.razor	New test asset for “leading text prevents shared-node view” fallback
tests/bunit.testassets/SampleComponents/ParentWithEmptyChild.razor	New test asset for empty child rendering behavior
tests/bunit.testassets/SampleComponents/ParentFormWithChildButton.razor	New test asset for submit bubbling into parent form
tests/bunit.testassets/SampleComponents/ParentDivWithChildButton.razor	New test asset for click bubbling + stopPropagation
tests/bunit.testassets/SampleComponents/LeadingTextChild.razor	New test asset rendering markup with leading text
tests/bunit.testassets/SampleComponents/GrandParentDivWithChildButton.razor	New test asset for 3-level bubbling / ancestor navigation
tests/bunit.testassets/SampleComponents/EmptyChild.razor	New test asset for “renders nothing” scenario
tests/bunit.testassets/SampleComponents/CounterChild.razor	New test asset used for sibling re-render and filtering tests
tests/bunit.testassets/SampleComponents/ChildWithButton.razor	New test asset for basic child button interactions
tests/bunit.testassets/SampleComponents/ChildTableRow.razor	New test asset for <tr> rendered by child component
tests/bunit.testassets/SampleComponents/ChildOption.razor	New test asset for <option> rendered by child component
src/bunit/Rendering/RootRenderedComponent.cs	Adds root rendered component that owns the shared snapshot
src/bunit/Rendering/RenderedComponent.cs	Reworks per-component markup/nodes to be snapshot “slices” + invalidation signaling
src/bunit/Rendering/IRenderedComponent.cs	Extends internal contracts for root access + markup-updated signaling
src/bunit/Rendering/Internal/RootMarkupSnapshot.cs	Implements shared markup/document storage and per-component node-range views
src/bunit/Rendering/Internal/NodeRangeList.cs	Adds INodeList view over sibling node ranges
src/bunit/Rendering/Internal/Htmlizer.cs	Records component markup ranges while generating shared markup
src/bunit/Rendering/Internal/ComponentMarkupRange.cs	Adds range struct + Htmlizer result record type
src/bunit/Rendering/BunitRenderer.cs	Adds root snapshot regeneration + markup-updated propagation + private-document tracking
src/bunit/Extensions/RenderedComponentTreeExtensions.cs	Adds public component tree navigation extensions
src/bunit/Extensions/ElementOwningComponentExtensions.cs	Adds public DOM-node-to-rendered-component lookup extensions
docs/site/docs/verification/index.md	Adds verification docs entry for “find owning component”
docs/site/docs/verification/find-owning-component.md	New documentation for GetOwningComponent* and behavior details
docs/site/docs/toc.md	Adds doc TOC link for new verification topic
docs/site/docs/interaction/trigger-event-handlers.md	Documents cross-component event bubbling behavior
CHANGELOG.md	Notes new APIs and breaking behavior change under Unreleased

Review details

• Files reviewed: 35/35 changed files
• Comments generated: 2
• Review effort level: Lite

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[linkdotnet]

@egil I started to have a v3 branch - I am much inclined to have this in v3 with all the issues flagged for that milestone in our github issue tracker. So we can release roughly with net11.

For sure we need a release party somewhere :D