[Windows]Fix: Label.FormattedText does not clear previous TextHighlighters

[SubhikshaSf4851]

Note

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This pull request addresses an issue where updating a Label's FormattedText on Windows did not clear previous text highlighting, causing stale highlighter ranges to persist and affect new text. The fix ensures that highlighter state is properly reset when the formatted text changes. Additionally, a new test is added to verify this behavior across platforms, with extra checks for Windows.

Description of Change

Bug fix:

• FormattedStringExtensions.cs: Ensures that TextBlock.TextHighlighters is cleared whenever the inlines are updated, preventing highlighter leakage when FormattedText is changed.

Testing improvements:

• FormattedStringTests.cs: Adds a new test, UpdatingFormattedTextClearsPreviousHighlights, to confirm that updating a label’s formatted text clears any previous highlight/background color state, with specific validation for the Windows platform.

Issues Fixed

Fixes #36519

Tested the behavior in the following platforms

• Windows
• Android
• iOS
• Mac

Before Issue Fix	After Issue Fix
BeforeFix36519.mp4	AfterFix36519.mp4

[github-actions]

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.sh | bash -s -- 36608

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 36608"

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[dotnet-policy-service]

Hey there @@SubhikshaSf4851! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

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[Copilot]

Pull request overview

Fixes a Windows-specific Label.FormattedText bug where TextBlock.TextHighlighters were not cleared when rebuilding inlines, causing stale highlight ranges (and potential TextHighlighter accumulation) to persist across FormattedText updates. Adds a device test to validate that updating formatted text removes prior highlight/background state, with an additional native assertion on Windows.

Changes:

• Windows: clear TextBlock.TextHighlighters whenever FormattedStringExtensions.UpdateInlines rebuilds the Inlines collection.
• Tests: add UpdatingFormattedTextClearsPreviousHighlights to verify stale highlight/background state does not persist after updating Label.FormattedText (including a Windows-only native TextHighlighters check).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/Controls/src/Core/Platform/Windows/Extensions/FormattedStringExtensions.cs	Clears TextHighlighters alongside Inlines.Clear() so prior span highlight ranges don’t leak into subsequent FormattedText updates.
src/Controls/tests/DeviceTests/Elements/FormattedStringTests.cs	Adds a regression test that asserts highlight color is present initially and removed after updating to non-highlighted formatted text (plus Windows-only TextHighlighters collection assertions).

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[vishnumenon2684]

/azp run maui-pr-uitests , maui-pr-devicetests

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[MauiBot]

AI Review Summary

@SubhikshaSf4851 — new AI review results are available based on this last commit: 30f500f. To request a fresh review after new comments or commits, comment /review rerun.

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🗂️ Review Sessions — click to expand

🚦 Gate — Test Before & After Fix

Gate Result: ⚠️ INCONCLUSIVE

Platform: WINDOWS · Base: main · Merge base: 0188c0c6

Test	Without Fix (expect FAIL)	With Fix (expect PASS)
📱 FormattedStringTests (UpdatingFormattedTextClearsPreviousHighlights) Category=Label	⚠️ ENV ERROR	⚠️ ENV ERROR

🔴 Without fix — 📱 FormattedStringTests (UpdatingFormattedTextClearsPreviousHighlights): ⚠️ ENV ERROR · 325s

No log file found

🟢 With fix — 📱 FormattedStringTests (UpdatingFormattedTextClearsPreviousHighlights): ⚠️ ENV ERROR · 154s

No log file found

⚠️ Failure Details

• ⚠️ FormattedStringTests (UpdatingFormattedTextClearsPreviousHighlights) without fix: Windows device test result file 'artifacts\log\TestResults-Microsoft_Maui_Controls_DeviceTests_Label.xml' is empty or not valid XML (the device-test app likely crashed or exited before writing results).
• ⚠️ FormattedStringTests (UpdatingFormattedTextClearsPreviousHighlights) with fix: Windows device test result file 'artifacts\log\TestResults-Microsoft_Maui_Controls_DeviceTests_Label.xml' is empty or not valid XML (the device-test app likely crashed or exited before writing results).

📁 Fix files reverted (1 files)

• src/Controls/src/Core/Platform/Windows/Extensions/FormattedStringExtensions.cs

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📱 UI Tests — Button,Label,Layout

Detected UI test categories: Button,Label,Layout

✅ Deep UI tests — 351 passed, 0 failed across 3 categories on platform-pool agent (replaces in-process counts above).

🧪 UI Test Execution Results (deep, platform pool)

Category	Tests	Snapshot diffs
Button	69/70 ✓	—
Label	91/94 ✓	—
Layout	191/195 ✓	—
📎 Download drop-deep-uitests artifact (TRX + snapshot diffs)

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📋 Pre-Flight — Context & Validation

Issue: #36519 - [Windows, 10.0.71] Windows Label.FormattedText does not clear previous TextHighlighters when updating spans, leading to overlapping highlights & memory leaks
PR: #36608 - [Windows]Fix: Label.FormattedText does not clear previous TextHighlighters
Platforms Affected: Windows
Files Changed: 1 implementation, 1 test

Key Findings

• Issue #36519 reports that Windows Label.FormattedText updates leave previous TextBlock.TextHighlighters in place when new formatted spans are assigned, causing stale highlighting and retaining old TextHighlighter instances.
• PR fix changes src/Controls/src/Core/Platform/Windows/Extensions/FormattedStringExtensions.cs to clear textBlock.TextHighlighters whenever UpdateInlines rebuilds formatted text.
• Regression coverage was added in src/Controls/tests/DeviceTests/Elements/FormattedStringTests.cs for updating from highlighted formatted text to unhighlighted formatted text, including a Windows native TextHighlighters assertion.
• Gate result supplied by caller is inconclusive due to build/environment error; per instruction, this pre-flight does not treat it as a failing fix and does not re-run gate verification.

Code Review Summary

Verdict: NEEDS_DISCUSSION
Confidence: low
Errors: 0 | Warnings: 0 | Suggestions: 0

Key code review findings:

• ℹ No code correctness findings were identified by the independent code-review pass.
• ℹ Blast radius is localized to Windows formatted-label text rendering; no startup or static state impact.
• ℹ CI/required-check state was not fully verifiable in the unauthenticated environment, so the code-review verdict cannot be LGTM even though the code change is targeted.

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #36608	Clear TextBlock.TextHighlighters at the start of Windows formatted-text inline rebuild and reuse the cached highlighter collection for additions.	⚠️ INCONCLUSIVE (Gate)	src/Controls/src/Core/Platform/Windows/Extensions/FormattedStringExtensions.cs, src/Controls/tests/DeviceTests/Elements/FormattedStringTests.cs	Original PR fix; gate could not build/run in prior step.

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🔬 Code Review — Deep Analysis

Code Review — PR #36608

Independent Assessment

What this changes: Windows FormattedStringExtensions.UpdateInlines now clears TextBlock.TextHighlighters before rebuilding formatted-label inlines (FormattedStringExtensions.cs:61-62) and reuses the cached collection when adding new highlighters (:102). A device test verifies updating Label.FormattedText removes stale highlight state (FormattedStringTests.cs:61-102).

Inferred motivation: Prevent stale Windows TextHighlighter ranges from accumulating when a formatted label is updated.

Reconciliation with PR Narrative

Author claims: Fixes #36519: Windows Label.FormattedText did not clear old highlighters, causing visual overlap and leaks.
Agreement/disagreement: Agrees. The issue root cause names the same missing clear, and the PR applies it at the correct rebuild point.

Prior Review Reconciliation

No prior ❌ Error code findings found. Prior human comments requested using the cached textHighlighters local for later additions; current code does that. MauiBot ❌ markers were CI/gate related, not unresolved code findings.

Blast Radius Assessment

• Runs for all instances: Only Windows labels using formatted text when UpdateInlines runs.
• Startup impact: No.
• Static/shared state: No.
• Platform scope: Windows text rendering path; confidence capped below high.

CI Status

• Required-check result: gh pr checks --required unavailable because gh is unauthenticated.
• Public checks observed: maui-pr success; Build Analysis, maui-pr-uitests, and maui-pr-devicetests failing.
• Classification: likely unrelated/infra or unrelated platform failures (macOS timeout, binlog read EndOfStream, MacCatalyst BadExit, Android/iOS UI failures). Windows device-test leg passed. Full required-check classification remains limited by unauthenticated environment.
• Action taken: Invoked azdo-build-investigator; used public GitHub/AzDO REST where available; confidence capped low.

Findings

No ❌ Errors, ⚠️ Warnings, or 💡 Suggestions from code review. Expert reviewer also reported no high-confidence inline findings.

Failure-Mode Probing

• Updating highlighted formatted text to unhighlighted formatted text: old TextHighlighters are cleared before new runs are added.
• Updating highlighted formatted text to plain text: existing plain-text path already clears highlighters.
• Initial handler connection: clearing an empty collection is safe; new highlighters are added normally.
• Null/default FormattedText: existing tuple conversion handles null spans; no new null path introduced.

Verdict: NEEDS_DISCUSSION

Confidence: low
Summary: Code change looks correct and targeted, with appropriate regression coverage. I cannot give LGTM because CI is red and required-check status could not be fully verified in this unauthenticated environment.

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🛠️ Fix — Analysis & Comparison

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
1	try-fix	Track and remove only MAUI-owned Windows TextHighlighter instances via attached state.	❌ Fail	2 files	Built with 0 errors, but Windows device-test runner produced empty/invalid Label XML; more complex than PR fix.
2	try-fix	Clear Windows TextBlock.TextHighlighters in the Controls Label.FormattedText mapper before rebuilding text.	❌ Fail	3 files	Built with 0 errors, same empty/invalid Label XML; weaker encapsulation because direct UpdateInlines callers remain unprotected.
3	try-fix	Reconcile TextBlock.TextHighlighters to the desired current formatted-string projection without a blanket clear.	❌ Fail	1 file	Built with 0 errors, same empty/invalid Label XML; more complex than PR fix.
PR	PR #36608	Clear TextBlock.TextHighlighters at the start of Windows formatted-text inline rebuild.	⚠️ INCONCLUSIVE (Gate)	2 files	Original PR; gate could not build/run in prior step.

Cross-Pollination

Model	Round	New Ideas?	Details
gpt-5.5 expert	1	Yes	Candidate 1: MAUI-owned highlighter lifecycle tracking.
gpt-5.5 expert	2	Yes	Candidate 2: mapper-level rich-text reset.
gpt-5.5 expert	3	Yes	Candidate 3: deterministic highlighter reconciliation in UpdateInlines.
gpt-5.5 expert	4	No	NO NEW IDEAS: viable fixes reduce to clearing stale native highlighters during UpdateInlines, tracking/removing MAUI-owned highlighters, mapper-level cleanup before text remap, or reconciling the desired highlighter set; remaining options are relocations or disproportionately broad rewrites.

Exhausted: Yes
Selected Fix: PR #36608 — Among explored candidates, no alternative passed the Windows test command or was demonstrably better. Code review found the PR fix targeted and simpler; all alternatives added complexity or weaker encapsulation.

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📝 Recommended PR Title & Description

Assessment: ✏️ Recommend updating — the current description is accurate and detailed, but the title does not follow the [Platform] Component: What changed formula and still describes the pre-fix bug state.

Recommended title

[Windows] Label: Clear TextHighlighters when FormattedText changes

Recommended description

This pull request addresses an issue where updating a `Label`'s `FormattedText` on Windows did not clear previous text highlighting, causing stale highlighter ranges to persist and affect new text. The fix ensures that highlighter state is properly reset when the formatted text changes. Additionally, a new test is added to verify this behavior across platforms, with extra checks for Windows.

### Description of Change

**Bug fix:**
* [`FormattedStringExtensions.cs`](diffhunk://#diff-3846573c00e8c480581599035bcc2e2aa18da8b62da4d0304c52b6e1b970fa7aR61): Ensures that `TextBlock.TextHighlighters` is cleared whenever the inlines are updated, preventing highlighter leakage when `FormattedText` is changed.

**Testing improvements:**
* [`FormattedStringTests.cs`](diffhunk://#diff-24cf35347d91a39e18539e140d96549832bb6897cbfcd80ae3d0acbd96f5f192R53-R103): Adds a new test, `UpdatingFormattedTextClearsPreviousHighlights`, to confirm that updating a label's formatted text clears any previous highlight/background color state, with specific validation for the Windows platform.

### Issues Fixed

Fixes #36519

### Tested the behavior in the following platforms

- [x] Windows
- [ ] Android
- [ ] iOS
- [ ] Mac

| Before Issue Fix | After Issue Fix |
|----------|----------|
| <video src="https://github.com/user-attachments/assets/2c4e9dd6-7dde-445d-8900-02fd86ba383a"> | <video src="https://github.com/user-attachments/assets/8983aca5-672e-4d8d-911e-6470fd463ee9"> |

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🏁 Report — Final Recommendation

Comparative Fix Report — PR #36608

Candidate ranking

Rank	Candidate	Result	Assessment
1	pr	⚠️ Gate inconclusive	Best candidate. Clears Windows TextBlock.TextHighlighters inside FormattedStringExtensions.UpdateInlines, the same place that rebuilds native inlines and creates new MAUI highlighters. It is localized, simple, and protects all formatted-string inline rebuild callers.
2	pr-plus-reviewer	⚠️ Gate inconclusive	Equivalent to pr; the expert reviewer produced no actionable source changes, so this candidate has no behavioral or code-quality advantage over the raw PR fix.
3	try-fix-3	❌ Fail	Reconciles desired highlighters instead of blanket clearing. It keeps cleanup encapsulated in UpdateInlines, but is more complex than the PR and still failed the recorded Windows test command.
4	try-fix-1	❌ Fail	Tracks MAUI-owned highlighters with attached state and removes only those. This avoids clearing possible external highlighters, but adds lifecycle state and changes plain-text cleanup behavior; it also failed the recorded Windows test command.
5	try-fix-2	❌ Fail	Clears highlighters from the Controls Label.FormattedText mapper. This is less well encapsulated because direct UpdateInlines callers remain unprotected, and it failed the recorded Windows test command.

Comparison

The raw PR fix addresses the root cause at the narrowest useful layer: Windows formatted-text projection. Every time MAUI rebuilds formatted inlines, it also resets the corresponding native highlighter collection before adding highlighters for the current spans. This is easier to reason about than tracking ownership state or reconciling highlighter objects, and it avoids the mapper-level candidate's coverage gap.

The STEP 5a try-fix candidates all failed their recorded regression command with an invalid or empty Windows device-test result file. Even though those failures may reflect the same local runner environment problem seen in the gate, the recorded result is still lower confidence than the PR candidate, and the alternatives are not simpler or more complete than the PR fix.

Winner

pr is the winning candidate. It is the simplest complete fix, has no expert-reviewer source findings, has targeted regression coverage, and no try-fix candidate demonstrated a better verified outcome.

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🧭 Next Steps — review latest findings

No alternative fix was selected for this run. Review the session findings and CI results before merging.