XAML Hot Reload: Improve incremental generation and coverage by Redth · Pull Request #36730 · dotnet/maui

Redth · 2026-07-22T16:34:51Z

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Description of Change

This PR improves incremental XAML Hot Reload source generation and expands deterministic coverage for generator, compilation, and in-process metadata-update behavior.

Preserves supported complex properties such as CollectionView.ItemTemplate when an update replaces a root element.
Buffers diagnostics from speculative source generation so rejected attempts do not leak or duplicate diagnostics.
Conservatively emits the existing explicit skipped (not yet supported) marker for inline-resource and StaticResource-dependent complex-property subtrees that cannot be resolved safely in the isolated speculative context.
Adds a reusable source-generator Hot Reload harness for strict or diagnostic-tolerant generation, compilation, live metadata updates, chained deltas, multiple XAML documents, optional stable C# inputs, multiple retained instances, and application-host resource/theme scenarios.
Reorganizes the larger AI-assisted behavior suites into logical partial-class files while preserving their fully qualified test names.

Root Cause and Wave-1 Fix

UpdateComponentCodeWriter could create a newly added replacement root, but it skipped element-valued properties instead of applying the same value-creation and property-setting pipeline used by InitializeComponent. That silently dropped properties such as CollectionView.ItemTemplate in #36256.

The replacement-root path now speculatively emits supported complex properties and assigns them to the existing live page. The #36256 coverage verifies both generated source/compilation and a real metadata update on the same page instance, including a non-null CollectionView.ItemTemplate whose content contains the updated label.

Speculative generation introduced two safety constraints:

Diagnostics must remain isolated until emission is accepted. SourceGenContext now supports explicit diagnostic buffering, flush, and discard behavior.
A fresh speculative context cannot safely resolve ancestor resources or run the complete resource pipeline. Inline resources and direct, nested-markup, or element-form StaticResource references are therefore declined explicitly instead of producing a compileable false-success update that fails or resolves to null at runtime.

Only the expected unsupported InvalidOperationException falls back to the skip marker; unexpected exceptions continue to propagate.

#36157 is covered only at the generator boundary: malformed-to-repaired input recomputes generator diagnostics and the repaired output compiles. This does not claim IDE Error List, Roslyn edit-session, or dotnet watch recovery. #36156 remains deferred to an IDE/Roslyn host test because its rude-edit session-poisoning behavior cannot be reproduced faithfully by a generator unit test.

Reusable Hot Reload Harness

The harness:

keeps one incremental generator driver and advances the Roslyn EmitBaseline through successive deltas;
gives each scenario unique assembly, XAML path, and collectible AssemblyLoadContext identities;
supports generation-only, compile-only, and full live-update paths;
supports diagnostic-tolerant versions, multiple XAML documents, optional stable C# sources, and multiple retained roots;
uses metadata-aware fact and theory attributes so live-update tests skip, rather than fail, when the runtime does not support MetadataUpdater.ApplyUpdate;
resets XamlHotReloadState, restores Application.Current, unregisters roots from XamlComponentRegistry, disposes metadata/streams, and unloads the collectible context.

Generated x:Name fields still require manual C# stubs because CodeBehindCodeWriter is outside this harness.

Wave-2 Coverage

The living AI-assisted index accounts for 55 test methods across 35 behavior IDs/capabilities covering:

dynamic and merged resources, styles, themes, and application resources;
visual states and behaviors;
data/control templates, selectors, compiled bindings, and BindableLayout;
bindings, markup extensions, and MultiBinding;
nested generated controls and namescopes;
multi-document and cross-assembly generator invalidation.

The metadata-enabled AI-assisted run reports 41 passed, 18 intentionally skipped, and 0 failed. Theory rows affect the reported case count.

Passing tests are classified as live, construction, generator/compile guards, or explicit decline guards. Each skip-gated RED-PROBE names a nearby executable passing guard. The 18 skipped probes encode desired behavior for known gaps; they are not claimed as passing runtime coverage.

The larger resource/theme, visual-state, template, binding/markup, and nested-control suites are split into behavior-named partial files for reviewability without changing xUnit discovery, attributes, fixtures, or method identities.

Known Limitations and Deferred Lanes

A compiled ResourceDictionary Source= payload is unavailable in the in-memory collectible load context. Multi-document and Source= tests therefore verify tracking, generation, and compilation; their live payload probes remain skip-gated.
Cross-assembly tests cover incremental-generator reference invalidation and caching only. Applying deltas to a separately loaded runtime assembly remains an integration lane.
IDE/Hot Reload host behavior, Roslyn rude-edit recovery, dotnet watch, devices, native handlers, rendered output, and lifecycle behavior remain integration/host lanes.
The AppThemeBinding live probe remains skip-gated because the current update writer supplies an IProvideValueTarget with a null TargetProperty; its passing guard proves generated branch capture only.
Future keyed-template and selector factories remain tracked by [XAML Hot Reload] SourceGen HR: successive DataTemplate edits under dotnet watch crash the app / poison HR / kill the watcher (PR #34338) #36482. Passing construction/source guards do not prove post-update future realization.
Complex-property and collection reconciliation remains tracked by [XAML Hot Reload] Reconcile complex property and collection updates #36732. Explicit decline guards prove that unsupported updates are skipped and compile, not that live reconciliation succeeds.

What NOT to Do

Do not send speculative visitor diagnostics directly to the production diagnostic sink; rejected attempts must discard them.
Do not emit resource-dependent subtrees from an isolated context and treat successful compilation as proof of runtime resolution.
Do not catch broad exceptions and silently degrade unexpected generator failures.
Do not use generated-source markers as evidence of live runtime behavior.
Do not treat generator-only recovery coverage as proof of IDE or dotnet watch recovery.

Issues Fixed

Fixes #36256

Related coverage and roadmap issues:

XIHR: stale MAUIG1003 diagnostic persists after fixing a malformed XAML expression (dotnet watch) #36157: generator diagnostic recomputation coverage only; host recovery is not fixed here.
XIHR: a rude edit (failed-compile) breaks the hot reload session permanently — valid edits no longer apply until full restart #36156: deferred IDE/Roslyn host scenario.
[XAML Hot Reload] SourceGen HR: successive DataTemplate edits under dotnet watch crash the app / poison HR / kill the watcher (PR #34338) #36482: future template/selector factory roadmap; not fixed by this PR.
[XAML Hot Reload] Reconcile complex property and collection updates #36732: complex-property and collection reconciliation roadmap; not fixed by this PR.

Test Coverage

DOTNET_MODIFIABLE_ASSEMBLIES=debug dotnet test src/Controls/tests/SourceGen.UnitTests/SourceGen.UnitTests.csproj -c Debug
DOTNET_MODIFIABLE_ASSEMBLIES=debug dotnet test src/Controls/tests/SourceGen.UnitTests/SourceGen.UnitTests.csproj -c Release
env -u DOTNET_MODIFIABLE_ASSEMBLIES dotnet test src/Controls/tests/SourceGen.UnitTests/SourceGen.UnitTests.csproj -c Debug

SourceGen.UnitTests Debug: 497 passed / 18 skipped / 0 failed (515 total).
SourceGen.UnitTests Release: 497 passed / 18 skipped / 0 failed (515 total).
XamlIncrementalHotReloadE2ETests: 13 passed / 0 skipped / 0 failed.
HotReload.AiAssisted: 41 passed / 18 skipped / 0 failed.
Default Debug with metadata updates explicitly unavailable: 475 passed / 37 skipped / 0 failed (512 total). xUnit reports each skip-gated theory once rather than once per data row.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 1b9bf3f3-3e24-49bf-b3eb-c075858ee563

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 8dc5778b-13c3-40aa-8b21-76617ea71b69

github-actions · 2026-07-22T16:35:00Z

🚀 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 -- 36730

Or

Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 36730"

azure-pipelines · 2026-07-22T16:35:09Z

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Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 8dc5778b-13c3-40aa-8b21-76617ea71b69

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: f093ec6b-e912-40c6-acae-f308f79ee558

Adds ResourceAndThemeHotReloadTests.cs covering DynamicResource key rename/reversal (RT-01, live GREEN across Color/Double/String), merged-dictionary and BasedOn/trigger-style complex-property skip markers (RT-02/04/06, live GREEN guards), and their corresponding honest skip-gated RED probes (RT-03/05/07) tracked by #36732 for collection/property reconciliation gaps. Empirically corrected 3 XAML shapes relative to the literal contract assumption, verified against real generator output: - RT-02/03: root ContentPage.Resources with an explicit <ResourceDictionary><ResourceDictionary.MergedDictionaries>> wrapper is silently dropped by TryEmitResourceDictionaryChange (unkeyed ElementNode, no marker). Moved MergedDictionaries under a non-root element's Resources (VerticalStackLayout.Resources) to correctly hit the generic "Complex property 'Resources' ... skipped" marker. - RT-04/05: keyed Style resources wrapped in an explicit <ResourceDictionary> tag also hit the silent unkeyed-node bailout. Removed the wrapper so XAML's implicit dictionary conversion emits a keyed ListNode, producing the expected per-key "Cannot encode resource '...' — left untouched" markers. - RT-06/07: removing Label.Style entirely hits the "Style cleared" ClearValue path, not the complex-property marker. Changed V2 to a different-but-still-present inline Style so the change is detected as a complex-property replacement instead of a removal. Scope: new test file only; no README, harness, or product code changes. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 8191a632-a704-4949-865b-a38bd8133f6d

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 96ebbad1-0079-4d43-a464-bb0b9ebadd89

…1..06) Add TemplateAndSelectorHotReloadTests covering DataTemplate/ControlTemplate/ DataTemplateSelector behavior under XAML Incremental Hot Reload (PR #36730). Empirically, editing a keyed template resource makes UpdateComponent replace the entry with a factory-less `new DataTemplate()`, and a held template keeps its construction-time factory delegate (not EnC-refreshed). So future CreateContent()/SelectTemplate() does NOT reflect the edit. Per the robustness rule the "future realization uses the new factory" claim is reclassified (not weakened) into skip-gated RED-PROBEs; each family keeps a faithful GREEN anchor. - TS-01/02/03/04 GREEN anchors: construction realization correctness (per-realization namescope isolation, selector branch selection, compiled binding, x:Reference, VSM TargetName isolation), already-realized-subtree stability across an update, and generated-source oracles (new factory in InitializeComponent; exact resource-replacement marker in UpdateComponent). - TS-01/02/03/04 RED-PROBEs: future realization reflects the edit — skip-gated on #36482. - TS-05 GREEN guard: BindableLayout.ItemTemplate emits the attached-complex skip marker and still compiles. - TS-06 RED-PROBE: BindableLayout retype/reverse controller children — skip-gated on #36732; green anchor is TS-05. Verified with DOTNET_MODIFIABLE_ASSEMBLIES=debug: 6 passed, 5 skipped. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: d5e424fa-b2af-4909-9a4d-3b2114ac147d

Adds src/Controls/tests/SourceGen.UnitTests/HotReload/AiAssisted/NestedControlHotReloadTests.cs covering same-compilation nested custom controls (generic ProbeCard fixtures) per the Wave-2 final test plan sections 3.5/7/8/10: - NC-01 (GREEN): NestedCustomControls_Construct_HaveIndependentIdentityAndNamescope - two ProbeCard instances construct with independent identity, namescope, per-instance local Resources, and correct per-card x:Reference resolution; mutating one card never bleeds into the other. - NC-02 (DOC-SKIP-GUARD): NestedLocalResources_CustomConverter_EmitsSkipMarker - asserts the writer's non-root complex-property skip marker for a nested ProbeCard.Resources converter edit. Empirically verified the actually-reached site is UpdateComponentCodeWriter.cs:1194 (EmitPropertyChange, isRoot: false), not the plan's cited L929 (TryEmitResourceDictionaryChange), which is root-only (single caller: EmitRootPropertyChange). - NC-03 (RED-PROBE, Skip-gated): NestedControls_LocalResources_XReference_RebindIndependently - 3-version (V1/V2/V1) live probe referencing #36732: the nested-Resources skip means a converter-type swap never applies, while the sibling Value mutation still applies and re-invokes the ORIGINAL converter - asserted via per-card label text and static invocation counters (no invocation multiplication, no cross-card bleed, new converter never invoked). Skip-gated per plan's STOP RULE; paired DOC-SKIP-GUARD (NC-02) stays green. Includes test-local workarounds (scoped to this file only, no harness/product edits): a minimal synchronous IDispatcher/IDispatcherProvider stub (live Binding/PropertyChanged paths require a registered dispatcher, which no prior hot-reload test exercised), and manually-declared private fields on the PageStub for x:Name'd elements (the harness only wires the InitializeComponent/UpdateComponent generator, not the separate code-behind field-declaration generator that normally supplies these). Validated: dotnet test --filter FullyQualifiedName~HotReload.AiAssisted.NestedControlHotReloadTests under DOTNET_MODIFIABLE_ASSEMBLIES=debug - 2 passed, 1 skipped, 0 failed. dotnet format --verify-no-changes clean on this file. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: ba10e73c-e9b1-46c7-8bf6-c7cd0a2fa15c

Verified NC-03's faithfulness before deciding whether to keep it Skip-gated: the generated V2 UpdateComponent retrieves each ProbeCard via XamlComponentRegistry.TryGet (never `new ProbeCard(...)`) in the exact same diff block that emits the nested-Resources skip comment, confirming the test reaches the intended retained nested-resource + x:Reference rebind path rather than passing because a subtree/root was replaced. Strengthened the test itself to assert this permanently: - Added an inline check on generation[1].UpdateComponentSource for both the TryGet-based lookup and the Resources skip marker, plus a negative check that no ProbeCard is reconstructed. - Added explicit ReferenceEquals identity guards for page, both ProbeCard instances, and both Labels after each ApplyUpdate (V2 and V3), proving nothing is reconstructed across V1->V2->V1. - Added ReferenceEquals guards on each card's resolved converter instance after each update, proving left/right local-resource independence holds throughout, not just at construction. All invariants hold empirically (visible prefixes genuinely change A1/B1->A2/B2->A1/B1, invocation counts increase by exactly 2 per version with no multiplication, no cross-card bleed) with no incorrect/multiplied/cross-bled behavior, so this is a well-defined, side-effect-free fallback rather than a red probe. Promoted from [MetadataUpdateFact(Skip = ...)] to [MetadataUpdateFact], updated the provenance header to "Expected: GREEN", and removed the #36732 skip-rationale linkage (NC-02 keeps its own, unrelated Issue reference for the underlying writer-roadmap gap). Targeted class run: 3 passed, 0 skipped, 0 failed. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: ba10e73c-e9b1-46c7-8bf6-c7cd0a2fa15c

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 8dc5778b-13c3-40aa-8b21-76617ea71b69

Implements faithful Phase-2 coverage in ResourceAndThemeHotReloadTests, building on the integrated Phase-0/1 harness (app host, theme flip, multi-instance, multi-document). - RT-08 AppThemeBinding branch edit/reverse: split into a GREEN generation-atomic anchor (branch literal Light1->Light2->Light1 captured in the generated component, Dark untouched, all versions compile) plus a Skip-gated live RED-PROBE. The live re-provide is unsupported because the generated UpdateComponent re-provides the AppThemeBinding through an IProvideValueTarget whose TargetProperty is null, so AppThemeBindingExtension.ProvideValue throws "Cannot determine property to provide the value for" (tracked by #36732). - RT-09 application-scope DynamicResource fanout (GREEN): two retained roots update once each plus a fresh post-update root starts latest, via app-scoped key swap (AccentA/AccentB) under a live Application host; app dictionary identity asserted stable. - RT-10 Source= merged dictionary reorder/removal: GREEN generator/compile anchor tracking document reorder+removal and recompiling every version, plus a Skip-gated live RED-PROBE documenting the Source= resource-payload harness boundary (no faked ResourceLoader; tracked by #36732). - RT-11 multi-document malformed->repair atomicity (GREEN, generator-atomic): a malformed page in a two-AdditionalText batch surfaces a parser error and does not phantom-advance to a compilable page; the repaired version fully recovers and compiles, with the sibling dictionary tracked throughout. Labeled generator-atomic (not live-resource atomic) because Source= cannot wire the dictionary in this harness (same boundary as RT-10). Empirically run with DOTNET_MODIFIABLE_ASSEMBLIES=debug: the class is green (10 passed, 5 skipped, 0 failed); the two new skips are documented live RED-PROBEs with real bodies, never empty always-skipped tests. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 3954ca4a-026e-46b1-a878-8ed0ba5224be

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 3aecbe3b-4302-428f-a397-9f0923d19656

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 60c67cff-beec-4a4b-848d-fafbe39b837b

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 1b9bf3f3-3e24-49bf-b3eb-c075858ee563

MauiBot · 2026-07-26T21:53:05Z

AI Review Summary

@Redth — new AI review results are available based on this last commit: 523ee85.

🗂️ Review Sessions — click to expand

🚦 Gate — Test Before & After Fix

Gate Result: ⚠️ INCONCLUSIVE

Platform: WINDOWS · Base: net11.0 · Merge base: bbcba3ff

🩺 Base branch does not compile — the without-fix build failed. The gate's "does the test fail without the fix" check is unreliable here; this usually means main is broken or a merge-base file went missing. Investigate before trusting this gate.

D:\a\1\s\src\Controls\tests\SourceGen.UnitTests\SourceGenContextTests.cs(15,34): error CS1501: No overload for method 'CreateNewForTests' takes 1 arguments [D:\a\1\s\src\Controls\tests\SourceGen.UnitT...

Test	Without Fix (expect FAIL)	With Fix (expect PASS)
🧪 BindingAndMarkupHotReloadTests `BindingAndMarkupHotReloadTests`	🛠️ BUILD ERROR	✅ PASS — 42s
🧪 CrossAssemblyHotReloadTests `CrossAssemblyHotReloadTests`	🛠️ BUILD ERROR	✅ PASS — 32s
🧪 GeneratorRecoveryHotReloadTests `GeneratorRecoveryHotReloadTests`	🛠️ BUILD ERROR	✅ PASS — 31s
🧪 HarnessCapabilityTests `HarnessCapabilityTests`	🛠️ BUILD ERROR	✅ PASS — 31s
🧪 NestedControlHotReloadTests `NestedControlHotReloadTests`	🛠️ BUILD ERROR	✅ PASS — 30s
🧪 ResourceAndThemeHotReloadTests `ResourceAndThemeHotReloadTests`	🛠️ BUILD ERROR	✅ PASS — 33s
🧪 SourceGenContextTests `SourceGenContextTests`	🛠️ BUILD ERROR	✅ PASS — 27s
🧪 StructuralHotReloadTests `StructuralHotReloadTests`	🛠️ BUILD ERROR	✅ PASS — 31s
🧪 TemplateAndSelectorHotReloadTests `TemplateAndSelectorHotReloadTests`	🛠️ BUILD ERROR	✅ PASS — 30s
🧪 VisualStateHotReloadTests `VisualStateHotReloadTests`	🛠️ BUILD ERROR	✅ PASS — 30s
🧪 XamlIncrementalHotReloadE2ETests `XamlIncrementalHotReloadE2ETests`	🛠️ BUILD ERROR	✅ PASS — 31s

🔴 Without fix — 🧪 BindingAndMarkupHotReloadTests: 🛠️ BUILD ERROR · 181s