[TrimmableTypeMap] Per-assembly typemap universes with startup hook initialization by simonrozsival · Pull Request #11181 · dotnet/android

simonrozsival · 2026-04-22T11:49:51Z

Summary

Implements per-assembly typemap universes for incremental Debug builds and merged Release builds, as described in #11180.

Changes

Runtime (`Mono.Android`)

ITypeMapWithAliasing (new) — interface abstracting type map lookups with alias resolution
- SingleUniverseTypeMap — wraps one IReadOnlyDictionary pair, handles alias holders within a single universe
- AggregateTypeMap — wraps N SingleUniverseTypeMap instances, flattens results across universes (Debug only)
TrimmableTypeMap — two Initialize overloads accepting BCL types:
- Single dict pair (Release/shared universe)
- Two parallel arrays (Debug/per-assembly universes)
- Re-initialization guard (InvalidOperationException)
- Length-0 validation on array overload
JNIEnvInit — removed old TrimmableTypeMap.Initialize() call (now done via startup hook)

Generator (`Microsoft.Android.Sdk.TrimmableTypeMap`)

TypeMapAssemblyEmitter — emits per-assembly __TypeMapAnchor type (Debug) or references Java.Lang.Object as shared anchor (Release)
RootTypeMapAssemblyGenerator — complete rewrite: emits StartupHook.Initialize() IL that constructs the appropriate type map and calls TrimmableTypeMap.Initialize():
- Option A (shared universe): calls single-dict Initialize with Java.Lang.Object anchor
- Option B (per-assembly): builds arrays and calls array Initialize with per-assembly __TypeMapAnchor types
- Emits [assembly: IgnoresAccessChecksTo] for Mono.Android + per-assembly DLLs

MSBuild

Trimmable targets — force-enables StartupHookSupport, adds DOTNET_STARTUP_HOOKS env var
HotReload targets — composes startup hooks instead of clobbering

Tests

5 new tests for both modes (valid PE, assembly refs, IgnoresAccessChecksTo attributes)
All 410 generator tests pass

Key design decisions

useSharedTypemapUniverse flag controls the mode throughout the pipeline
Shared universe uses Java.Lang.Object as the anchor type (all per-assembly DLLs share the same universe)
Per-assembly universe uses a generated __TypeMapAnchor per DLL (isolated dictionaries)
Two separate Initialize overloads kept for trimming benefits
Root assembly is a startup hook (DOTNET_STARTUP_HOOKS) — runs before JNIEnvInit

Fixes #11180
Part of #10788

Implements #11180: Each assembly gets its own typemap universe via a generated __TypeMapAnchor type (instead of sharing Java.Lang.Object), creating isolated TypeMapLazyDictionary instances per assembly. Runtime layer: - Add ITypeMapWithAliasing interface with GetTypes() and TryGetProxyType() - Add SingleUniverseTypeMap (handles alias resolution within one universe) - Add AggregateTypeMap (flattens across N universes, Debug-only) - Simplify TrimmableTypeMap to consume ITypeMapWithAliasing - Remove TrimmableTypeMap.Initialize() call from JNIEnvInit Generator layer: - Emit __TypeMapAnchor in each per-assembly typemap DLL - Use TypeMap<__TypeMapAnchor> instead of TypeMap<Java.Lang.Object> - Add isRelease parameter to control universe merging - Root assembly emits StartupHook class with Initialize() IL method - Debug: constructs N SingleUniverseTypeMap + AggregateTypeMap - Release: single SingleUniverseTypeMap - Root assembly emits IgnoresAccessChecksTo for internal type access MSBuild layer: - Enable StartupHookSupport for trimmable typemap builds - Configure DOTNET_STARTUP_HOOKS to point to root typemap assembly - Fix HotReload targets to compose startup hooks instead of replacing Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…, startup hook fixes, tests - Rename isRelease -> mergeAssemblyTypeMaps throughout generator and MSBuild task - Rename EmitReleaseInitialize -> EmitInitializeWithSingleTypeMap - Rename EmitDebugInitialize -> EmitInitializeWithAggregateTypeMap - Change TrimmableTypeMap.Initialize to two overloads with BCL types only: - Initialize(IReadOnlyDictionary<string, Type>, IReadOnlyDictionary<Type, Type>) - Initialize(IReadOnlyDictionary<string, Type>[], IReadOnlyDictionary<Type, Type>[]) - Generated assembly no longer references SingleUniverseTypeMap/AggregateTypeMap - Add InitializeCore that throws InvalidOperationException on re-initialization - Force-enable StartupHookSupport unconditionally in targets - Remove MonoVM STARTUP_HOOKS line (trimmable typemaps don't work with Mono) - Add tests for both mergeAssemblyTypeMaps modes (true/false) - Add tests for IgnoresAccessChecksTo attribute in both modes - Fix locals encoding for aggregate mode (pass type refs to encodeLocals lambda) Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

In merged mode (Release), all per-assembly typemap DLLs must use the same anchor type so TypeMapping.GetOrCreateExternalTypeMapping<T>() finds all entries across all assemblies. Previously each DLL emitted its own __TypeMapAnchor, causing the root assembly's GetOrCreate call (using its own anchor) to find nothing. Fix: when mergeAssemblyTypeMaps=true, per-assembly DLLs reference Java.Lang.Object as the anchor type instead of emitting __TypeMapAnchor. The root assembly also references Java.Lang.Object in merged mode. In aggregate mode (Debug), each DLL keeps its own __TypeMapAnchor for isolated per-assembly universes. The root references each per-assembly anchor individually. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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

- Merge two TrimmableTypeMap.Initialize overloads into one that takes arrays and optimizes for single-element case (uses SingleUniverseTypeMap) - Add length-zero validation - Unify IL emission: both modes now use same EmitInitializeBody (always builds arrays), removing EmitInitializeWithSingleTypeMap - Remove AddInitializeSingleRef (only AddInitializeRef remains) - Update doc comments: Option A (shared universe) / Option B (per-assembly) - Fix doc to show Java.Lang.Object as anchor for shared universe mode Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…omments" This reverts commit a25b04a.

- Doc comments: Option A (shared universe) / Option B (per-assembly) - Show Java.Lang.Object as anchor for shared universe mode - Add length-zero check in array Initialize overload Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Implements per-assembly typemap “universes” (Debug) vs a shared merged universe (Release) for the TrimmableTypeMap pipeline, and moves runtime initialization into a generated startup hook assembly (_Microsoft.Android.TypeMaps).

Changes:

Add alias-aware typemap abstraction in Mono.Android (ITypeMapWithAliasing, SingleUniverseTypeMap, AggregateTypeMap) and update TrimmableTypeMap to initialize from startup hook–provided dictionaries.
Update the generator to emit per-assembly anchors (Debug) or use Java.Lang.Object as a shared anchor (Release) and generate startup-hook IL to call TrimmableTypeMap.Initialize(...).
Enable startup hooks via MSBuild (StartupHookSupport, DOTNET_STARTUP_HOOKS) and update Hot Reload targets to compose startup hook values; expand generator tests for both modes.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/Generator/TrimmableTypeMapGeneratorTests.cs	Updates generator invocation to pass the new `useSharedTypemapUniverse` option.
tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/Generator/RootTypeMapAssemblyGeneratorTests.cs	Adds coverage for both merge modes, assembly refs, and `IgnoresAccessChecksTo` emission.
src/Xamarin.Android.Build.Tasks/Tasks/GenerateTrimmableTypeMap.cs	Selects shared universe for Release (`useSharedTypemapUniverse: !Debug`).
src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.TypeMap.Trimmable.targets	Enables startup hooks and sets `DOTNET_STARTUP_HOOKS` for typemap initialization.
src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.HotReload.targets	Preserves existing `DOTNET_STARTUP_HOOKS` values by composing with Hot Reload agent hook.
src/Mono.Android/Microsoft.Android.Runtime/TrimmableTypeMap.cs	Reworks initialization to accept dictionaries/universes and delegates alias logic to `ITypeMapWithAliasing`.
src/Mono.Android/Microsoft.Android.Runtime/ITypeMapWithAliasing.cs	Introduces alias-aware typemap interfaces/implementations for single and aggregate universes.
src/Mono.Android/Android.Runtime/JNIEnvInit.cs	Removes the old direct `TrimmableTypeMap.Initialize()` call (startup hook now owns initialization).
src/Microsoft.Android.Sdk.TrimmableTypeMap/TrimmableTypeMapGenerator.cs	Threads `useSharedTypemapUniverse` through generator execution and assembly generation.
src/Microsoft.Android.Sdk.TrimmableTypeMap/Generator/TypeMapAssemblyGenerator.cs	Adds `useSharedTypemapUniverse` argument and forwards to emitter.
src/Microsoft.Android.Sdk.TrimmableTypeMap/Generator/TypeMapAssemblyEmitter.cs	Emits per-assembly `__TypeMapAnchor` (Debug) or uses `Java.Lang.Object` as anchor (Release).
src/Microsoft.Android.Sdk.TrimmableTypeMap/Generator/RootTypeMapAssemblyGenerator.cs	Rewrites root assembly generation to emit startup-hook IL and mode-specific initialization.

…d using - Make Initialize() method public (startup hooks require public static) - Keep StartupHook class internal (allowed by runtime) - Use ':' literal instead of Path.PathSeparator for DOTNET_STARTUP_HOOKS composition (target is Android/Linux, not the build host) - Remove unused 'using System.Runtime.InteropServices' from ITypeMapWithAliasing.cs Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Don't clobber existing DOTNET_STARTUP_HOOKS entries (e.g., from VS tooling). Use the same compose pattern as HotReload targets with ':' separator. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

simonrozsival · 2026-04-22T12:15:06Z

/review

github-actions · 2026-04-22T12:15:35Z

✅ Android PR Reviewer completed successfully!

github-actions

✅ LGTM — Clean design with minor suggestions

Well-structured implementation of per-assembly typemap universes. The architecture separates concerns nicely: ITypeMapWithAliasing abstracts Debug vs Release, the generator emits correct IL for both startup hook paths, and the MSBuild targets properly compose DOTNET_STARTUP_HOOKS.

Positive callouts:

The ITypeMapWithAliasing abstraction cleanly isolates alias resolution from the TrimmableTypeMap singleton
Startup hook composition in both Trimmable and HotReload targets correctly handles the capture→remove→compose pattern
The InvalidOperationException re-initialization guard is a good fail-fast improvement over the old silent return
Generated IL signatures and metadata encoding are consistent across both modes
Tests cover both merge modes for valid PE, assembly refs, and IgnoresAccessChecksTo attributes

Summary: 4 💡 suggestions (code organization, DCL simplification, runtime unit tests, MSBuild dedup). No blocking issues found. CI public checks pass.

Generated by Android PR Reviewer for issue #11181 · ● 6.8M

- Remove outer null check in InitializeCore (single-threaded init via startup hook, lock alone is sufficient) - Split ITypeMapWithAliasing.cs into three files: ITypeMapWithAliasing.cs, SingleUniverseTypeMap.cs, AggregateTypeMap.cs Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Mono.Android uses explicit Compile includes, not globbing. Add the three new files split from ITypeMapWithAliasing.cs. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

MSBuild does not allow built-in metadata references like %(Identity) in Condition attributes of static ItemGroup elements. This caused all trimmable typemap builds to fail during evaluation with: error MSB4190: The reference to the built-in metadata "Identity" at position 2 is not allowed in this condition. Simplify to just add the startup hook directly. Other targets (HotReload) compose on top inside proper Target elements where %(Identity) is allowed. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

The previous commit simplified too aggressively — just adding a static RuntimeEnvironmentVariable item would overwrite any existing DOTNET_STARTUP_HOOKS entries (e.g. from VS tooling). Move the compose-with-existing logic into a proper Target where %(Identity) metadata batching is allowed. The Target runs before _AndroidConfigureHotReloadEnvironment so HotReload can compose on top. Verified locally: all 3 TrimmableTypeMapBuildTests pass. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

simonrozsival · 2026-04-22T19:50:12Z

CI failures unrelated:

jonathanpeppers · 2026-04-22T20:02:42Z

+      <RuntimeEnvironmentVariable Remove="DOTNET_STARTUP_HOOKS" />
+      <RuntimeEnvironmentVariable Include="DOTNET_STARTUP_HOOKS"
+          Value="$(_TypeMapAssemblyName):@(_ExistingStartupHooks->'%(Value)', ':')"
+          Condition=" '@(_ExistingStartupHooks)' != '' " />
+      <RuntimeEnvironmentVariable Include="DOTNET_STARTUP_HOOKS"
+          Value="$(_TypeMapAssemblyName)"
+          Condition=" '@(_ExistingStartupHooks)' == '' " />


dotnet watch is probably the first feature that relies on $DOTNET_STARTUP_HOOKS on Android.

But you are supposed to be able to append : and list multiple.

This just clobbers the existing value:

android/src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.HotReload.targets

Lines 48 to 49 in 6106016

<RuntimeEnvironmentVariable Remove="DOTNET_STARTUP_HOOKS" />

<RuntimeEnvironmentVariable Include="DOTNET_STARTUP_HOOKS" Value="$(_AndroidHotReloadAgentAssemblyName)" />

I suppose someone could also have an AndroidEnvironment file with the contents:

DOTNET_STARTUP_HOOKS=MyHook.dll

Should we somehow merge the values for $DOTNET_STARTUP_HOOKS to account for both @(RuntimeEnvironmentVariable) and @(AndroidEnvironment)? We could fix in a new PR, the existing HotReload.targets is also wrong.

I thought about that and that's why there's this

<RuntimeEnvironmentVariable Include="DOTNET_STARTUP_HOOKS" Value="$(_TypeMapAssemblyName):@(_ExistingStartupHooks->'%(Value)', ':')" Condition=" '@(_ExistingStartupHooks)' != '' " />

which should preserve the previous value(s) of the existing startup hooks.

I suppose someone could also have an AndroidEnvironment file with the contents:

right, that would be an issue. I suggest we fix that in a separate PR.

I opened an issue #11186 and I'll let copilot look into it overnight

simonrozsival and others added 7 commits April 22, 2026 12:04

Rename mergeAssemblyTypeMaps -> useSharedTypemapUniverse

50cb15e

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

Revert "Consolidate Initialize to single array overload, update doc c…

126d65c

…omments" This reverts commit a25b04a.

Copilot AI review requested due to automatic review settings April 22, 2026 11:49

simonrozsival requested a review from jonathanpeppers as a code owner April 22, 2026 11:49

simonrozsival added the trimmable-type-map label Apr 22, 2026

Copilot started reviewing on behalf of simonrozsival April 22, 2026 11:50 View session

Copilot AI reviewed Apr 22, 2026

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simonrozsival and others added 2 commits April 22, 2026 14:02

Compose DOTNET_STARTUP_HOOKS with existing values in trimmable targets

71d7eb1

Don't clobber existing DOTNET_STARTUP_HOOKS entries (e.g., from VS tooling). Use the same compose pattern as HotReload targets with ':' separator. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

github-actions Bot reviewed Apr 22, 2026

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simonrozsival and others added 2 commits April 22, 2026 14:33

Add new files to Mono.Android.csproj explicit includes

bb3885a

Mono.Android uses explicit Compile includes, not globbing. Add the three new files split from ITypeMapWithAliasing.cs. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

simonrozsival added the copilot `copilot-cli` or other AIs were used to author this label Apr 22, 2026

jonathanpeppers added ready-to-review This PR is ready to review/merge, I think any CI failures are just flaky (ignorable). and removed copilot `copilot-cli` or other AIs were used to author this labels Apr 22, 2026

simonrozsival added copilot `copilot-cli` or other AIs were used to author this and removed ready-to-review This PR is ready to review/merge, I think any CI failures are just flaky (ignorable). labels Apr 22, 2026

simonrozsival and others added 2 commits April 22, 2026 18:11

simonrozsival added the ready-to-review This PR is ready to review/merge, I think any CI failures are just flaky (ignorable). label Apr 22, 2026

jonathanpeppers reviewed Apr 22, 2026

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simonrozsival mentioned this pull request Apr 22, 2026

DOTNET_STARTUP_HOOKS from @(AndroidEnvironment) files is silently overwritten #11186

Open

Copilot AI mentioned this pull request Apr 22, 2026

Compose DOTNET_STARTUP_HOOKS across all Android environment sources instead of overwriting #11187

Draft

jonathanpeppers approved these changes Apr 22, 2026

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jonathanpeppers merged commit 6240086 into main Apr 22, 2026
2 of 3 checks passed

jonathanpeppers deleted the dev/simonrozsival/per-assembly-typemap-universes branch April 22, 2026 21:13

This was referenced Apr 23, 2026

[TrimmableTypeMap] Revisit usage of startup hooks to initialize the type map #11196

Closed

Flaky test analysis: Xamarin.Android-PR pipeline, April 10–24 2026 #11203

Open

	<RuntimeEnvironmentVariable Remove="DOTNET_STARTUP_HOOKS" />
	<RuntimeEnvironmentVariable Include="DOTNET_STARTUP_HOOKS" Value="$(_AndroidHotReloadAgentAssemblyName)" />

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simonrozsival commented Apr 22, 2026

Summary

Changes

Runtime (Mono.Android)

Generator (Microsoft.Android.Sdk.TrimmableTypeMap)

MSBuild

Tests

Key design decisions

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simonrozsival commented Apr 22, 2026

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✅ LGTM — Clean design with minor suggestions

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simonrozsival commented Apr 22, 2026

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