Compose DOTNET_STARTUP_HOOKS across all Android environment sources instead of overwriting

[Copilot]

DOTNET_STARTUP_HOOKS was being rewritten from @(RuntimeEnvironmentVariable) only, which could drop values coming from @(AndroidEnvironment) files. This change keeps startup hook composition explicit and ensures final environment generation merges all sources without duplicate-effective definitions.

• Use a single startup-hook item flow

  • _ComposeDotNetStartupHooks in Xamarin.Android.Common.targets now builds @(_AndroidDotnetStartupHooksDistinct) from:
    • internal contributors via @(_AndroidDotnetStartupHooks)
    • existing @(RuntimeEnvironmentVariable) entries for DOTNET_STARTUP_HOOKS
  • DOTNET_STARTUP_HOOKS is removed from @(RuntimeEnvironmentVariable) and startup hooks are carried via @(_AndroidDotnetStartupHooksDistinct).

• Generate environment file from composed hooks

  • _GenerateEnvironmentFiles writes DOTNET_STARTUP_HOOKS=... from @(_AndroidDotnetStartupHooksDistinct, ':') into __environment__.txt.

• Pass startup hooks into environment-producing tasks

  • Added DotNetStartupHooks task input and wired it from @(_AndroidDotnetStartupHooksDistinct) for:
    • GenerateNativeApplicationConfigSources
    • GenerateAdditionalProviderSources
    • GenerateNativeAotEnvironmentAssemblerSources

• Merge at consolidation point

  • EnvironmentBuilder now accepts explicit startup hooks via AddDotNetStartupHooks(...).
  • It merges those with any DOTNET_STARTUP_HOOKS found while parsing @(AndroidEnvironment) / @(LibraryEnvironments) using colon-separated dedupe.

• Hot Reload behavior remains compatible

  • _AndroidConfigureHotReloadEnvironment continues contributing normalized startup hook assembly names to @(_AndroidDotnetStartupHooks) and keeps RuntimeHostConfigurationOption behavior unchanged.

• Focused test coverage

  • EnvironmentContentTests verifies final DOTNET_STARTUP_HOOKS contains values from both RuntimeEnvironmentVariable and AndroidEnvironment.

<ItemGroup>
  <_AndroidStartupHooksFromRuntimeEnvironmentVariable Include="@(RuntimeEnvironmentVariable->WithMetadataValue('Identity', 'DOTNET_STARTUP_HOOKS'))" />
  <_AndroidDotnetStartupHooks Include="@(_AndroidStartupHooksFromRuntimeEnvironmentVariable->'%(Value)')" />
</ItemGroup>

<RemoveDuplicates Inputs="@(_AndroidDotnetStartupHooks)">
  <Output TaskParameter="Filtered" ItemName="_AndroidDotnetStartupHooksDistinct" />
</RemoveDuplicates>

<ItemGroup>
  <RuntimeEnvironmentVariable Remove="DOTNET_STARTUP_HOOKS" />
</ItemGroup>

envBuilder.Read (Environments);
envBuilder.AddDotNetStartupHooks (DotNetStartupHooks);

[simonrozsival]

@copilot address my questions

[simonrozsival]

This target does not have Inputs and Outputs, should it have them?

[Copilot]

Good question. I kept _ComposeDotNetStartupHooks without Inputs/Outputs intentionally because it only transforms in-memory MSBuild items/properties for the current build graph; persisting incremental state there could skip needed recomposition. I also moved the final cross-file merge to EnvironmentBuilder in 120aedf, so this target stays lightweight and order-safe.

[simonrozsival]

If I understand it correctly, we will leave the original DOTNET_STARTUP_HOOKS values in the env files? Doesn't this mean that we will have multiple definitions of DOTNET_STARTUP_HOOKS in the final list of environment variables? Shouldn't we move the merging logic to the GenerateAdditionalProviderSources or EnvironmentBuilder or some other place where we eventually merge all the environment variables into a single list of definitions?

[Copilot]

You're right. I changed this in 120aedf: _ComposeDotNetStartupHooks no longer reads @(AndroidEnvironment)/@(LibraryEnvironments) lines, and EnvironmentBuilder now merges repeated DOTNET_STARTUP_HOOKS definitions while parsing the final environment inputs. This moves merging to the consolidation point and avoids duplicate final definitions.

[Copilot]

@copilot address my questions

Addressed in 120aedf. I answered both review questions and updated the implementation so final DOTNET_STARTUP_HOOKS merging happens in EnvironmentBuilder (the environment consolidation point), while _ComposeDotNetStartupHooks only prepares runtime/internal contributions.

[jonathanpeppers]

@copilot can you simplify the changes here?

• Use the @(_AndroidDotnetStartupHooks) item group throughout, pass it into the task that writes environment variables
• Clear startup hooks from @(RuntimeEnvironmentVariable), and rely on @(_AndroidDotnetStartupHooks)
• The task that writes environment variables merges @(_AndroidDotnetStartupHooks) and any found from @(AndroidEnvironment) files

[Copilot]

@copilot can you simplify the changes here?

• Use the @(_AndroidDotnetStartupHooks) item group throughout, pass it into the task that writes environment variables
• Clear startup hooks from `@(Runti...

Done in 56b9467 (building on 22ec383). I simplified the flow to keep startup hooks in @(_AndroidDotnetStartupHooks)/@(_AndroidDotnetStartupHooksDistinct), remove DOTNET_STARTUP_HOOKS from @(RuntimeEnvironmentVariable), pass the startup-hook items into the environment-producing tasks, and merge them with hooks from @(AndroidEnvironment)/@(LibraryEnvironments) in EnvironmentBuilder.