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

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

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adfc7f4
Initial plan
Copilot Apr 22, 2026
a033158
Compose DOTNET_STARTUP_HOOKS from runtime and environment files
Copilot Apr 22, 2026
74f6906
Document startup hook prefix length in composition target
Copilot Apr 22, 2026
120aedf
Move DOTNET_STARTUP_HOOKS merge to EnvironmentBuilder
Copilot Apr 23, 2026
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11 changes: 3 additions & 8 deletions ...Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.HotReload.targets
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Expand Up @@ -23,8 +23,7 @@ See: https://github.com/dotnet/sdk/pull/52581
<!--
_AndroidConfigureHotReloadEnvironment:
Configures Hot Reload when dotnet-watch passes environment variables via @(RuntimeEnvironmentVariable).
- Adds the Hot Reload agent DLL as a reference so it gets deployed
- Updates DOTNET_STARTUP_HOOKS to use just the assembly name (not the full path)
- Adds the Hot Reload startup hook assembly name to @(_AndroidDotnetStartupHooks)
- Sets up STARTUP_HOOKS via RuntimeHostConfigurationOption for MonoVM
-->
<Target Name="_AndroidConfigureHotReloadEnvironment"
Expand All @@ -40,13 +39,9 @@ See: https://github.com/dotnet/sdk/pull/52581
<_AndroidHotReloadAgentAssemblyName>$([System.IO.Path]::GetFileNameWithoutExtension('$(_AndroidHotReloadAgentAssemblyPath)'))</_AndroidHotReloadAgentAssemblyName>
</PropertyGroup>

<!--
Update DOTNET_STARTUP_HOOKS in @(RuntimeEnvironmentVariable) to use just the assembly name.
The full path doesn't work on Android since the DLL is deployed alongside the app.
-->
<!-- The full path doesn't work on Android since the DLL is deployed alongside the app. -->
<ItemGroup Condition=" '$(_AndroidHotReloadAgentAssemblyName)' != '' ">
<RuntimeEnvironmentVariable Remove="DOTNET_STARTUP_HOOKS" />
<RuntimeEnvironmentVariable Include="DOTNET_STARTUP_HOOKS" Value="$(_AndroidHotReloadAgentAssemblyName)" />
<_AndroidDotnetStartupHooks Include="$(_AndroidHotReloadAgentAssemblyName)" />
<!-- Set STARTUP_HOOKS via RuntimeHostConfigurationOption for MonoVM (read by Mono runtime) -->
<RuntimeHostConfigurationOption Include="STARTUP_HOOKS" Value="$(_AndroidHotReloadAgentAssemblyName)" Condition=" '$(UseMonoRuntime)' == 'true' " />
</ItemGroup>
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44 changes: 44 additions & 0 deletions src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/EnvironmentContentTests.cs
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Expand Up @@ -14,6 +14,15 @@ namespace Xamarin.Android.Build.Tests
[Parallelizable (ParallelScope.Children)]
public class EnvironmentContentTests : BaseTest
{
class StartupHookEnvironmentProject : XamarinAndroidApplicationProject
{
protected override string ExtraDirectoryBuildTargetsContent => """
<ItemGroup>
<RuntimeEnvironmentVariable Include="DOTNET_STARTUP_HOOKS" Value="$(MSBuildProjectDirectory)/hotreload/Microsoft.Extensions.DotNetDeltaApplier.dll" />
</ItemGroup>
""";
}

[Test]
[NonParallelizable]
public void BuildApplicationWithMonoEnvironment ([Values ("", "Normal", "Offline")] string sequencePointsMode, [Values] AndroidRuntime runtime)
Expand Down Expand Up @@ -161,6 +170,41 @@ public void CheckConcurrentGC ()
}
}

[Test]
public void DotNetStartupHooksAreMergedFromRuntimeEnvironmentVariableAndAndroidEnvironment ()
{
const string supportedAbis = "armeabi-v7a;x86";

var proj = new StartupHookEnvironmentProject {
IsRelease = false,
OtherBuildItems = {
new BuildItem.NoActionResource ("hotreload/Microsoft.Extensions.DotNetDeltaApplier.dll") {
BinaryContent = () => [],
},
new AndroidItem.AndroidEnvironment ("startup.env") {
TextContent = () => "DOTNET_STARTUP_HOOKS=MyStartupHook.dll",
},
},
};
proj.SetRuntime (AndroidRuntime.MonoVM);
proj.SetAndroidSupportedAbis (supportedAbis);

using (var b = CreateApkBuilder ()) {
Assert.IsTrue (b.Build (proj), "Build should have succeeded.");

string intermediateOutputDir = Path.Combine (Root, b.ProjectDirectory, proj.IntermediateOutputPath);
List<EnvironmentHelper.EnvironmentFile> envFiles = EnvironmentHelper.GatherEnvironmentFiles (intermediateOutputDir, supportedAbis, true, AndroidRuntime.MonoVM);
Dictionary<string, string> envvars = EnvironmentHelper.ReadEnvironmentVariables (envFiles, AndroidRuntime.MonoVM);

Assert.IsTrue (envvars.TryGetValue ("DOTNET_STARTUP_HOOKS", out string startupHooks), "Environment should contain DOTNET_STARTUP_HOOKS");
CollectionAssert.AreEquivalent (
new [] { "Microsoft.Extensions.DotNetDeltaApplier", "MyStartupHook.dll" },
startupHooks.Split (':'),
"DOTNET_STARTUP_HOOKS should merge values from RuntimeEnvironmentVariable and AndroidEnvironment."
);
}
}

[Test]
public void CheckForInvalidHttpClientHandlerType ([Values] AndroidRuntime runtime)
{
Expand Down
33 changes: 31 additions & 2 deletions src/Xamarin.Android.Build.Tasks/Utilities/EnvironmentBuilder.cs
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Expand Up @@ -7,6 +7,8 @@ namespace Xamarin.Android.Tasks;

class EnvironmentBuilder
{
const string DotNetStartupHooks = "DOTNET_STARTUP_HOOKS";

static readonly string[] defaultLogLevel = {"MONO_LOG_LEVEL", "info"};
static readonly string[] defaultMonoDebug = {"MONO_DEBUG", "gen-compact-seq-points"};
static readonly string defaultHttpMessageHandler = "System.Net.Http.HttpClientHandler, System.Net.Http";
Expand Down Expand Up @@ -50,10 +52,17 @@ public void Read (ITaskItem[]? envItems)

public void AddEnvironmentVariable (string name, string value)
{
string escapedName = ValidAssemblerString (name);
string escapedValue = ValidAssemblerString (value);

if (Char.IsUpper(name [0]) || !Char.IsLetter(name [0])) {
environmentVariables [ValidAssemblerString (name)] = ValidAssemblerString (value);
if (name == DotNetStartupHooks && environmentVariables.TryGetValue (escapedName, out string? existingStartupHooks)) {
environmentVariables [escapedName] = MergeDotNetStartupHooks (existingStartupHooks, escapedValue);
} else {
environmentVariables [escapedName] = escapedValue;
}
} else {
systemProperties [ValidAssemblerString (name)] = ValidAssemblerString (value);
systemProperties [escapedName] = escapedValue;
}
}

Expand Down Expand Up @@ -108,5 +117,25 @@ public void AddMonoGcParams (bool enableSgenConcurrent)
AddEnvironmentVariable ("MONO_GC_PARAMS", enableSgenConcurrent ? "major=marksweep-conc" : "major=marksweep");
}

static string MergeDotNetStartupHooks (string first, string second)
{
var mergedHooks = new List<string> ();
var seenHooks = new HashSet<string> (StringComparer.Ordinal);

foreach (string hook in first.Split (new char [] { ':' }, StringSplitOptions.RemoveEmptyEntries)) {
if (seenHooks.Add (hook)) {
mergedHooks.Add (hook);
}
}

foreach (string hook in second.Split (new char [] { ':' }, StringSplitOptions.RemoveEmptyEntries)) {
if (seenHooks.Add (hook)) {
mergedHooks.Add (hook);
}
}

return String.Join (":", mergedHooks);
}

static string ValidAssemblerString (string s) => s.Replace ("\\", "\\\\").Replace ("\"", "\\\"");
}
26 changes: 25 additions & 1 deletion src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets
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Expand Up @@ -1587,7 +1587,31 @@ because xbuild doesn't support framework reference assemblies.
</PrepareAbiItems>
</Target>

<Target Name="_GenerateEnvironmentFiles" DependsOnTargets="_AndroidConfigureHotReloadEnvironment">
<Target Name="_ComposeDotNetStartupHooks"
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@simonrozsival simonrozsival Apr 23, 2026

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

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Copilot AI Apr 23, 2026

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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.

DependsOnTargets="_AndroidConfigureHotReloadEnvironment">
<ItemGroup>
<_AndroidStartupHooksFromRuntimeEnvironmentVariable Include="@(RuntimeEnvironmentVariable->WithMetadataValue('Identity', 'DOTNET_STARTUP_HOOKS'))" />
<_AndroidStartupHooksFromRuntimeEnvironmentVariable Remove="@(_AndroidStartupHooksFromRuntimeEnvironmentVariable)"
Condition=" '$(_AndroidHotReloadAgentAssemblyPath)' != '' And '%(_AndroidStartupHooksFromRuntimeEnvironmentVariable.Value)' == '$(_AndroidHotReloadAgentAssemblyPath)' " />
<_AndroidDotnetStartupHooks Include="@(_AndroidStartupHooksFromRuntimeEnvironmentVariable->'%(Value)')" />
</ItemGroup>

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

<CreateProperty Value="@(_AndroidDotnetStartupHooksDistinct,':')">
<Output TaskParameter="Value" PropertyName="_AndroidDotnetStartupHooksValue" />
</CreateProperty>

<ItemGroup>
<RuntimeEnvironmentVariable Remove="DOTNET_STARTUP_HOOKS" />
<RuntimeEnvironmentVariable Include="DOTNET_STARTUP_HOOKS" Value="$(_AndroidDotnetStartupHooksValue)"
Condition=" '$(_AndroidDotnetStartupHooksValue)' != '' " />
</ItemGroup>
</Target>

<Target Name="_GenerateEnvironmentFiles" DependsOnTargets="_ComposeDotNetStartupHooks">
<ItemGroup>
<_GeneratedAndroidEnvironment Include="mono.enable_assembly_preload=0" Condition=" '$(AndroidEnablePreloadAssemblies)' != 'True' " />
<_GeneratedAndroidEnvironment Include="DOTNET_MODIFIABLE_ASSEMBLIES=Debug" Condition=" '$(AndroidIncludeDebugSymbols)' == 'true' and '$(AndroidUseInterpreter)' == 'true' " />
Expand Down