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[HotReloadAgent] fix possible NullReferenceException #52367

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Merged
jonathanpeppers merged 4 commits into from
Jan 10, 2026
Merged

[HotReloadAgent] fix possible NullReferenceException #52367

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d546c10
[HotReloadAgent] fix possible `NullReferenceException`
jonathanpeppers Jan 8, 2026
2096751
Add tests for RemoveCurrentAssembly edge cases
jonathanpeppers Jan 9, 2026
5b5f50b
Code review feedback
jonathanpeppers Jan 9, 2026
d1402d7
Update HotReloadAgent.cs
jonathanpeppers Jan 10, 2026
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13 changes: 7 additions & 6 deletions src/BuiltInTools/HotReloadAgent/HotReloadAgent.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -297,8 +297,12 @@ public void ApplyStaticAssetUpdate(RuntimeStaticAssetUpdate update)
/// </summary>
public static void ClearHotReloadEnvironmentVariables(Type startupHookType)
{
Environment.SetEnvironmentVariable(AgentEnvironmentVariables.DotNetStartupHooks,
RemoveCurrentAssembly(startupHookType, Environment.GetEnvironmentVariable(AgentEnvironmentVariables.DotNetStartupHooks)!));
var startupHooks = Environment.GetEnvironmentVariable(AgentEnvironmentVariables.DotNetStartupHooks);
if (!string.IsNullOrEmpty(startupHooks))
{
Environment.SetEnvironmentVariable(AgentEnvironmentVariables.DotNetStartupHooks,
RemoveCurrentAssembly(startupHookType, startupHooks));
}

Environment.SetEnvironmentVariable(AgentEnvironmentVariables.DotNetWatchHotReloadNamedPipeName, null);
Environment.SetEnvironmentVariable(AgentEnvironmentVariables.HotReloadDeltaClientLogMessages, null);
Expand All @@ -307,10 +311,7 @@ public static void ClearHotReloadEnvironmentVariables(Type startupHookType)
// internal for testing
internal static string RemoveCurrentAssembly(Type startupHookType, string environment)
{
if (environment is "")
{
return environment;
}
Debug.Assert(!string.IsNullOrEmpty(environment), $"{nameof(environment)} must be set");

var comparison = Path.DirectorySeparatorChar == '\\' ? StringComparison.OrdinalIgnoreCase : StringComparison.Ordinal;

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18 changes: 18 additions & 0 deletions test/Microsoft.Extensions.DotNetDeltaApplier.Tests/HotReloadAgentTest.cs
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Expand Up @@ -9,6 +9,24 @@ namespace Microsoft.DotNet.Watch.UnitTests
{
public class HotReloadAgentTest
{
[Fact]
public void ClearHotReloadEnvironmentVariables_DoesNotThrow_WhenStartupHooksNotSet()
{
// Ensure DOTNET_STARTUP_HOOKS is not set
var original = Environment.GetEnvironmentVariable("DOTNET_STARTUP_HOOKS");
try
{
Environment.SetEnvironmentVariable("DOTNET_STARTUP_HOOKS", null);

// Should not throw NullReferenceException
HotReloadAgent.ClearHotReloadEnvironmentVariables(typeof(StartupHook));
}
finally
{
Environment.SetEnvironmentVariable("DOTNET_STARTUP_HOOKS", original);
}
}

[Fact]
public void ClearHotReloadEnvironmentVariables_ClearsStartupHook()
{
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