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Basic hot reload support for mod development #160

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Basic hot reload support for mod development #160

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41c9f54
build: copy files to <CopyDir> if set
jakobhellermann Jun 25, 2025
a8d1c21
hot reload: load mods from `ModsHotReload` folder
jakobhellermann Jul 7, 2025
3d45283
hot reload: just reload mods from regular mods folder
jakobhellermann Jul 7, 2025
7f96f2c
hot reload: add mod directories to hot reload search path
jakobhellermann Jul 7, 2025
82f5fb1
hot reload: fix out of order event processing and idempotence
jakobhellermann Jul 7, 2025
723c58e
hot reload: read debug symbols
jakobhellermann Jul 7, 2025
9e4a3e4
hot reload: silence warning and hot reload only after startup
jakobhellermann Jul 7, 2025
9ef2793
hot reload: handle events in unity update thread
jakobhellermann Jul 7, 2025
0325ec9
hot reload: make configurable via `EnableHotReload` setting
jakobhellermann Jul 7, 2025
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12 changes: 12 additions & 0 deletions Assembly-CSharp/Assembly-CSharp.csproj
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,11 @@

<PropertyGroup>
<OutputDir>$(SolutionDir)/OutputFinal</OutputDir>
<!-- todo macOS -->
<GamePath Condition="'$(OS)' == 'Windows_NT'">C:/Program Files (x86)/Steam/steamapps/common/Hollow Knight</GamePath>
<GamePath Condition="'$(OS)' != 'Windows_NT'">$(HOME)/.local/share/Steam/steamapps/common/Hollow Knight</GamePath>
<CopyDir>$(GamePath)/hollow_knight_Data/Managed</CopyDir>

<Mono Condition="$(OS) == WINDOWS_NT" />
<Mono Condition="$(OS) != WINDOWS_NT">mono</Mono>
</PropertyGroup>
Expand Down Expand Up @@ -78,6 +83,13 @@
<Copy SourceFiles="@(Dependencies)" DestinationFolder="$(OutputDir)" />
</Target>

<Target Name="CopyOutputAfterFinal" AfterTargets="OutputFinal" Condition="'$(CopyDir)' != ''">
<ItemGroup>
<OutputFiles Include="$(OutputDir)\**\*" />
</ItemGroup>
<Copy SourceFiles="@(OutputFiles)" DestinationFolder="$(CopyDir)" />
</Target>

<PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
<DebugType>full</DebugType>
<DocumentationFile>bin\$(Configuration)\Assembly-CSharp.mm.xml</DocumentationFile>
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14 changes: 8 additions & 6 deletions Assembly-CSharp/Mod.cs
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Expand Up @@ -110,13 +110,15 @@ private string GetGlobalSettingsPath()
string globalSettingsFileName = $"{GetType().Name}.GlobalSettings.json";

string location = GetType().Assembly.Location;
string directory = Path.GetDirectoryName(location);
string globalSettingsOverride = Path.Combine(directory, globalSettingsFileName);
if (location != "") { // TODO: not set while hot reloading
string directory = Path.GetDirectoryName(location);
string globalSettingsOverride = Path.Combine(directory, globalSettingsFileName);

if (File.Exists(globalSettingsOverride))
{
Log("Overriding Global Settings path with Mod directory");
return globalSettingsOverride;
if (File.Exists(globalSettingsOverride))
{
Log("Overriding Global Settings path with Mod directory");
return globalSettingsOverride;
}
}

return Path.Combine(Application.persistentDataPath, globalSettingsFileName);
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18 changes: 18 additions & 0 deletions Assembly-CSharp/ModHooksGlobalSettings.cs
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Expand Up @@ -44,6 +44,24 @@ public class ModHooksGlobalSettings
/// </summary>
public int PreloadBatchSize = 5;

/// <summary>
/// When enabled, listens for filesystem changes to mod DLLs.
/// On modification, mods will be unloaded, and the new copy of the assembly gets loaded as well.
/// <para><b>Limitations:</b></para>
/// <list type="bullet">
/// <item><description>
/// The old assembly does not get unloaded. If you have created any unity game objects or components,
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This seems rough, not because of needing to destroy stuff in unload but because it makes a reload costly.

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Costly compared to what?

The regular use case should be unchanged, even with EnableHotReload enabled, and only subsequent changes will incur the extra assembly overhead.
And I think even that overhead is not too bad, when developing with scriptengine in nine sols I rarely had to restart the game because it became laggy after too many hot reload cycles.

/// make sure to Destroy them in the mod's Unload function.
/// </description></item>k
/// <item><description>
/// Dependencies of mods cannot be hot reloaded. When you modify a dependency DLL, no change will be made to the mod depending on it.
/// </description></item>
/// <item><description>
/// <c>Assembly.location</c> will return an empty string for hot-reloaded mods
/// </description></item>
/// </list>
/// </summary>
public bool EnableHotReload = false;

/// <summary>
/// Maximum number of days to preserve modlogs for.
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