Fix: Godot 4 C# Export Stripping Removed Class Attributes

Editor runs your inventory system, all good. Export build crashes with “Type ‘Game.Items.Sword’ not found.” The trimmer didn’t see the type used statically and stripped it from the assembly. C# in Godot 4 .NET ships with IL trimming on by default.

The Symptom

Editor and editor playtest work; export build throws TypeLoadException, MissingMethodException, or returns null from Assembly.GetType(name). Often the failure is a missing class or constructor that exists in source but not in the trimmed assembly.

What Causes This

The IL trimmer (linker) walks the assembly graph from the entry point and keeps only what’s reachable. Reflective access — Type.GetType("Foo"), JSON deserialization, scene tscn-loaded scripts — isn’t visible to the trimmer. The class compiles but is removed from the export.

The Fix Patterns

Pattern 1: Static reference in code. Cheapest for one or two types:

internal static class _KeepTypes
{
    internal static readonly Type[] _kept = new[]
    {
        typeof(Game.Items.Sword),
        typeof(Game.Items.Shield),
        typeof(Game.Enemies.Goblin),
    };
}

Each typeof roots the type so the trimmer keeps it.

Pattern 2: linker.xml. For many types, ship a descriptor:

<!-- linker.xml -->
<linker>
  <assembly fullname="YourGame">
    <type fullname="Game.Items.*" preserve="all" />
    <type fullname="Game.Enemies.*" preserve="all" />
  </assembly>
</linker>

Reference it in the .csproj:

<ItemGroup>
  <TrimmerRootDescriptor Include="linker.xml" />
</ItemGroup>

Pattern 3: Disable trimming for the assembly. In .csproj:

<PropertyGroup>
  <TrimMode>copy</TrimMode>
</PropertyGroup>

Bundles the entire assembly without trimming. Larger export, simpler. Good for game logic; reserve trimming for runtime libraries.

JSON Deserialization Trap

System.Text.Json with default reflection-based deserialization is the most common offender. The deserializer reflects over property setters; trimming removes them. Either:

• Use source-generated JsonSerializerContext (Trim-friendly).
• Apply [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)] to the model type.
• Add the model class to linker.xml.

Verifying

After export, decompile the resulting DLL with ILSpy or dotPeek. Confirm the class and members survived. If they didn’t, your descriptor doesn’t cover them or the .csproj reference is wrong.

Or run with --verbose and watch trimmer output during build — it logs which types are stripped.

Understanding the issue

Export pipelines transform development assets into shipping packages. Each transformation can introduce subtle changes that produce bugs only visible in the exported build.

The specific bug described above is the kind that surfaces during integration rather than unit testing. It depends on a combination of factors: the asset configuration, the runtime state, the platform's specific behavior. In isolation, each piece looks correct; in combination, the bug emerges. This is why thorough integration testing - playing the actual game in realistic conditions - catches things that automated tests miss.

Why this happens

The triage path for this kind of bug is long. The symptom appears in gameplay, but the cause is in a different system. The reporter describes the gameplay effect; the engineer has to translate that into a hypothesis about the underlying cause. Misdirection is common.

At the engine level, the behavior comes from a deliberate design decision in Godot. The engine team chose a particular trade-off - usually performance versus convenience, or generality versus specificity - and that trade-off has consequences when you push against it. Understanding the trade-off is what turns 'this bug is mysterious' into 'this bug is the expected consequence of this design'.

Verifying the fix

Verifying this fix in isolation is straightforward: reproduce the bug, apply the change, confirm the bug no longer reproduces. The harder verification is regression - did this fix introduce a new bug elsewhere? Run your standard regression suite, plus any tests that exercise the same code path with different inputs.

Reproducibility is the prerequisite for verification. If you can't reliably reproduce the bug pre-fix, you can't reliably verify it post-fix. Spend time getting a clean reproduction before you write any fix code. The fix is fast once you understand the reproduction; the reproduction is the slow part.

Variations to watch for

There's almost always a less obvious case where the same problem applies. The reported case is the one a player hit; the related cases hide because they're rarer or affect fewer players. After fixing the reported case, search the codebase for the pattern - one fix often unlocks several.

Adjacent bugs often share a root cause. After fixing the case you've found, spend an hour searching the codebase for similar patterns. What's the same call with different arguments? The same data flow with a different entity type? The same lifecycle issue in a sibling system? Each match is a candidate for the same fix, or a related fix that prevents future bugs of the same class.

In production

For shipping titles with a long support window, watch for this issue resurfacing after dependency updates. Engine upgrades, driver updates, OS releases - each one can resurface a bug class you thought you'd fixed because the underlying behavior changed slightly. Regression tests catch the obvious ones; player reports catch the rest.

When triaging a similar issue in production, prioritize gathering data over hypothesizing causes. A player report describes a symptom; what you need is a build SHA, a session timestamp, and ideally a screen recording or session replay. With those, the bug becomes tractable. Without them, you're guessing at hypothetical reproductions that may not match what the player actually hit.

Performance considerations

Performance implications matter when this bug class scales with player count or asset count. A bug that fires once per session is annoying; a bug that fires once per frame compounds. After fixing, profile the affected code path under realistic load. The fix that's correct for one entity may be too slow for ten thousand.

Diagnostic approach

The diagnostic tools available depend on your engine and platform. Use the engine's native profilers and debug overlays before reaching for external tools. The native tools have context that external tools lack - they know which subsystem owns the code, which assets are loaded, and what state the engine is in.

For Godot-specific diagnostics, the editor's profiler is the canonical starting point. Capture a representative frame with the symptom present; compare against a frame without the symptom; the diff often points directly at the cause. If the symptom is non-deterministic, capture multiple frames and look for the pattern - the cause is usually a state transition or a specific input value rather than a continuous effect.

Tooling and ecosystem

The tooling around this bug class matters as much as the fix itself. Good logging, accessible profilers, and clear error messages turn 30-minute investigations into 5-minute ones. If your project doesn't have visibility into this code path, the first fix should add the visibility - the second fix uses it.

Within Godot, the relevant diagnostic surfaces include the standard frame debugger, memory profiler, and engine-specific debug overlays. Each one shows a different facet of what's happening. The frame debugger reveals draw call ordering and state transitions; the memory profiler shows allocation patterns; the debug overlay reveals per-system state. Bugs that resist one tool usually surrender to another - the trick is knowing which tool to reach for first.

Edge cases and pitfalls

Boundary conditions deserve specific testing attention. What happens when the input is zero, maximum, negative, or NaN? What happens at the start of a session vs hours in? What happens at the boundary between two systems handling the same data? These are where bugs hide and where regression tests are most valuable.

When writing a regression test for this fix, focus on the boundary conditions that surfaced the original bug. Tests that exercise the happy path catch obvious regressions; tests that exercise the boundary catch the subtler regressions that look like new bugs but are really the original returning. The latter are the tests that earn their keep over the long life of the project.

Team communication

Document the fix and its rationale in the commit message or attached engineering doc. Future engineers will encounter related issues; the rationale tells them whether your fix is reusable or specific to the case at hand. Without rationale, the fix gets reverted or copied incorrectly.

If this fix touches a system several engineers work in, a short writeup in the team's engineering channel helps. Not a full design doc - a paragraph explaining what was wrong, what's fixed, and what to watch for. Future engineers encountering similar symptoms will search for the fix; making it findable is a small investment that pays back later.

“Static typeof. Or linker.xml. Or copy mode for the whole assembly. Reflective loads survive the export.”

Related Issues

For Godot resource load failures, see resource not found. For C# scripts not attaching, see Godot async/await.

Keep what reflection touches. Trimmer obeys descriptors.