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build: revert FPSemantics (drops the shared PCH); answer the FP question in the test instead

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Setting FPSemantics on VoxelForge broke the build with ~30 "undefined type"
errors -- UMaterialInterface, USoundBase, TSubclassOf<AActor>, APawn,
ENABLE_DRAW_DEBUG -- none of them FP-related. UBT can only share a precompiled
header between modules whose compile environments match, so changing FPSemantics
cost the module the engine's shared PCH and with it ~30 includes the plugin has
always relied on getting for free.

That is a genuine latent IWYU debt in seven files, and worth fixing on its own
terms one day, but not inside an unrelated diagnostic. Reverted, with the reason
recorded in Build.cs so nobody retries it blind.

The question it was meant to settle is now answered without touching any build
setting: MazeEquivalence compiles a verbatim copy of the Maze core into the
TEST's translation unit and compares three implementations of identical source --
the generator's TU, the op stack's TU, and the test's own.

  A != C          -> same source, different TU, different result: the compiler.
                     Nothing to fix in the port.
  A == C, B != C  -> source is TU-stable, so the op stack differs for a LOGIC
                     reason, and it is in FLatticeCorridorSource or FSdfCarveOp.

Duplicating code is normally a fault. Here it is the only instrument that can
answer the question, because three careful readings all concluded "identical" and
the test keeps disagreeing. Marked diagnostic-only; it comes out once answered.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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Fr0zka
2026-07-27 14:39:09 +02:00
parent a49d440bf6
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@@ -491,3 +491,49 @@ marked as a temporary experiment with removal instructions and a read-the-result
paused.
---
## 2026-07-27 — FPSemantics on VoxelForge does not build. Reverted; measuring a safer way.
**What happened:** setting `FPSemantics` on the VoxelForge module broke the build with ~30 errors —
`UMaterialInterface`, `USoundBase`, `TSubclassOf<AActor>`, `APawn`, `ENABLE_DRAW_DEBUG` all
"undefined type". **None of them are FP-related.**
**Why:** UBT can only share a precompiled header between modules whose **compile environments
match**. Changing `FPSemantics` changed VoxelForge's environment, so it lost eligibility for the
engine's shared PCH — and with it ~30 includes the plugin has always been getting for free.
**Genuine latent finding, worth its own item some day:** several public headers use engine types they
never include (`VoxelBiomeDefinition.h`, `VoxelStrateDefinition.h`, `VoxelSettings.h`,
`VoxelStrateTypes.h`, `VoxelContentManager.h`, `VoxelDensityVolume.h`, and `VoxelWorld.cpp`). The
plugin compiles today only because the shared PCH supplies them. UE has been moving away from
implicit shared-PCH includes for years, so this will need doing eventually — **but not inside an
unrelated diagnostic**, which is why it was reverted rather than chased.
**Reverted**, with the reason written into `VoxelForge.Build.cs` so nobody retries it blind.
### The FP question, answered without touching build settings
`MazeEquivalence` now compiles a **verbatim copy of the Maze core into the TEST's translation unit**
and compares three implementations of the same source:
```
A = GetMazeDensity (VoxelGenerator.cpp TU)
B = the operator stack (VoxelDensityOpStack.cpp TU)
C = MazeCoreVerbatim (the test's own TU)
```
- **A != C** ⇒ identical source, different TU, different result ⇒ the compiler, not the port.
Nothing to fix; record it and move on.
- **A == C, B != C** ⇒ the source IS stable across TUs ⇒ the operator stack differs for a **logic**
reason, and it is in `FLatticeCorridorSource` or `FSdfCarveOp`.
Duplicating code is normally a fault; here it is the only instrument that answers the question,
because three careful readings all concluded "identical" and the test disagrees. It is marked
diagnostic-only and comes out once the answer is in.
**UNVERIFIED:** everything in this entry.
**Next single action:** rebuild (normal incremental now — the Build.cs change is reverted) and read
the THREE-WAY block. Phase 1 step 3 still paused.
---