fastfields · balbasty · Aug 20, 2026 · Aug 20, 2026 · Aug 20, 2026 · Aug 20, 2026
diff --git a/CLAUDE.md b/CLAUDE.md
@@ -205,8 +205,28 @@ pushpull's fully-static order×bound compile is nightly
  which category a dependency is in, not about lookup.
  `tools/normalise-include-delimiters.py --check` enforces it, and also checks
  the converse: every quoted include must resolve beside its includer.
+- **`#pragma once` on line 1 of every header — no `#ifndef` include guards.**
+ Line 1 with no exception, licence and provenance comments included; they keep
+ their text and sit one line lower. **`include/fastfields/core/dlpack.h` is
+ the one exception and must keep its upstream `DLPACK_DLPACK_H_` guard** — it
+ is a verbatim vendored copy, and that macro is what lets it and a *system*
+ DLPack header carrying the same guard collapse into one inclusion, which
+ `#pragma once` cannot do for two distinct files. Do not "finish the job" on
+ it. The seven other headers with third-party provenance (`impl/kernels/`'s
+ `atomic.h`, `parallel{,_impl}.h`, `threadpool.{h,inl}`, `distance/mesh.h`,
+ and `impl/cuda/utils.h`) are adaptations, not drop-in copies: each is
+ re-namespaced into `ff::` and none carries an upstream guard macro, so there
+ is nothing for a guard to interoperate with and the pragma applies to them.
+ A partial-file `#ifndef` is *not* a header guard and this rule leaves it
+ alone — `FF_LIB_BOUND_SPLINE_T` (eight `api/*.h` headers share it so they
+ co-include; `fastfields-dlpack`'s `ext.cpp` depends on that and says so) and
+ the `FF_*_MAX_NBATCH` / `FF_AUTOCAST_PINNED_HOST` build knobs all stay.
+ Enforced by `tools/normalise-header-guards.py --check`, which also applies
+ the convention and audits that no guard macro is tested from another file —
+ the one way deleting a `#define` could change what compiles.
 - `include/fastfields/core/dlpack.h` is vendored upstream code: do not edit it,
- and it is skipped by `codespell` (see `.codespellrc`).
+ and it is skipped by `codespell` (see `.codespellrc`). It is the only
+ verbatim third-party file in the tree.
 
 ## Pointers
 

diff --git a/include/fastfields/api/checks.h b/include/fastfields/api/checks.h
@@ -1,5 +1,4 @@
-#ifndef FF_LIB_CHECKS
-#define FF_LIB_CHECKS
+#pragma once
 #include <stdexcept>
 #include <fastfields/core/dlpack.h>
 #include <fastfields/core/defines.h>
@@ -56,5 +55,3 @@ inline void require_same_device(const DLTensor & ref, const DLTensor & t, const
 }
 
 FF_NAMESPACE_END(FF_NS)
-
-#endif // FF_LIB_CHECKS
diff --git a/include/fastfields/api/cpu/distance.h b/include/fastfields/api/cpu/distance.h
@@ -1,5 +1,4 @@
-#ifndef FF_CPU_DISTANCE
-#define FF_CPU_DISTANCE
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 
@@ -62,5 +61,3 @@ void dt_mesh(
 
 } // namespace cpu
 } // namespace ff
-
-#endif // FF_CPU_DISTANCE
diff --git a/include/fastfields/api/cpu/posdef.h b/include/fastfields/api/cpu/posdef.h
@@ -1,5 +1,4 @@
-#ifndef FF_CPU_POSDEF
-#define FF_CPU_POSDEF
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 
@@ -80,5 +79,3 @@ void sym_invert_(
 
 } // namespace cpu
 } // namespace ff
-
-#endif // FF_CPU_POSDEF
diff --git a/include/fastfields/api/cpu/pushpull.h b/include/fastfields/api/cpu/pushpull.h
@@ -1,5 +1,4 @@
-#ifndef FF_CPU_PUSHPULL
-#define FF_CPU_PUSHPULL
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 
@@ -199,5 +198,3 @@ void grad_backward(
 
 } // namespace cpu
 } // namespace ff
-
-#endif // FF_CPU_PUSHPULL
diff --git a/include/fastfields/api/cpu/pushpull_dispatch.h b/include/fastfields/api/cpu/pushpull_dispatch.h
@@ -1,5 +1,4 @@
-#ifndef FF_CPU_PUSHPULL_DISPATCH
-#define FF_CPU_PUSHPULL_DISPATCH
+#pragma once
 /**
  * Private (not installed) header: the argument-marshalling helpers, the
  * argument checks and the ndim x order x bound x dtype dispatch matrix
@@ -103,5 +102,3 @@ typedef double reduce_t;
 
 FF_NAMESPACE_END(FF_DEVICE)
 FF_NAMESPACE_END(FF_NS)
-
-#endif // FF_CPU_PUSHPULL_DISPATCH
diff --git a/include/fastfields/api/cpu/reg_field.h b/include/fastfields/api/cpu/reg_field.h
@@ -1,5 +1,4 @@
-#ifndef FF_CPU_REG_FIELD
-#define FF_CPU_REG_FIELD
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 
@@ -368,5 +367,3 @@ void field_relax_rls(
 
 } // namespace cpu
 } // namespace ff
-
-#endif // FF_CPU_REG_FIELD
diff --git a/include/fastfields/api/cpu/reg_flow.h b/include/fastfields/api/cpu/reg_flow.h
@@ -1,5 +1,4 @@
-#ifndef FF_CPU_REG_FLOW
-#define FF_CPU_REG_FLOW
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 
@@ -404,5 +403,3 @@ void flow_relax_rls(
 
 } // namespace cpu
 } // namespace ff
-
-#endif // FF_CPU_REG_FLOW
diff --git a/include/fastfields/api/cpu/resize.h b/include/fastfields/api/cpu/resize.h
@@ -1,5 +1,4 @@
-#ifndef FF_CPU_RESIZE
-#define FF_CPU_RESIZE
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 
@@ -38,5 +37,3 @@ void resample(
 
 } // namespace cpu
 } // namespace ff
-
-#endif // FF_CPU_RESIZE
diff --git a/include/fastfields/api/cpu/restrict.h b/include/fastfields/api/cpu/restrict.h
@@ -1,5 +1,4 @@
-#ifndef FF_CPU_RESTRICT
-#define FF_CPU_RESTRICT
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 
@@ -40,5 +39,3 @@ void restriction(
 
 } // namespace cpu
 } // namespace ff
-
-#endif // FF_CPU_RESTRICT
diff --git a/include/fastfields/api/cpu/solve_field.h b/include/fastfields/api/cpu/solve_field.h
@@ -1,5 +1,4 @@
-#ifndef FF_CPU_SOLVE_FIELD
-#define FF_CPU_SOLVE_FIELD
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 
@@ -66,5 +65,3 @@ void field_cg(
 
 } // namespace cpu
 } // namespace ff
-
-#endif // FF_CPU_SOLVE_FIELD
diff --git a/include/fastfields/api/cpu/splinc.h b/include/fastfields/api/cpu/splinc.h
@@ -1,5 +1,4 @@
-#ifndef FF_CPU_SPLINC
-#define FF_CPU_SPLINC
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 
@@ -28,5 +27,3 @@ void spline_coeff(
 
 } // namespace cpu
 } // namespace ff
-
-#endif // FF_CPU_SPLINC
diff --git a/include/fastfields/api/cuda/distance.h b/include/fastfields/api/cuda/distance.h
@@ -1,5 +1,4 @@
-#ifndef FF_CUDA_DISTANCE
-#define FF_CUDA_DISTANCE
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 
@@ -62,5 +61,3 @@ void dt_mesh(
 
 } // namespace cuda
 } // namespace ff
-
-#endif // FF_CUDA_DISTANCE
diff --git a/include/fastfields/api/cuda/posdef.h b/include/fastfields/api/cuda/posdef.h
@@ -1,5 +1,4 @@
-#ifndef FF_CUDA_POSDEF
-#define FF_CUDA_POSDEF
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 
@@ -80,5 +79,3 @@ void sym_invert_(
 
 } // namespace cuda
 } // namespace ff
-
-#endif // FF_CUDA_POSDEF
diff --git a/include/fastfields/api/cuda/pushpull.h b/include/fastfields/api/cuda/pushpull.h
@@ -1,5 +1,4 @@
-#ifndef FF_CUDA_PUSHPULL
-#define FF_CUDA_PUSHPULL
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 
@@ -199,5 +198,3 @@ void grad_backward(
 
 } // namespace cuda
 } // namespace ff
-
-#endif // FF_CUDA_PUSHPULL
diff --git a/include/fastfields/api/cuda/pushpull_dispatch.h b/include/fastfields/api/cuda/pushpull_dispatch.h
@@ -1,5 +1,4 @@
-#ifndef FF_CUDA_PUSHPULL_DISPATCH
-#define FF_CUDA_PUSHPULL_DISPATCH
+#pragma once
 /**
  * Private (not installed) header: the argument-marshalling helpers, the
  * argument checks and the ndim x order x bound x dtype dispatch matrix
@@ -92,5 +91,3 @@ typedef double reduce_t;
 
 FF_NAMESPACE_END(FF_DEVICE)
 FF_NAMESPACE_END(FF_NS)
-
-#endif // FF_CUDA_PUSHPULL_DISPATCH
diff --git a/include/fastfields/api/cuda/reg_field.h b/include/fastfields/api/cuda/reg_field.h
@@ -1,5 +1,4 @@
-#ifndef FF_CUDA_REG_FIELD
-#define FF_CUDA_REG_FIELD
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 
@@ -332,5 +331,3 @@ void field_relax_rls(
 
 } // namespace cuda
 } // namespace ff
-
-#endif // FF_CUDA_REG_FIELD
diff --git a/include/fastfields/api/cuda/reg_flow.h b/include/fastfields/api/cuda/reg_flow.h
@@ -1,5 +1,4 @@
-#ifndef FF_CUDA_REG_FLOW
-#define FF_CUDA_REG_FLOW
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 
@@ -359,5 +358,3 @@ void flow_relax_rls(
 
 } // namespace cuda
 } // namespace ff
-
-#endif // FF_CUDA_REG_FLOW
diff --git a/include/fastfields/api/cuda/resize.h b/include/fastfields/api/cuda/resize.h
@@ -1,5 +1,4 @@
-#ifndef FF_CUDA_RESIZE
-#define FF_CUDA_RESIZE
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 
@@ -38,5 +37,3 @@ void resample(
 
 } // namespace cuda
 } // namespace ff
-
-#endif // FF_CUDA_RESIZE
diff --git a/include/fastfields/api/cuda/restrict.h b/include/fastfields/api/cuda/restrict.h
@@ -1,5 +1,4 @@
-#ifndef FF_CUDA_RESTRICT
-#define FF_CUDA_RESTRICT
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 
@@ -40,5 +39,3 @@ void restriction(
 
 } // namespace cuda
 } // namespace ff
-
-#endif // FF_CUDA_RESTRICT
diff --git a/include/fastfields/api/cuda/splinc.h b/include/fastfields/api/cuda/splinc.h
@@ -1,5 +1,4 @@
-#ifndef FF_CUDA_SPLINC
-#define FF_CUDA_SPLINC
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 
@@ -28,5 +27,3 @@ void spline_coeff(
 
 } // namespace cuda
 } // namespace ff
-
-#endif // FF_CUDA_SPLINC
diff --git a/include/fastfields/api/cuda/stream.h b/include/fastfields/api/cuda/stream.h
@@ -1,7 +1,4 @@
 #pragma once
-#ifndef FF_CUDA_STREAM
-#define FF_CUDA_STREAM
-
 /**
  * The public ABI carries a CUDA stream as an `intptr_t` (no CUDA types leak
  * into the exported signatures); the cuda-impl launchers take a real
@@ -29,5 +26,3 @@ static inline cudaStream_t _reg_stream(intptr_t stream)
 
 FF_NAMESPACE_END(FF_DEVICE)
 FF_NAMESPACE_END(FF_NS)
-
-#endif // FF_CUDA_STREAM
diff --git a/include/fastfields/api/distance.h b/include/fastfields/api/distance.h
@@ -1,5 +1,4 @@
-#ifndef FF_LIB_DISTANCE
-#define FF_LIB_DISTANCE
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 #include <fastfields/core/defines.h>
@@ -176,5 +175,3 @@ void dt_mesh(
 );
 
 FF_NAMESPACE_END(FF_NS)
-
-#endif // FF_LIB_DISTANCE
diff --git a/include/fastfields/api/posdef.h b/include/fastfields/api/posdef.h
@@ -1,5 +1,4 @@
-#ifndef FF_LIB_POSDEF
-#define FF_LIB_POSDEF
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 #include <fastfields/core/defines.h>
@@ -80,5 +79,3 @@ void sym_invert_(
 );
 
 FF_NAMESPACE_END(FF_NS)
-
-#endif // FF_LIB_POSDEF
diff --git a/include/fastfields/api/pushpull.h b/include/fastfields/api/pushpull.h
@@ -1,5 +1,4 @@
-#ifndef FF_LIB_PUSHPULL
-#define FF_LIB_PUSHPULL
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 #include <fastfields/core/defines.h>
@@ -228,5 +227,3 @@ void grad_backward(
 );
 
 FF_NAMESPACE_END(FF_NS)
-
-#endif // FF_LIB_PUSHPULL
diff --git a/include/fastfields/api/reg_field.h b/include/fastfields/api/reg_field.h
@@ -1,5 +1,4 @@
-#ifndef FF_LIB_REG_FIELD
-#define FF_LIB_REG_FIELD
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 #include <fastfields/core/defines.h>
@@ -376,5 +375,3 @@ void field_relax_rls(
 );
 
 FF_NAMESPACE_END(FF_NS)
-
-#endif // FF_LIB_REG_FIELD
diff --git a/include/fastfields/api/reg_flow.h b/include/fastfields/api/reg_flow.h
@@ -1,5 +1,4 @@
-#ifndef FF_LIB_REG_FLOW
-#define FF_LIB_REG_FLOW
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 #include <fastfields/core/defines.h>
@@ -397,5 +396,3 @@ void flow_relax_rls(
 );
 
 FF_NAMESPACE_END(FF_NS)
-
-#endif // FF_LIB_REG_FLOW
diff --git a/include/fastfields/api/resize.h b/include/fastfields/api/resize.h
@@ -1,5 +1,4 @@
-#ifndef FF_LIB_RESIZE
-#define FF_LIB_RESIZE
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 #include <fastfields/core/defines.h>
@@ -68,5 +67,3 @@ void resample(
 );
 
 FF_NAMESPACE_END(FF_NS)
-
-#endif // FF_LIB_RESIZE
diff --git a/include/fastfields/api/restrict.h b/include/fastfields/api/restrict.h
@@ -1,5 +1,4 @@
-#ifndef FF_LIB_RESTRICT
-#define FF_LIB_RESTRICT
+#pragma once
 #include <fastfields/core/dlpack.h>
 #include <cstdint>
 #include <fastfields/core/defines.h>
@@ -67,5 +66,3 @@ void restriction(
 );
 
 FF_NAMESPACE_END(FF_NS)
-
-#endif // FF_LIB_RESTRICT