feat(eigen): Feature System v2 — eigen_blas provider + use_blas/use_lapacke/mpl2only#52
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Requires mcpp >= 0.0.69 (feature defines + capabilities); older mcpp ignores the
new keys (skip-unknown), so the recipe stays parseable everywhere.
- eigen_blas : compile Eigen's own reference BLAS AND advertise the 'blas'
capability (provides=["blas"]).
- use_blas : define EIGEN_USE_BLAS + requires=["blas"] — Eigen delegates to
an external BLAS bound by the resolver.
- use_lapacke : define EIGEN_USE_LAPACKE + requires=["lapack"].
- mpl2only : define EIGEN_MPL2_ONLY (no capability).
Header comment documents the provider-vs-consumer split and the verified mutual
exclusion: enabling eigen_blas + use_blas together is self-contradictory (the
blas/*_impl.h functype dispatch tables vs the -DEIGEN_USE_BLAS backend signature)
— use eigen_blas alone, or use_blas with a separate provider.
Verified on mcpp 0.0.69: header-only mpl2only consumer builds+runs; eigen_blas
alone compiles; compile_commands.json carries EIGEN_USE_BLAS / EIGEN_MPL2_ONLY.
…las') The recipe renamed the BLAS-provider feature blas -> eigen_blas; update the example's dependency spec to match (it referenced the now-removed 'blas', failing the smoke). eigen_blas alone (no EIGEN_USE_BLAS) compiles cleanly.
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Brings
compat.eigenonto mcpp's Feature System v2 (mcpp ≥ 0.0.69). Older mcpp ignores the newdefines/requires/provideskeys (skip-unknown), so the recipe stays parseable everywhere — the v2 behaviours are simply inert there.Features
eigen_blas— compile Eigen's own reference BLAS (blas/*.cpp+blas/f2c/*.c) AND advertise theblascapability (provides = ["blas"]). Self-contained, no Fortran.use_blas—defines = ["EIGEN_USE_BLAS"]+requires = ["blas"]: Eigen's kernels delegate to an external BLAS that the resolver binds.use_lapacke—EIGEN_USE_LAPACKE+requires = ["lapack"].mpl2only—EIGEN_MPL2_ONLY(no capability).This fixes the original report: enabling Eigen's BLAS feature now actually emits
-DEIGEN_USE_BLAS(not only-DMCPP_FEATURE_BLAS).Mutual exclusion (documented in the recipe header)
eigen_blasanduse_blasare opposite roles and must not be combined: compiling Eigen's own BLAS sources with-DEIGEN_USE_BLASdefined is self-contradictory (theblas/*_impl.hfunctype dispatch tables stop matching the by-value backendrunsignatures →[-fpermissive]on level2/level3). Useeigen_blasalone, oruse_blaswith a separate provider.Verified (mcpp 0.0.69)
mpl2onlyconsumer builds + runs;eigen_blasalone compiles;compile_commands.jsoncarriesEIGEN_USE_BLAS/EIGEN_MPL2_ONLY.Design: mcpp
.agents/docs/2026-06-29-feature-capability-model-design.md.