docs: warn agents about misuse of OMPI_HIDDEN - #14318
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Add guidance explaining when it is (and is not) safe to annotate a symbol with OMPI_HIDDEN, so that contributors -- and AI coding agents in particular -- do not reintroduce the class of build breakage that need to be fixed in the initial version of code present in PR open-mpi#14317. As of Open MPI v6.0 the MPI interface is split across libmpi (Open MPI ABI) and libmpi_abi (standard MPI ABI), both of which link against the internal libopen_mpi. Many ompi_* symbols are defined in libopen_mpi but used from the bindings compiled into libmpi and libmpi_abi (for example, predefined handle objects like ompi_mpi_comm_parent and helpers like ompi_comm_split_type_hw_guided_support). Marking such a symbol OMPI_HIDDEN prevents it from being exported from libopen_mpi, so the links of both libmpi and libmpi_abi fail with unresolved symbols. Two files are updated: - AGENTS.md: add a "Golden rules" bullet describing the hazard and the rule of thumb -- if a symbol crosses a library boundary, use OMPI_DECLSPEC (or leave it un-annotated), never OMPI_HIDDEN. Only hide symbols that are certainly private to a single DSO. - docs/developers/source-code.rst: add a "Hiding symbols with OMPI_HIDDEN" subsection under Symbol Visibility that documents the v6.0 library structure and includes a warning admonition covering the unresolved-symbol failure mode and the same rule of thumb. These are documentation-only changes. CLAUDE.md is a symlink to AGENTS.md and is covered automatically. Signed-off-by: Howard Pritchard <howardp@lanl.gov>
jsquyres
approved these changes
Aug 13, 2026
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Add guidance explaining when it is (and is not) safe to annotate a symbol with OMPI_HIDDEN, so that contributors -- and AI coding agents in particular -- do not reintroduce the class of build breakage that need to be fixed in the initial version of code present in PR #14317.
As of Open MPI v6.0 the MPI interface is split across libmpi (Open MPI ABI) and libmpi_abi (standard MPI ABI), both of which link against the internal libopen_mpi. Many ompi_* symbols are defined in libopen_mpi but used from the bindings compiled into libmpi and libmpi_abi (for example, predefined handle objects like ompi_mpi_comm_parent and helpers like ompi_comm_split_type_hw_guided_support). Marking such a symbol OMPI_HIDDEN prevents it from being exported from libopen_mpi, so the links of both libmpi and libmpi_abi fail with unresolved symbols.
Two files are updated:
AGENTS.md: add a "Golden rules" bullet describing the hazard and the rule of thumb -- if a symbol crosses a library boundary, use OMPI_DECLSPEC (or leave it un-annotated), never OMPI_HIDDEN. Only hide symbols that are certainly private to a single DSO.
docs/developers/source-code.rst: add a "Hiding symbols with OMPI_HIDDEN" subsection under Symbol Visibility that documents the v6.0 library structure and includes a warning admonition covering the unresolved-symbol failure mode and the same rule of thumb.
These are documentation-only changes. CLAUDE.md is a symlink to AGENTS.md and is covered automatically.