Add constexpr variant of --bfbs-gen-embed for compile-time schema processing#9063
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BenniRip wants to merge 1 commit intogoogle:masterfrom
Open
Add constexpr variant of --bfbs-gen-embed for compile-time schema processing#9063BenniRip wants to merge 1 commit intogoogle:masterfrom
BenniRip wants to merge 1 commit intogoogle:masterfrom
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Why: The existing --bfbs-gen-embed generates a struct with a
function-local static array, making the binary schema inaccessible
in constexpr contexts (e.g. compile-time schema processing).
How: A new flag --bfbs-gen-embed-constexpr generates an inline
constexpr file-scope array and size constant instead:
inline constexpr uint8_t FooBinarySchema[] = { ... };
inline constexpr size_t FooBinarySchemaSize = N;
The existing --bfbs-gen-embed output is unchanged.
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Summary
Add
--bfbs-gen-embed-constexprflag that generates a file-scopeinline constexprarray for the binary schema, as an alternative to the existing--bfbs-gen-embedstruct wrapper.Motivation
The current
--bfbs-gen-embedwraps the binary schema in a struct with a function-local static:Function-local statics are not usable in constant expressions which prevents compile-time schema processing, e.g. computing worst-case serialized sizes from
(capacity: N)attributes at compile time.What this PR does
Adds a new flag
--bfbs-gen-embed-constexprthat produces:The existing
--bfbs-gen-embedoutput is unchanged. The two flags are mutually exclusive (same output filename, different content).Changes
include/flatbuffers/idl.h— newbinary_schema_gen_embed_constexproptionsrc/flatc.cpp— flag declaration and parsingsrc/idl_gen_cpp.cpp— conditional codegen ingenerate_bfbs_embed(); skipBinarySchematypedef inGenBinarySchemaTypeDef()in constexpr mode (the typedef references a struct type, but constexpr mode generates a bare array instead)The generated output requires C++17 (
inline constexpr), which is expected since the flag is opt-in for users who needconstexpr.Testing
flattests— ALL TESTS PASSEDscripts/generate_code.py— no C++ diffscripts/clang-format-git.sh— no modificationsmonster_test.fbswith the new flagNote on goldens
Both flags produce the same output filename (
<name>_bfbs_generated.h). Happy to add a golden for the new flag if you'd like. Would you prefer a separate filename suffix (e.g._bfbs_constexpr_generated.h) so both can coexist, or is the current shared filename appropriate?Generated output for basic.fbs