mirror of
https://github.com/nlohmann/json.git
synced 2026-10-03 05:00:30 +00:00
Niels Lohmann
7aeb98414e
tools/macro_builder only emitted NLOHMANN_JSON_EXPAND..PASTE64, so two other tables that scale with the same max_args stayed hand-maintained with nothing checking them: NLOHMANN_JSON_DOUBLE_PASTE (added by hand in #4563 for the *_WITH_NAMES macros) and the 64-slot dispatch table of NLOHMANN_JSON_TYPE_BODY (the #4041 zero-member/one-or-more-member switch). Both tables pass one macro name per slot to the same NLOHMANN_JSON_GET_MACRO dispatch as PASTE, so they can drift out of sync with max_args exactly the way _dp did in the ABI tag list fixed by #5544. Extend main.cpp with build_double_paste_code() (same recursive-doubling shape as build_paste_code(), but DOUBLE_PASTE consumes two arguments per member, so an even slot index falls back to the next lower odd DOUBLE_PASTE<N>) and build_type_body_table() (max_args - 1 MEMBERS slots and one trailing EMPTY slot, 8 per line, matching how it is written by hand today). Add a "type_body" argument that selects the TYPE_BODY block, since it lives at a separate location in macro_scope.hpp from the EXPAND..DOUBLE_PASTE63 block; plain invocation is unchanged apart from covering the extended range. No longer emit the tool's old trailing blank line, so its output is directly diffable without post-processing. Verified with c++ -std=c++11: running the tool (with and without "type_body") and piping the raw output through the pinned astyle reproduces both blocks of the current macro_scope.hpp byte for byte. tests/src/unit-udt_macro.cpp (all NLOHMANN_DEFINE_TYPE_*/_WITH_NAMES/ zero-member variants) passes unchanged under -std=c++11 and -std=c++17 with -fsanitize=address,undefined. Add a "macro_builder_check" Makefile target that builds main.cpp, regenerates both blocks into a scratch directory inside the repository (astyle's --project lookup needs the target files under the same tree as .astylerc, unlike an external /tmp directory), and diffs them against the corresponding ranges of macro_scope.hpp; wire it into check-amalgamation next to the natvis check. Wire the same regeneration into check_amalgamation.yml, splicing the (still unindented) generated blocks back into the PR's own macro_scope.hpp before the existing astyle/amalgamation step runs, so that step's own tree-wide astyle pass both indents them and folds any drift into the amalgamation patch/diff the workflow already produces. Unlike amalgamate.py and generate_natvis.py, this step builds tools/macro_builder/main.cpp from the pull request's own checkout ($MAIN_DIR) rather than a separate checkout of tools/ at develop: this tool has no independent source of truth to regenerate against (its README documents that it must reproduce macro_scope.hpp byte for byte), so a develop-pinned copy would only reproduce the generate_natvis.py trap fixed in a previous commit on this branch, where a PR that teaches the tool to cover more of the file fails its own CI until that PR merges and updates the develop copy. Add tools/macro_builder/README.md documentation for both new tables and the two-invocation usage, and a short pointer comment above NLOHMANN_JSON_TYPE_BODY (the EXPAND pointer already covered the first block; extended its wording to include DOUBLE_PASTE63). Closes #5717 item 5 in full, completing what the documentation-only "Document tools/macro_builder..." commit already on this branch left open (that commit's README/pointer-comment half stands; it also covers item 7). Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2.7 KiB
2.7 KiB
macro_builder
Generates the argument-counting macros behind the NLOHMANN_DEFINE_TYPE_* and NLOHMANN_DEFINE_DERIVED_TYPE_*
macros in include/nlohmann/detail/macro_scope.hpp:
NLOHMANN_JSON_EXPANDNLOHMANN_JSON_GET_MACRO, which selects a macro by the number of its arguments (64 slots)NLOHMANN_JSON_PASTE, which calls a function-like macro for each member, and its helpersNLOHMANN_JSON_PASTE2toNLOHMANN_JSON_PASTE64NLOHMANN_JSON_DOUBLE_PASTE, which the*_WITH_NAMESmacros use to call a function-like macro for each (JSON name, member) pair, and its helpersNLOHMANN_JSON_DOUBLE_PASTE3toNLOHMANN_JSON_DOUBLE_PASTE63- the slot table of
NLOHMANN_JSON_TYPE_BODY, which dispatchesNLOHMANN_DEFINE_TYPE_*(Type)(no further arguments) to the zero-member implementation and every other argument count to the one-or-more-member implementation
The number of slots (max_args in main.cpp) sets the member limit of these macros.
NLOHMANN_JSON_PASTE and NLOHMANN_JSON_TYPE_BODY take the function/prefix as their first argument, so 64 slots
allow 63 members; NLOHMANN_JSON_DOUBLE_PASTE additionally consumes its members two at a time (name, member), so
it only defines the odd helpers up to NLOHMANN_JSON_DOUBLE_PASTE63.
Usage
From the project root:
c++ -std=c++11 tools/macro_builder/main.cpp -o macro_builder
./macro_builder
./macro_builder type_body
- Run
./macro_builder(no arguments). Ininclude/nlohmann/detail/macro_scope.hpp, replace the lines from#define NLOHMANN_JSON_EXPAND( x ) xto the#define NLOHMANN_JSON_DOUBLE_PASTE63(...)line with the output, without its trailing empty line. - Run
./macro_builder type_body. Replace the lines from#define NLOHMANN_JSON_TYPE_BODY(Prefix, ...)to theNLOHMANN_JSON_TYPE_BODY_SENTINEL))line with the output. - Run
make amalgamate. It updatessingle_include/nlohmann/json.hppand runsmake pretty, which indents the continuation lines that the tool writes unindented.
With an unchanged main.cpp, these steps reproduce both blocks of macro_scope.hpp byte for byte. make macro_builder_check (also run by CI, see .github/workflows/check_amalgamation.yml) automates this: it builds
main.cpp, regenerates both blocks, and fails on a diff against the checked-in header.
Maintained by hand
The tool does not generate everything that depends on the number of slots. When changing max_args, also update:
- the documented limit of 63 members in
docs/mkdocs/docsand the tests at that limit intests/src/unit-udt_macro.cpp
All three tables pass one macro name per slot to NLOHMANN_JSON_GET_MACRO, so they need exactly as many entries as
it has slots.