mirror of
https://github.com/nlohmann/json.git
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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>
52 lines
2.7 KiB
Markdown
52 lines
2.7 KiB
Markdown
# macro_builder
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Generates the argument-counting macros behind the `NLOHMANN_DEFINE_TYPE_*` and `NLOHMANN_DEFINE_DERIVED_TYPE_*`
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macros in [`include/nlohmann/detail/macro_scope.hpp`](../../include/nlohmann/detail/macro_scope.hpp):
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- `NLOHMANN_JSON_EXPAND`
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- `NLOHMANN_JSON_GET_MACRO`, which selects a macro by the number of its arguments (64 slots)
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- `NLOHMANN_JSON_PASTE`, which calls a function-like macro for each member, and its helpers `NLOHMANN_JSON_PASTE2`
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to `NLOHMANN_JSON_PASTE64`
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- `NLOHMANN_JSON_DOUBLE_PASTE`, which the `*_WITH_NAMES` macros use to call a function-like macro for each
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(JSON name, member) pair, and its helpers `NLOHMANN_JSON_DOUBLE_PASTE3` to `NLOHMANN_JSON_DOUBLE_PASTE63`
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- the slot table of `NLOHMANN_JSON_TYPE_BODY`, which dispatches `NLOHMANN_DEFINE_TYPE_*(Type)` (no further
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arguments) to the zero-member implementation and every other argument count to the one-or-more-member
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implementation
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The number of slots (`max_args` in [`main.cpp`](main.cpp)) sets the member limit of these macros.
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`NLOHMANN_JSON_PASTE` and `NLOHMANN_JSON_TYPE_BODY` take the function/prefix as their first argument, so 64 slots
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allow 63 members; `NLOHMANN_JSON_DOUBLE_PASTE` additionally consumes its members two at a time (name, member), so
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it only defines the odd helpers up to `NLOHMANN_JSON_DOUBLE_PASTE63`.
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## Usage
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From the project root:
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```shell
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c++ -std=c++11 tools/macro_builder/main.cpp -o macro_builder
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./macro_builder
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./macro_builder type_body
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```
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1. Run `./macro_builder` (no arguments). In `include/nlohmann/detail/macro_scope.hpp`, replace the lines from
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`#define NLOHMANN_JSON_EXPAND( x ) x` to the `#define NLOHMANN_JSON_DOUBLE_PASTE63(...)` line with the output,
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without its trailing empty line.
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2. Run `./macro_builder type_body`. Replace the lines from `#define NLOHMANN_JSON_TYPE_BODY(Prefix, ...)` to the
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`NLOHMANN_JSON_TYPE_BODY_SENTINEL))` line with the output.
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3. Run `make amalgamate`. It updates `single_include/nlohmann/json.hpp` and runs `make pretty`, which indents the
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continuation lines that the tool writes unindented.
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With an unchanged `main.cpp`, these steps reproduce both blocks of `macro_scope.hpp` byte for byte. `make
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macro_builder_check` (also run by CI, see `.github/workflows/check_amalgamation.yml`) automates this: it builds
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`main.cpp`, regenerates both blocks, and fails on a diff against the checked-in header.
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## Maintained by hand
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The tool does not generate everything that depends on the number of slots. When changing `max_args`, also update:
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- the documented limit of 63 members in `docs/mkdocs/docs` and the tests at that limit in
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`tests/src/unit-udt_macro.cpp`
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All three tables pass one macro name per slot to `NLOHMANN_JSON_GET_MACRO`, so they need exactly as many entries as
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it has slots.
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