Fix incomplete-type error in set_parents with ordered_json#5167
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nlohmann merged 1 commit intoMay 14, 2026
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When iteration_proxy_value<iter_impl<ordered_json>> appears in a context
that requires it to be complete (function or lambda parameter), the
compiler instantiates basic_json<ordered_map> and walks into
set_parents(iterator, typename iterator::difference_type)
while iterator is still incomplete, failing with "invalid use of
incomplete type".
basic_json::difference_type is already std::ptrdiff_t, so just naming
the underlying type directly avoids the dependent lookup. Behavior and
ABI are unchanged. This was the approach suggested in the issue thread.
Added a regression case in unit-ordered_json.cpp using the same trigger
pattern (lambda parameter naming the proxy type).
Fixes nlohmann#3732
Signed-off-by: Akhilesh Arora <akhildawra@gmail.com>
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May 19, 2026
…5167) When iteration_proxy_value<iter_impl<ordered_json>> appears in a context that requires it to be complete (function or lambda parameter), the compiler instantiates basic_json<ordered_map> and walks into set_parents(iterator, typename iterator::difference_type) while iterator is still incomplete, failing with "invalid use of incomplete type". basic_json::difference_type is already std::ptrdiff_t, so just naming the underlying type directly avoids the dependent lookup. Behavior and ABI are unchanged. This was the approach suggested in the issue thread. Added a regression case in unit-ordered_json.cpp using the same trigger pattern (lambda parameter naming the proxy type). Fixes nlohmann#3732 Signed-off-by: Akhilesh Arora <akhildawra@gmail.com> Signed-off-by: Vaibhav Sharma <48472541+GhostVaibhav@users.noreply.github.com>
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Fixes #3732 (label: confirmed).
If you name
detail::iteration_proxy_value<detail::iter_impl<ordered_json>>where it has to be complete (function or lambda parameter), the compile blows up:The cascade is
proxy -> iter_impl<ordered_json> -> basic_json<ordered_map>, and duringbasic_json's instantiation the compiler hitsset_parents(iterator, typename iterator::difference_type)beforeiteratoris complete.basic_json::difference_typeis alreadystd::ptrdiff_t, so just using the underlying type directly avoids the dependent lookup. Same behavior, no ABI change. This was suggested in the issue thread.Added a regression case in
tests/src/unit-ordered_json.cpp(lambda parameter naming the proxy type — same trigger as the minimal repro). Full localctestrun passes (102/102).The frozen ABI snapshot at
tests/abi/include/nlohmann/json_v3_10_5.hppis intentionally left alone.single_include/nlohmann/json.hppupdated to match).