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Do not use thread_local storage with Clang targeting MinGW

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Every test that copies a value segfaults there - 42 of 105 on clang
11.0.1, 39 of 102 on clang 18.1.8 - while the same tests pass with GCC
targeting MinGW, with Clang targeting MSVC, and with every other
toolchain the library is tested on. The counter that bounds the copy
constructor's descent is the library's first use of thread_local, so
that job had never exercised it before.

JSON_NO_THREAD_LOCAL already covers toolchains without thread_local
storage, and copying yields the same values with it, only more slowly.
Define it for this one automatically.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-08-21 00:48:42 +02:00
parent 6305cc9f72
commit 540f6d11cc
3 changed files with 21 additions and 0 deletions
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single_include/nlohmann/json.hpp
+9
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@@ -2561,6 +2561,15 @@ JSON_HEDLEY_DIAGNOSTIC_POP
#define JSON_NO_UNIQUE_ADDRESS
#endif
// Clang targeting MinGW does not survive the thread_local storage the copy
// constructor uses to bound its descent: every test that copies a value
// segfaults with clang 11.0.1 and clang 18.1.8, while the same tests pass with
// GCC targeting MinGW and with every other toolchain the library is tested on.
// Copying works the same way without the counter, only more slowly.
#if !defined(JSON_NO_THREAD_LOCAL) && defined(__clang__) && defined(__MINGW32__)
#define JSON_NO_THREAD_LOCAL 1
#endif
// disable documentation warnings on clang
#if defined(__clang__)
#pragma clang diagnostic push