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Fix module-import-in-extern-c compiler error (3.6) #10489

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Fix module-import-in-extern-c compiler error (3.6) #10489

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@zacharykeyessonos zacharykeyessonos commented Oct 31, 2025 •
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Description

This fixes #10490.

This fixes a compiler error when building C++ projects that use the 'modules' C++ language feature consume Mbed TLS. The specific error is module-import-in-extern-c, which occurs when #includes occur within extern C blocks.

Example:

$ clang-17 -std=c++20 -fmodules -Iinclude sample.cpp     
In file included from sample.cpp:2:
In file included from include/mbedtls/platform_util.h:18:
include/mbedtls/platform_time.h:33:1: error: import of C++ module '_Builtin_stdint' appears within extern "C" language linkage specification [-Wmodule-import-in-extern-c]
   33 | #include <stdint.h>
      | ^
include/mbedtls/platform_time.h:16:1: note: extern "C" language linkage specification begins here
   16 | extern "C" {
      | ^
include/mbedtls/platform_time.h:34:1: error: import of C++ module '_Builtin_inttypes' appears within extern "C" language linkage specification [-Wmodule-import-in-extern-c]
   34 | #include <inttypes.h>
      | ^
include/mbedtls/platform_time.h:16:1: note: extern "C" language linkage specification begins here
   16 | extern "C" {
      | ^
2 errors generated.

This seems to primarily be an issue with clang. See https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-fmodules

PR checklist

@zacharykeyessonos
Fix module-import-in-extern-c compiler error
1465f6d 
This fixes a compiler error when building C++ projects that use the
'modules' C++ language feature consume Mbed TLS. The specific error is
module-import-in-extern-c, which occurs when `#include`s occur within
`extern C` blocks.

```
$ clang-17 -std=c++20 -fmodules -Itf-psa-crypto/include -Itf-psa-crypto/drivers/builtin/include -o sample sample.cpp
In file included from sample.cpp:8:
In file included from tf-psa-crypto/drivers/builtin/include/mbedtls/private/chachapoly.h:44:
tf-psa-crypto/drivers/builtin/include/mbedtls/private/chacha20.h:26:1: error: import of C++ module '_Builtin_stdint' appears within extern "C" language linkage specification [-Wmodule-import-in-extern-c]
   26 | #include <stdint.h>
      | ^
tf-psa-crypto/drivers/builtin/include/mbedtls/private/chachapoly.h:35:1: note: extern "C" language linkage specification begins here
   35 | extern "C" {
      | ^
1 error generated.
```

This seems to primarily be an issue with clang. See
https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-fmodules

Signed-off-by: zacharykeyessonos <zachary.keyes@sonos.com>
This was referenced Oct 31, 2025
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@zacharykeyessonos zacharykeyessonos changed the title Fix module-import-in-extern-c compiler error Fix module-import-in-extern-c compiler error (3.6) Oct 31, 2025
@zacharykeyessonos
Add changelog entry
c4f118a 
Signed-off-by: zacharykeyessonos <zachary.keyes@sonos.com>
@zacharykeyessonos
Add the -fmodules flag to the cpp_dummy_build_cpp test program
8add50f 
Signed-off-by: zacharykeyessonos <zachary.keyes@sonos.com>
@zacharykeyessonos zacharykeyessonos force-pushed the fix-module-import-in-extern-c-compiler-error_3.6 branch from f1254b3 to 8add50f Compare November 4, 2025 17:46
@minosgalanakis minosgalanakis added size-s Estimated task size: small (~2d) bug component-platform Portability layer and build scripts priority-low Low priority - this may not receive review soon needs-review Every commit must be reviewed by at least two team members, needs-ci Needs to pass CI tests needs-reviewer This PR needs someone to pick it up for review labels Nov 5, 2025
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bug component-platform Portability layer and build scripts needs-ci Needs to pass CI tests needs-review Every commit must be reviewed by at least two team members, needs-reviewer This PR needs someone to pick it up for review priority-low Low priority - this may not receive review soon size-s Estimated task size: small (~2d)

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@zacharykeyessonos @minosgalanakis