Annotate facade header with IWYU export annotation

[hzeller]

Without that annotation, tools such as clang-tidy or the clangd language server (as well as many other tools) will complain about headers not directly providing a symbol if users include beast.hpp; With this annotation, they know.

Documentation IWYU
https://github.com/include-what-you-use/include-what-you-use/blob/master/docs/IWYUPragmas.md#iwyu-pragma-begin_exportsend_exports

Documentation llvm include cleaner/clang-tidy/clangd https://clangd.llvm.org/design/include-cleaner#iwyu-pragmas

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.11%. Comparing base (9b24b28) to head (17604c3).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3027      +/-   ##
===========================================
+ Coverage    93.09%   93.11%   +0.02%     
===========================================
  Files          176      176              
  Lines        13647    13647              
===========================================
+ Hits         12704    12708       +4     
+ Misses         943      939       -4     

see 1 file with indirect coverage changes

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[sehe]

Does IWYU not honour -isystem includes (e.g. via CMake SYSTEM includes)?

[hzeller]

-isystem does not make a difference here.

Often, warnings for -isystem-provided headers would be suppressed.

But here we have a different situation, and want to guide warnings in the project itself: IWYU marks includes relevant or not given if they provide a symbol directly in a particular header (and by default it does not follow further includes). That makes sure that symbols don't come from transitive dependencies (accidental visibility of symbols due to the textual concatenation of C headers, the very thing that IWYU wants to help prevent).

So if we have a header that is indeed meant to provide a symbol one nest-level deeper, we can annotate it like what I've done here.

[vinniefalco]

This looks benign

[sehe]

But here we have a different situation

Thank you. It's more clear to me now that this is not "silencing warnings" but annotating the facade header(s) specifically.

[ashtum]

@hzeller, I'm using clangd-20 and clang-tidy-20 with the -misc-include-cleaner check, but I wasn't able to reproduce the warning you mentioned. Could you please provide more details on how to reproduce the issue?