Extend IWYU checks to headers without a matching .cc file

[om7057]

Context

While working on PR #4574, we found that sdk/include/opentelemetry/sdk/metrics/view/predicate_factory.h uses uint8_t without including <cstdint>. It compiled only because something else in the same translation unit happened to pull that header in transitively. This kind of bug is exactly what include-what-you-use (IWYU) checks are meant to catch, but it slipped through because this header has no matching .cc file of its own to anchor an IWYU check against.

Proposal

Look into extending the project's IWYU tooling/CI so that header-only files (headers with no corresponding .cc translation unit in the same directory) are also checked for missing or unnecessary includes, rather than relying on incidental coverage from whichever .cc file happens to include them first.

Related

• [SDK] Add missing cstdint include to predicate_factory.h #4574

[om7057]

Thanks for the suggestion, @lalitb. Opening this to track it separately as discussed in #4574.

[marcalff]

Fixing this is especially valuable for all the header only files under api.

In my understanding, IWYU will work with the CMAKE compilation database, and this database only knows about foo.cc files.

A possible fix/work around might be to also add foo.h in a CMake library, creating a fake one if necessary, for IWYU to "see" these files and do something about it.

Purely speculative, I never got time to investigate further.

[dbarker]

Part the of the broader fix should be to complete #1429 and move the SDK implementations to .cc files if header only now.

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