[CMAKE] remove global include_directories usage and rely on target properties

[dbarker]

More cmake cleanup.

Changes

• Remove more global include_directories calls in favor of target_include_directories. Make sure the targets relying on these global includes link/include what they need.
• Make the api target an interface link to the sdk target
• Remove usage of the sdk headers in the foo_* example libraries (These example libraries should link to the api only)

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.04%. Comparing base (29ac517) to head (37b0364).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3426   +/-   ##
=======================================
  Coverage   90.04%   90.04%           
=======================================
  Files         212      212           
  Lines        6937     6937           
=======================================
  Hits         6246     6246           
  Misses        691      691           

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[marcalff]

LGTM

[ThomsonTan]

Seems this is a breaking change if the user relies on the include_directories() behavior?

[dbarker]

Seems this is a breaking change if the user relies on the include_directories() behavior?

@ThomsonTan I don't expect any breaking changes to users. The scope of the include_directories call covers all targets defined in the same CMakeLists.txt file and the sub directories it adds. User code shouldn't be included in this scope.

[ThomsonTan]

Seems this is a breaking change if the user relies on the include_directories() behavior?

@ThomsonTan I don't expect any breaking changes to users. The scope of the include_directories call covers all targets defined in the same CMakeLists.txt file and the sub directories it adds. User code shouldn't be included in this scope.

FYI, here is one case which relied on include_directories() to work, but needs to switch to target_link_libraries() now.

open-telemetry/opentelemetry-cpp-contrib#551

[dbarker]

Seems this is a breaking change if the user relies on the include_directories() behavior?

@ThomsonTan I don't expect any breaking changes to users. The scope of the include_directories call covers all targets defined in the same CMakeLists.txt file and the sub directories it adds. User code shouldn't be included in this scope.

FYI, here is one case which relied on include_directories() to work, but needs to switch to target_link_libraries() now.

open-telemetry/opentelemetry-cpp-contrib#551

That is a good catch. One of the drawbacks with the global include_directories (and why it is good to move towards target_include_directories) is that it can hide issues like this since the global includes are not transitive with the targets. The fix you made in open-telemetry/opentelemetry-cpp-contrib#551 is a good one.

Another instance where issues were hidden is with the foo_* library examples. They had included the sdk headers but did not link to the sdk targets (and shouldn't have). If a user copied those examples and the cmake files to build in their project - they would have previously failed to find the sdk headers at compile time.