Library symbols should be hidden by default

[azeey]

Environment

• OS Version: Ubuntu 18.04
• Source or binary build? source, ign-cmake2 (17b7058)

Description

• Expected behavior: Symbols are hidden by default as stated in https://github.com/ignitionrobotics/ign-cmake/blob/17b7058ff5c9de2f6f396d1a000dd0366481d621/cmake/Export.hh.in#L45-L52
• Actual behavior: Symbols without the *_HIDDEN macro are visible

Steps to reproduce

Here's an MWE: https://github.com/azeey/sandbox/tree/master/ign-cmake-visibility

After building, use nm -C lib/libtset_ign_cmake_visibility.so | grep test_ to see which symbols are hidden:

 nm -C lib/libtest_ign_cmake_visibility.so | grep test_
00000000000005c0 T test_hidden_func(int, int)
00000000000005e0 T test_visible_func(int, int)
00000000000005d0 t test_explicitly_hidden_func(int, int)

test_hidden_func should be hidden by default, but as the T (global symbol) in the nm output shows, it is visibile.

[chapulina]

Something to target ign-cmake3. We could at least update the docs now.

[scpeters]

keep open until we change the default behavior in ignition-cmake3

[scpeters]

I guess we forgot to reconfigure the default behavior in gz-cmake3

[j-rivero]

I guess we forgot to reconfigure the default behavior in gz-cmake3

Unfortunately we lost the moment to get the changes done. I've renamed the label to gz-cmake4. I've a testing workspace ready for testing but last time it was broken on gz-math7 with was quite early in the dependency chain. We probably want to fix the issues before committing the change to gz-cmake to avoid broken compilations on gz family.

[j-rivero]

As suggested by @azeey and @scpeters in gazebosim/gz-math#566 (comment). Best way to test CI could be:

• Pass HIDE_SYMBOLS_BY_DEFAULT to the gz_configure_build calls in every gz-* package
• Test and verify that CI / nightly builds are happy
• Remove HIDE_SYMBOLS_BY_DEFAULT from the gz_configure_build calls in every gz-* package
• Merge Use visibility hidden by default #392

[j-rivero]

As suggested by @azeey and @scpeters in gazebosim/gz-math#566 (comment). Best way to test CI could be:

* Pass HIDE_SYMBOLS_BY_DEFAULT to the gz_configure_build calls in every gz-* package

* Test and verify that CI / nightly builds are happy

All until here is now done.

* Remove HIDE_SYMBOLS_BY_DEFAULT from the gz_configure_build calls in every gz-*    * Merge

As pointed by @scpeters we are here. Let's remove the added symbols from all libs.