Boost_USE_STATIC_LIBS deviates from FindBoost.cmake behaviour

[jpfeuffer]

In the Find module, Boost_USE_STATIC_LIBS=OFF means that it is allowed to find either a dynamic version of boost or a static version.

With your config file, Boost_USE_STATIC_LIBS=OFF forces shared-only.

a) Why the deviation? This makes consistent CMake scripts very difficult if one wants to support older boosts without the config.
b) Why those arbitrary choices for the value OFF? Shouldn't the consumer decide?! How would one even choose shared/dynamic boost on Windows with this? Edit: corrected

While this is considered, can you recommend a quick fix on how to use this config to find either shared or static? After all, many builds are agnostic to how boost was linked.

[jpfeuffer]

Sorry, I just saw that I confused OFF with not set, or overlooked the "third option" of not setting the variable. Let me reevaluate.

[jpfeuffer]

Ok so ignore point b) but the rest of the issue still stands:

• Why deviate from the FindModule for the same variable?
• How to look for both, either shared or static? (Without triggering two searches where one will unnecessarily clutter the CMake configuration logs.)

[jpfeuffer]

IMHO the behaviour should be at least:

(changes in bold)

Boost_USE_STATIC_LIBS: When ON, uses static Boost libraries; when OFF,
uses shared Boost libraries; when not set, PREFERS
static on Windows, shared otherwise but accepts both.

Or just follow the behaviour from the FindModule.

[pdimov]

Our generated config files don't have the ability to accept both static and shared. It needs to be chosen beforehand. That's why we don't match the FindBoost behavior.

[jpfeuffer]

I see. Is this a general limitation of how boost is designed or was it "just not implemented yet"? If it's a limitation, can you very shortly elaborate on the problem?

In general I think CMake config files can support that.

[Andrej730]

Also stumbled upon this - on windows, if there are multiple variants, it's preferring static over shared - basically implying Boost_USE_STATIC_LIBS=ON by default.

Previously I thought I could rely on https://cmake.org/cmake/help/latest/module/FindBoost.html as boost cmake configs format description, but I guess it's not entirely reliable.

In theory there should be a dedicated page on boost cmake config variables, where this can be documented (and perhaps other differences, if they exist).

If anyone else stumbling on this - the conclusion is, if you plan to support both boost configs and modules (FindBoost) and want to keep it consistent, then the script should explicitly set Boost_USE_STATIC_LIBS as OFF and not rely on unset Boost_USE_STATIC_LIBS interpreted as OFF by FindBoost.