-Werror in GTSAM forces errors in downstream projects

[varunagrawal]

#1959 introduced -Werror in the GTSAM_COMPILE_OPTIONS_PRIVATE_COMMON variable in GtsamBuildTypes.cmake. This forces the compiler to treat all warnings as errors.

Unfortunately, this also propagates this behavior to downstream projects. This is not ideal since many (smaller) organizations choose to ignore warnings in favor of fast iteration, and this flag causes them to have to fight the compiler.

The simplest fix for this would be to remove GTSAM_COMPILE_OPTIONS_PRIVATE_COMMON as a CACHE variable. This would involve investigating other similar variables as well.

[Gold856]

So what is this issue actually about? Is it about downstream projects using FetchContent or similar, just building gtsam from source, or something else? As discussed in #2516, it's not clear and the proposed solution doesn't make sense.

[varunagrawal]

I am not familiar with the other issue, but at least for this one the Cmake flag being forcibly propagated to other projects which link against GTSAM is a no-go from me.

E.g. I clone a repo which uses GTSAM as a dependency and the repo owners didn't bother fixing some warnings. Since I compile the latest develop branch of GTSAM and link against that, all those warnings in the new repo now become errors for me and stops compilation, not something I want to deal with at the time.

[Gold856]

That's not how that works though. Compile options that are set with PRIVATE scope only apply to building the target (gtsam in this instance.) They do not propagate to consumers, and I verified they do not end up in the PUBLIC scope, or in the CMake config files. Someone else must be setting -Werror and propagating that.

[varunagrawal]

That's what I thought as well, which is why I narrowed it down to the variable being in the Cmake cache that is the problem. I edited that and it worked fine after.

[Gold856]

That is strange... is this repo using gtsam's functions for applying build flags then? And just to be clear, the warnings emitted are coming from this repo's own code, not gtsam?

[ProfFan]

I think the issue probably related to used GTSAM macros for external targets

[mvanhorn]

Implemented in #2560.