FEI: build fails with Epetra disabled

[tjfulle]

@trilinos/fei

With Trilinos_ENABLE_Epetra:BOOL=OFF defined, I get the following build error:

packages/fei/support-Trilinos/fei_Include_Trilinos.hpp:84:10: fatal error: BelosEpetraAdapter.hpp: No such file or directory
 #include <BelosEpetraAdapter.hpp>

Full configure:

/projects/sems/install/rhel6-x86_64/sems/utility/cmake/3.12.2/bin/cmake \
  -G "Ninja" \
  -D Trilinos_CONFIGURE_OPTIONS_FILE:FILEPATH=$TRILINOS_DIR/cmake/std/PullRequestLinuxCommonTestingSettings.cmake \
  -D Trilinos_ENABLE_Tpetra:BOOL=ON \
  -D Trilinos_ENABLE_Epetra:BOOL=OFF \
  -D Trilinos_ENABLE_Moertel:BOOL=OFF \
  -D Trilinos_ENABLE_ShyLU_DDFROSch:BOOL=OFF \
  -D Trilinos_ENABLE_Stokhos:BOOL=OFF \
  -D ROL_ENABLE_EXAMPLES:BOOL=OFF \
  -D Tpetra_ENABLE_DEPRECATED_CODE:BOOL=OFF \
  -D Xpetra_ENABLE_DEPRECATED_CODE:BOOL=OFF \
  -D Trilinos_ENABLE_Galeri:BOOL=OFF \
  -D Rythmos_ENABLE_TESTS:BOOL=OFF \
  $TRILINOS_DIR

[alanw0]

Hmm, this is a tough one. FEI isn't going to live into the Tpetra era, it really needs Epetra. Perhaps we need to add some cmake logic such that epetra is a mandatory dependency and FEI is disabled if Epetra is not available.

[tjfulle]

@alanw0 that would be fine, and I'm happy to add such logic to CMake. Does FEI have any Tpetra code? If so, I'll have to be careful about how Tpetra is instantiated in the event that Tpetra+Epetra are enabled. If not, I can just put a hard stop in CMake if Epetra is not enabled.

[rppawlo]

Would this be the time to consider removing FEI from trilinos?

[alanw0]

@tjfulle No, FEI doesn't have any Tpetra code. In packages/fei/CMakeLists.txt it mentions Tpetra but that's it. (That reference could probably be removed too.)

[alanw0]

@rppawlo Probably getting close, although the thermal/fluid folks in Sierra haven't finished deprecating it yet... hopefully soon.

[mhoemmen]

@alanw0 There are some plans to finish FEI and Epetra stack deprecation next FY. Not sure how the priorities will fall.

[mhoemmen]

epetra is a mandatory dependency and FEI is disabled if Epetra is not available.

FEI declares Epetra as an optional dependency:

Trilinos/packages/fei/cmake/Dependencies.cmake

Line 2 in 5ee7c7c

SET(LIB_OPTIONAL_DEP_PACKAGES Epetra AztecOO Belos Amesos Ifpack ML)

Best practice would be for FEI to use macros to protect code that depends on Epetra. Not sure if anyone wants to touch FEI, though, so perhaps we should just make Epetra mandatory. @alanw0 , what do you think?

[tjfulle]

I wasn't planning on touching FEI, apart from making Epetra mandatory. @alanw0 if that is what we want, I'll do it.

[alanw0]

@mhoemmen If we want to remove FEI from trilinos and Sierra is the last user of it, then I suppose we could just adopt a snapshot of FEI into Sierra and then Trilinos could drop it.
@tjfulle If you are willing to go ahead and make Epetra mandatory in FEI, that would be great, thanks!

[mhoemmen]

@alanw0 wrote:

If we want to remove FEI from trilinos and Sierra is the last user of it, then I suppose we could just adopt a snapshot of FEI into Sierra and then Trilinos could drop it.

That's something we should do eventually, but I think it's better if we do one thing at a time. This round of changes intends to make Trilinos build correctly with Tpetra_ENABLE_DEPRECATED_CODE=OFF.