[ET Trac] [Einstein Toolkit] #1173: ExternalLibraries build environment problems

[Einstein Toolkit]

#1173: ExternalLibraries build environment problems
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  Reporter:  hinder                 |       Owner:            
      Type:  defect                 |      Status:  review    
  Priority:  major                  |   Milestone:            
 Component:  EinsteinToolkit thorn  |     Version:            
Resolution:                         |    Keywords:  zlib hwloc
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Comment (by eschnett):

 NO_BUILD is usually only used if autodetection is unlikely to find
 something, and if the library does really not need to be built. Examples
 are BLAS/LAPACK when Intel's option "-mkl" can be used, or the MPI library
 when it is built-in (e.g. on a Cray). In these cases, the library paths
 are unused, and hence we didn't notice that they are nonsensical.

 The only thorn that supports NO_BUILD explicitly is HDF5. I don't know
 when one would use NO_BUILD with HDF5; maybe if one is sure that the
 library will be found in the default search path? That is a slightly
 different case than above, where no searching is necessary. I think these
 two cases should be distinct. Maybe we should call them IMPLICIT and
 SEARCH instead, but these names are not ideal either.

 In the second case, which is relevant here, we actually want to abort if
 ZLIB_DIR=NO_BUILD at the end of the script. This means that zlib was not
 found, and linking will then fail, independent of whether ZLIB_DIR is
 nonsensical or empty. Of course, it may also be that the search code is
 inaccurate, and linking will actually succeed even though searching
 failed, e.g. if zlib is located near HDF5... Anyway, I think the script
 should abort when ZLIB_DIR=NO_BUILD after searching.

 Note that a nonsensical search path is not that bad as it will be ignored
 by the linker.

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/1173#comment:5>
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