TLDR

A summary of my arguments in support of using Release as default:

debugging a RelWithDebInfo software may be a pain (and not so useful due to compiler optimizations)
we'll be wasting some disk space due to debug info (which sometimes is relevant, like in the llvm case)

More generally I think that for any build system we should default to installations that are not inserting debug symbols and are compiled in "release" mode.

Regardless of the default we'll choose, I think it would be nice if for anything that asks for debug symbols we could copy the stage directory in <prefix>/.src or similar and patch in some way the dwarf section to point to that directory. This would probably build on the work already done by @junghans in #4102.

Longer explanation

For 1. I must say that maybe it's just my personal experience, but the first thing I usually do when I see a production bug on a C++ app is trying to reproduce it on a debug version (-O0 -g or lately -Og). The unfortunate cases where the bug occurs only in release mode are usually not the most pleasing debugging experiences one may have.

For 2. the mileage may vary depending on the packages. I tried to see the impact of debug symbols on 2 packages to have an idea:

$ spack find -p openmpi
==> 2 installed packages.
-- linux-ubuntu14.04-x86_64 / gcc@4.8 ---------------------------
    openmpi@2.1.1  /home/mculpo/PycharmProjects/spack/opt/spack/linux-ubuntu14.04-x86_64/gcc-4.8/openmpi-2.1.1-wbyfkrrj2m35owiiavkktcfmu6bivsnu
    openmpi@2.1.1  /home/mculpo/PycharmProjects/spack/opt/spack/linux-ubuntu14.04-x86_64/gcc-4.8/openmpi-2.1.1-5csqo5vovfbiroy3dl6lyj2yrrm7la7g

$ du -sh /home/mculpo/PycharmProjects/spack/opt/spack/linux-ubuntu14.04-x86_64/gcc-4.8/openmpi-2.1.1-wbyfkrrj2m35owiiavkktcfmu6bivsnu /home/mculpo/PycharmProjects/spack/opt/spack/linux-ubuntu14.04-x86_64/gcc-4.8/openmpi-2.1.1-5csqo5vovfbiroy3dl6lyj2yrrm7la7g
26M	/home/mculpo/PycharmProjects/spack/opt/spack/linux-ubuntu14.04-x86_64/gcc-4.8/openmpi-2.1.1-wbyfkrrj2m35owiiavkktcfmu6bivsnu
129M	/home/mculpo/PycharmProjects/spack/opt/spack/linux-ubuntu14.04-x86_64/gcc-4.8/openmpi-2.1.1-5csqo5vovfbiroy3dl6lyj2yrrm7la7g

$ spack find -p hdf5
==> 2 installed packages.
-- linux-ubuntu14.04-x86_64 / gcc@4.8 ---------------------------
    hdf5@1.10.1  /home/mculpo/PycharmProjects/spack/opt/spack/linux-ubuntu14.04-x86_64/gcc-4.8/hdf5-1.10.1-rh62esj7salbazymxh25vllami3o3ehd
    hdf5@1.10.1  /home/mculpo/PycharmProjects/spack/opt/spack/linux-ubuntu14.04-x86_64/gcc-4.8/hdf5-1.10.1-fa5xpyl3nfpebwytheq3ck4llhfzqcom

$ du -sh /home/mculpo/PycharmProjects/spack/opt/spack/linux-ubuntu14.04-x86_64/gcc-4.8/hdf5-1.10.1-rh62esj7salbazymxh25vllami3o3ehd /home/mculpo/PycharmProjects/spack/opt/spack/linux-ubuntu14.04-x86_64/gcc-4.8/hdf5-1.10.1-fa5xpyl3nfpebwytheq3ck4llhfzqcom
54M	/home/mculpo/PycharmProjects/spack/opt/spack/linux-ubuntu14.04-x86_64/gcc-4.8/hdf5-1.10.1-rh62esj7salbazymxh25vllami3o3ehd
95M	/home/mculpo/PycharmProjects/spack/opt/spack/linux-ubuntu14.04-x86_64/gcc-4.8/hdf5-1.10.1-fa5xpyl3nfpebwytheq3ck4llhfzqcom

In the end I don't see a lot of benefits in having debug symbols by default in release builds - they are wasting space and if I had to debug something I would probably start by building a debug version of the application (not a release + debug symbols).

Finally:

If we have source and know the version etc, we can just do :

"etc" means knowing exactly what Spack did (patches applied, commit hash retrieved, or similar). I wouldn't recommend doing this because if you don't put the same sources you used in compilation you'll end up mapping the execution to the wrong line of the file. And I believe that could cause more headaches than it cures.

Set default CMake build_type to 'Release'? #5265

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