openmpi-default should not offer gcc variants on platforms that do not support them

[cwmccurdy]

After installing Macports for Catalina, gnuplot build failed because it was trying to build gcc49. This happened after an operating system update and having uninstalled and clean the old gnuplot from macports. The error is:

sudo port install gnuplot
Password:
--->  Computing dependencies for gnuplot
--->  Cleaning gnuplot
--->  Scanning binaries for linking errors
--->  Found 131 broken files, matching files to ports
Warning: No port llvm-3.8 found in the index; can't rebuild
--->  Found 1 broken port, determining rebuild order
You can always run 'port rev-upgrade' again to fix errors.
The following ports will be rebuilt: openmpi-default @1.10.3+gcc49
Continue? [Y/n]: y
Warning: Your DNS servers incorrectly claim to know the address of nonexistent hosts. This may cause checksum mismatches for some ports. See this page for more information: <https://trac.macports.org/wiki/MisbehavingServers>
--->  Fetching distfiles for gcc49
Error: building gcc49 is not supported with Xcode 9 or greater
Error: Failed to fetch gcc49: unsupported platform

[kencu (Ken)]

It looks like you've been migrating along for a while now, and finally your old variants are no longer supported.

You have openmpi-default using gcc49 and that is just too out of date to keep with now. The current default as of 2021 is gcc10:

$ port info openmpi-default
openmpi-default @4.0.1_1 (science, parallel, net)
Variants:             g95, [+]gcc10, gcc44, gcc45, gcc46, gcc47, gcc48, gcc49, gcc5, gcc6, gcc7, gcc8, gcc9, gccdevel, universal, valgrind

You are right -- somehow MacPorts should have flagged / fixed / updated / sorted this out for you, but -- nobody volunteered to do that work as yet.

So for now, you should manually do this (or something like it):

sudo port -f uninstall openmpi-default
sudo port -v install openmpi-default

and then you will get the gcc10 variant. Things should just then work for you, unless you have some other gcc49 variants some where that will need a similar fix.

Hope this helps!