port install gmp fails on macOS Big Sur

[JayReynoldsFreeman]

I am running MacOS 11.6.5 (Big Sur) on a 2019 Mac Pro with Intel hardware. I have Xcode 13.2.1 installed, and have installed the associated command-line tools. I downloaded the MacPorts distribution for Big Sur and ran an apparently clean install via the installer. After some searching, I tried: "sudo port install gmp" and got the following:

#### SNIP ####

sudo port install gmp                             
Password:
--->  Cleaning gmp
--->  Scanning binaries for linking errors
--->  Found 12 broken files, matching files to ports
Warning: No port llvm-3.0 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: gcc46 @4.6.3
Continue? [Y/n]: Y 
--->  Fetching distfiles for gcc46
Error: building gcc46 is not supported with Xcode 9 or greater
Error: Failed to fetch gcc46: unsupported platform
Error: See /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_lang_gcc46/gcc46/main.log for details.
Error: rev-upgrade failed: Error rebuilding gcc46
Error: Follow https://guide.macports.org/#project.tickets if you believe there is a bug.

#### UNSNIP ####

The log file cited gives a long trace of what happened, but the ultimate error is indeed

   :error:fetch building gcc46 is not supported with Xcode 9 or greater
   :error:fetch Failed to fetch gcc46: unsupported platform

The advice in the first snipped output, to run "port rev-upgrade" isn't very useful:

#### SNIP ####

sudo port rev-upgrade
Password:
--->  Scanning binaries for linking errors
--->  Found 12 broken files, matching files to ports
Warning: No port llvm-3.0 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: gcc46 @4.6.3
Continue? [Y/n]: Y
--->  Fetching distfiles for gcc46
Error: building gcc46 is not supported with Xcode 9 or greater
Error: Failed to fetch gcc46: unsupported platform
Error: See /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_lang_gcc46/gcc46/main.log for details.
Error: rev-upgrade failed: Error rebuilding gcc46
Error: Follow https://guide.macports.org/#project.tickets if you believe there is a bug.

#### UNSNIP ####

I learned a little more about what is actually installed:

#### SNIP ####

port installed gcc46
The following ports are currently installed:
 gcc46 @4.6.3_3 (active)

#### UNSNIP ####

I posted on the GMP mailing list about this with no useful response so far.

[jmroot (Joshua Root)]

It looks like gmp installed with no problems. After every install or upgrade, rev-upgrade runs automatically, and that checks for broken linking in all installed ports. It found that llvm-3.0 and gcc46 are broken. You should probably just uninstall those, because they aren't going to work on Big Sur anyway.

The fact that you have those ports installed most likely means your MacPorts installation was migrated from an older OS version, and you should follow the wiki:Migration procedure.