[MacPorts] Migration modified

[MacPorts Wiki]

Page "Migration" was changed by gctwnl
Diff URL: <https://trac.macports.org/wiki/Migration?action=diff&version=123>
Revision 123
Comment: I ran into the problem mentioned at the end of the page. It seems to be a generic thing, an older macOS may be able to install a variant while the new one does not. If such a variant is not essential (as with gcc10 versus gcc11 for building OpenBLAS) one can work around it. My workaround was cumbersome, so I have not added it here.
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Index: Migration
=========================================================================
--- Migration (version: 122)
+++ Migration (version: 123)
@@ -95,3 +95,5 @@
 sudo bash -c "ulimit -n 4096; ./restore_ports.tcl myports.txt"
 }}}
 This will raise the file limit for the duration of the `restore_ports.tcl` command.
+
+Another potential problem comes from possible differences between ports that do compile on an older macOS, but no longer on the newer. For instance, you might have installed OpenBLAS om macOS Mojave. This was built with gcc10, the then preferred version of gcc. OpenBLAS sets a +gcc10 variant for this and it has remained like that as long as you were updating it. When upgrading to macOS Monterey according to the procedure above, MacPorts will try to exactly recreate what was on Mojave, hence OpenBLAS +gcc10. But gcc10 may not compile on macOS Monterey (it does not as I write this example). Hence, the migration of OpenBLAS and everything that depends on it fails.
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