High sip-build memory usage when configuring PyQt

[Dmitry Shachnev]

Hi Phil, and merry Christmas!

When sip-build is generating bindings for PyQt5, the memory usage constantly
grows, and by the end of generation reaches about 3.5 GB.

I am using --no-make option, so this is only about generating code, not
building it. The memory grows during the phase when SIP prints messages like
these:

  Generating the QtCore bindings...
  Generating the QtCore .pyi file...
  Generating the QtNetwork bindings...
  Generating the QtNetwork .pyi file...

This is a big problem for us in Debian, because in the Debian MIPS port, a
process can allocate a maximum of 2 GB of memory [1]. Because of this, pyqt5
build keeps failing with MemoryError [2].

I use the latest versions of everything:
- SIP 6.7.5
- PyQt-builder 1.14.0
- PyQt5 5.15.7 (I believe it will happen with PyQt6 too)

This is a regression between SIP 6.6 and 6.7. With SIP 6.6 there were no such
issues.

Is it possible to free some memory after generating every binding? Or maybe
you can suggest some workaround to reduce memory consumption?

[1]: https://wiki.debian.org/MIPSPort#Generic_issues
[2]: https://buildd.debian.org/status/fetch.php?pkg=pyqt5&arch=mipsel&ver=5.15.7%2Bdfsg-2%2Bb1&stamp=1671885622&raw=0

--
Dmitry Shachnev