Version 3.0 breaks builds on certain applications

[kekePower]

Describe the bug
I built Botan on Mageia Cauldron x86_64 and the build failed when using Sphix to build the documentation. Using Doxygen worked fine.

You can see the full build log and my bug report over at Botan.

To Reproduce
Steps to reproduce the behavior: Build Botan using --with-sphinx and see that it fails.

$ git clone https://github.com/randombit/botan
$ cd botan
$ ./configure.py --with-sphinx
$ make

Expected behavior
I expect Sphinx to build the docs successfully.

Environment info

• OS: Mageia Cauldron x86_64
• Python version: 3.8.2
• Sphinx version: 3.0.0
• Sphinx extensions: N/A
• Extra tools: N/A

Additional context
Full build log: https://raw.githubusercontent.com/kekePower/mmbl/6ddfe29086def989b9867c1893548acd716a5939/2020/04/07/20%3A07%3A51/botan2-2.14.0-1.mga8.src.rpm/build.0.20200407175517.log

[jakobandersen]

Thanks for reporting! It looks like a tricky bug with the merging of data that only happens when using parallel building (-j 2 or more), and with a specific order of merging.

[jakobandersen]

This should be fixed in branch 3.0.x (future v3.0.1).