burdiyan / redo-virtual-targets-issue

Steps to reproduce a virtual target issue with the redo build system: https://github.com/apenwarr/redo

Background

1. We have a list of directories and each contains a software package with sources in src.
2. Packages are independent from one another.
3. Assume that packages must be built using virtual targets - for whatever reason the build process can't produce a stable output in $3.
4. Build produces a dist directory with multiple outputs next to our src dir inside each package.
5. In this example there's only one such package called bar. It's enough to demonstrate the problem.
6. Rule default.list.do produces a list of sources then redo-stamp it.
7. Rule default.build.do depends on the list rule and on each file mentioned in the resulting *.list file.
8. The same default.build.do rule runs the build, then it redo-ifchange one arbitrary build output file inside the dist directory, so that we redo if dist directory gets deleted somehow. Very similar to LaTex example from the redo cookbook: https://github.com/apenwarr/redo/blob/main/docs/cookbook/latex/default.runtex.do#L51

Problem: default.build.do target becomes "dirty" twice when newly introduced inputs change, but it happens only once (which is expected) when the old inputs change.

Steps To Reproduce

1. Clone repo.
2. redo all - make sure bar.list was created and bar/dist/fake-output as well.
3. redo all - no rebuild.
4. touch bar/src/2.txt.
5. redo all - rebuild.
6. redo all again - should NOT rebuild, but rebuilds.
7. redo all again several times - now it's not being rebuilt.
8. touch bar/src/1.txt then redo several times - rebuilds only once. Fine!
9. touch bar/src/2.txt then redo several times - rebuilds twice. Why?