Hello! Today I merged commits for automatic reconfiguration and rebuilding of a package as necessary when 'cabal test' and 'cabal bench' are invoked. The automatic reconfiguration code is based on the code already used to reconfigure packages when './Setup build' and 'cabal build' are invoked. I noticed that the existing reconfiguration code does not account for ConfigExFlags that may have been passed to 'cabal configure' the last time the package was configured. (My alterations do not affect this behaviour.) The purpose of this message is to bring attention to the problems I think this could cause and with the help of the community, determine the actual severity of the issue. Then we can decide if/when and how to resolve it. Obviously, if Cabal is being invoked through a 'Setup' script, there is no need for concern. However, ConfigExFlags affect dependency resolution during configuration, so automatic reconfiguration that ignores them may silently and unexpectedly change how the package is linked. I'm concerned this could (hypothetically) lead to linking to a different version of a dependency, causing build failure (or worse, if different versions of the dependency have different behaviours). I also have some reason to believe the situation is not that dire. After the initial configuration, the resolved dependencies are saved in the ConfigFlags in the LocalBuildInfo. When reconfiguring, the worst possible outcome should be that the dependency resolver cannot resolve the given dependencies and versions without some ConfigExFlags that would now be missing. To get my patches merged, I ignored this issue. The easiest solution is simply to include the ConfigExFlags in the LocalBuildInfo. That is something that could be done when/if the 'Setup' script builds actually become deprecated, since the ConfigExFlags reside in cabal-install, but the LocalBuildInfo is in Cabal. We may want to take care of this in the short term, but on the other hand, it could probably wait: this is far from a new issue, and I can't document any case of someone actually bitten by this bug. Feel free to tell me I'm making this out to be more than it is, but I thought I should present it before the community. Thanks! -- Thomas Tuegel