Expand and unify --keep-temp-files

[9999years]

This is blocking #9367.

Currently, cabal repl has a --keep-temp-files option, and cabal.project has a keep-temp-files option but it only affects Haddock builds.

This patch adds --keep-temp-files to CommonSetupFlags, making it available to all commands. The expanded --keep-temp-files flag is used for the cabal repl command and Haddock builds (retaining compatibility with the previous behavior). The flag will also be used for response files; see #9367.

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[sheaf]

One concern I have is that CommonSetupFlags is meant to be for flags common to all Setup invocations (it's a Cabal library concept). I don't think cabal-install should directly be re-using it unless it is for the purpose of invoking Setup.

I don't fully understand how the haddock-project command was implemented. I thought it was supposed to be a cabal-install-only concept, yet I see that there is a fair amount of code related to "haddock project" in the Cabal library as well, which doesn't really make sense to me.

I'm not objecting to this PR (which I am happy to see), but I would like to make sure that you have taken into consideration the logical separation between the Cabal library and cabal-install.

[9999years]

One concern I have is that CommonSetupFlags is meant to be for flags common to all Setup invocations ...

Yes, I wasn't entirely sure where to put this flag. There seem to be a lot of flags that are shared between multiple commands (like --enable-split-objs or --builddir or --with-compiler or --package-db etc. etc. etc. — in fact, diffing the --help messages for cabal build and cabal install reveals that the vast majority of the flags are identical). These flags seem to be placed in essentially random places in the code (if there's a schema for these decisions, it's not documented in any place I looked).

I picked CommonSetupFlags because it's already passed to all the places I need it in #9367. I think that adding it to (e.g.) the build flags or install flags or configure flags specifically would result in a much more invasive change. However, if there's some place you know it should be, I can look into moving it.