Resolve circular dependencies

[swamp-agr]

As it was initially discussed in #469, there is circular dependencies between fay and fay-base:

• fay-base depends on fay.
• fay-base contains modules with same names as in base (Prelude, Data.Maybe and so on). In order to prevent ambiguous modules names error, it was not exposed by default.
• fay-tests executable which is hidden by flag test and disabled by default from fay package depends on fay-base.

Thus, fay-tests component could not be converted easily to enabled test-suite.

During discussion in #469 there were 2 proposals opened in order to mitigate circular dependencies:

1. Move fay-base into fay package as a (separate) library. (multi-component packages are enabled only since cabal 3.0).
2. Split tests into compiler-related and base-related and convert them to corresponding test-suites.

I would prefer to keep two separate packages and relocate tests accordingly to their purpose (compiler or base library).

[swamp-agr]

• Quick look shown that 185 out of 194 source-based tests failed without fay-base enabled.
• Test tool as a suite could be compiled without fay-base.
• @ezzieyguywuf, motivation around splitting package on two parts described in Reduce boilerplate #134.

Options:

Option	Pros	Cons
Manual control (almost the same, but losing flag -ftest and dependency on fay-base)	few changes required	new contract for maintainers (almost the same as right now but a bit worse)
Moving the whole test-suite and test sources to fay-base package	few changes required	fay tests also will be moved to fay-base. fay will live without tests.
Move the most tests to fay-base, leave a few tests in fay	Both compiler and base will be covered	average code changes: partial code overlap in test-suites, subject of moving test tool into fay library.
Investigate new cabal features (dropping < 8.8 compilers support) and adopt them to move fay-base back inside fay	If it is possible then the best of two worlds would be under one package, fay-base could be dropped	It is an area of uncertainty: research required. Might be impossible.

[ezzieyguywuf]

@swamp-agr thanks for your help in getting #469 resolved, and for opening this new issue.

I'm still struggling to get tests working, though, and I think it may be related to something in this bug report, or maybe #459 . Here is how you can reproduce my issue:

# Get the sources
cabal unpack fay
cd fay-0.24.2.0
ls # uh-oh, notice there's no fay-base here...

# Configure and build
ghc Setup.hs -o setup
./setup configure --flag=test
./setup build

# Try to run the tests
export LD_LIBRARY_PATH="${PWD}/dist/build"
./dist/build/fay-tests/fay-tests --num-threads/${nproc} -random 20

This results in many tests failing with ghc-pkg: cannot find package fay-base

If you think about it, this makes sense, as the release tarbal doesn't include fay-base, and the cabal files don't list it at all (you took it out, to resolve the circular dependency: thanks!)

Further investigation shows me how you worked around this on travis, i.e. you just manually install fay-base. However, I can't do this in gentoo, because it drops me right back into the circular dependency issue.

I've seen some packages (for example, parser-combinators) split out tests into a separate package altogether (i.e. parser-combinators-tests). I don't know their motivation for doing so, but it seems that this may be "cheap" for you to implement (fay-tests is already a separate executable) and would resolve my circular dependency problem (I think!).

I don't love that option, though, as it separates the test from the code under test. I guess it is essentially what you've listed in row 2 in your table above.