Workaround for a GHC bug with -XTemplateHaskell and ghci (fixes #303) #312
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| @@ -55,13 +56,17 @@ withInterpreter flags action = do | |||
| let | |||
| args = flags ++ [ | |||
| "--interactive" | |||
| , xTemplateHaskell | |||
| #if __GLASGOW_HASKELL__ >= 802 | |||
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What is the meaning of such an #if? The #if is evaluated when doctest is compiled, and we use such #ifs all over the place to ensure compilation with different GHCs. But this #if does not make to seem a difference on the compilation of doctest, but when I run doctest.
Could it be a problem when I run doctest with a different GHC version than it was compiled with?
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doctest uses both ghc (the library) and ghc --interactive (the executable). The former is used to extract Haddock comments, the later is used to check examples. If we would only depend on the executable, we could just use whatever ghc is on the PATH. But with ghc the library we can only depend on one version (specifically, the version we compile doctest with). For that reason we fix both, ghc the library and ghc the executable to the ghc version we compile against at compile time. The library version is fixed simply by depending on it. To fix the executable version we use ghc-paths.
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Ah, this makes sense if doctest sits within a per-GHC buildtree.
(For some reason, I have doctest in my PATH, but that does not make sense in such a scenario.)
Related GHC bug: https://gitlab.haskell.org/ghc/ghc/-/issues/20670