Avoid Windows linker errors with GHC 9.4.5+ #6
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Previously, `text-ansi` declared a direct `foreign import` on the `isatty` function. This is subtly incorrect on Windows, which provides an `_isatty` function rather than `isatty`. (See https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/posix-isatty?view=msvc-170) This happened to work on pre-9.4.5 versions of GHC due to them linking against the `msvcrt` C runtime (which still provided `isatty`), but GHC 9.4.5 and later link against `ucrt`, which does not provide `isatty` at all. This manifests in linker errors when using `text-ansi` in GHCi or Template Haskell on Windows, as seen in https://gitlab.haskell.org/ghc/ghc/-/issues/23378 and in this `hledger` build: https://github.com/simonmichael/hledger/actions/runs/4931242306/jobs/8815809083 The solution is to instead declare a foreign import on `_isatty`. The `c_isatty` function from `System.Posix.Internals` in `base` already does this, in fact, so I have removed the hand-written `c_isatty` functions in `text-ansi` in favor of the one in `System.Posix.Internals`. (Despite that module's name, `System.Posix.Internals` is cross-platform and does in fact work on Windows.)
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Excellent, thank you! |
mitchellwrosen
approved these changes
May 11, 2023
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Thanks! |
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Previously,
text-ansideclared a directforeign importon theisattyfunction. This is subtly incorrect on Windows, which provides an_isattyfunction rather thanisatty. (See https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/posix-isatty?view=msvc-170)This happened to work on pre-9.4.5 versions of GHC due to them linking against the
msvcrtC runtime (which still providedisatty), but GHC 9.4.5 and later link againstucrt, which does not provideisattyat all. This manifests in linker errors when usingtext-ansiin GHCi or Template Haskell on Windows, as seen in https://gitlab.haskell.org/ghc/ghc/-/issues/23378 and in thishledgerbuild: https://github.com/simonmichael/hledger/actions/runs/4931242306/jobs/8815809083The solution is to instead declare a foreign import on
_isatty. Thec_isattyfunction fromSystem.Posix.Internalsinbasealready does this, in fact, so I have removed the hand-writtenc_isattyfunctions intext-ansiin favor of the one inSystem.Posix.Internals. (Despite that module's name,System.Posix.Internalsis cross-platform and does in fact work on Windows.)