How do you get cabal to look in `/usr/include` for include files when using ghcup on windows?

Question

I am trying to build hlibgit2 on windows. It's a wrapper around a c library, libgit2. After locating and installing the c dependencies the recommended cabal from ghcup can't find include files that are in /usr/include. This seems trivial. Surely I must be missing something big.

Collecting dependencies

The cabal file for hlibgit2 lists additional c dependencies with extra-libraries:

    extra-libraries:
      ws2_32, regex, winhttp, crypt32, rpcrt4, ssl, crypto

Running cabal build in the mingw64 msys2 terminal on a fairly fresh ghcup installation resulted in the following

Error: cabal-3.10.3.0.exe: Missing dependencies on foreign libraries:
* Missing (or bad) C libraries: regex, ssl, crypto
This problem can usually be solved by installing the system packages that
provide these libraries (you may need the "-dev" versions). If the libraries
are already installed but in a non-standard location then you can use the
flags --extra-include-dirs= and --extra-lib-dirs= to specify where they are.If
the library files do exist, it may contain errors that are caught by the C
compiler at the preprocessing stage. In this case you can re-run configure
with the verbosity flag -v3 to see the error messages.

regex

After some difficulty I was able to locate where regex.h is in msys2. It includes the following include file

/mingw64/include/regex.h

I installed the corresponding msys2 package with pacman.

pacman --noconfirm -S mingw-w64-x86_64-libsystre

Rerunning cabal build removes regex from the list of missing libraries, as expected.

openssl

Since ssl.h is a tiny bit easier to find and is also where crypto.h comes from I also installed openssl-devel

pacman --noconfirm -S openssl-devel

It includes the following files (among many others)

/usr/include/openssl/crypto.h
/usr/include/openssl/ssl.h

Rerunning cabal build does not find ssl or crypto. Rerunning it with -v3 as suggested by the error message reveals that cabal isn't trying to include headers from /usr/include:

Running: "C:\ghcup\ghc\9.4.8\lib\../mingw/bin\clang.exe"
    "--rtlib=compiler-rt" "-D_UCRT"
    "-IC:\ghcup\ghc\9.4.8\lib\../mingw/include"
    "-fuse-ld=lld" "--rtlib=compiler-rt" "-D_UCRT"
    "-LC:\ghcup\ghc\9.4.8\lib\../mingw/lib"
    "-LC:\ghcup\ghc\9.4.8\lib\../mingw/x86_64-w64-mingw32/lib" 
    "C:\ghcup\msys64\tmp\ghc6DB7.c" "-o" "C:\ghcup\msys64\tmp\ghc6DB8"
    "-lcrypto"
    "-LC:\ghcup\msys64\mingw64\lib"
    "-LC:\cabal\store\ghc-9.4.8\zlib-0.7.0.0-d2a93d80eb2a797e52d57c85d77b6e24ad2240b4\lib" 
    "-LC:\ghcup\msys64\mingw64\lib"
    "-LC:\ghcup\ghc\9.4.8\lib\x86_64-windows-ghc-9.4.8\bytestring-0.11.5.3"
    "-LC:\ghcup\ghc\9.4.8\lib\x86_64-windows-ghc-9.4.8\template-haskell-2.19.0.0"
    "-LC:\ghcup\ghc\9.4.8\lib\x86_64-windows-ghc-9.4.8\pretty-1.1.3.6"
    "-LC:\ghcup\ghc\9.4.8\lib\x86_64-windows-ghc-9.4.8\ghc-boot-th-9.4.8"
    "-LC:\ghcup\ghc\9.4.8\lib\x86_64-windows-ghc-9.4.8\deepseq-1.4.8.0"
    "-LC:\cabal\store\ghc-9.4.8\bindings-DSL-1.0.25-187bcd9b3e2210e6eff5543318f9f7a5f5429c7b\lib"
    "-LC:\ghcup\ghc\9.4.8\lib\x86_64-windows-ghc-9.4.8\array-0.5.4.0"
    "-LC:\ghcup\ghc\9.4.8\lib\x86_64-windows-ghc-9.4.8\base-4.17.2.1"
    "-LC:\ghcup\ghc\9.4.8\lib\x86_64-windows-ghc-9.4.8\ghc-bignum-1.3"
    "-LC:\ghcup\ghc\9.4.8\lib\x86_64-windows-ghc-9.4.8\ghc-prim-0.9.1"
    "-LC:\ghcup\ghc\9.4.8\lib\x86_64-windows-ghc-9.4.8\rts-1.0.2"
with environment: [
    ("CABAL_DIR","C:\\cabal"),
    ("CONFIG_SITE","C:/ghcup/msys64/etc/config.site"),
    ("GHCUP_INSTALL_BASE_PREFIX","C:\\"),
    ("GHCUP_MSYS2_ENV","MINGW64"),
    ("HASKELL_DIST_DIR","G:\\Dev\\gitlib\\hlibgit2\\dist-newstyle\\build\\x86_64-windows\\ghc-9.4.8\\hlibgit2-0.18.0.16"), 
    ("HLIBGIT2_DATADIR","G:\\Dev\\gitlib\\hlibgit2\\.\\."),
    ("MINGW_CHOST","x86_64-w64-mingw32"),
    ("MINGW_PACKAGE_PREFIX","mingw-w64-x86_64"),
    ("MINGW_PREFIX","C:/ghcup/msys64/mingw64"),
    ("MSYSCON","mintty.exe"),
    ("MSYSTEM","MINGW64"),("MSYSTEM_CARCH","x86_64"),("MSYSTEM_CHOST","x86_64-w64-mingw32"),
    ("MSYSTEM_PREFIX","C:/ghcup/msys64/mingw64"),
    ("PKG_CONFIG_PATH","C:\\ghcup\\msys64\\mingw64\\lib\\pkgconfig;C:\\ghcup\\msys64\\mingw64\\share\\pkgconfig"),
    ("PKG_CONFIG_SYSTEM_INCLUDE_PATH","C:/ghcup/msys64/mingw64/include"), 
    ("PKG_CONFIG_SYSTEM_LIBRARY_PATH","C:/ghcup/msys64/mingw64/lib"), 
    ("SHELL","C:\\ghcup\\msys64\\usr\\bin\\bash.exe"),
    ("TEMP","C:\\ghcup\\msys64\\tmp"),("TMP","C:\\ghcup\\msys64\\tmp"),
    ("XDG_DATA_DIRS","C:\\ghcup\\msys64\\mingw64\\share\\;C:\\ghcup\\msys64\\usr\\local\\share\\;C:\\ghcup\\msys64\\usr\\share\\"),
    ("_","C:/ghcup/bin/cabal")
]
C:\ghcup\ghc\9.4.8\lib\../mingw/bin\clang.exe returned ExitFailure 1
C:\ghcup\ghc\9.4.8\lib\../mingw/bin\clang.exe returned ExitFailure 1 with
error message:
lld: error: unable to find library -lcrypto
clang: error: linker command failed with exit code 1 (use -v to see
invocation)

Running cabal user-config diff results in the following

cabal user-config diff
+ C: \ghcup\msys64\usr\bin
+ extra-include-dirs: C:\ghcup\msys64\mingw64\include
+ extra-lib-dirs: C:\ghcup\msys64\mingw64\lib
+ extra-prog-path: C:\ghcup\bin,

I could edit c:\cabal\config to list more extra-include-dirs, but this seems so basic that I must be missing something big. What is it?

Answer 1

There is a much easier way to find pacman packages.

pacman -Fy to update the database of pacman packages to search

pacman -F regex.h to find a package containing regex.h

It seems the only pacman packages that are useful are those in mingw64, in this case the package I wanted for openssl is

pacman -F ssl.h

There does not seem to be an easy way to filter pacman packages found by -F. Specifying --arch doesn't restrict the architecture, glob patterns don't work for the file, --regex searches don't take advantage of the index and take forever, and --machinereadable output isn't machine readable to use with another tool to filter them.