How to correctly build cabal project using hmatrix under Windows 10?

Using Windows 10 64-bit, Cabal-3.4.0.0, ghc-8.10.7. I installed OpenBLAS in MSYS2 environment with command pacman -S mingw-w64-x86_64-openblas. Than, I successfully installed hmatrix-0.20.2 with command

cabal install --lib hmatrix --flags=openblas --extra-include-dirs="C:\\ghcup\\msys64\\mingw64\\include\\OpenBLAS" --extra-lib-dirs="C:\\ghcup\\msys64\\mingw64\\bin" --extra-lib-dirs="C:\\ghcup\\msys64\\mingw64\\lib"

I am trying to build simple test project using cabal build cabalhmatrix with Main

module Main where

import Numeric.LinearAlgebra

main :: IO ()
main = do
  putStrLn $ show $ vector [1,2,3] * vector [3,0,-2]

But now I am getting output

Resolving dependencies...
Build profile: -w ghc-8.10.7 -O1
In order, the following will be built (use -v for more details):
- hmatrix-0.20.2 (lib) (requires build)
- cabalhmatrix-0.1.0.0 (exe:cabalhmatrix) (first run)
Starting     hmatrix-0.20.2 (lib)

Failed to build hmatrix-0.20.2. The failure occurred during the configure
step.
Build log (
C:\cabal\logs\ghc-8.10.7\hmatrix-0.20.2-6dd2e8f2795550e4dd624770ac98c326dacc0cac.log
):
Warning: hmatrix.cabal:21:28: Packages with 'cabal-version: 1.12' or later
should specify a specific version of the Cabal spec of the form
'cabal-version: x.y'. Use 'cabal-version: 1.18'.
Configuring library for hmatrix-0.20.2..
cabal-3.4.0.0.exe: Missing dependencies on foreign libraries:
* Missing (or bad) C libraries: blas, lapack
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.

cabal-3.4.0.0.exe: Failed to build hmatrix-0.20.2 (which is required by
exe:cabalhmatrix from cabalhmatrix-0.1.0.0). See the build log above for
details.

What should I do to correctly build that package? I guess I need to somehow pass arguments --flags=openblas --extra-include-dirs="C:\\ghcup\\msys64\\mingw64\\include\\OpenBLAS" --extra-lib-dirs="C:\\ghcup\\msys64\\mingw64\\bin" --extra-lib-dirs="C:\\ghcup\\msys64\\mingw64\\lib" to hmatrix during compilation, but don't know how to do that. To be honest, I don't understand for what program exactly are those arguments (cabal, ghc, ghc-pkg or something else) and why cabal is trying to install hmatrix again. I see hmatrix in directory "C:\cabal\store\ghc-8.10.7\hmatrix-0.20.2-e917eca0fc7690010007a19f4f2a3602d86df0f0".

Created cabal.project file:

packages: .

package hmatrix
  flags: +openblas
  extra-include-dirs: C:\\ghcup\\msys64\\mingw64\\include\\OpenBLAS
  extra-lib-dirs: C:\\ghcup\\msys64\\mingw64\\bin, C:\\ghcup\\msys64\\mingw64\\libenter code here

After adding libopenblas.dll location to PATH variable cabal project is working.

Solution

Even though there is the --lib flag, it's generally best to work under the assumption that Cabal doesn't do library installs. Never install a library, instead just depend on it – and have Cabal install, update etc. it whenever necessary.

But then how can you pass the necessary flags? With a cabal.project file.

packages: .

package hmatrix
   flags: openblas
   extra-include-dirs: C:\\ghcup\\msys64\\mingw64\\include\\OpenBLAS
   ...

Put this file in the working directory of your own project, together with cabalhmatrix.cabal. Then running cabal build in that directory will use a hmatrix install with the suitable library etc. flags.