From 07c789ccc3e207f6e9d6e717e34f0a16255343af Mon Sep 17 00:00:00 2001
From: sheaf <sam.derbyshire@gmail.com>
Date: Tue, 8 Sep 2020 15:21:32 +0200
Subject: [PATCH] easier install instructions, using openblas

---
 cabal.project         |  1 +
 installation_notes.md | 58 +++++++++++++++++++++++++++++--------------
 2 files changed, 41 insertions(+), 18 deletions(-)

diff --git a/cabal.project b/cabal.project
index 97d114c..8bf8a5f 100644
--- a/cabal.project
+++ b/cabal.project
@@ -22,6 +22,7 @@ source-repository-package
 
 package hmatrix
   ghc-options: "-w"
+  flags: +openblas
 
 -- adds MonadTrans Decoder instance to waargonaut Decoder
 source-repository-package
diff --git a/installation_notes.md b/installation_notes.md
index 6639a39..9a6f466 100644
--- a/installation_notes.md
+++ b/installation_notes.md
@@ -12,10 +12,11 @@ With an `MSYS2` installation, the following environment variables will need to b
 `PKG_CONFIG_PATH`: `C:\msys64\mingw64\lib\pkgconfig`    
 `XDG_DATA_DIRS`: `C:\msys64\mingw64\share;C:\msys64\usr\share`    
 
+
 Then we install some necessary packages using the following command:
 
 ```bash
-pacman -S -q --noconfirm mingw64/mingw-w64-x86_64-pkg-config mingw64/mingw-w64-x86_64-gobject-introspection mingw64/mingw-w64-x86_64-gtksourceview3
+pacman -S -q --noconfirm mingw64/mingw-w64-x86_64-pkg-config mingw64/mingw-w64-x86_64-gobject-introspection mingw64/mingw-w64-x86_64-gtksourceview3 mingw64/mingw-w64-x86_64-openblas
 ```
 
 ## Possible errors
@@ -62,10 +63,25 @@ Any error of the form:
 include-dirs: /mingw64/bin is a relative path which makes no sense
 ```
 
-indicates that one of the packages is incorrectly using a Unix-style path.
-This was the case with `fontconfig`, which was resolved in [this patch](https://github.com/msys2/MINGW-packages/issues/872). 
+indicates that one of the packages is incorrectly configured with a Unix-style path.
 
-At the time of writing, another dependency suffers from the same issue: `graphite2`. To fix this, change its `pkg-config` package file `graphite2.pc` as follows:
+The version of `pkg-config` packaged with MSYS2 should automatically convert into the correct full filepaths.
+So you might need to uninstall the currently installed `pkg-config`, and install the `MSYS2` one:
+
+```
+pacman -S -q --noconfirm mingw64/mingw-w64-x86_64-pkg-config
+```
+
+This should fix the issue. Another solution is to pass the `--force` flag to `ghc-pkg` for the problematic packages.
+At the time of writing, the only dependency which presents this problem is `graphite2`, which is a dependency of `cairo`.
+This causes a problem with the `gi-cairo-render` library, so in the `cabal.project` file we can specify:
+
+```
+package gi-cairo-render
+  ghc-pkg-options: "--force"
+```
+
+We can otherwise manually fix this issue by changing the `pkg-config` package file `graphite2.pc` as follows:
 
 ```
 >>> before:
@@ -77,33 +93,35 @@ Libs: -L${libdir} -lgraphite2
 Cflags: -I${includedir}
 ```
 
-### Missing C library `blas` or `lapack`
+The package `fontconfig` also presented this issue; this was resolved in [this patch](https://github.com/msys2/MINGW-packages/issues/872). 
+
+### Missing C library `openblas`
 
 The error message
 
 ```
 Missing dependencies on foreign libraries:
-* Missing (or bad) C libraries: blas, lapack
+* Missing (or bad) C library: openblas
 ```
 
-indicates that `cabal` could not find the C libraries that `hmatrix` depends on.
+indicates that `cabal` could not find a C library that `hmatrix` depends on.
 
-These can be downloaded [here](https://icl.cs.utk.edu/lapack-for-windows/lapack/). You will need:
+Make sure that `openblas` is installed:
 
-  * `BLAS` x64 dll,
-  * `LAPACK` x64 dll,
+```
+pacman -S -q --noconfirm mingw64/mingw-w64-x86_64-openblas
+```
 
-Put these in some folder, say "C:/GSL", then:
-
-  * add the folder to the PATH environment variable,
-  * add the following to your `cabal.project` file:
+then ensure that `cabal` can find it, for instance:
 
 ```
 package hmatrix
-  extra-lib-dirs: "C:/GSL"
-  extra-include-dirs: "C:/GSL"
+  extra-lib-dirs: "C:/msys64/mingw64/bin"
+  extra-include-dirs: "C:/msys64/mingw64/include"
 ```
 
+enables `cabal` to find `C:/msys64/mingw64/bin/libopenblas.dll`.
+
 ### The code execution cannot proceed because libgfortran_64-3.dll was not found
 
 An error such as
@@ -118,14 +136,18 @@ or
 The code execution cannot proceed because libgcc_s_seh_64-1.dll was not found
 ```
 
-indicates that a dependency of `BLAS`/`LAPACK` could not be loaded. Download these DLLs and add them to the `PATH`.
+indicates that a dependency of `BLAS` could not be loaded. These should have been installed as dependencies of `openblas` (see previous error), but otherwise you can try:
+
+```
+pacman -S -q --noconfirm mingw64/mingw-w64-x86_64-gcc-fortran mingw64/mingw-w64-x86_64-gcc
+```
 
 ### addDLL: library not loaded
 
 The error message
 
 ```
-addDLL: C:\GSL\libblas or dependencies not loaded. (Win32 error 126)
+addDLL: libopenblas or dependencies not loaded. (Win32 error 126)
 ```
 
 means that `GHC` was not able to find the `BLAS` library, or a dependency thereof.