openblas: fix single threaded build

Patch conditional on single threadedness to avoid mass rebuilds;
moved to finalAttrs to avoid dynamic attrs in rec warnings.

pkgs/development/libraries/science/math/openblas/default.nix

@@ -2,6 +2,7 @@
   lib,
   stdenv,
   fetchFromGitHub,
+  fetchpatch,
   perl,
   which,
   # Most packages depending on openblas expect integer width to match
@@ -178,7 +179,7 @@ let
   shlibExt = stdenv.hostPlatform.extensions.sharedLibrary;
 
 in
-stdenv.mkDerivation rec {
+stdenv.mkDerivation(finalAttrs: {
   pname = "openblas";
   version = "0.3.31";
 
@@ -190,10 +191,18 @@ stdenv.mkDerivation rec {
   src = fetchFromGitHub {
     owner = "OpenMathLib";
     repo = "OpenBLAS";
-    rev = "v${version}";
+    rev = "v${finalAttrs.version}";
     hash = "sha256-YBR81GOLnTsc0g1SZL+j31/OFucJrBRFqtOTV8lcy8U=";
   };
 
+  ${if singleThreaded then "patches" else null} = [
+    # fix single threaded build
+    (fetchpatch {
+      url = "https://github.com/OpenMathLib/OpenBLAS/commit/874243421298866d116e1e8bdbd7e0ed4e31e4f6.diff";
+      hash = "sha256-+L98AjuMaDdmEdF8yruvBpljQ+hGmsfNuJSLxB4quDU=";
+    })
+  ];
+
   inherit blas64;
 
   # Some hardening features are disabled due to sporadic failures in
@@ -271,7 +280,7 @@ stdenv.mkDerivation rec {
   );
 
   # The default "all" target unconditionally builds the "tests" target.
-  buildFlags = lib.optionals (!doCheck) [ "shared" ];
+  buildFlags = lib.optionals (!finalAttrs.doCheck) [ "shared" ];
 
   doCheck = true;
   checkTarget = "tests";
@@ -282,7 +291,7 @@ stdenv.mkDerivation rec {
         for alias in blas cblas lapack; do
           cat <<EOF > $out/lib/pkgconfig/$alias.pc
     Name: $alias
-    Version: ${version}
+    Version: ${finalAttrs.version}
     Description: $alias provided by the OpenBLAS package.
     Cflags: -I$dev/include
     Libs: -L$out/lib -lopenblas
@@ -330,4 +339,4 @@ stdenv.mkDerivation rec {
     platforms = lib.attrNames configs;
     maintainers = with lib.maintainers; [ ttuegel ];
   };
-}
+})