add(nix): why3 (with provers)

nix/custom/why3.nix

@@ -0,0 +1,27 @@
+{
+  symlinkJoin,
+  makeWrapper,
+  why3,
+  alt-ergo,
+  cvc4,
+  z3_4_12,
+}: let
+  provers = [
+    alt-ergo
+    cvc4
+    z3_4_12
+  ];
+in
+  symlinkJoin {
+    name = "why3";
+    # Generate configuration in the store, and wrap why3 with the corresponding option
+    paths = [
+      (why3.override {version = "1.6.0";})
+    ];
+    buildInputs = provers;
+    nativeBuildInputs = [makeWrapper];
+    postBuild = ''
+      $out/bin/why3 config detect --config=$out/why3.conf
+      wrapProgram $out/bin/why3 --add-flags "--config=$out/why3.conf"
+    '';
+  }