improve release setup

- use a build flag to turn on static system libraries
- generate shell completion scripts
- externalise the generate cabal2nix function

bisc.cabal

@@ -29,6 +29,10 @@ source-repository head
   type: git
   location: https://maxwell.ydns.eu/git/rnhmjoj/bisc
 
+flag static
+  default: False
+  description: Create a statically-linked binary
+
 executable bisc
   main-is:             Main.hs
   build-depends:       base ==4.* , selda ==0.*,
@@ -40,4 +44,5 @@ executable bisc
                        optparse-applicative
   default-language:    Haskell2010
   ghc-options:         -Wall
-  extra-libraries:     snappy stdc++
+  if flag(static)
+    extra-libraries:   snappy stdc++

default.nix

@@ -10,38 +10,31 @@ let
   basepkgs = import nixpkgs { inherit system; };
   pkgs = if static then basepkgs.pkgsStatic else basepkgs.pkgs;
 
-  f = { mkDerivation, base, bytestring, configurator, data-default
-      , directory, exceptions, filepath, leveldb-haskell, mtl, selda
-      , selda-sqlite, lib, text, optparse-applicative
-      }:
-      mkDerivation {
-        pname = "bisc";
-        version = "0.3.0.0";
-        src = ./.;
-        isLibrary = false;
-        isExecutable = true;
-        executableHaskellDepends = [
-          base bytestring configurator data-default directory exceptions
-          filepath leveldb-haskell mtl selda selda-sqlite text
-          optparse-applicative
-        ];
-        executableSystemDepends = [ pkgs.snappy ];
-        buildFlags = lib.optionals static [
-          "--ld-option=-lstdc++"
-          "--ld-option=-lsnappy"
-        ];
-        homepage = "https://maxwell.ydns.eu/git/rnhmjoj/bisc";
-        description = "A small tool that clears cookies (and more)";
-        license = lib.licenses.gpl3;
-      };
-
   ghc =  if static then pkgs.haskell.packages.integer-simple.ghc8104
     else if compiler == "default" then pkgs.haskellPackages
     else pkgs.haskell.packages.${compiler};
 
   variant = if doBenchmark then pkgs.haskell.lib.doBenchmark else pkgs.lib.id;
 
-  drv = variant (ghc.callPackage f {});
+  drv = variant (override (ghc.callPackage ./bisc.nix {}));
+
+  override = drv: pkgs.haskell.lib.overrideCabal drv (old: with pkgs.lib; {
+    buildTools = [ pkgs.installShellFiles ];
+    configureFlags = optional static "-f static";
+    buildFlags = optionals static [
+      "--ld-option=-lstdc++"
+      "--ld-option=-lsnappy"
+    ];
+    postInstall = ''
+      # generate completion
+      $out/bin/bisc --bash-completion-script "$out/bin/bisc" > bisc.bash
+      $out/bin/bisc --fish-completion-script "$out/bin/bisc" > bisc.fish
+      $out/bin/bisc --zsh-completion-script  "$out/bin/bisc" > bisc.zsh
+
+      installShellCompletion bisc.{bash,fish,zsh}
+    '';
+    postFixup = optionalString static "rm -r $out/nix-support";
+  });
 
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