exa: adopt installShellFiles

Also declare a separate "man" output.

pkgs/tools/misc/exa/default.nix

@@ -1,5 +1,5 @@
 { stdenv, fetchFromGitHub, rustPlatform, cmake, perl, pkgconfig, zlib
-, darwin, libiconv
+, darwin, libiconv, installShellFiles
 }:
 
 with rustPlatform;
@@ -17,24 +17,20 @@ buildRustPackage rec {
     sha256 = "14qlm9zb9v22hxbbi833xaq2b7qsxnmh15s317200vz5f1305hhw";
   };
 
-  nativeBuildInputs = [ cmake pkgconfig perl ];
+  nativeBuildInputs = [ cmake pkgconfig perl installShellFiles ];
   buildInputs = [ zlib ]
   ++ stdenv.lib.optionals stdenv.isDarwin [
     libiconv darwin.apple_sdk.frameworks.Security ]
   ;
 
+  outputs = [ "out" "man" ];
+
   postInstall = ''
-    mkdir -p $out/share/man/man1
-    cp contrib/man/exa.1 $out/share/man/man1/
-
-    mkdir -p $out/share/bash-completion/completions
-    cp contrib/completions.bash $out/share/bash-completion/completions/exa
-
-    mkdir -p $out/share/fish/vendor_completions.d
-    cp contrib/completions.fish $out/share/fish/vendor_completions.d/exa.fish
-
-    mkdir -p $out/share/zsh/site-functions
-    cp contrib/completions.zsh $out/share/zsh/site-functions/_exa
+    installManPage contrib/man/exa.1
+    installShellCompletion \
+      --name exa contrib/completions.bash \
+      --name exa.fish contrib/completions.fish \
+      --name _exa contrib/completions.zsh
   '';
 
   # Some tests fail, but Travis ensures a proper build