postgresql: Build with icu support

pkgs/servers/sql/postgresql/default.nix

@@ -1,9 +1,14 @@
-{ lib, stdenv, glibc, fetchurl, zlib, readline, libossp_uuid, openssl, libxml2, makeWrapper, tzdata, systemd }:
+{ lib, stdenv, glibc, fetchurl, zlib, readline, libossp_uuid, openssl, libxml2, makeWrapper, tzdata, systemd, icu, pkgconfig }:
 
 let
 
   common = { version, sha256, psqlSchema }:
-   let atLeast = lib.versionAtLeast version; in stdenv.mkDerivation (rec {
+  let
+    atLeast = lib.versionAtLeast version;
+
+    # Build with ICU by default on versions that support it
+    icuEnabled = atLeast "10";
+  in stdenv.mkDerivation (rec {
     name = "postgresql-${version}";
     inherit version;
 
@@ -17,9 +22,12 @@ let
 
     buildInputs =
       [ zlib readline openssl libxml2 makeWrapper ]
+      ++ lib.optionals icuEnabled [ icu ]
       ++ lib.optionals (atLeast "9.6" && !stdenv.isDarwin) [ systemd ]
       ++ lib.optionals (!stdenv.isDarwin) [ libossp_uuid ];
 
+    nativeBuildInputs = lib.optionals icuEnabled [ pkgconfig ];
+
     enableParallelBuilding = !stdenv.isDarwin;
 
     makeFlags = [ "world" ];
@@ -37,7 +45,7 @@ let
       "--with-system-tzdata=${tzdata}/share/zoneinfo"
       (lib.optionalString (atLeast "9.6" && !stdenv.isDarwin) "--with-systemd")
       (if stdenv.isDarwin then "--with-uuid=e2fs" else "--with-ossp-uuid")
-    ];
+    ] ++ lib.optionals icuEnabled [ "--with-icu" ];
 
     patches =
       [ (if atLeast "9.4" then ./disable-resolve_symlinks-94.patch else ./disable-resolve_symlinks.patch)