watchman: new package

This adds `watchman`, a CLI utility that watches files and takes action when
they change.

pkgs/development/tools/watchman/default.nix

@@ -0,0 +1,35 @@
+{ stdenv, lib, config, fetchFromGitHub, autoconf, automake, pcre
+, confFile ? config.watchman.confFile or null
+}:
+
+stdenv.mkDerivation rec {
+  name = "watchman-${version}";
+
+  version = "2.9.8";
+
+  src = fetchFromGitHub {
+    owner = "facebook";
+    repo = "watchman";
+    rev = "v${version}";
+    sha256 = "196d71ci7ki4p6xx49w55cqd0bqrx19nf79na3a91mrfa6f22sp6";
+  };
+
+  buildInputs = [ autoconf automake pcre ];
+
+  configureFlags = [
+      "--enable-conffile=${if confFile == null then "no" else confFile}"
+      "--with-pcre=yes"
+  ];
+
+  preConfigure = ''
+    ./autogen.sh
+  '';
+
+  meta = with lib; {
+    description = "Watches files and takes action when they change";
+    homepage    = https://facebook.github.io/watchman;
+    maintainers = with maintainers; [ cstrahan ];
+    platforms   = with platforms; linux ++ darwin;
+    license     = licenses.asl20;
+  };
+}

pkgs/top-level/all-packages.nix

@@ -2254,6 +2254,8 @@ let
 
   wal_e = callPackage ../tools/backup/wal-e { };
 
+  watchman = callPackage ../development/tools/watchman { };
+
   wbox = callPackage ../tools/networking/wbox {};
 
   welkin = callPackage ../tools/graphics/welkin {};