m4: build offline documentation

pkgs/development/tools/misc/gnum4/default.nix

@@ -1,4 +1,4 @@
-{ lib, stdenv, fetchurl }:
+{ lib, stdenv, fetchurl, texinfo4 }:
 
 # Note: this package is used for bootstrapping fetchurl, and thus
 # cannot use fetchpatch! All mutable patches (generated by GitHub or
@@ -8,6 +8,9 @@
 stdenv.mkDerivation rec {
   pname = "gnum4";
   version = "1.4.19";
+  outputs = [ "out" "doc" ];
+
+  nativeBuildInputs = [ texinfo4 ];
 
   src = fetchurl {
     url = "mirror://gnu/m4/m4-${version}.tar.bz2";
@@ -22,6 +25,15 @@ stdenv.mkDerivation rec {
   configureFlags = [ "--with-syscmd-shell=${stdenv.shell}" ]
     ++ lib.optional stdenv.hostPlatform.isMinGW "CFLAGS=-fno-stack-protector";
 
+  postBuild = ''
+    makeinfo --html --no-split doc/m4.texi
+  '';
+
+  postInstall = ''
+    mkdir -p $doc/share/doc/m4
+    cp ./m4.html $doc/share/doc/m4
+  '';
+
   meta = {
     description = "GNU M4, a macro processor";
     longDescription = ''