libxml2: Refactor and fix library propagation

pkgs/development/libraries/libxml2/default.nix

@@ -1,49 +1,63 @@
-{ stdenv, fetchurl, zlib, xz, python ? null, pythonSupport ? true, findXMLCatalogs }:
+{ stdenv, fetchurl, findXMLCatalogs
 
-assert pythonSupport -> python != null;
+# Optional Dependencies
+, icu ? null, python ? null, readline ? null, zlib ? null, xz ? null
+}:
 
 #TODO: share most stuff between python and non-python builds, perhaps via multiple-output
 
 let
-  version = "2.9.2";
-in
+  mkFlag = trueStr: falseStr: cond: name: val:
+    if cond == null then null else
+      "--${if cond != false then trueStr else falseStr}${name}${if val != null && cond != false then "=${val}" else ""}";
+  mkEnable = mkFlag "enable-" "disable-";
+  mkWith = mkFlag "with-" "without-";
+  mkOther = mkFlag "" "" true;
 
-stdenv.mkDerivation (rec {
+  shouldUsePkg = pkg: if pkg != null && stdenv.lib.any (x: x == stdenv.system) pkg.meta.platforms then pkg else null;
+
+  optIcu = shouldUsePkg icu;
+  optPython = shouldUsePkg python;
+  optReadline = shouldUsePkg readline;
+  optZlib = shouldUsePkg zlib;
+  optXz = shouldUsePkg xz;
+
+  sitePackages = if optPython == null then null else
+    "\${out}/lib/${python.libPrefix}/site-packages";
+in
+stdenv.mkDerivation rec {
   name = "libxml2-${version}";
+  version = "2.9.2";
 
   src = fetchurl {
     url = "http://xmlsoft.org/sources/${name}.tar.gz";
     sha256 = "1g6mf03xcabmk5ing1lwqmasr803616gb2xhn7pll10x2l5w6y2i";
   };
 
-  buildInputs = stdenv.lib.optional pythonSupport python
-    # Libxml2 has an optional dependency on liblzma.  However, on impure
-    # platforms, it may end up using that from /usr/lib, and thus lack a
-    # RUNPATH for that, leading to undefined references for its users.
-    ++ (stdenv.lib.optional stdenv.isFreeBSD xz);
+  buildInputs = [ optIcu optPython optReadline optZlib optXz ];
+  propagatedBuildInputs = [ findXMLCatalogs ];
 
-  propagatedBuildInputs = [ zlib findXMLCatalogs ];
-
-  passthru = { inherit pythonSupport version; };
+  configureFlags = [
+    (mkWith (optIcu != null)      "icu"                optIcu)
+    (mkWith (optPython != null)   "python"             optPython)
+    (mkWith (optPython != null)   "python-install-dir" sitePackages)
+    (mkWith (optReadline != null) "readline"           optReadline)
+    (mkWith (optZlib != null)     "zlib"               optZlib)
+    (mkWith (optXz != null)       "lzma"               optXz)
+  ];
 
   enableParallelBuilding = true;
 
-  meta = {
+  meta = with stdenv.lib; {
     homepage = http://xmlsoft.org/;
     description = "An XML parsing library for C";
-    license = "bsd";
-    platforms = stdenv.lib.platforms.unix;
-    maintainers = [ stdenv.lib.maintainers.eelco ];
+    license = licenses.mit;
+    platforms = platforms.unix;
+    maintainers = with maintainers; [ eelco wkennington ];
   };
 
-} // stdenv.lib.optionalAttrs pythonSupport {
-  configureFlags = "--with-python=${python}";
-
-  # this is a pair of ugly hacks to make python stuff install into the right place
-  preInstall = ''substituteInPlace python/libxml2mod.la --replace "${python}" "$out"'';
-  installFlags = ''pythondir="$(out)/lib/${python.libPrefix}/site-packages"'';
-
-} // stdenv.lib.optionalAttrs (!pythonSupport) {
-  configureFlags = "--with-python=no"; # otherwise build impurity bites us
-})
-
+  passthru = {
+    inherit version;
+    pythonSupport = python != null;
+  };
+}

pkgs/top-level/all-packages.nix

@@ -6996,11 +6996,11 @@ let
   libxmi = callPackage ../development/libraries/libxmi { };
 
   libxml2 = callPackage ../development/libraries/libxml2 {
-    pythonSupport = false;
+    python = null;
   };
 
   libxml2Python = lowPrio (libxml2.override {
-    pythonSupport = true;
+    inherit python;
   });
 
   libxmlxx = callPackage ../development/libraries/libxmlxx { };