experimental/multiple-versions-in-one-file

pkgs/lib/misc.nix

@@ -315,6 +315,48 @@ rec {
       )
     ];
   mergeAttrsByFuncDefaults = foldl mergeAttrByFunc { inherit mergeAttrBy; };
+  mergeAttrsByFuncDefaultsClean = list: removeAttrs (mergeAttrsByFuncDefaults list) ["mergeAttrBy"];
+
+  # merge attrs based on version key into mkDerivation args, see mergeAttrBy to learn about smart merge defaults
+  #
+  # This function is best explained by an example:
+  #
+  #     {version ? "2.x"} :
+  #
+  #     mkDerivation (mergeAttrsByVersion "package-name" version 
+  #       { # version specific settings
+  #         "git" = { src = ..; preConfigre = "autogen.sh"; buildInputs = [automake autoconf libtool];  };
+  #         "2.x" = { src = ..; };
+  #       }
+  #       {  // shared settings
+  #          buildInputs = [ common build inputs ];
+  #          meta = { .. }
+  #       }
+  #     )
+  #
+  # Please note that e.g. Eelco Dolstra usually prefers having one file for
+  # each version. On the other hand there are valuable additional design goals
+  #  - readability
+  #  - do it once only
+  #  - try to avoid duplication
+  #
+  # Marc Weber and Michael Raskin sometimes prefer keeping older
+  # versions around for testing and regression tests - as long as its cheap to
+  # do so.
+  #
+  # Very often it just happens that the "shared" code is the bigger part.
+  # Then using this function might be appropriate.
+  #
+  # Be aware that its easy to cause recompilations in all versions when using
+  # this function - also if derivations get too complex splitting into multiple
+  # files is the way to go.
+  #
+  # See misc.nix -> versionedDerivation
+  # discussion: nixpkgs: pull/310
+  mergeAttrsByVersion = name: version: attrsByVersion: base:
+    mergeAttrsByFuncDefaultsClean [ { name = "${name}-${version}"; } base (maybeAttr version (throw "bad version ${version} for ${name}") attrsByVersion)];
+
+
   # sane defaults (same name as attr name so that inherit can be used)
   mergeAttrBy = # { buildInputs = concatList; [...]; passthru = mergeAttr; [..]; }
     listToAttrs (map (n : nameValuePair n lib.concat) [ "buildNativeInputs" "buildInputs" "propagatedBuildInputs" "configureFlags" "prePhases" "postAll" ])

pkgs/misc/misc.nix

@@ -6,6 +6,10 @@ in
 
 {
 
+  # description see mergeAttrsByVersion in lib/misc.nix
+  versionedDerivation = name: version: attrsByVersion: base:
+    pkgs.stdenv.mkDerivation (stdenv.lib.mergeAttrsByVersion name version attrsByVersion base);
+
   /*
     Usage example creating a derivation installing ruby, sup and a lib:
 

pkgs/top-level/all-packages.nix

@@ -176,6 +176,7 @@ let
   inherit lib config stdenvAdapters;
 
   inherit (lib) lowPrio hiPrio appendToName makeOverridable;
+  inherit (misc) versionedDerivation;
 
   # Applying this to an attribute set will cause nix-env to look
   # inside the set for derivations.