[RFC] add ability to merge structured configs

lib/kernel.nix

@@ -1,57 +1,21 @@
-{ lib
-# we pass the kernel version here to keep a nice syntax `whenOlder "4.13"`
-# kernelVersion, e.g., config.boot.kernelPackages.version
-, version
-, mkValuePreprocess ? null
-}:
+{ lib, version }:
 
 with lib;
 rec {
-  # Common patterns
-  when        = cond: opt: if cond then opt else null;
-  whenAtLeast = ver: when (versionAtLeast version ver);
-  whenOlder   = ver: when (versionOlder version ver);
-  whenBetween = verLow: verHigh: when (versionAtLeast version verLow && versionOlder version verHigh);
+  # Common patterns/legacy
+  whenAtLeast = ver: mkIf (versionAtLeast version ver);
+  whenOlder   = ver: mkIf (versionOlder version ver);
+  # range is (inclusive, exclusive)
+  whenBetween = verLow: verHigh: mkIf (versionAtLeast version verLow && versionOlder version verHigh);
 
-  # Keeping these around in case we decide to change this horrible implementation :)
-  option = x: if x == null then null else "?${x}";
-  yes    = "y";
-  no     = "n";
-  module = "m";
 
-  mkValue = val:
-  let
-    isNumber = c: elem c ["0" "1" "2" "3" "4" "5" "6" "7" "8" "9"];
-  in
-    if val == "" then "\"\""
-    else if val == yes || val == module || val == no then val
-    else if all isNumber (stringToCharacters val) then val
-    else if substring 0 2 val == "0x" then val
-    else val; # FIXME: fix quoting one day
+  # Keeping these around in case we decide to change this horrible implementation :)
+  option = x:
+      x // { optional = true; };
 
+  yes      = { tristate    = "y"; };
+  no       = { tristate    = "n"; };
+  module   = { tristate    = "m"; };
+  freeform = x: { freeform = x; };
 
-  # generate nix intermediate kernel config file of the form
-  #
-  #       VIRTIO_MMIO m
-  #       VIRTIO_BLK y
-  #       VIRTIO_CONSOLE n
-  #       NET_9P_VIRTIO? y
-  #
-  # Use mkValuePreprocess to preprocess option values, aka mark 'modules' as
-  # 'yes' or vice-versa
-  # Borrowed from copumpkin https://github.com/NixOS/nixpkgs/pull/12158
-  # returns a string, expr should be an attribute set
-  generateNixKConf = exprs: mkValuePreprocess:
-  let
-    mkConfigLine = key: rawval:
-    let
-      val = if builtins.isFunction mkValuePreprocess then mkValuePreprocess rawval else rawval;
-    in
-      if val == null
-        then ""
-        else if hasPrefix "?" val
-          then "${key}? ${mkValue (removePrefix "?" val)}\n"
-          else "${key} ${mkValue val}\n";
-    mkConf = cfg: concatStrings (mapAttrsToList mkConfigLine cfg);
-  in mkConf exprs;
 }

nixos/modules/system/boot/kernel_config.nix

@@ -0,0 +1,137 @@
+{ lib, config, ... }:
+
+with lib;
+let
+  findWinner = candidates: winner:
+    any (x: x == winner) candidates;
+
+  # winners is an ordered list where first item wins over 2nd etc
+  mergeAnswer = winners: locs: defs:
+    let
+      values = map (x: x.value) defs;
+      freeformAnswer = intersectLists values winners;
+      inter = intersectLists values winners;
+      winner = head winners;
+    in
+    if defs == [] then abort "This case should never happen."
+    else if winner == [] then abort "Give a valid list of winner"
+    else if inter == [] then mergeOneOption locs defs
+    else if findWinner values winner then
+      winner
+    else
+      mergeAnswer (tail winners) locs defs;
+
+  mergeFalseByDefault = locs: defs:
+    if defs == [] then abort "This case should never happen."
+    else if any (x: x == false) defs then false
+    else true;
+
+  kernelItem = types.submodule {
+    options = {
+      tristate = mkOption {
+        type = types.enum [ "y" "m" "n" null ] // {
+          merge = mergeAnswer [ "y" "m" "n" ];
+        };
+        default = null;
+        internal = true;
+        visible = true;
+        description = ''
+          Use this field for tristate kernel options expecting a "y" or "m" or "n".
+        '';
+      };
+
+      freeform = mkOption {
+        type = types.nullOr types.str // {
+          merge = mergeEqualOption;
+        };
+        default = null;
+        example = ''MMC_BLOCK_MINORS.freeform = "32";'';
+        description = ''
+          Freeform description of a kernel configuration item value.
+        '';
+      };
+
+      optional = mkOption {
+        type = types.bool // { merge = mergeFalseByDefault; };
+        default = false;
+        description = ''
+          Wether option should generate a failure when unused.
+        '';
+      };
+    };
+  };
+
+  mkValue = with lib; val:
+  let
+    isNumber = c: elem c ["0" "1" "2" "3" "4" "5" "6" "7" "8" "9"];
+
+  in
+    if (val == "") then "\"\""
+    else if val == "y" || val == "m" || val == "n" then val
+    else if all isNumber (stringToCharacters val) then val
+    else if substring 0 2 val == "0x" then val
+    else val; # FIXME: fix quoting one day
+
+
+  # generate nix intermediate kernel config file of the form
+  #
+  #       VIRTIO_MMIO m
+  #       VIRTIO_BLK y
+  #       VIRTIO_CONSOLE n
+  #       NET_9P_VIRTIO? y
+  #
+  # Borrowed from copumpkin https://github.com/NixOS/nixpkgs/pull/12158
+  # returns a string, expr should be an attribute set
+  # Use mkValuePreprocess to preprocess option values, aka mark 'modules' as 'yes' or vice-versa
+  # use the identity if you don't want to override the configured values
+  generateNixKConf = exprs:
+  let
+    mkConfigLine = key: item:
+      let
+        val = if item.freeform != null then item.freeform else item.tristate;
+      in
+        if val == null
+          then ""
+          else if (item.optional)
+            then "${key}? ${mkValue val}\n"
+            else "${key} ${mkValue val}\n";
+
+    mkConf = cfg: concatStrings (mapAttrsToList mkConfigLine cfg);
+  in mkConf exprs;
+
+in
+{
+
+  options = {
+
+    intermediateNixConfig = mkOption {
+      readOnly = true;
+      type = types.lines;
+      example = ''
+        USB? y
+        DEBUG n
+      '';
+      description = ''
+        The result of converting the structured kernel configuration in settings
+        to an intermediate string that can be parsed by generate-config.pl to
+        answer the kernel `make defconfig`.
+      '';
+    };
+
+    settings = mkOption {
+      type = types.attrsOf kernelItem;
+      example = literalExample '' with lib.kernel; {
+        "9P_NET" = yes;
+        USB = optional yes;
+        MMC_BLOCK_MINORS = freeform "32";
+      }'';
+      description = ''
+        Structured kernel configuration.
+      '';
+    };
+  };
+
+  config = {
+    intermediateNixConfig = generateNixKConf config.settings;
+  };
+}