boot/script-loader: Add mruby-lvgui-native-fragment

boot/script-loader/mruby-lvgui-native-fragment/README.adoc

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+= mruby-lvgui-native-fragment
+
+This is glue code to build the mruby interpreter with the proper libraries.
+
+The actual library parts are found under /boot/lib/

boot/script-loader/mruby-lvgui-native-fragment/default.nix

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+{ mrbgems
+, callPackage
+, fetchFromGitHub
+, pkg-config
+, buildPackages
+
+# Configuration
+, withSimulator ? false
+}:
+let
+  # This is an implementation detail of this gem.
+  # Even if unusual, let's keep it private.
+  lvgui = (callPackage ./lvgui.nix {
+    inherit withSimulator;
+  });
+in
+mrbgems.mkGem {
+  # Dirty since `default.nix` and `lvgui.nix` modifications will
+  # needlessly cause a rebuild, but good enough in reality.
+  src = ./.;
+
+  gemBuildInputs = [
+    lvgui
+  ] ++ lvgui.buildInputs;
+  gemNativeBuildInputs = [
+    buildPackages.pkg-config
+  ];
+
+  requiredGems = with mrbgems; [
+    mruby-fiddle
+  ];
+}

boot/script-loader/mruby-lvgui-native-fragment/lvgui.nix

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+{ stdenv
+, pkgs
+, lib
+, fetchFromGitHub
+, pkg-config
+, SDL2
+, withSimulator ? false
+}:
+
+let
+  inherit (lib) optional optionals optionalString;
+  simulatorDeps = [
+    SDL2
+  ];
+
+  # Allow libevdev to cross-compile.
+  libevdev = (pkgs.libevdev.override({
+    python3 = null;
+  })).overrideAttrs({nativeBuildsInputs ? [], ...}: {
+    nativeBuildInputs = nativeBuildsInputs ++ [
+      pkgs.buildPackages.python3
+    ];
+  });
+  libxkbcommon = pkgs.callPackage (
+    { stdenv                                             
+    , libxkbcommon                             
+    , meson             
+    , ninja                                         
+    , pkgconfig               
+    , yacc                              
+    }:                            
+
+    libxkbcommon.overrideAttrs({...}: {
+      nativeBuildInputs = [ meson ninja pkgconfig yacc ];
+      buildInputs = [ ];                                     
+
+      mesonFlags = [   
+        "-Denable-wayland=false"
+        "-Denable-x11=false"             
+        "-Denable-docs=false"            
+
+        # This is because we're forcing uses of this build
+        # to define config and locale root; for stage-1 use.
+        # In stage-2, use the regular xkbcommon lib.
+        "-Dxkb-config-root=/NEEDS/OVERRIDE/etc/X11/xkb"
+        "-Dx-locale-root=/NEEDS/OVERRIDE/share/X11/locale"
+      ];
+
+      outputs = [ "out" "dev" ];
+
+      # Ensures we don't get any stray dependencies.
+      allowedReferences = [
+        "out"
+        "dev"
+        stdenv.cc.libc_lib
+      ];
+    })
+
+  ) {};
+
+in
+  stdenv.mkDerivation {
+    pname = "lvgui";
+    version = "2020-11-20";
+
+    src = fetchFromGitHub {
+      repo = "lvgui";
+      owner = "mobile-nixos";
+      rev = "c94c3916012f5615af027389e77e7a974cc3e634";
+      sha256 = "16dfdky5v72jqs9v22h1k73g74bnif6fg52vhxw2k8sh6mw1cmzp";
+    };
+
+    # Document `LVGL_ENV_SIMULATOR` in the built headers.
+    # This allows the mrbgem to know about it.
+    # (In reality this should be part of a ./configure step or something similar.)
+    postPatch = ''
+      sed -i"" '/^#define LV_CONF_H/a #define LVGL_ENV_SIMULATOR ${if withSimulator then "1" else "0"}' lv_conf.h
+    '';
+
+    nativeBuildInputs = [
+      pkg-config
+    ];
+
+    buildInputs = [
+      libevdev
+      libxkbcommon
+    ]
+    ++ optionals withSimulator simulatorDeps
+    ;
+
+    NIX_CFLAGS_COMPILE = [
+      "-DX_DISPLAY_MISSING"
+    ];
+
+    makeFlags = [
+      "PREFIX=${placeholder "out"}"
+    ]
+    ++ optional withSimulator "LVGL_ENV_SIMULATOR=1"
+    ++ optional (!withSimulator) "LVGL_ENV_SIMULATOR=0"
+    ;
+
+    enableParallelBuilding = true;
+  }

boot/script-loader/mruby-lvgui-native-fragment/mrbgem.rake

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+MRuby::Gem::Specification.new("mruby-lvgui-native-fragment") do |spec|
+  spec.license = "MIT"
+  spec.authors = "Samuel Dionne-Riel"
+  spec.version = "0.0.1"
+
+  # Ensures `lvgui` is built into the mruby interpreter.
+  spec.cc.include_paths << `pkg-config --cflags lvgui`.chomp
+  spec.linker.flags_after_libraries << `pkg-config --libs lvgui`.chomp
+
+  # Also declare dependencies properly here.
+  spec.add_dependency('mruby-fiddle')
+
+  spec.rbfiles = [
+    # Left empty by design, look under boot/lib
+  ]
+end