nixpkgs: Add NerdFont-patched Iosevka (called Imposevka)

Patching script from ryanoasis/nerd-fonts#83 (comment)

.nixpkgs/config.nix

@@ -9,5 +9,7 @@
     otfcc = callPackage ./pkgs/otfcc/default.nix {};
 
     iosevka = callPackage ./pkgs/iosevka/default.nix {};
+
+    imposevka = callPackage ./pkgs/iosevka/imposevka.nix {};
   };
 }

.nixpkgs/pkgs/iosevka/imposevka-patcher/makefile

@@ -0,0 +1,18 @@
+SRCFILES=$(shell ls src/)
+SOURCES=$(addprefix src/,$(SRCFILES))
+TARGETS=$(addprefix dst/,$(subst iosevka-,imposevka-,$(SRCFILES)))
+SOURCE_OTDS=$(addprefix tmp/,$(subst .ttf,.otd,$(SRCFILES)))
+TARGET_OTDS=$(addprefix tmp/,$(subst iosevka-,imposevka-,$(subst .ttf,.otd,$(SRCFILES))))
+
+all : $(TARGETS)
+
+tmp/nerd.otd : nerd.ttf
+	otfccdump $< -o $@ --glyph-name-prefix .2. --ignore-hints
+
+$(TARGETS) : dst/imposevka-%.ttf : tmp/imposevka-%.otd
+	@otfccbuild $< -o $@ --keep-average-char-width --ship
+	@echo Patched $@
+$(TARGET_OTDS) : tmp/imposevka-%.otd : merge.js tmp/iosevka-%.otd tmp/nerd.otd
+	@node $^ $@
+$(SOURCE_OTDS) : tmp/iosevka-%.otd : src/iosevka-%.ttf
+	@otfccdump $< -o $@ --glyph-name-prefix .1.

.nixpkgs/pkgs/iosevka/imposevka-patcher/merge.js

@@ -0,0 +1,13 @@
+var fs = require('fs');
+var orig = JSON.parse(fs.readFileSync(process.argv[2], 'utf-8'));
+var patch = JSON.parse(fs.readFileSync(process.argv[3], 'utf-8'));
+for(var k in patch.cmap) {
+	if(!orig.cmap[k]) { orig.cmap[k] = patch.cmap[k] }
+}
+for(var k in patch.glyf) {
+	if(!orig.glyf[k]) { orig.glyf[k] = patch.glyf[k] }
+}
+for(var j = 0; j < orig.name.length; j++){
+	orig.name[j].nameString = orig.name[j].nameString.replace(/Iosevka/g, 'Imposevka');
+}
+fs.writeFileSync(process.argv[4], JSON.stringify(orig))

.nixpkgs/pkgs/iosevka/imposevka.nix

@@ -0,0 +1,33 @@
+{ stdenv, otfcc, iosevka, nodejs-6_x }:
+
+stdenv.mkDerivation rec {
+  name = "imposevka-${iosevka.version}";
+
+  src = ./imposevka-patcher;
+
+  nativeBuildInputs = [ otfcc nodejs-6_x ];
+
+  buildPhase = ''
+    mkdir src
+    mkdir dst
+    mkdir tmp
+
+    cp -v ${iosevka}/share/fonts/truetype/iosevka-* src/
+    make
+  '';
+
+  installPhase = ''
+    fontdir=$out/share/fonts/truetype
+    mkdir -p $fontdir
+    cp -v dst/* $fontdir
+  '';
+
+  meta = with stdenv.lib; {
+    homepage = "https://github.com/ryanoasis/nerd-fonts";
+    description = ''
+      NerdFont patched Iosevka
+    '';
+    platforms = platforms.all;
+    maintainers = [ maintainers.fmthoma ];
+  };
+}