packages: rework package set organisation

make package set self referential

collapse redundant files for package plumbing

rework packages overlay and simplify scope

update altiosevka font

make altiosevka an overlay instead

note

invert package logic

scope overlay

unify package overlay logic

fix overlay reference

nix/overlays/iosevka.nix

@@ -0,0 +1,95 @@
+final: prev: rec {
+  nerd-fonts = let
+    mkNerdFont = final.callPackage ../lib/mkNerdFont.nix {};
+  in
+    prev.nerd-fonts
+    // {
+      iosevka = mkNerdFont {
+        font = iosevka;
+        extraArgs = [
+          "--name {/.}-NFM"
+          "--use-single-width-glyphs"
+        ];
+      };
+    };
+
+  iosevka = prev.iosevka.override {
+    set = "custom";
+    /*
+    Guide: https://github.com/be5invis/Iosevka/blob/main/doc/custom-build.md
+
+    Use `term` spacing to avoid dashed arrow issue
+    https://github.com/ryanoasis/nerd-fonts/issues/1018
+    */
+    privateBuildPlan = {
+      family = "Iosevka";
+      noLigation = true;
+      serifs = "sans";
+      spacing = "term";
+
+      variants = {
+        design = {
+          ampersand = "et-tailed";
+          capital-q = "crossing";
+          capital-z = "straight-serifless-with-crossbar";
+          cent = "open";
+          dollar = "open";
+          lig-double-arrow-bar = "with-notch";
+          lig-equal-chain = "with-notch";
+          lig-hyphen-chain = "with-notch";
+          lig-plus-chain = "with-notch";
+          lig-single-arrow-bar = "with-notch";
+          lower-lambda = "tailed-turn";
+          number-sign = "slanted";
+          percent = "rings-continuous-slash-also-connected";
+          seven = "straight-serifless-crossbar";
+        };
+        italic = {
+          v = "cursive-serifless";
+          w = "cursive-serifless";
+        };
+      };
+
+      weights = {
+        Bold = {
+          shape = 680;
+          menu = 680;
+          css = 680;
+        };
+        Regular = {
+          shape = 480;
+          menu = 480;
+          css = 480;
+        };
+      };
+
+      widths = {
+        Extended = {
+          shape = 600;
+          menu = 7;
+          css = "expanded";
+        };
+        Normal = {
+          shape = 500;
+          menu = 5;
+          css = "normal";
+        };
+      };
+
+      slopes = {
+        Upright = {
+          angle = 0;
+          css = "normal";
+          menu = "upright";
+          shape = "upright";
+        };
+        Italic = {
+          angle = 9.4;
+          shape = "italic";
+          menu = "italic";
+          css = "italic";
+        };
+      };
+    };
+  };
+}