feat(wpcarro/emacs): Package string.el

Mostly just a wrapper around s.el (for now?). Eventually I'd like to prune the
dependency on dash.el (and maybe s.el).

Change-Id: I5c2ba256524bedd93fcd13933fdbd95b1ddff6f8
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6002
Reviewed-by: wpcarro <wpcarro@gmail.com>
Autosubmit: wpcarro <wpcarro@gmail.com>
Tested-by: BuildkiteCI

users/wpcarro/emacs/pkgs/string/default.nix

@@ -0,0 +1,27 @@
+{ pkgs, depot, ... }:
+
+let
+  string = pkgs.callPackage
+    ({ emacsPackages }:
+      emacsPackages.trivialBuild {
+        pname = "string";
+        version = "1.0.0";
+        src = ./string.el;
+        packageRequires = [
+          emacsPackages.dash
+          emacsPackages.s
+        ];
+      })
+    { };
+
+  emacs = (pkgs.emacsPackagesFor pkgs.emacs28).emacsWithPackages (epkgs: [
+    string
+  ]);
+in
+string.overrideAttrs (_old: {
+  doCheck = true;
+  checkPhase = ''
+    ${emacs}/bin/emacs -batch \
+      -l ert -l ${./tests.el} -f ert-run-tests-batch-and-exit
+  '';
+})