deno: add updateScript for automatic updates

This'll save time and avoid human error.
Wrote in deno typescript because why not.

pkgs/development/web/deno/update/src.ts

@@ -0,0 +1,67 @@
+import {
+  genValueRegExp,
+  logger,
+  nixPrefetch,
+  read,
+  sha256RegExp,
+  versionRegExp,
+  write,
+} from "./common.ts";
+
+interface Replacer {
+  regex: RegExp;
+  value: string;
+}
+
+const log = logger("src");
+
+const prefetchSha256 = (nixpkgs: string, version: string) =>
+  nixPrefetch(["-f", nixpkgs, "deno.src", "--rev", version]);
+const prefetchCargoSha256 = (nixpkgs: string) =>
+  nixPrefetch(
+    [`{ sha256 }: (import ${nixpkgs} {}).deno.cargoDeps.overrideAttrs (_: { outputHash = sha256; })`],
+  );
+
+const replace = (str: string, replacers: Replacer[]) =>
+  replacers.reduce(
+    (str, r) => str.replace(r.regex, r.value),
+    str,
+  );
+
+const updateNix = (filePath: string, replacers: Replacer[]) =>
+  read(filePath).then((str) => write(filePath, replace(str, replacers)));
+
+const genVerReplacer = (k: string, value: string): Replacer => (
+  { regex: genValueRegExp(k, versionRegExp), value }
+);
+const genShaReplacer = (k: string, value: string): Replacer => (
+  { regex: genValueRegExp(k, sha256RegExp), value }
+);
+
+export async function updateSrc(
+  filePath: string,
+  nixpkgs: string,
+  denoVersion: string,
+) {
+  log("Starting src update");
+  const trimVersion = denoVersion.substr(1);
+  log("Fetching sha256 for:", trimVersion);
+  const sha256 = await prefetchSha256(nixpkgs, denoVersion);
+  log("sha256 to update:", sha256);
+  await updateNix(
+    filePath,
+    [
+      genVerReplacer("version", trimVersion),
+      genShaReplacer("sha256", sha256),
+      genShaReplacer("cargoSha256", ""), // Empty ready for prefetchCargoSha256
+    ],
+  );
+  log("Fetching cargoSha256 for:", sha256);
+  const cargoSha256 = await prefetchCargoSha256(nixpkgs);
+  log("cargoSha256 to update:", cargoSha256);
+  await updateNix(
+    filePath,
+    [genShaReplacer("cargoSha256", cargoSha256)],
+  );
+  log("Finished src update");
+}