Refactor scripts (#2465)

* Refactor all kinds of scripts

* Update docs to ensure linter passes

scripts/_upstream.js

@@ -0,0 +1,37 @@
+/* eslint-disable no-process-exit */
+"use strict"
+
+const {execFileSync} = require("child_process")
+
+const remoteInfo = execFileSync("git", ["remote", "-v"], {
+	windowsHide: true,
+	stdio: ["inherit", "pipe", "inherit"],
+	encoding: "utf-8",
+}).trim().split(/\r\n?|\n/g)
+
+function find(type) {
+	const regexp = new RegExp(
+		"\t(?:" +
+		"(?:(?:git+)?https?|git|ssh)://(?:[^@\\s]+@)?github\\.com/|" +
+		"git@github\\.com:" +
+		")" +
+		`MithrilJS/mithril\\.js\\.git \\(${type}\\)$`
+	)
+
+	const line = remoteInfo.find((line) => regexp.test(line))
+
+	if (line == null) {
+		console.error(
+			"An upstream must be configured with both fetch and push!"
+		)
+		process.exit(1)
+	}
+
+	return {
+		branch: line.slice(0, line.indexOf("\t")),
+		repo: line.slice(line.lastIndexOf("\t") + 1, -(type.length + 3)),
+	}
+}
+
+exports.fetch = find("fetch")
+exports.push = find("push")