webstrand

A Method for Imposing Arbitrary Parameter Constraints at Function Call Sites

Without assistance, the only thing TypeScript can prove about an argument is that it is a subtype of the parameter's annotation. Given a function (x: `foo${string}`) => void, the compiler will prove for all call sites that x is always a subtype of `foo${string}` and never an unrelated type. But it cannot prove properties outside of subtyping. It cannot directly prove that a string is exactly 6 characters long, that a string contains no spaces, that a type is non-union, or that a type satisfies many other useful properties.

The technique described here, which I call the type-validator pattern, allows us to teach the compiler to prove arbitrary properties about an argument's type at each call site, rejecting the call site if they do not hold.

An Example

Consider a simple event subscription system. Users subscribe to events by passing a dictionary of event handlers to a subscribe function. The set of valid event

Git Namespace Vendoring

A method for vendoring git dependencies into the host repository using git namespaces, so that installation from git remotes resolves using the local git namespaces rather than over the network. This makes installs faster, eliminates dependency on upstream availability, protects against remote force-pushes rewriting history, and protects against link rot rendering a package unbuildable.

The Technique

Git namespaces allow us to treat a prefix under refs/namespaces/<n> as a remote repository root. This enables us to mirror a foreign repository into that prefix on our local repository: head, branches, tags, notes, replacements, and any other refs the remote exposes. The underlying objects (commits, trees, blobs) are deduplicated into the shared object store. Git invoked via git --namespace=<ns> or GIT_NAMESPACE=<ns> treats refs/namespaces/<ns>/ as the ref root for operations against remote URLs.

By configuring git's url.*.insteadOf rules to rewrite a git dependency's re

	#!/bin/bash

	load-environ() {
	local -
	set -euo pipefail

	if [[ "${1:-}" == "--help" \|\| "${1:-}" == "-h" \|\| -z "${1:-}" ]]; then
	cat <<'EOF'
	load-environ — import variables from an environ(7) file

	#!/bin/bash
	set -euo pipefail

	if [ $# -eq 0 ]; then
	echo "Usage: $(basename "$0") <command> [args...]" >&2
	exit 1
	fi

	# ── Read-only paths to expose under $HOME ──
	# Add or remove entries as needed

	// 3D Dom viewer, copy-paste this into your console to visualise the DOM as a stack of solid blocks.
	// You can also minify and save it as a bookmarklet (https://www.freecodecamp.org/news/what-are-bookmarklets/)
	(() => {
	const SHOW_SIDES = false; // color sides of DOM nodes?
	const COLOR_SURFACE = true; // color tops of DOM nodes?
	const COLOR_RANDOM = false; // randomise color?
	const COLOR_HUE = 190; // hue in HSL (https://hslpicker.com)
	const MAX_ROTATION = 180; // set to 360 to rotate all the way round
	const THICKNESS = 20; // thickness of layers
	const DISTANCE = 10000; // ¯\\_(ツ)_/¯

	#!/usr/bin/env -S cargo +nightly -Z script
	---
	edition = "2024"
	[dependencies]
	tempfile = "3"
	thiserror = "1"
	reflink-copy = "0.1"
	chrono = "0.4"
	---

	[NetDev]
	Name=wg0
	Kind=wireguard

	[WireGuard]
	PrivateKey=[snip]
	RouteMetric=1000
	# Table and fwmark are arbitrary
	RouteTable=73547
	FirewallMark=0x11f4b

	import { type Plugin } from "vite";
	import { default as parseBasicAuth, type BasicAuthResult } from "basic-auth";
	import { createHash, timingSafeEqual, randomBytes } from "node:crypto";
	import { type IncomingMessage } from "node:http";

	const HASH_FUNCTION = "sha256";
	const HASH_SIZE = createHash(HASH_FUNCTION).digest().length;
	const SALT_SIZE = 16;

	export type HashedPassword = readonly [hash: Buffer, salt: Buffer];

	class Multimap<K, V> {
	#buckets = new Map<K, Map<V, readonly [K, V]>>();
	#order = new Set<readonly [K, V]>();
	constructor(from?: Iterable<readonly [K, V]> \| null) {
	if(from != null) for(const { 0: key, 1: value } of from) {
	this.add(key, value);
	}
	}

	static fromHeaders<K, V>(headers: Iterable<{name: K, value: V}>) {

	#!/usr/bin/env -S cargo +nightly -Zscript

	---cargo
	[dependencies]
	futures = "0.3.31"
	input-linux = { version = "0.7.1", features = ["codec", "tokio-util-0_7"] }
	tokio = { version = "1.46.1", features = ["full"] }
	tokio-util = { version = "0.7.15", features = ["full"] }
	---