Make Camino examples and scaffolds complete Yarn and Nix packages

src/capability-language/component-nix.ts

@@ -0,0 +1,52 @@
+import { execFile as callback } from "node:child_process";
+import { promisify } from "node:util";
+const execFile = promisify(callback);
+export const nixLiteral = (value: string): string => JSON.stringify(value).replace(/\$\{/g, "\\${");
+
+/** Recognize the deliberately small scaffold edit surface, never evaluate Nix.
+ * Authors may replace it with arbitrary Nix; then scaffolding declines the edit. */
+export async function componentEntries(source: string): Promise<Record<string, { entry: string; export: string }>> {
+  const { stdout } = await execFile("nix-instantiate", ["--parse", "--expr", source], { maxBuffer: 1024 * 1024 });
+  const tokens = stdout.match(/"(?:\\.|[^"\\])*"|[A-Za-z_][A-Za-z0-9_-]*|[{}=;]/g) ?? [];
+  if (stdout.replace(/"(?:\\.|[^"\\])*"|[A-Za-z_][A-Za-z0-9_-]*|[{}=;]|\s+/g, ""))
+    throw Error("components.nix is outside the supported literal-entry shape");
+  let cursor = 0;
+  const expect = (token: string) => {
+    if (tokens[cursor++] !== token) throw Error("components.nix is outside the supported literal-entry shape");
+  };
+  const string = () => {
+    const token = tokens[cursor++];
+    if (!token?.startsWith('"')) throw Error("Component entries must use literal strings");
+    const json = token.replace(/(\\*)\$\{/g, (_match, escapes: string) => {
+      if (escapes.length % 2 === 0) throw Error("Component entries must use literal strings");
+      return escapes.slice(1) + "${";
+    });
+    return JSON.parse(json) as string;
+  };
+  const entries: Record<string, { entry: string; export: string }> = Object.create(null);
+  expect("{");
+  while (tokens[cursor] !== "}") {
+    const id = tokens[cursor]?.startsWith('"') ? string() : tokens[cursor++];
+    if (!id) throw Error("Missing component identity");
+    if (Object.hasOwn(entries, id)) throw Error("Duplicate component entry");
+    expect("=");
+    expect("{");
+    const properties: Record<string, string> = Object.create(null);
+    while (tokens[cursor] !== "}") {
+      const key = tokens[cursor]?.startsWith('"') ? string() : tokens[cursor++];
+      if (!key || !["entry", "export"].includes(key) || Object.hasOwn(properties, key))
+        throw Error("Unsupported component entry property");
+      expect("=");
+      properties[key] = string();
+      expect(";");
+    }
+    expect("}");
+    expect(";");
+    if (!properties.entry || !properties.export) throw Error("Component entry needs entry and export");
+    entries[id] = { entry: properties.entry, export: properties.export };
+  }
+  expect("}");
+  if (cursor !== tokens.length || !/\n}\s*$/.test(source))
+    throw Error("components.nix is outside the supported scaffold shape");
+  return entries;
+}