Application configuration management

[vim89]

Problem

Cask has no configuration management. Every app manually reads environment variables with no validation, type safety, or profiles.

// Current - scattered, unsafe, unvalidated
val port = sys.env.getOrElse("PORT", "8080").toInt
val dbUrl = sys.env.getOrElse("DATABASE_URL", "jdbc:sqlite:./app.db")
val secret = sys.env("SECRET_KEY")  // Runtime crash if missing

---

Solution

Auto-load application.conf (HOCON) at startup with Lightbend Config.

# application.conf (auto-loaded)
app {
  name = "my-app"
  server.port = 8080
  database.url = ${?DATABASE_URL}  # Env override
}

// Type-safe, validated at startup
override def port = cask.config.getInt("app.server.port")
val dbUrl = cask.config.getString("app.database.url")

---

Must have

• application.conf auto-loads at startup
• Environment variables override config (${?VAR})
• Profile loading works (CASK_ENV=prod) // Show dev/prod profiles
• Database examples use config for URLs
• Missing required config fails at startup
• API: config.getString(), config.getInt(), etc.

---

Dependency libraries:

• com.typesafe:config:1.4.3 (~300KB)

Question: Is that fine? or should we use Properties Files (Java built-in) - this comes with lot of limitations: No nesting , All values are strings

---

References

• Lightbend Config: https://github.com/lightbend/config
• HOCON spec: https://github.com/lightbend/config/blob/main/HOCON.md

[lihaoyi]

The only question I have here is HOCON, which isn't super widely used, but then again config languages are pretty diverse and there isn't really a dominant entity. I think we can maybe provide both HOCON and a JSON syntax for loading config, on the assumption that anyone who wants to use Cask in a larger codebase using some other config language (TOML, Jsonnet, etc.) can integrate at the JSON-level without needing to go through HOCON

[KaranAhlawat]

I don't see why this would be a part of Cask, as the original author said, you can use Lightbend Config (or any other config library of your choice) very easily at startup

[vim89]

Great point about JSON support! Good news: Typesafe Config natively supports JSON, HOCON, and Java properties

The library automatically loads in this priority order:

1. System properties
2. application.conf (HOCON)
3. application.json (JSON)
4. application.properties (Java properties)
5. Environment-specific overrides

Integration with other formats

For TOML/Jsonnet/etc., you're right - they can convert to JSON and integrate at that level. Typesafe Config also supports:

• Programmatic config: ConfigFactory.parseMap(...)
• Custom parsers via ConfigParseOptions

Updated PR #186 now documents all format support with examples.