Profiles & Discovery

name + paths

#![allow(unused)]
fn main() {
DbConfig::builder("db")
    .discover("config", ["/etc/myapp", "~/.config/myapp", "."])
    .init()?;
}

.discover(name, paths) looks for {name}.{ext} in each directory, in order. Every directory with a match contributes one file, layered in search order — so /etc defaults, ~/.config overrides and a local ./config.toml all apply, in that order. (Stopping at the first hit would make naming both pointless: a machine-wide file and a user's file are layers, not alternatives.)

Within one directory the extensions are tried .toml, .json, .yaml, .yml, skipping any whose feature is off, and the first hit wins — so a stray config.json next to a config.toml resolves the same way every run.

~ expands via HOME, or USERPROFILE on Windows. Resolution happens per load, so a file that appears later is picked up by the next reload rather than requiring a restart.

Neither half works alone — a name without directories would search nowhere, directories without a name would search for nothing — which is why .discover takes both in one call rather than as two options that could be stated separately.

profile_env

#![allow(unused)]
fn main() {
DbConfig::builder("db").file("config.toml").profile_env("APP_ENV")
}

Names the variable holding the active profile. With APP_ENV=production, every file gains a sibling layered over it: config.toml, then config.production.toml. Works for discovered files too; a variant that does not exist is skipped like any other missing file.

The profile is read at load time, so it follows the environment rather than the build.

A variant sits directly on top of its own base, not above the search order:

/etc/myapp/config.toml
/etc/myapp/config.production.toml
~/.config/myapp/config.toml            ← still wins over the line above it
~/.config/myapp/config.production.toml

So a later directory's plain file beats an earlier directory's variant. That is the search order doing its job — a user's file is more specific to the machine than a package's production defaults — but it is worth knowing before relying on the opposite.