Derive Macro Config 

#[derive(Config)]
{
    // Attributes available to this derive:
    #[confroid]
}

Derive confroid::FromEnv for a named struct.

Config maps struct fields to environment variables. Field names are converted to SCREAMING_SNAKE_CASE, and nested segments are joined with __.

Example

#[derive(confroid::Config)]
#[confroid(prefix = "GUPPY")]
struct Config {
    #[confroid(default = 8080)]
    port: u16,
    database: Database,
}

#[derive(confroid::Config)]
struct Database {
    #[confroid(name = "URL")]
    connection_string: String,
}

// Reads `GUPPY__PORT` and `GUPPY__DATABASE__URL`.
let config: Config = confroid::from_env()?;

Container attributes

Container attributes are placed on the struct below #[derive(Config)]:

• prefix = "..." — prepend a segment to every environment variable represented by the struct. For example, #[confroid(prefix = "GUPPY")] makes a field named port read from GUPPY__PORT. Prefixes compose when a prefixed struct is nested inside another config.

Field attributes

Field attributes customize naming, fallback values, parsing, and generated configuration documentation:

• name = "..." — override the field’s environment-variable segment. On a nested field, the override applies to the entire nested prefix.
• default — use Default::default() when the variable is absent.
• default = expression — use an explicit fallback when the variable is absent. String literals and compatible expressions are converted with Into::into. A present value that fails to parse still returns an error.
• example = expression — attach an example value for confroid::env_example and confroid::markdown_table when the docs feature is enabled. It does not affect parsing.
• auto_vec — parse a Vec<T> from one delimited variable rather than indexed variables such as NAMES__0 and NAMES__1.
• auto_vec_delimiter = "..." — set the delimiter used by auto_vec; the default is ,.
• humantime — parse a std::time::Duration or Option<std::time::Duration> using values such as 30s or 1h 15m. This requires confroid’s humantime feature.

Attributes can be combined:

#[derive(confroid::Config)]
struct Config {
    #[confroid(
        name = "ALLOWED_HOSTS",
        auto_vec,
        auto_vec_delimiter = ";",
        default
    )]
    hosts: Vec<String>,
}

Error reporting

All fields are evaluated before a failed read returns. Independent failures are flattened into confroid::ConfroidError::Multiple in field declaration order, allowing all missing and invalid variables to be fixed in one pass. A single failure is returned as its leaf variant.

Parser failures are retained as boxed error sources rather than converted to strings. Consequently, custom scalar parse errors must implement std::error::Error + Send + Sync + 'static.

Supported structs

The derive supports structs with named fields. Each field’s type must implement confroid::FromEnv. Optional values, nested configs, vectors, and hash maps use their FromEnv implementations to determine presence and deserialize their children.