structured_email_address/

lib.rs

//! # structured-email-address
//!
//! RFC 5321/5322/6531 conformant email address parser, validator, and normalizer.
//!
//! Unlike existing Rust crates that stop at RFC validation, this crate provides:
//! - **Subaddress extraction**: `user+tag@domain` → separate `user`, `tag`, `domain`
//! - **Provider-aware normalization**: Gmail dot-stripping, configurable case folding
//! - **PSL domain validation**: verify domain against the Public Suffix List
//! - **Anti-homoglyph protection**: detect Cyrillic/Latin lookalikes via Unicode skeleton
//! - **Configurable strictness**: Strict (5321), Standard (5322), Lax (obs-* allowed)
//! - **Zero-copy parsing**: internal spans into the input string
//!
//! # Quick Start
//!
//! ```
//! use structured_email_address::{EmailAddress, Config};
//!
//! // Simple: parse with defaults
//! let email: EmailAddress = "user+tag@example.com".parse().unwrap();
//! assert_eq!(email.local_part(), "user+tag");
//! assert_eq!(email.tag(), Some("tag"));
//! assert_eq!(email.domain(), "example.com");
//!
//! // Configured: Gmail normalization pipeline
//! let config = Config::builder()
//!     .strip_subaddress()
//!     .dots_gmail_only()
//!     .lowercase_all()
//!     .build();
//!
//! let email = EmailAddress::parse_with("A.L.I.C.E+promo@Gmail.COM", &config).unwrap();
//! assert_eq!(email.canonical(), "alice@gmail.com");
//! assert_eq!(email.tag(), Some("promo"));
//! ```

#![cfg_attr(
    not(test),
    deny(clippy::unwrap_used, clippy::expect_used, clippy::panic)
)]

mod config;
mod error;
mod normalize;
mod parser;
mod provider;
mod validate;

pub use config::{
    CasePolicy, Config, ConfigBuilder, DomainCheck, DotPolicy, Strictness, SubaddressPolicy,
};
pub use error::{Error, ErrorKind};
pub use normalize::confusable_skeleton;
pub use provider::{ProviderRegistry, ProviderRule};

/// A parsed, validated, and normalized email address.
///
/// Immutable after construction. All accessors return borrowed data.
#[derive(Debug, Clone)]
pub struct EmailAddress {
    /// Original input, exactly as supplied to the parser.
    original: String,
    /// Canonical local part (after normalization).
    local_part: String,
    /// Extracted subaddress tag, if any.
    tag: Option<String>,
    /// Canonical domain (IDNA-encoded, lowercased).
    domain: String,
    /// Unicode form of the domain (only when domain has punycode labels).
    domain_unicode: Option<String>,
    /// Display name, if parsed from `name-addr` format.
    display_name: Option<String>,
    /// Confusable skeleton, if config enabled it.
    skeleton: Option<String>,
    /// Whether the domain is a known freemail provider (from the registry).
    freemail: bool,
}

impl EmailAddress {
    /// Parse and validate with the given configuration.
    pub fn parse_with(input: &str, config: &Config) -> Result<Self, Error> {
        let parsed = parser::parse(
            input,
            config.strictness,
            config.allow_display_name,
            config.allow_domain_literal,
        )?;

        let normalized = normalize::normalize(&parsed, config)?;
        validate::validate(&parsed, &normalized, config)?;

        // Freemail status comes from the provider registry (built-ins + any
        // custom rules), independent of provider-aware normalization.
        let freemail = config
            .providers
            .lookup(&normalized.domain)
            .is_some_and(|p| p.is_freemail());

        Ok(Self {
            original: parsed.input.to_string(),
            local_part: normalized.local_part,
            tag: normalized.tag,
            domain: normalized.domain,
            domain_unicode: normalized.domain_unicode,
            display_name: normalized.display_name,
            skeleton: normalized.skeleton,
            freemail,
        })
    }

    /// The canonical local part (after normalization).
    ///
    /// If subaddress stripping is enabled, this excludes the `+tag`.
    /// If dot stripping is enabled, dots are removed.
    pub fn local_part(&self) -> &str {
        &self.local_part
    }

    /// The extracted subaddress tag, if present.
    ///
    /// For `user+promo@example.com`, returns `Some("promo")`.
    /// Always extracted regardless of [`SubaddressPolicy`] — the policy only
    /// affects whether it appears in [`canonical()`](Self::canonical).
    pub fn tag(&self) -> Option<&str> {
        self.tag.as_deref()
    }

    /// The canonical domain (IDNA-encoded, lowercased).
    pub fn domain(&self) -> &str {
        &self.domain
    }

    /// The canonical domain in Unicode form.
    ///
    /// For internationalized domains (`münchen.de` → `xn--mnchen-3ya.de`),
    /// returns the Unicode form of the canonical domain. For ASCII-only
    /// domains, returns the same value as [`domain()`](Self::domain).
    ///
    /// # Security
    ///
    /// The Unicode form is intended for **display only**. It may reintroduce
    /// [IDN homograph attacks](https://en.wikipedia.org/wiki/IDN_homograph_attack)
    /// where visually similar characters from different scripts produce
    /// different domain names (e.g. Cyrillic `а` vs Latin `a`).
    ///
    /// For security-sensitive comparisons (allow-lists, deduplication, access
    /// control), always use [`domain()`](Self::domain) which returns the
    /// ACE/Punycode form. If you must compare Unicode domains, apply your own
    /// confusable-detection logic (see [`confusable_skeleton()`]).
    ///
    /// ```
    /// use structured_email_address::EmailAddress;
    ///
    /// let email: EmailAddress = "user@münchen.de".parse().unwrap();
    /// assert_eq!(email.domain(), "xn--mnchen-3ya.de");
    /// assert_eq!(email.domain_unicode(), "münchen.de");
    ///
    /// let ascii: EmailAddress = "user@example.com".parse().unwrap();
    /// assert_eq!(ascii.domain_unicode(), "example.com");
    /// ```
    pub fn domain_unicode(&self) -> &str {
        self.domain_unicode.as_deref().unwrap_or(&self.domain)
    }

    /// The display name, if parsed from `"Name" <addr>` or `Name <addr>` format.
    pub fn display_name(&self) -> Option<&str> {
        self.display_name.as_deref()
    }

    /// The full canonical address: `local_part@domain`.
    ///
    /// If the local part contains characters that require quoting (spaces,
    /// special chars), it is wrapped in quotes for RFC compliance.
    pub fn canonical(&self) -> String {
        if needs_quoting(&self.local_part) {
            let escaped = escape_local_part(&self.local_part);
            format!("\"{}\"@{}", escaped, self.domain)
        } else {
            format!("{}@{}", self.local_part, self.domain)
        }
    }

    /// The original input, exactly as supplied to the parser (not trimmed).
    pub fn original(&self) -> &str {
        &self.original
    }

    /// The confusable skeleton of the local part (if config enabled it).
    ///
    /// Two addresses with the same skeleton + domain are visually confusable.
    pub fn skeleton(&self) -> Option<&str> {
        self.skeleton.as_deref()
    }

    /// Check if the domain is a known freemail provider.
    ///
    /// Determined from the [`ProviderRegistry`] in the [`Config`] used to parse
    /// (built-in providers plus any registered via
    /// [`ConfigBuilder::add_provider`]).
    pub fn is_freemail(&self) -> bool {
        self.freemail
    }

    /// Parse a batch of email addresses with the given configuration.
    ///
    /// Returns one `Result` per input, in the same order. The config is
    /// shared across all inputs, amortizing setup cost.
    ///
    /// # Example
    ///
    /// ```
    /// use structured_email_address::{EmailAddress, Config};
    ///
    /// let config = Config::default();
    /// let results = EmailAddress::parse_batch(
    ///     &["alice@example.com", "invalid", "bob@example.org"],
    ///     &config,
    /// );
    /// assert!(results[0].is_ok());
    /// assert!(results[1].is_err());
    /// assert!(results[2].is_ok());
    /// ```
    pub fn parse_batch(inputs: &[&str], config: &Config) -> Vec<Result<Self, Error>> {
        inputs
            .iter()
            .map(|input| Self::parse_with(input, config))
            .collect()
    }

    /// Parse a batch of email addresses in parallel using rayon.
    ///
    /// Same semantics as [`parse_batch`](Self::parse_batch), but distributes
    /// work across rayon's thread pool. Useful for bulk import/validation of
    /// large lists (10K+ addresses).
    ///
    /// Requires the `rayon` feature.
    ///
    /// # Example
    ///
    /// ```
    /// use structured_email_address::{EmailAddress, Config};
    ///
    /// let config = Config::default();
    /// let results = EmailAddress::parse_batch_par(
    ///     &["alice@example.com", "bob@example.org"],
    ///     &config,
    /// );
    /// assert!(results.iter().all(|r| r.is_ok()));
    /// ```
    #[cfg(feature = "rayon")]
    pub fn parse_batch_par(inputs: &[&str], config: &Config) -> Vec<Result<Self, Error>> {
        use rayon::prelude::*;

        inputs
            .par_iter()
            .map(|input| Self::parse_with(input, config))
            .collect()
    }
}

impl std::fmt::Display for EmailAddress {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let local = if needs_quoting(&self.local_part) {
            format!("\"{}\"", escape_local_part(&self.local_part))
        } else {
            self.local_part.clone()
        };
        match &self.display_name {
            Some(name) => write!(
                f,
                "\"{}\" <{}@{}>",
                escape_display_name(name),
                local,
                self.domain
            ),
            None => write!(f, "{}@{}", local, self.domain),
        }
    }
}

/// Check if a local-part needs quoting for RFC 5321/5322 serialization.
/// Returns true if the local part contains characters outside of atext.
fn needs_quoting(local: &str) -> bool {
    if local.is_empty() {
        return true;
    }
    // Dots are only safe in valid dot-atom form (no leading/trailing/consecutive dots).
    if local.starts_with('.') || local.ends_with('.') || local.contains("..") {
        return true;
    }
    local.chars().any(|ch| {
        !ch.is_ascii_alphanumeric()
            && !matches!(
                ch,
                '!' | '#'
                    | '$'
                    | '%'
                    | '&'
                    | '\''
                    | '*'
                    | '+'
                    | '-'
                    | '/'
                    | '='
                    | '?'
                    | '^'
                    | '_'
                    | '`'
                    | '{'
                    | '|'
                    | '}'
                    | '~'
                    | '.'
            )
            && (ch as u32) < 0x80 // non-ASCII doesn't need quoting per RFC 6531
    })
}

/// Escape a local-part for use inside quotes: backslash-escape `"` and `\`,
/// strip CR/LF to prevent header injection (FWS is collapsed during normalization).
fn escape_local_part(local: &str) -> String {
    let mut escaped = String::with_capacity(local.len());
    for ch in local.chars() {
        match ch {
            '"' | '\\' => {
                escaped.push('\\');
                escaped.push(ch);
            }
            '\r' | '\n' => {} // strip CRLF to prevent header injection
            _ => escaped.push(ch),
        }
    }
    escaped
}

/// Backslash-escapes `"` and `\`, and strips bare CR/LF to prevent
/// header injection in serialized output.
fn escape_display_name(name: &str) -> String {
    let mut escaped = String::with_capacity(name.len());
    for ch in name.chars() {
        match ch {
            '"' => {
                escaped.push('\\');
                escaped.push('"');
            }
            '\\' => {
                escaped.push('\\');
                escaped.push('\\');
            }
            '\r' | '\n' => {} // strip CRLF
            _ => escaped.push(ch),
        }
    }
    escaped
}

/// Equality is based on canonical form (`local_part` + `domain`) only.
/// Display name, tag, and skeleton are intentionally excluded —
/// `"John" <user@example.com>` equals `"Jane" <user@example.com>`
/// because they route to the same mailbox.
impl PartialEq for EmailAddress {
    fn eq(&self, other: &Self) -> bool {
        self.local_part == other.local_part && self.domain == other.domain
    }
}

impl Eq for EmailAddress {}

impl std::hash::Hash for EmailAddress {
    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
        self.local_part.hash(state);
        self.domain.hash(state);
    }
}

impl std::str::FromStr for EmailAddress {
    type Err = Error;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        Self::parse_with(s, &Config::default())
    }
}

#[cfg(feature = "serde")]
impl serde::Serialize for EmailAddress {
    fn serialize<S: serde::Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
        self.canonical().serialize(serializer)
    }
}

#[cfg(feature = "serde")]
impl<'de> serde::Deserialize<'de> for EmailAddress {
    fn deserialize<D: serde::Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
        let s = String::deserialize(deserializer)?;
        s.parse().map_err(serde::de::Error::custom)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    // ── FromStr (default config) ──

    #[test]
    fn parse_simple() {
        let email: EmailAddress = "user@example.com".parse().unwrap_or_else(|e| panic!("{e}"));
        assert_eq!(email.local_part(), "user");
        assert_eq!(email.domain(), "example.com");
        assert_eq!(email.tag(), None);
        assert_eq!(email.canonical(), "user@example.com");
    }

    #[test]
    fn parse_with_tag() {
        let email: EmailAddress = "user+newsletter@example.com"
            .parse()
            .unwrap_or_else(|e| panic!("{e}"));
        assert_eq!(email.local_part(), "user+newsletter");
        assert_eq!(email.tag(), Some("newsletter"));
    }

    #[test]
    fn display_format() {
        let email: EmailAddress = "user@example.com".parse().unwrap_or_else(|e| panic!("{e}"));
        assert_eq!(format!("{email}"), "user@example.com");
    }

    #[test]
    fn display_name_escaping() {
        let config = Config::builder().allow_display_name().build();
        // Display name with quotes should be escaped
        let email = EmailAddress::parse_with("John \"Johnny\" Doe <user@example.com>", &config)
            .unwrap_or_else(|e| panic!("{e}"));
        let formatted = format!("{email}");
        assert!(
            formatted.contains("\\\"Johnny\\\""),
            "Expected escaped quotes in: {formatted}"
        );
    }

    #[test]
    fn equality_by_canonical() {
        let a: EmailAddress = "user@example.com".parse().unwrap_or_else(|e| panic!("{e}"));
        let b: EmailAddress = "user@Example.COM".parse().unwrap_or_else(|e| panic!("{e}"));
        // Default config: domain-only lowercase, so local parts same case → equal
        assert_eq!(a, b);
    }

    #[test]
    fn freemail_detection() {
        let email: EmailAddress = "user@gmail.com".parse().unwrap_or_else(|e| panic!("{e}"));
        assert!(email.is_freemail());

        let email: EmailAddress = "user@company.com".parse().unwrap_or_else(|e| panic!("{e}"));
        assert!(!email.is_freemail());
    }

    #[test]
    fn freemail_via_custom_provider() {
        // A registered custom provider marked freemail is reported by is_freemail().
        use crate::ProviderRule;
        let config = Config::builder()
            .add_provider(ProviderRule::new(["freebie.example"]).freemail(true))
            .build();
        let email = EmailAddress::parse_with("user@freebie.example", &config)
            .unwrap_or_else(|e| panic!("{e}"));
        assert!(email.is_freemail());
    }

    // ── Provider-aware normalization (#5) ──

    #[test]
    fn provider_aware_gmail_normalizes_by_rule() {
        // provider_aware applies Gmail's rule (strip dots, fold case, '+' tag)
        // without setting any global dot/case policy. strip_subaddress drops the
        // extracted tag from the canonical form.
        let config = Config::builder()
            .provider_aware()
            .strip_subaddress()
            .build();
        let email = EmailAddress::parse_with("A.Li.Ce+promo@Gmail.com", &config)
            .unwrap_or_else(|e| panic!("{e}"));
        assert_eq!(email.local_part(), "alice");
        assert_eq!(email.tag(), Some("promo"));
        assert_eq!(email.domain(), "gmail.com");
    }

    #[test]
    fn provider_aware_gmail_preserves_tag_by_default() {
        // Default subaddress policy keeps the tag in the canonical local part;
        // dots are still stripped and case folded by the Gmail rule.
        let config = Config::builder().provider_aware().build();
        let email = EmailAddress::parse_with("A.Li.Ce+promo@Gmail.com", &config)
            .unwrap_or_else(|e| panic!("{e}"));
        assert_eq!(email.local_part(), "alice+promo");
        assert_eq!(email.tag(), Some("promo"));
    }

    #[test]
    fn provider_aware_leaves_non_provider_domains_to_global_policy() {
        // A non-provider domain is untouched by provider rules: dots preserved,
        // local-part case preserved (global defaults).
        let config = Config::builder().provider_aware().build();
        let email = EmailAddress::parse_with("A.L.I.C.E@example.com", &config)
            .unwrap_or_else(|e| panic!("{e}"));
        assert_eq!(email.local_part(), "A.L.I.C.E");
        assert_eq!(email.domain(), "example.com");
    }

    #[test]
    fn provider_aware_quoted_local_preserves_case() {
        // A quoted local-part is literal: the provider rule's case folding
        // (Gmail) must NOT apply inside it, just as dots and the subaddress
        // separator don't. Without a global lowercase policy, case is preserved.
        let config = Config::builder().provider_aware().build();
        let email = EmailAddress::parse_with("\"A.B\"@gmail.com", &config)
            .unwrap_or_else(|e| panic!("{e}"));
        assert_eq!(email.local_part(), "A.B");

        // A global lowercase policy is not provider-specific, so it still folds
        // a quoted local-part — even when a provider rule matches (the rule's
        // own folding is skipped for quoted, but the global policy still applies).
        let config = Config::builder().provider_aware().lowercase_all().build();
        let email = EmailAddress::parse_with("\"A.B\"@gmail.com", &config)
            .unwrap_or_else(|e| panic!("{e}"));
        assert_eq!(email.local_part(), "a.b");
    }

    #[test]
    fn provider_aware_off_does_not_strip_gmail_dots() {
        // Without provider_aware and without dots_gmail_only, gmail dots stay.
        let email: EmailAddress = "a.b.c@gmail.com".parse().unwrap_or_else(|e| panic!("{e}"));
        assert_eq!(email.local_part(), "a.b.c");
    }

    #[test]
    fn custom_provider_aware_rule_applies() {
        use crate::ProviderRule;
        // Custom provider: strips dots, '-' separator.
        let config = Config::builder()
            .provider_aware()
            .strip_subaddress()
            .add_provider(
                ProviderRule::new(["corp.example"])
                    .strip_dots(true)
                    .lowercase_local(true)
                    .subaddress_separator(Some('-')),
            )
            .build();
        let email = EmailAddress::parse_with("John.Doe-tag@corp.example", &config)
            .unwrap_or_else(|e| panic!("{e}"));
        assert_eq!(email.local_part(), "johndoe");
        assert_eq!(email.tag(), Some("tag"));
    }

    #[test]
    fn idn_provider_rule_consistent_across_normalization_and_freemail() {
        use crate::ProviderRule;
        // A provider rule registered with the Unicode domain must apply to the
        // IDNA-encoded address for BOTH provider-aware normalization and
        // is_freemail() — the canonical domain is used at both call sites.
        let config = Config::builder()
            .provider_aware()
            .add_provider(
                ProviderRule::new(["münchen.de"])
                    .strip_dots(true)
                    .lowercase_local(true)
                    .freemail(true),
            )
            .build();
        let email =
            EmailAddress::parse_with("A.B@münchen.de", &config).unwrap_or_else(|e| panic!("{e}"));
        assert_eq!(email.domain(), "xn--mnchen-3ya.de");
        assert_eq!(
            email.local_part(),
            "ab",
            "provider rule strips dots + folds case"
        );
        assert!(email.is_freemail(), "same rule drives is_freemail");
    }

    #[test]
    fn dots_gmail_only_ignores_custom_providers() {
        use crate::ProviderRule;
        // GmailOnly is a legacy mode tied to the built-in dot-stripping providers
        // (Gmail/Googlemail). Custom providers affect normalization ONLY under
        // provider_aware(); a custom strip_dots rule must NOT leak into GmailOnly
        // when provider_aware is off.
        let config = Config::builder()
            .dots_gmail_only()
            .add_provider(ProviderRule::new(["corp.example"]).strip_dots(true))
            .build();

        // The custom provider's strip_dots is ignored: dots are preserved.
        let email =
            EmailAddress::parse_with("a.b@corp.example", &config).unwrap_or_else(|e| panic!("{e}"));
        assert_eq!(email.local_part(), "a.b");

        // Built-in Gmail still strips dots under GmailOnly.
        let email =
            EmailAddress::parse_with("a.b.c@gmail.com", &config).unwrap_or_else(|e| panic!("{e}"));
        assert_eq!(email.local_part(), "abc");
    }

    // ── Configured parsing ──

    #[test]
    fn full_normalization_pipeline() {
        let config = Config::builder()
            .strip_subaddress()
            .dots_gmail_only()
            .lowercase_all()
            .check_confusables()
            .build();

        let email = EmailAddress::parse_with("A.L.I.C.E+promo@Gmail.COM", &config)
            .unwrap_or_else(|e| panic!("{e}"));
        assert_eq!(email.canonical(), "alice@gmail.com");
        assert_eq!(email.tag(), Some("promo"));
        assert!(email.skeleton().is_some());
    }

    #[test]
    fn display_name_parsing() {
        let config = Config::builder().allow_display_name().build();

        let email = EmailAddress::parse_with("John Doe <user@example.com>", &config)
            .unwrap_or_else(|e| panic!("{e}"));
        assert_eq!(email.display_name(), Some("John Doe"));
        assert_eq!(email.local_part(), "user");
        assert_eq!(email.domain(), "example.com");
    }

    #[test]
    fn leading_comment_full_pipeline() {
        // #40: a leading RFC 5322 comment before the local-part must parse
        // end-to-end, with the comment stripped from the canonical address.
        let config = Config::builder()
            .strictness(Strictness::Lax)
            .allow_display_name()
            .allow_domain_literal()
            .allow_single_label_domain()
            .lowercase_all()
            .build();

        for input in [
            "(comment)jane.smith@example.com",
            "jane(comment).smith@example.com",
            "jane.smith(comment)@example.com",
            "jane.smith@example.com",
        ] {
            let email = EmailAddress::parse_with(input, &config)
                .unwrap_or_else(|e| panic!("'{input}' must parse: {e}"));
            assert_eq!(email.canonical(), "jane.smith@example.com");
        }
    }

    #[test]
    fn rejects_newline_in_address() {
        // Header-injection hardening: a trailing newline must not be silently
        // accepted (it previously survived an over-eager input.trim()).
        let config = Config::default();
        assert!("user@example.com\n".parse::<EmailAddress>().is_err());
        assert!(EmailAddress::parse_with("user@example.com\r\n", &config).is_err());
    }

    // ── Serde ──

    #[cfg(feature = "serde")]
    #[test]
    fn serde_roundtrip() {
        let email: EmailAddress = "user@example.com".parse().unwrap_or_else(|e| panic!("{e}"));
        let json = serde_json::to_string(&email).unwrap_or_else(|e| panic!("{e}"));
        assert_eq!(json, "\"user@example.com\"");

        let back: EmailAddress = serde_json::from_str(&json).unwrap_or_else(|e| panic!("{e}"));
        assert_eq!(email, back);
    }

    // ── Validation errors ──

    #[test]
    fn rejects_empty() {
        let result: Result<EmailAddress, _> = "".parse();
        assert!(result.is_err());
    }

    #[test]
    fn rejects_no_domain_dot() {
        let result: Result<EmailAddress, _> = "user@localhost".parse();
        assert!(result.is_err());
        assert!(matches!(result.unwrap_err().kind(), ErrorKind::DomainNoDot));
    }

    #[test]
    fn allows_single_label_when_configured() {
        let config = Config::builder().allow_single_label_domain().build();
        let email =
            EmailAddress::parse_with("user@localhost", &config).unwrap_or_else(|e| panic!("{e}"));
        assert_eq!(email.domain(), "localhost");
    }

    // ── Batch parsing ──

    #[test]
    fn batch_parse_mixed_results() {
        // Verifies that parse_batch returns Ok for valid and Err for invalid
        // inputs, preserving input order.
        let config = Config::default();
        let results = EmailAddress::parse_batch(
            &["alice@example.com", "invalid", "bob@example.org"],
            &config,
        );
        assert_eq!(results.len(), 3);
        assert!(results[0].is_ok());
        assert!(results[1].is_err());
        assert!(results[2].is_ok());
        assert_eq!(results[0].as_ref().map(|e| e.domain()), Ok("example.com"));
        assert_eq!(results[2].as_ref().map(|e| e.domain()), Ok("example.org"));
    }

    #[test]
    fn batch_parse_empty_input() {
        // Empty slice returns empty vec.
        let config = Config::default();
        let results = EmailAddress::parse_batch(&[], &config);
        assert!(results.is_empty());
    }

    #[test]
    fn batch_parse_all_valid() {
        // Batch of valid addresses all succeed.
        let config = Config::default();
        let inputs = &["a@b.com", "x@y.org", "test+tag@example.com"];
        let results = EmailAddress::parse_batch(inputs, &config);
        assert!(results.iter().all(|r| r.is_ok()));
    }

    #[test]
    fn batch_parse_all_invalid() {
        // Batch of invalid addresses all fail.
        let config = Config::default();
        let results = EmailAddress::parse_batch(&["", "noatsign", "@missing-local.com"], &config);
        assert!(results.iter().all(|r| r.is_err()));
    }

    #[test]
    fn batch_parse_with_config() {
        // Batch parsing respects config (e.g., subaddress stripping).
        let config = Config::builder()
            .strip_subaddress()
            .dots_gmail_only()
            .lowercase_all()
            .build();
        let results =
            EmailAddress::parse_batch(&["A.L.I.C.E+promo@Gmail.COM", "BOB@example.com"], &config);
        assert_eq!(results.len(), 2);
        assert_eq!(
            results[0].as_ref().map(|e| e.canonical()),
            Ok("alice@gmail.com".to_string())
        );
        assert_eq!(
            results[1].as_ref().map(|e| e.canonical()),
            Ok("bob@example.com".to_string())
        );
    }

    // ── domain_unicode() accessor ──

    #[test]
    fn domain_unicode_roundtrip() {
        // IDN domain: input Unicode → domain() punycode → domain_unicode() back to Unicode.
        let email: EmailAddress = "user@münchen.de".parse().unwrap_or_else(|e| panic!("{e}"));
        assert_eq!(email.domain(), "xn--mnchen-3ya.de");
        assert_eq!(email.domain_unicode(), "münchen.de");
    }

    #[test]
    fn domain_unicode_ascii_fallback() {
        // ASCII domain: domain_unicode() returns same as domain().
        let email: EmailAddress = "user@example.com".parse().unwrap_or_else(|e| panic!("{e}"));
        assert_eq!(email.domain_unicode(), "example.com");
        assert_eq!(email.domain_unicode(), email.domain());
    }

    #[test]
    fn domain_unicode_mixed_labels() {
        // Domain with one IDN label and one ASCII label.
        let email: EmailAddress = "user@über.example.com"
            .parse()
            .unwrap_or_else(|e| panic!("{e}"));
        assert_eq!(email.domain(), "xn--ber-goa.example.com");
        assert_eq!(email.domain_unicode(), "über.example.com");
    }

    #[test]
    fn domain_unicode_japanese() {
        // Japanese domain roundtrip.
        let email: EmailAddress = "user@例え.jp".parse().unwrap_or_else(|e| panic!("{e}"));
        assert!(email.domain().contains("xn--"));
        assert_eq!(email.domain_unicode(), "例え.jp");
    }

    #[cfg(feature = "rayon")]
    #[test]
    fn batch_par_matches_sequential() {
        // Parallel variant produces identical results to sequential.
        let config = Config::builder().strip_subaddress().lowercase_all().build();
        let inputs = &[
            "alice@example.com",
            "invalid",
            "BOB+tag@Example.ORG",
            "",
            "user@test.com",
        ];
        let seq = EmailAddress::parse_batch(inputs, &config);
        let par = EmailAddress::parse_batch_par(inputs, &config);
        assert_eq!(seq.len(), par.len());
        for (i, (s, p)) in seq.iter().zip(par.iter()).enumerate() {
            match (s, p) {
                (Ok(a), Ok(b)) => assert_eq!(a, b, "result {i} diverges"),
                (Err(a), Err(b)) => assert_eq!(a, b, "error {i} diverges: {a} vs {b}"),
                _ => panic!("result {i}: one Ok, one Err"),
            }
        }
    }
}