oxc-project/oxc · error · OxcDiagnostic

Unexpected joined character sequence in character class.

Error message

Unexpected joined character sequence in character class.

What it means

Lint diagnostic from eslint/no-misleading-character-class (zwj_sequences): a character class contains characters joined by ZWJ (U+200D), such as family or rainbow-flag emoji. A character class matches only the individual atoms, never the joined sequence as a whole, so the regex silently fails to match the intended emoji.

Source

Thrown at crates/oxc_linter/src/rules/eslint/no_misleading_character_class.rs:60

    OxcDiagnostic::warn("Unexpected combining class in character class.")
        .with_help("Replace the character with its normalized form (NFC) or use Unicode code point escapes instead of combining sequences.")
        .with_label(span)
}

fn emoji_modifiers_diagnostic(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("Unexpected emoji modifier in character class.")
        .with_help("Use Unicode code point escapes (e.g., \\u{1F3FB} for the light skin tone modifier) instead of emoji modifier sequences in character classes.")
        .with_label(span)
}

fn regional_indicator_diagnostic(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("Unexpected regional indicator in character class.")
        .with_help("Use Unicode code point escapes (e.g., \\u{1F1EF} for the regional indicator symbol for 'J') instead of regional indicator symbol pairs in character classes.")
        .with_label(span)
}

fn zwj_diagnostic(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("Unexpected joined character sequence in character class.")
        .with_help("Use Unicode code point escapes (e.g., \\u{1F468}\\u200D\\u{1F469} for '👨‍👩') instead of zero-width joiner sequences in character classes.")
        .with_label(span)
}

#[derive(Debug, Default, Clone, JsonSchema, Deserialize)]
#[serde(rename_all = "camelCase", default, deny_unknown_fields)]
pub struct NoMisleadingCharacterClass {
    /// When set to `true`, the rule allows any grouping of code points
    /// inside a character class as long as they are written using escape sequences.
    ///
    /// Examples of **incorrect** code for this rule with `{ "allowEscape": true }`:
    /// ```javascript
    /// /[\uD83D]/; // backslash can be omitted
    /// new RegExp("[\ud83d" + "\udc4d]");
    /// ```
    ///
    /// Examples of **correct** code for this rule with `{ "allowEscape": true }`:
    /// ```javascript

View on GitHub (pinned to e1e7af627c)

Solutions

1. Use Unicode code point escapes (e.g. \u{1F468}\u{200D}\u{1F469}) for the full joined sequence
2. Move the ZWJ sequence out of the character class into the pattern

When it happens

Trigger: Thrown at crates/oxc_linter/src/rules/eslint/no_misleading_character_class.rs:60 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/4ad7e6ebb92563d0. Report an issue: GitHub.