qubit-redact-derive 0.8.1

// =============================================================================
//    Copyright (c) 2025 - 2026 Haixing Hu.
//
//    SPDX-License-Identifier: Apache-2.0
//
//    Licensed under the Apache License, Version 2.0.
// =============================================================================
//! Tuple-field attribute parsing shared by structs and enum variants.

use syn::Error;
use syn::FieldsUnnamed;
use syn::Ident;
use syn::Index;
use syn::Result;

use super::FieldMode;
use super::UnnamedField;
use crate::attributes::FieldAttributes;
use crate::attributes::SerdeAttributes;
/// Parses every unnamed field in source order.
///
/// # Type Parameters
///
/// * `'a` - Lifetime of the borrowed positional-field syntax retained by the
///   result.
///
/// # Parameters
///
/// * `fields` - Tuple fields to validate.
/// * `type_name` - Derived type used in targeted diagnostics.
/// * `serde_enabled` - Whether supported serde controls are validated.
///
/// # Returns
///
/// Parsed positional fields carrying stable zero-based indexes.
///
/// # Errors
///
/// Returns a targeted error when a field attribute is invalid.
pub(crate) fn parse<'a>(
    fields: &'a FieldsUnnamed,
    type_name: &Ident,
    serde_enabled: bool,
) -> Result<Vec<UnnamedField<'a>>> {
    fields
        .unnamed
        .iter()
        .enumerate()
        .map(|(position, field)| {
            let field_name = position.to_string();
            let attributes = FieldAttributes::parse(field, type_name, &field_name)?;
            if matches!(attributes.mode(), FieldMode::KeyedBy(_)) {
                return Err(Error::new_spanned(
                    field,
                    format!(
                        "Redact derive for `{type_name}` tuple field `{field_name}` cannot use \
                         `keyed_by`; use it only on named fields with a sibling key",
                    ),
                ));
            }
            let serde_attributes = SerdeAttributes::parse(field, type_name, &field_name, serde_enabled)?;
            serde_attributes.validate_redaction_mode(field, type_name, &field_name, attributes.mode())?;
            Ok(UnnamedField::new(
                field,
                Index::from(position),
                attributes,
                serde_attributes,
            ))
        })
        .collect()
}