Module fold

Available on crate feature fold only.

Syntax tree traversal to transform the nodes of an owned syntax tree.

Each method of the Fold trait is a hook that can be overridden to customize the behavior when transforming the corresponding type of node. By default, every method recursively visits the substructure of the input by invoking the right visitor method of each of its fields.

pub trait Fold {
    /* ... */

    fn fold_expr_binary(&mut self, node: ExprBinary) -> ExprBinary {
        fold_expr_binary(self, node)
    }

    /* ... */
}

pub fn fold_expr_binary<V>(v: &mut V, node: ExprBinary) -> ExprBinary
where
    V: Fold + ?Sized,
{
    ExprBinary {
        attrs: node
            .attrs
            .into_iter()
            .map(|attr| v.fold_attribute(attr))
            .collect(),
        left: Box::new(v.fold_expr(*node.left)),
        op: v.fold_bin_op(node.op),
        right: Box::new(v.fold_expr(*node.right)),
    }
}

/* ... */

Example

This fold inserts parentheses to fully parenthesizes any expression.

// [dependencies]
// quote = "1.0"
// syn = { version = "2.0", features = ["fold", "full"] }

use quote::quote;
use syn::fold::{fold_expr, Fold};
use syn::{token, Expr, ExprParen};

struct ParenthesizeEveryExpr;

impl Fold for ParenthesizeEveryExpr {
    fn fold_expr(&mut self, expr: Expr) -> Expr {
        Expr::Paren(ExprParen {
            attrs: Vec::new(),
            expr: Box::new(fold_expr(self, expr)),
            paren_token: token::Paren::default(),
        })
    }
}

fn main() {
    let code = quote! { a() + b(1) * c.d };
    let expr: Expr = syn::parse2(code).unwrap();
    let parenthesized = ParenthesizeEveryExpr.fold_expr(expr);
    println!("{}", quote!(#parenthesized));

    // Output: (((a)()) + (((b)((1))) * ((c).d)))
}

Traits

Fold

Syntax tree traversal to transform the nodes of an owned syntax tree.

Functions

fold_abiderive or full

fold_angle_bracketed_generic_argumentsderive or full

fold_armfull

fold_assoc_constderive or full

fold_assoc_typederive or full

fold_attr_stylederive or full

fold_attributederive or full

fold_bare_fn_argderive or full

fold_bare_variadicderive or full

fold_bin_opderive or full

fold_blockfull

fold_bound_lifetimesderive or full

fold_captured_paramfull

fold_const_paramderive or full

fold_constraintderive or full

fold_dataderive

fold_data_enumderive

fold_data_structderive

fold_data_unionderive

fold_derive_inputderive

fold_exprderive or full

fold_expr_arrayfull

fold_expr_assignfull

fold_expr_asyncfull

fold_expr_awaitfull

fold_expr_binaryderive or full

fold_expr_blockfull

fold_expr_breakfull

fold_expr_callderive or full

fold_expr_castderive or full

fold_expr_closurefull

fold_expr_constfull

fold_expr_continuefull

fold_expr_fieldderive or full

fold_expr_for_loopfull

fold_expr_groupderive or full

fold_expr_iffull

fold_expr_indexderive or full

fold_expr_inferfull

fold_expr_letfull

fold_expr_litderive or full

fold_expr_loopfull

fold_expr_macroderive or full

fold_expr_matchfull

fold_expr_method_callderive or full

fold_expr_parenderive or full

fold_expr_pathderive or full

fold_expr_rangefull

fold_expr_raw_addrfull

fold_expr_referencederive or full

fold_expr_repeatfull

fold_expr_returnfull

fold_expr_structderive or full

fold_expr_tryfull

fold_expr_try_blockfull

fold_expr_tuplederive or full

fold_expr_unaryderive or full

fold_expr_unsafefull

fold_expr_whilefull

fold_expr_yieldfull

fold_fieldderive or full

fold_field_mutabilityderive or full

fold_field_patfull

fold_field_valuederive or full

fold_fieldsderive or full

fold_fields_namedderive or full

fold_fields_unnamedderive or full

fold_filefull

fold_fn_argfull

fold_foreign_itemfull

fold_foreign_item_fnfull

fold_foreign_item_macrofull

fold_foreign_item_staticfull

fold_foreign_item_typefull

fold_generic_argumentderive or full

fold_generic_paramderive or full

fold_genericsderive or full

fold_ident

fold_impl_itemfull

fold_impl_item_constfull

fold_impl_item_fnfull

fold_impl_item_macrofull

fold_impl_item_typefull

fold_impl_restrictionfull

fold_indexderive or full

fold_itemfull

fold_item_constfull

fold_item_enumfull

fold_item_extern_cratefull

fold_item_fnfull

fold_item_foreign_modfull

fold_item_implfull

fold_item_macrofull

fold_item_modfull

fold_item_staticfull

fold_item_structfull

fold_item_traitfull

fold_item_trait_aliasfull

fold_item_typefull

fold_item_unionfull

fold_item_usefull

fold_labelfull

fold_lifetime

fold_lifetime_paramderive or full

fold_lit

fold_lit_bool

fold_lit_byte

fold_lit_byte_str

fold_lit_char

fold_lit_cstr

fold_lit_float

fold_lit_int

fold_lit_str

fold_localfull

fold_local_initfull

fold_macroderive or full

fold_macro_delimiterderive or full

fold_memberderive or full

fold_metaderive or full

fold_meta_listderive or full

fold_meta_name_valuederive or full

fold_parenthesized_generic_argumentsderive or full

fold_patfull

fold_pat_identfull

fold_pat_orfull

fold_pat_parenfull

fold_pat_referencefull

fold_pat_restfull

fold_pat_slicefull

fold_pat_structfull

fold_pat_tuplefull

fold_pat_tuple_structfull

fold_pat_typefull

fold_pat_wildfull

fold_pathderive or full

fold_path_argumentsderive or full

fold_path_segmentderive or full

fold_pointer_mutabilityfull

fold_precise_capturefull

fold_predicate_lifetimederive or full

fold_predicate_typederive or full

fold_qselfderive or full

fold_range_limitsfull

fold_receiverfull

fold_return_typederive or full

fold_signaturefull

fold_span

fold_static_mutabilityfull

fold_stmtfull

fold_stmt_macrofull

fold_trait_boundderive or full

fold_trait_bound_modifierderive or full

fold_trait_itemfull

fold_trait_item_constfull

fold_trait_item_fnfull

fold_trait_item_macrofull

fold_trait_item_typefull

fold_typederive or full

fold_type_arrayderive or full

fold_type_bare_fnderive or full

fold_type_groupderive or full

fold_type_impl_traitderive or full

fold_type_inferderive or full

fold_type_macroderive or full

fold_type_neverderive or full

fold_type_paramderive or full

fold_type_param_boundderive or full

fold_type_parenderive or full

fold_type_pathderive or full

fold_type_ptrderive or full

fold_type_referencederive or full

fold_type_slicederive or full

fold_type_trait_objectderive or full

fold_type_tuplederive or full

fold_un_opderive or full

fold_use_globfull

fold_use_groupfull

fold_use_namefull

fold_use_pathfull

fold_use_renamefull

fold_use_treefull

fold_variadicfull

fold_variantderive or full

fold_vis_restrictedderive or full

fold_visibilityderive or full

fold_where_clausederive or full

fold_where_predicatederive or full