Module visit

Available on crate feature visit only.

Syntax tree traversal to walk a shared borrow of a syntax tree.

Each method of the Visit trait is a hook that can be overridden to customize the behavior when visiting 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 Visit<'ast> {
    /* ... */

    fn visit_expr_binary(&mut self, node: &'ast ExprBinary) {
        visit_expr_binary(self, node);
    }

    /* ... */
}

pub fn visit_expr_binary<'ast, V>(v: &mut V, node: &'ast ExprBinary)
where
    V: Visit<'ast> + ?Sized,
{
    for attr in &node.attrs {
        v.visit_attribute(attr);
    }
    v.visit_expr(&*node.left);
    v.visit_bin_op(&node.op);
    v.visit_expr(&*node.right);
}

/* ... */

Example

This visitor will print the name of every freestanding function in the syntax tree, including nested functions.

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

use quote::quote;
use syn::visit::{self, Visit};
use syn::{File, ItemFn};

struct FnVisitor;

impl<'ast> Visit<'ast> for FnVisitor {
    fn visit_item_fn(&mut self, node: &'ast ItemFn) {
        println!("Function with name={}", node.sig.ident);

        // Delegate to the default impl to visit any nested functions.
        visit::visit_item_fn(self, node);
    }
}

fn main() {
    let code = quote! {
        pub fn f() {
            fn g() {}
        }
    };

    let syntax_tree: File = syn::parse2(code).unwrap();
    FnVisitor.visit_file(&syntax_tree);
}

The 'ast lifetime on the input references means that the syntax tree outlives the complete recursive visit call, so the visitor is allowed to hold on to references into the syntax tree.

use quote::quote;
use syn::visit::{self, Visit};
use syn::{File, ItemFn};

struct FnVisitor<'ast> {
    functions: Vec<&'ast ItemFn>,
}

impl<'ast> Visit<'ast> for FnVisitor<'ast> {
    fn visit_item_fn(&mut self, node: &'ast ItemFn) {
        self.functions.push(node);
        visit::visit_item_fn(self, node);
    }
}

fn main() {
    let code = quote! {
        pub fn f() {
            fn g() {}
        }
    };

    let syntax_tree: File = syn::parse2(code).unwrap();
    let mut visitor = FnVisitor { functions: Vec::new() };
    visitor.visit_file(&syntax_tree);
    for f in visitor.functions {
        println!("Function with name={}", f.sig.ident);
    }
}

Traits

Visit

Syntax tree traversal to walk a shared borrow of a syntax tree.

Functions

visit_abiderive or full

visit_angle_bracketed_generic_argumentsderive or full

visit_armfull

visit_assoc_constderive or full

visit_assoc_typederive or full

visit_attr_stylederive or full

visit_attributederive or full

visit_bare_fn_argderive or full

visit_bare_variadicderive or full

visit_bin_opderive or full

visit_blockfull

visit_bound_lifetimesderive or full

visit_captured_paramfull

visit_const_paramderive or full

visit_constraintderive or full

visit_dataderive

visit_data_enumderive

visit_data_structderive

visit_data_unionderive

visit_derive_inputderive

visit_exprderive or full

visit_expr_arrayfull

visit_expr_assignfull

visit_expr_asyncfull

visit_expr_awaitfull

visit_expr_binaryderive or full

visit_expr_blockfull

visit_expr_breakfull

visit_expr_callderive or full

visit_expr_castderive or full

visit_expr_closurefull

visit_expr_constfull

visit_expr_continuefull

visit_expr_fieldderive or full

visit_expr_for_loopfull

visit_expr_groupderive or full

visit_expr_iffull

visit_expr_indexderive or full

visit_expr_inferfull

visit_expr_letfull

visit_expr_litderive or full

visit_expr_loopfull

visit_expr_macroderive or full

visit_expr_matchfull

visit_expr_method_callderive or full

visit_expr_parenderive or full

visit_expr_pathderive or full

visit_expr_rangefull

visit_expr_raw_addrfull

visit_expr_referencederive or full

visit_expr_repeatfull

visit_expr_returnfull

visit_expr_structderive or full

visit_expr_tryfull

visit_expr_try_blockfull

visit_expr_tuplederive or full

visit_expr_unaryderive or full

visit_expr_unsafefull

visit_expr_whilefull

visit_expr_yieldfull

visit_fieldderive or full

visit_field_mutabilityderive or full

visit_field_patfull

visit_field_valuederive or full

visit_fieldsderive or full

visit_fields_namedderive or full

visit_fields_unnamedderive or full

visit_filefull

visit_fn_argfull

visit_foreign_itemfull

visit_foreign_item_fnfull

visit_foreign_item_macrofull

visit_foreign_item_staticfull

visit_foreign_item_typefull

visit_generic_argumentderive or full

visit_generic_paramderive or full

visit_genericsderive or full

visit_ident

visit_impl_itemfull

visit_impl_item_constfull

visit_impl_item_fnfull

visit_impl_item_macrofull

visit_impl_item_typefull

visit_impl_restrictionfull

visit_indexderive or full

visit_itemfull

visit_item_constfull

visit_item_enumfull

visit_item_extern_cratefull

visit_item_fnfull

visit_item_foreign_modfull

visit_item_implfull

visit_item_macrofull

visit_item_modfull

visit_item_staticfull

visit_item_structfull

visit_item_traitfull

visit_item_trait_aliasfull

visit_item_typefull

visit_item_unionfull

visit_item_usefull

visit_labelfull

visit_lifetime

visit_lifetime_paramderive or full

visit_lit

visit_lit_bool

visit_lit_byte

visit_lit_byte_str

visit_lit_char

visit_lit_cstr

visit_lit_float

visit_lit_int

visit_lit_str

visit_localfull

visit_local_initfull

visit_macroderive or full

visit_macro_delimiterderive or full

visit_memberderive or full

visit_metaderive or full

visit_meta_listderive or full

visit_meta_name_valuederive or full

visit_parenthesized_generic_argumentsderive or full

visit_patfull

visit_pat_identfull

visit_pat_orfull

visit_pat_parenfull

visit_pat_referencefull

visit_pat_restfull

visit_pat_slicefull

visit_pat_structfull

visit_pat_tuplefull

visit_pat_tuple_structfull

visit_pat_typefull

visit_pat_wildfull

visit_pathderive or full

visit_path_argumentsderive or full

visit_path_segmentderive or full

visit_pointer_mutabilityfull

visit_precise_capturefull

visit_predicate_lifetimederive or full

visit_predicate_typederive or full

visit_qselfderive or full

visit_range_limitsfull

visit_receiverfull

visit_return_typederive or full

visit_signaturefull

visit_span

visit_static_mutabilityfull

visit_stmtfull

visit_stmt_macrofull

visit_trait_boundderive or full

visit_trait_bound_modifierderive or full

visit_trait_itemfull

visit_trait_item_constfull

visit_trait_item_fnfull

visit_trait_item_macrofull

visit_trait_item_typefull

visit_typederive or full

visit_type_arrayderive or full

visit_type_bare_fnderive or full

visit_type_groupderive or full

visit_type_impl_traitderive or full

visit_type_inferderive or full

visit_type_macroderive or full

visit_type_neverderive or full

visit_type_paramderive or full

visit_type_param_boundderive or full

visit_type_parenderive or full

visit_type_pathderive or full

visit_type_ptrderive or full

visit_type_referencederive or full

visit_type_slicederive or full

visit_type_trait_objectderive or full

visit_type_tuplederive or full

visit_un_opderive or full

visit_use_globfull

visit_use_groupfull

visit_use_namefull

visit_use_pathfull

visit_use_renamefull

visit_use_treefull

visit_variadicfull

visit_variantderive or full

visit_vis_restrictedderive or full

visit_visibilityderive or full

visit_where_clausederive or full

visit_where_predicatederive or full