rustc_ast_pretty/pprust/state/

item.rs

use ast::StaticItem;
use itertools::{Itertools, Position};
use rustc_ast as ast;
use rustc_ast::ModKind;
use rustc_span::Ident;

use crate::pp::BoxMarker;
use crate::pp::Breaks::Inconsistent;
use crate::pprust::state::fixup::FixupContext;
use crate::pprust::state::{AnnNode, INDENT_UNIT, PrintState, State};

enum DelegationKind<'a> {
    Single,
    List(&'a [(Ident, Option<Ident>)]),
    Glob,
}

fn visibility_qualified(vis: &ast::Visibility, s: &str) -> String {
    format!("{}{}", State::to_string(|s| s.print_visibility(vis)), s)
}

impl<'a> State<'a> {
    fn print_foreign_mod(&mut self, nmod: &ast::ForeignMod, attrs: &[ast::Attribute]) {
        self.print_inner_attributes(attrs);
        for item in &nmod.items {
            self.print_foreign_item(item);
        }
    }

    pub(crate) fn print_foreign_item(&mut self, item: &ast::ForeignItem) {
        let ast::Item { id, span, ref attrs, ref kind, ref vis, tokens: _ } = *item;
        self.ann.pre(self, AnnNode::SubItem(id));
        self.hardbreak_if_not_bol();
        self.maybe_print_comment(span.lo());
        self.print_outer_attributes(attrs);
        match kind {
            ast::ForeignItemKind::Fn(func) => {
                self.print_fn_full(vis, attrs, &*func);
            }
            ast::ForeignItemKind::Static(box ast::StaticItem {
                ident,
                ty,
                mutability,
                expr,
                safety,
                define_opaque,
            }) => self.print_item_const(
                *ident,
                Some(*mutability),
                &ast::Generics::default(),
                ty,
                expr.as_deref(),
                vis,
                *safety,
                ast::Defaultness::Final,
                define_opaque.as_deref(),
            ),
            ast::ForeignItemKind::TyAlias(box ast::TyAlias {
                defaultness,
                ident,
                generics,
                after_where_clause,
                bounds,
                ty,
            }) => {
                self.print_associated_type(
                    *ident,
                    generics,
                    after_where_clause,
                    bounds,
                    ty.as_deref(),
                    vis,
                    *defaultness,
                );
            }
            ast::ForeignItemKind::MacCall(m) => {
                self.print_mac(m);
                if m.args.need_semicolon() {
                    self.word(";");
                }
            }
        }
        self.ann.post(self, AnnNode::SubItem(id))
    }

    fn print_item_const(
        &mut self,
        ident: Ident,
        mutbl: Option<ast::Mutability>,
        generics: &ast::Generics,
        ty: &ast::Ty,
        body: Option<&ast::Expr>,
        vis: &ast::Visibility,
        safety: ast::Safety,
        defaultness: ast::Defaultness,
        define_opaque: Option<&[(ast::NodeId, ast::Path)]>,
    ) {
        self.print_define_opaques(define_opaque);
        let (cb, ib) = self.head("");
        self.print_visibility(vis);
        self.print_safety(safety);
        self.print_defaultness(defaultness);
        let leading = match mutbl {
            None => "const",
            Some(ast::Mutability::Not) => "static",
            Some(ast::Mutability::Mut) => "static mut",
        };
        self.word_space(leading);
        self.print_ident(ident);
        self.print_generic_params(&generics.params);
        self.word_space(":");
        self.print_type(ty);
        if body.is_some() {
            self.space();
        }
        self.end(ib);
        if let Some(body) = body {
            self.word_space("=");
            self.print_expr(body, FixupContext::default());
        }
        self.print_where_clause(&generics.where_clause);
        self.word(";");
        self.end(cb);
    }

    fn print_associated_type(
        &mut self,
        ident: Ident,
        generics: &ast::Generics,
        after_where_clause: &ast::WhereClause,
        bounds: &ast::GenericBounds,
        ty: Option<&ast::Ty>,
        vis: &ast::Visibility,
        defaultness: ast::Defaultness,
    ) {
        let (cb, ib) = self.head("");
        self.print_visibility(vis);
        self.print_defaultness(defaultness);
        self.word_space("type");
        self.print_ident(ident);
        self.print_generic_params(&generics.params);
        if !bounds.is_empty() {
            self.word_nbsp(":");
            self.print_type_bounds(bounds);
        }
        self.print_where_clause(&generics.where_clause);
        if let Some(ty) = ty {
            self.space();
            self.word_space("=");
            self.print_type(ty);
        }
        self.print_where_clause(&after_where_clause);
        self.word(";");
        self.end(ib);
        self.end(cb);
    }

    /// Pretty-prints an item.
    pub(crate) fn print_item(&mut self, item: &ast::Item) {
        if self.is_sdylib_interface && item.span.is_dummy() {
            // Do not print prelude for interface files.
            return;
        }
        self.hardbreak_if_not_bol();
        self.maybe_print_comment(item.span.lo());
        self.print_outer_attributes(&item.attrs);
        self.ann.pre(self, AnnNode::Item(item));
        match &item.kind {
            ast::ItemKind::ExternCrate(orig_name, ident) => {
                let (cb, ib) = self.head(visibility_qualified(&item.vis, "extern crate"));
                if let &Some(orig_name) = orig_name {
                    self.print_name(orig_name);
                    self.space();
                    self.word("as");
                    self.space();
                }
                self.print_ident(*ident);
                self.word(";");
                self.end(ib);
                self.end(cb);
            }
            ast::ItemKind::Use(tree) => {
                self.print_visibility(&item.vis);
                self.word_nbsp("use");
                self.print_use_tree(tree);
                self.word(";");
            }
            ast::ItemKind::Static(box StaticItem {
                ident,
                ty,
                safety,
                mutability: mutbl,
                expr: body,
                define_opaque,
            }) => {
                self.print_safety(*safety);
                self.print_item_const(
                    *ident,
                    Some(*mutbl),
                    &ast::Generics::default(),
                    ty,
                    body.as_deref(),
                    &item.vis,
                    ast::Safety::Default,
                    ast::Defaultness::Final,
                    define_opaque.as_deref(),
                );
            }
            ast::ItemKind::Const(box ast::ConstItem {
                defaultness,
                ident,
                generics,
                ty,
                expr,
                define_opaque,
            }) => {
                self.print_item_const(
                    *ident,
                    None,
                    generics,
                    ty,
                    expr.as_deref(),
                    &item.vis,
                    ast::Safety::Default,
                    *defaultness,
                    define_opaque.as_deref(),
                );
            }
            ast::ItemKind::Fn(func) => {
                self.print_fn_full(&item.vis, &item.attrs, &*func);
            }
            ast::ItemKind::Mod(safety, ident, mod_kind) => {
                let (cb, ib) = self.head(Self::to_string(|s| {
                    s.print_visibility(&item.vis);
                    s.print_safety(*safety);
                    s.word("mod");
                }));
                self.print_ident(*ident);

                match mod_kind {
                    ModKind::Loaded(items, ..) => {
                        self.nbsp();
                        self.bopen(ib);
                        self.print_inner_attributes(&item.attrs);
                        for item in items {
                            self.print_item(item);
                        }
                        let empty = item.attrs.is_empty() && items.is_empty();
                        self.bclose(item.span, empty, cb);
                    }
                    ModKind::Unloaded => {
                        self.word(";");
                        self.end(ib);
                        self.end(cb);
                    }
                }
            }
            ast::ItemKind::ForeignMod(nmod) => {
                let (cb, ib) = self.head(Self::to_string(|s| {
                    s.print_safety(nmod.safety);
                    s.word("extern");
                }));
                if let Some(abi) = nmod.abi {
                    self.print_token_literal(abi.as_token_lit(), abi.span);
                    self.nbsp();
                }
                self.bopen(ib);
                self.print_foreign_mod(nmod, &item.attrs);
                let empty = item.attrs.is_empty() && nmod.items.is_empty();
                self.bclose(item.span, empty, cb);
            }
            ast::ItemKind::GlobalAsm(asm) => {
                // FIXME: Print `builtin # global_asm` once macro `global_asm` uses `builtin_syntax`.
                let (cb, ib) = self.head(visibility_qualified(&item.vis, "global_asm!"));
                self.print_inline_asm(asm);
                self.word(";");
                self.end(ib);
                self.end(cb);
            }
            ast::ItemKind::TyAlias(box ast::TyAlias {
                defaultness,
                ident,
                generics,
                after_where_clause,
                bounds,
                ty,
            }) => {
                self.print_associated_type(
                    *ident,
                    generics,
                    after_where_clause,
                    bounds,
                    ty.as_deref(),
                    &item.vis,
                    *defaultness,
                );
            }
            ast::ItemKind::Enum(ident, generics, enum_definition) => {
                self.print_enum_def(enum_definition, generics, *ident, item.span, &item.vis);
            }
            ast::ItemKind::Struct(ident, generics, struct_def) => {
                let (cb, ib) = self.head(visibility_qualified(&item.vis, "struct"));
                self.print_struct(struct_def, generics, *ident, item.span, true, cb, ib);
            }
            ast::ItemKind::Union(ident, generics, struct_def) => {
                let (cb, ib) = self.head(visibility_qualified(&item.vis, "union"));
                self.print_struct(struct_def, generics, *ident, item.span, true, cb, ib);
            }
            ast::ItemKind::Impl(ast::Impl { generics, of_trait, self_ty, items }) => {
                let (cb, ib) = self.head("");
                self.print_visibility(&item.vis);

                let impl_generics = |this: &mut Self| {
                    this.word("impl");

                    if generics.params.is_empty() {
                        this.nbsp();
                    } else {
                        this.print_generic_params(&generics.params);
                        this.space();
                    }
                };

                if let Some(box of_trait) = of_trait {
                    let ast::TraitImplHeader {
                        defaultness,
                        safety,
                        constness,
                        polarity,
                        ref trait_ref,
                    } = *of_trait;
                    self.print_defaultness(defaultness);
                    self.print_safety(safety);
                    impl_generics(self);
                    self.print_constness(constness);
                    if let ast::ImplPolarity::Negative(_) = polarity {
                        self.word("!");
                    }
                    self.print_trait_ref(trait_ref);
                    self.space();
                    self.word_space("for");
                } else {
                    impl_generics(self);
                }

                self.print_type(self_ty);
                self.print_where_clause(&generics.where_clause);

                self.space();
                self.bopen(ib);
                self.print_inner_attributes(&item.attrs);
                for impl_item in items {
                    self.print_assoc_item(impl_item);
                }
                let empty = item.attrs.is_empty() && items.is_empty();
                self.bclose(item.span, empty, cb);
            }
            ast::ItemKind::Trait(box ast::Trait {
                constness,
                safety,
                is_auto,
                ident,
                generics,
                bounds,
                items,
            }) => {
                let (cb, ib) = self.head("");
                self.print_visibility(&item.vis);
                self.print_constness(*constness);
                self.print_safety(*safety);
                self.print_is_auto(*is_auto);
                self.word_nbsp("trait");
                self.print_ident(*ident);
                self.print_generic_params(&generics.params);
                if !bounds.is_empty() {
                    self.word_nbsp(":");
                    self.print_type_bounds(bounds);
                }
                self.print_where_clause(&generics.where_clause);
                self.word(" ");
                self.bopen(ib);
                self.print_inner_attributes(&item.attrs);
                for trait_item in items {
                    self.print_assoc_item(trait_item);
                }
                let empty = item.attrs.is_empty() && items.is_empty();
                self.bclose(item.span, empty, cb);
            }
            ast::ItemKind::TraitAlias(ident, generics, bounds) => {
                let (cb, ib) = self.head(visibility_qualified(&item.vis, "trait"));
                self.print_ident(*ident);
                self.print_generic_params(&generics.params);
                self.nbsp();
                if !bounds.is_empty() {
                    self.word_nbsp("=");
                    self.print_type_bounds(bounds);
                }
                self.print_where_clause(&generics.where_clause);
                self.word(";");
                self.end(ib);
                self.end(cb);
            }
            ast::ItemKind::MacCall(mac) => {
                self.print_mac(mac);
                if mac.args.need_semicolon() {
                    self.word(";");
                }
            }
            ast::ItemKind::MacroDef(ident, macro_def) => {
                self.print_mac_def(macro_def, &ident, item.span, |state| {
                    state.print_visibility(&item.vis)
                });
            }
            ast::ItemKind::Delegation(deleg) => self.print_delegation(
                &item.attrs,
                &item.vis,
                &deleg.qself,
                &deleg.path,
                DelegationKind::Single,
                &deleg.body,
            ),
            ast::ItemKind::DelegationMac(deleg) => self.print_delegation(
                &item.attrs,
                &item.vis,
                &deleg.qself,
                &deleg.prefix,
                deleg.suffixes.as_ref().map_or(DelegationKind::Glob, |s| DelegationKind::List(s)),
                &deleg.body,
            ),
        }
        self.ann.post(self, AnnNode::Item(item))
    }

    fn print_enum_def(
        &mut self,
        enum_definition: &ast::EnumDef,
        generics: &ast::Generics,
        ident: Ident,
        span: rustc_span::Span,
        visibility: &ast::Visibility,
    ) {
        let (cb, ib) = self.head(visibility_qualified(visibility, "enum"));
        self.print_ident(ident);
        self.print_generic_params(&generics.params);
        self.print_where_clause(&generics.where_clause);
        self.space();
        self.bopen(ib);
        for v in enum_definition.variants.iter() {
            self.space_if_not_bol();
            self.maybe_print_comment(v.span.lo());
            self.print_outer_attributes(&v.attrs);
            let ib = self.ibox(0);
            self.print_variant(v);
            self.word(",");
            self.end(ib);
            self.maybe_print_trailing_comment(v.span, None);
        }
        let empty = enum_definition.variants.is_empty();
        self.bclose(span, empty, cb)
    }

    pub(crate) fn print_visibility(&mut self, vis: &ast::Visibility) {
        match &vis.kind {
            ast::VisibilityKind::Public => self.word_nbsp("pub"),
            ast::VisibilityKind::Restricted { path, shorthand, .. } => {
                let path = Self::to_string(|s| s.print_path(path, false, 0));
                if *shorthand && (path == "crate" || path == "self" || path == "super") {
                    self.word_nbsp(format!("pub({path})"))
                } else {
                    self.word_nbsp(format!("pub(in {path})"))
                }
            }
            ast::VisibilityKind::Inherited => {}
        }
    }

    fn print_defaultness(&mut self, defaultness: ast::Defaultness) {
        if let ast::Defaultness::Default(_) = defaultness {
            self.word_nbsp("default");
        }
    }

    fn print_struct(
        &mut self,
        struct_def: &ast::VariantData,
        generics: &ast::Generics,
        ident: Ident,
        span: rustc_span::Span,
        print_finalizer: bool,
        cb: BoxMarker,
        ib: BoxMarker,
    ) {
        self.print_ident(ident);
        self.print_generic_params(&generics.params);
        match &struct_def {
            ast::VariantData::Tuple(..) | ast::VariantData::Unit(..) => {
                if let ast::VariantData::Tuple(..) = struct_def {
                    self.popen();
                    self.commasep(Inconsistent, struct_def.fields(), |s, field| {
                        s.maybe_print_comment(field.span.lo());
                        s.print_outer_attributes(&field.attrs);
                        s.print_visibility(&field.vis);
                        s.print_type(&field.ty)
                    });
                    self.pclose();
                }
                self.print_where_clause(&generics.where_clause);
                if print_finalizer {
                    self.word(";");
                }
                self.end(ib);
                self.end(cb);
            }
            ast::VariantData::Struct { fields, .. } => {
                self.print_where_clause(&generics.where_clause);
                self.nbsp();
                self.bopen(ib);

                let empty = fields.is_empty();
                if !empty {
                    self.hardbreak_if_not_bol();

                    for field in fields {
                        self.hardbreak_if_not_bol();
                        self.maybe_print_comment(field.span.lo());
                        self.print_outer_attributes(&field.attrs);
                        self.print_visibility(&field.vis);
                        self.print_ident(field.ident.unwrap());
                        self.word_nbsp(":");
                        self.print_type(&field.ty);
                        self.word(",");
                    }
                }

                self.bclose(span, empty, cb);
            }
        }
    }

    pub(crate) fn print_variant(&mut self, v: &ast::Variant) {
        let (cb, ib) = self.head("");
        self.print_visibility(&v.vis);
        let generics = ast::Generics::default();
        self.print_struct(&v.data, &generics, v.ident, v.span, false, cb, ib);
        if let Some(d) = &v.disr_expr {
            self.space();
            self.word_space("=");
            self.print_expr(&d.value, FixupContext::default())
        }
    }

    pub(crate) fn print_assoc_item(&mut self, item: &ast::AssocItem) {
        let ast::Item { id, span, ref attrs, ref kind, ref vis, tokens: _ } = *item;
        self.ann.pre(self, AnnNode::SubItem(id));
        self.hardbreak_if_not_bol();
        self.maybe_print_comment(span.lo());
        self.print_outer_attributes(attrs);
        match kind {
            ast::AssocItemKind::Fn(func) => {
                self.print_fn_full(vis, attrs, &*func);
            }
            ast::AssocItemKind::Const(box ast::ConstItem {
                defaultness,
                ident,
                generics,
                ty,
                expr,
                define_opaque,
            }) => {
                self.print_item_const(
                    *ident,
                    None,
                    generics,
                    ty,
                    expr.as_deref(),
                    vis,
                    ast::Safety::Default,
                    *defaultness,
                    define_opaque.as_deref(),
                );
            }
            ast::AssocItemKind::Type(box ast::TyAlias {
                defaultness,
                ident,
                generics,
                after_where_clause,
                bounds,
                ty,
            }) => {
                self.print_associated_type(
                    *ident,
                    generics,
                    after_where_clause,
                    bounds,
                    ty.as_deref(),
                    vis,
                    *defaultness,
                );
            }
            ast::AssocItemKind::MacCall(m) => {
                self.print_mac(m);
                if m.args.need_semicolon() {
                    self.word(";");
                }
            }
            ast::AssocItemKind::Delegation(deleg) => self.print_delegation(
                &item.attrs,
                vis,
                &deleg.qself,
                &deleg.path,
                DelegationKind::Single,
                &deleg.body,
            ),
            ast::AssocItemKind::DelegationMac(deleg) => self.print_delegation(
                &item.attrs,
                vis,
                &deleg.qself,
                &deleg.prefix,
                deleg.suffixes.as_ref().map_or(DelegationKind::Glob, |s| DelegationKind::List(s)),
                &deleg.body,
            ),
        }
        self.ann.post(self, AnnNode::SubItem(id))
    }

    fn print_delegation(
        &mut self,
        attrs: &[ast::Attribute],
        vis: &ast::Visibility,
        qself: &Option<Box<ast::QSelf>>,
        path: &ast::Path,
        kind: DelegationKind<'_>,
        body: &Option<Box<ast::Block>>,
    ) {
        let body_cb_ib = body.as_ref().map(|body| (body, self.head("")));
        self.print_visibility(vis);
        self.word_nbsp("reuse");

        if let Some(qself) = qself {
            self.print_qpath(path, qself, false);
        } else {
            self.print_path(path, false, 0);
        }
        match kind {
            DelegationKind::Single => {}
            DelegationKind::List(suffixes) => {
                self.word("::");
                self.word("{");
                for (i, (ident, rename)) in suffixes.iter().enumerate() {
                    self.print_ident(*ident);
                    if let Some(rename) = rename {
                        self.nbsp();
                        self.word_nbsp("as");
                        self.print_ident(*rename);
                    }
                    if i != suffixes.len() - 1 {
                        self.word_space(",");
                    }
                }
                self.word("}");
            }
            DelegationKind::Glob => {
                self.word("::");
                self.word("*");
            }
        }
        if let Some((body, (cb, ib))) = body_cb_ib {
            self.nbsp();
            self.print_block_with_attrs(body, attrs, cb, ib);
        } else {
            self.word(";");
        }
    }

    fn print_fn_full(&mut self, vis: &ast::Visibility, attrs: &[ast::Attribute], func: &ast::Fn) {
        let ast::Fn { defaultness, ident, generics, sig, contract, body, define_opaque } = func;

        self.print_define_opaques(define_opaque.as_deref());

        let body_cb_ib = body.as_ref().map(|body| (body, self.head("")));

        self.print_visibility(vis);
        self.print_defaultness(*defaultness);
        self.print_fn(&sig.decl, sig.header, Some(*ident), generics);
        if let Some(contract) = &contract {
            self.nbsp();
            self.print_contract(contract);
        }
        if let Some((body, (cb, ib))) = body_cb_ib {
            if self.is_sdylib_interface {
                self.word(";");
                self.end(ib); // end inner head-block
                self.end(cb); // end outer head-block
                return;
            }

            self.nbsp();
            self.print_block_with_attrs(body, attrs, cb, ib);
        } else {
            self.word(";");
        }
    }

    fn print_define_opaques(&mut self, define_opaque: Option<&[(ast::NodeId, ast::Path)]>) {
        if let Some(define_opaque) = define_opaque {
            self.word("#[define_opaque(");
            for (i, (_, path)) in define_opaque.iter().enumerate() {
                if i != 0 {
                    self.word_space(",");
                }

                self.print_path(path, false, 0);
            }
            self.word(")]");
        }
        self.hardbreak_if_not_bol();
    }

    fn print_contract(&mut self, contract: &ast::FnContract) {
        if let Some(pred) = &contract.requires {
            self.word("rustc_requires");
            self.popen();
            self.print_expr(pred, FixupContext::default());
            self.pclose();
        }
        if let Some(pred) = &contract.ensures {
            self.word("rustc_ensures");
            self.popen();
            self.print_expr(pred, FixupContext::default());
            self.pclose();
        }
    }

    pub(crate) fn print_fn(
        &mut self,
        decl: &ast::FnDecl,
        header: ast::FnHeader,
        ident: Option<Ident>,
        generics: &ast::Generics,
    ) {
        self.print_fn_header_info(header);
        if let Some(ident) = ident {
            self.nbsp();
            self.print_ident(ident);
        }
        self.print_generic_params(&generics.params);
        self.print_fn_params_and_ret(decl, false);
        self.print_where_clause(&generics.where_clause);
    }

    pub(crate) fn print_fn_params_and_ret(&mut self, decl: &ast::FnDecl, is_closure: bool) {
        let (open, close) = if is_closure { ("|", "|") } else { ("(", ")") };
        self.word(open);
        self.commasep(Inconsistent, &decl.inputs, |s, param| s.print_param(param, is_closure));
        self.word(close);
        self.print_fn_ret_ty(&decl.output)
    }

    fn print_where_clause(&mut self, where_clause: &ast::WhereClause) {
        let ast::WhereClause { has_where_token, ref predicates, span: _ } = *where_clause;
        if predicates.is_empty() && !has_where_token {
            return;
        }

        self.space();
        self.word_space("where");

        for (i, predicate) in predicates.iter().enumerate() {
            if i != 0 {
                self.word_space(",");
            }

            self.print_where_predicate(predicate);
        }
    }

    pub fn print_where_predicate(&mut self, predicate: &ast::WherePredicate) {
        let ast::WherePredicate { attrs, kind, id: _, span: _, is_placeholder: _ } = predicate;
        self.print_outer_attributes(attrs);
        match kind {
            ast::WherePredicateKind::BoundPredicate(where_bound_predicate) => {
                self.print_where_bound_predicate(where_bound_predicate);
            }
            ast::WherePredicateKind::RegionPredicate(ast::WhereRegionPredicate {
                lifetime,
                bounds,
                ..
            }) => {
                self.print_lifetime(*lifetime);
                self.word(":");
                if !bounds.is_empty() {
                    self.nbsp();
                    self.print_lifetime_bounds(bounds);
                }
            }
            ast::WherePredicateKind::EqPredicate(ast::WhereEqPredicate {
                lhs_ty, rhs_ty, ..
            }) => {
                self.print_type(lhs_ty);
                self.space();
                self.word_space("=");
                self.print_type(rhs_ty);
            }
        }
    }

    pub(crate) fn print_where_bound_predicate(
        &mut self,
        where_bound_predicate: &ast::WhereBoundPredicate,
    ) {
        self.print_formal_generic_params(&where_bound_predicate.bound_generic_params);
        self.print_type(&where_bound_predicate.bounded_ty);
        self.word(":");
        if !where_bound_predicate.bounds.is_empty() {
            self.nbsp();
            self.print_type_bounds(&where_bound_predicate.bounds);
        }
    }

    fn print_use_tree(&mut self, tree: &ast::UseTree) {
        match &tree.kind {
            ast::UseTreeKind::Simple(rename) => {
                self.print_path(&tree.prefix, false, 0);
                if let &Some(rename) = rename {
                    self.nbsp();
                    self.word_nbsp("as");
                    self.print_ident(rename);
                }
            }
            ast::UseTreeKind::Glob => {
                if !tree.prefix.segments.is_empty() {
                    self.print_path(&tree.prefix, false, 0);
                    self.word("::");
                }
                self.word("*");
            }
            ast::UseTreeKind::Nested { items, .. } => {
                if !tree.prefix.segments.is_empty() {
                    self.print_path(&tree.prefix, false, 0);
                    self.word("::");
                }
                if items.is_empty() {
                    self.word("{}");
                } else if let [(item, _)] = items.as_slice() {
                    self.print_use_tree(item);
                } else {
                    let cb = self.cbox(INDENT_UNIT);
                    self.word("{");
                    self.zerobreak();
                    let ib = self.ibox(0);
                    for (pos, use_tree) in items.iter().with_position() {
                        let is_last = matches!(pos, Position::Last | Position::Only);
                        self.print_use_tree(&use_tree.0);
                        if !is_last {
                            self.word(",");
                            if let ast::UseTreeKind::Nested { .. } = use_tree.0.kind {
                                self.hardbreak();
                            } else {
                                self.space();
                            }
                        }
                    }
                    self.end(ib);
                    self.trailing_comma();
                    self.offset(-INDENT_UNIT);
                    self.word("}");
                    self.end(cb);
                }
            }
        }
    }
}