1 use crate::deriving::generic::ty::*;
2 use crate::deriving::generic::*;
3 use crate::deriving::path_std;
5 use rustc_ast::{self as ast, MetaItem};
6 use rustc_expand::base::{Annotatable, ExtCtxt};
7 use rustc_span::symbol::{sym, Ident, Symbol};
10 pub fn expand_deriving_debug(
15 push: &mut dyn FnMut(Annotatable),
18 // &mut ::std::fmt::Formatter
19 let fmtr = Ref(Box::new(Path(path_std!(fmt::Formatter))), ast::Mutability::Mut);
21 let trait_def = TraitDef {
23 path: path_std!(fmt::Debug),
24 skip_path_as_bound: false,
25 additional_bounds: Vec::new(),
26 supports_unions: false,
27 methods: vec![MethodDef {
29 generics: Bounds::empty(),
31 nonself_args: vec![(fmtr, sym::f)],
32 ret_ty: Path(path_std!(fmt::Result)),
33 attributes: ast::AttrVec::new(),
34 fieldless_variants_strategy: FieldlessVariantsStrategy::Default,
35 combine_substructure: combine_substructure(Box::new(|a, b, c| {
36 show_substructure(a, b, c)
39 associated_types: Vec::new(),
42 trait_def.expand(cx, mitem, item, push)
45 fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>) -> BlockOrExpr {
46 // We want to make sure we have the ctxt set so that we can use unstable methods
47 let span = cx.with_def_site_ctxt(span);
49 let (ident, vdata, fields) = match substr.fields {
50 Struct(vdata, fields) => (substr.type_ident, *vdata, fields),
51 EnumMatching(_, _, v, fields) => (v.ident, &v.data, fields),
52 AllFieldlessEnum(..) | EnumTag(..) | StaticStruct(..) | StaticEnum(..) => {
53 cx.span_bug(span, "nonsensical .fields in `#[derive(Debug)]`")
57 let name = cx.expr_str(span, ident.name);
58 let fmt = substr.nonselflike_args[0].clone();
60 // Struct and tuples are similar enough that we use the same code for both,
61 // with some extra pieces for structs due to the field names.
62 let (is_struct, args_per_field) = match vdata {
63 ast::VariantData::Unit(..) => {
64 // Special fast path for unit variants.
65 assert!(fields.is_empty());
68 ast::VariantData::Tuple(..) => (false, 1),
69 ast::VariantData::Struct(..) => (true, 2),
72 // The number of fields that can be handled without an array.
73 const CUTOFF: usize = 5;
75 if fields.is_empty() {
76 // Special case for no fields.
77 let fn_path_write_str = cx.std_path(&[sym::fmt, sym::Formatter, sym::write_str]);
78 let expr = cx.expr_call_global(span, fn_path_write_str, vec![fmt, name]);
79 BlockOrExpr::new_expr(expr)
80 } else if fields.len() <= CUTOFF {
81 // Few enough fields that we can use a specific-length method.
82 let debug = if is_struct {
83 format!("debug_struct_field{}_finish", fields.len())
85 format!("debug_tuple_field{}_finish", fields.len())
87 let fn_path_debug = cx.std_path(&[sym::fmt, sym::Formatter, Symbol::intern(&debug)]);
89 let mut args = Vec::with_capacity(2 + fields.len() * args_per_field);
90 args.extend([fmt, name]);
91 for i in 0..fields.len() {
92 let field = &fields[i];
94 let name = cx.expr_str(field.span, field.name.unwrap().name);
97 // Use an extra indirection to make sure this works for unsized types.
98 let field = cx.expr_addr_of(field.span, field.self_expr.clone());
101 let expr = cx.expr_call_global(span, fn_path_debug, args);
102 BlockOrExpr::new_expr(expr)
104 // Enough fields that we must use the any-length method.
105 let mut name_exprs = Vec::with_capacity(fields.len());
106 let mut value_exprs = Vec::with_capacity(fields.len());
108 for field in fields {
110 name_exprs.push(cx.expr_str(field.span, field.name.unwrap().name));
113 // Use an extra indirection to make sure this works for unsized types.
114 let field = cx.expr_addr_of(field.span, field.self_expr.clone());
115 value_exprs.push(field);
118 // `let names: &'static _ = &["field1", "field2"];`
119 let names_let = if is_struct {
120 let lt_static = Some(cx.lifetime_static(span));
121 let ty_static_ref = cx.ty_ref(span, cx.ty_infer(span), lt_static, ast::Mutability::Not);
125 Ident::new(sym::names, span),
127 cx.expr_array_ref(span, name_exprs),
133 // `let values: &[&dyn Debug] = &[&&self.field1, &&self.field2];`
134 let path_debug = cx.path_global(span, cx.std_path(&[sym::fmt, sym::Debug]));
135 let ty_dyn_debug = cx.ty(
137 ast::TyKind::TraitObject(vec![cx.trait_bound(path_debug)], ast::TraitObjectSyntax::Dyn),
139 let ty_slice = cx.ty(
141 ast::TyKind::Slice(cx.ty_ref(span, ty_dyn_debug, None, ast::Mutability::Not)),
143 let values_let = cx.stmt_let_ty(
146 Ident::new(sym::values, span),
147 Some(cx.ty_ref(span, ty_slice, None, ast::Mutability::Not)),
148 cx.expr_array_ref(span, value_exprs),
151 // `fmt::Formatter::debug_struct_fields_finish(fmt, name, names, values)` or
152 // `fmt::Formatter::debug_tuple_fields_finish(fmt, name, values)`
153 let sym_debug = if is_struct {
154 sym::debug_struct_fields_finish
156 sym::debug_tuple_fields_finish
158 let fn_path_debug_internal = cx.std_path(&[sym::fmt, sym::Formatter, sym_debug]);
160 let mut args = Vec::with_capacity(4);
164 args.push(cx.expr_ident(span, Ident::new(sym::names, span)));
166 args.push(cx.expr_ident(span, Ident::new(sym::values, span)));
167 let expr = cx.expr_call_global(span, fn_path_debug_internal, args);
169 let mut stmts = Vec::with_capacity(3);
171 stmts.push(names_let.unwrap());
173 stmts.push(values_let);
174 BlockOrExpr::new_mixed(stmts, Some(expr))