1 use crate::deriving::generic::ty::*;
2 use crate::deriving::generic::*;
3 use crate::deriving::path_std;
6 use rustc_ast::{self as ast, MetaItem};
7 use rustc_expand::base::{Annotatable, ExtCtxt};
8 use rustc_span::symbol::{sym, Ident, Symbol};
11 pub fn expand_deriving_debug(
16 push: &mut dyn FnMut(Annotatable),
19 // &mut ::std::fmt::Formatter
20 let fmtr = Ref(Box::new(Path(path_std!(fmt::Formatter))), ast::Mutability::Mut);
22 let trait_def = TraitDef {
24 path: path_std!(fmt::Debug),
25 skip_path_as_bound: false,
26 additional_bounds: Vec::new(),
27 supports_unions: false,
28 methods: vec![MethodDef {
30 generics: Bounds::empty(),
32 nonself_args: vec![(fmtr, sym::f)],
33 ret_ty: Path(path_std!(fmt::Result)),
34 attributes: ast::AttrVec::new(),
35 fieldless_variants_strategy:
36 FieldlessVariantsStrategy::SpecializeIfAllVariantsFieldless,
37 combine_substructure: combine_substructure(Box::new(|a, b, c| {
38 show_substructure(a, b, c)
41 associated_types: Vec::new(),
44 trait_def.expand(cx, mitem, item, push)
47 fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>) -> BlockOrExpr {
48 // We want to make sure we have the ctxt set so that we can use unstable methods
49 let span = cx.with_def_site_ctxt(span);
51 let (ident, vdata, fields) = match substr.fields {
52 Struct(vdata, fields) => (substr.type_ident, *vdata, fields),
53 EnumMatching(_, _, v, fields) => (v.ident, &v.data, fields),
54 AllFieldlessEnum(enum_def) => return show_fieldless_enum(cx, span, enum_def, substr),
55 EnumTag(..) | StaticStruct(..) | StaticEnum(..) => {
56 cx.span_bug(span, "nonsensical .fields in `#[derive(Debug)]`")
60 let name = cx.expr_str(span, ident.name);
61 let fmt = substr.nonselflike_args[0].clone();
63 // Struct and tuples are similar enough that we use the same code for both,
64 // with some extra pieces for structs due to the field names.
65 let (is_struct, args_per_field) = match vdata {
66 ast::VariantData::Unit(..) => {
67 // Special fast path for unit variants.
68 assert!(fields.is_empty());
71 ast::VariantData::Tuple(..) => (false, 1),
72 ast::VariantData::Struct(..) => (true, 2),
75 // The number of fields that can be handled without an array.
76 const CUTOFF: usize = 5;
78 if fields.is_empty() {
79 // Special case for no fields.
80 let fn_path_write_str = cx.std_path(&[sym::fmt, sym::Formatter, sym::write_str]);
81 let expr = cx.expr_call_global(span, fn_path_write_str, vec![fmt, name]);
82 BlockOrExpr::new_expr(expr)
83 } else if fields.len() <= CUTOFF {
84 // Few enough fields that we can use a specific-length method.
85 let debug = if is_struct {
86 format!("debug_struct_field{}_finish", fields.len())
88 format!("debug_tuple_field{}_finish", fields.len())
90 let fn_path_debug = cx.std_path(&[sym::fmt, sym::Formatter, Symbol::intern(&debug)]);
92 let mut args = Vec::with_capacity(2 + fields.len() * args_per_field);
93 args.extend([fmt, name]);
94 for i in 0..fields.len() {
95 let field = &fields[i];
97 let name = cx.expr_str(field.span, field.name.unwrap().name);
100 // Use an extra indirection to make sure this works for unsized types.
101 let field = cx.expr_addr_of(field.span, field.self_expr.clone());
104 let expr = cx.expr_call_global(span, fn_path_debug, args);
105 BlockOrExpr::new_expr(expr)
107 // Enough fields that we must use the any-length method.
108 let mut name_exprs = Vec::with_capacity(fields.len());
109 let mut value_exprs = Vec::with_capacity(fields.len());
111 for field in fields {
113 name_exprs.push(cx.expr_str(field.span, field.name.unwrap().name));
116 // Use an extra indirection to make sure this works for unsized types.
117 let field = cx.expr_addr_of(field.span, field.self_expr.clone());
118 value_exprs.push(field);
121 // `let names: &'static _ = &["field1", "field2"];`
122 let names_let = if is_struct {
123 let lt_static = Some(cx.lifetime_static(span));
124 let ty_static_ref = cx.ty_ref(span, cx.ty_infer(span), lt_static, ast::Mutability::Not);
128 Ident::new(sym::names, span),
130 cx.expr_array_ref(span, name_exprs),
136 // `let values: &[&dyn Debug] = &[&&self.field1, &&self.field2];`
137 let path_debug = cx.path_global(span, cx.std_path(&[sym::fmt, sym::Debug]));
138 let ty_dyn_debug = cx.ty(
140 ast::TyKind::TraitObject(vec![cx.trait_bound(path_debug)], ast::TraitObjectSyntax::Dyn),
142 let ty_slice = cx.ty(
144 ast::TyKind::Slice(cx.ty_ref(span, ty_dyn_debug, None, ast::Mutability::Not)),
146 let values_let = cx.stmt_let_ty(
149 Ident::new(sym::values, span),
150 Some(cx.ty_ref(span, ty_slice, None, ast::Mutability::Not)),
151 cx.expr_array_ref(span, value_exprs),
154 // `fmt::Formatter::debug_struct_fields_finish(fmt, name, names, values)` or
155 // `fmt::Formatter::debug_tuple_fields_finish(fmt, name, values)`
156 let sym_debug = if is_struct {
157 sym::debug_struct_fields_finish
159 sym::debug_tuple_fields_finish
161 let fn_path_debug_internal = cx.std_path(&[sym::fmt, sym::Formatter, sym_debug]);
163 let mut args = Vec::with_capacity(4);
167 args.push(cx.expr_ident(span, Ident::new(sym::names, span)));
169 args.push(cx.expr_ident(span, Ident::new(sym::values, span)));
170 let expr = cx.expr_call_global(span, fn_path_debug_internal, args);
172 let mut stmts = Vec::with_capacity(3);
174 stmts.push(names_let.unwrap());
176 stmts.push(values_let);
177 BlockOrExpr::new_mixed(stmts, Some(expr))
181 /// Special case for enums with no fields. Builds:
183 /// impl ::core::fmt::Debug for A {
184 /// fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
185 /// ::core::fmt::Formatter::write_str(f,
194 fn show_fieldless_enum(
195 cx: &mut ExtCtxt<'_>,
198 substr: &Substructure<'_>,
200 let fmt = substr.nonselflike_args[0].clone();
205 let variant_path = cx.path(span, vec![substr.type_ident, v.ident]);
206 let pat = match &v.data {
207 ast::VariantData::Tuple(fields, _) => {
208 debug_assert!(fields.is_empty());
209 cx.pat_tuple_struct(span, variant_path, vec![])
211 ast::VariantData::Struct(fields, _) => {
212 debug_assert!(fields.is_empty());
213 cx.pat_struct(span, variant_path, vec![])
215 ast::VariantData::Unit(_) => cx.pat_path(span, variant_path),
217 cx.arm(span, pat, cx.expr_str(span, v.ident.name))
219 .collect::<Vec<_>>();
220 let name = cx.expr_match(span, cx.expr_self(span), arms);
221 let fn_path_write_str = cx.std_path(&[sym::fmt, sym::Formatter, sym::write_str]);
222 BlockOrExpr::new_expr(cx.expr_call_global(span, fn_path_write_str, vec![fmt, name]))