rustc_builtin_macros/deriving/
debug.rs

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1use rustc_ast::{self as ast, EnumDef, MetaItem};
2use rustc_expand::base::{Annotatable, ExtCtxt};
3use rustc_session::config::FmtDebug;
4use rustc_span::{Ident, Span, Symbol, sym};
5use thin_vec::{ThinVec, thin_vec};
6
7use crate::deriving::generic::ty::*;
8use crate::deriving::generic::*;
9use crate::deriving::path_std;
10
11pub(crate) fn expand_deriving_debug(
12    cx: &ExtCtxt<'_>,
13    span: Span,
14    mitem: &MetaItem,
15    item: &Annotatable,
16    push: &mut dyn FnMut(Annotatable),
17    is_const: bool,
18) {
19    // &mut ::std::fmt::Formatter
20    let fmtr = Ref(Box::new(Path(path_std!(fmt::Formatter))), ast::Mutability::Mut);
21
22    let trait_def = TraitDef {
23        span,
24        path: path_std!(fmt::Debug),
25        skip_path_as_bound: false,
26        needs_copy_as_bound_if_packed: true,
27        additional_bounds: Vec::new(),
28        supports_unions: false,
29        methods: vec![MethodDef {
30            name: sym::fmt,
31            generics: Bounds::empty(),
32            explicit_self: true,
33            nonself_args: vec![(fmtr, sym::f)],
34            ret_ty: Path(path_std!(fmt::Result)),
35            attributes: thin_vec![cx.attr_word(sym::inline, span)],
36            fieldless_variants_strategy:
37                FieldlessVariantsStrategy::SpecializeIfAllVariantsFieldless,
38            combine_substructure: combine_substructure(Box::new(|a, b, c| {
39                show_substructure(a, b, c)
40            })),
41        }],
42        associated_types: Vec::new(),
43        is_const,
44    };
45    trait_def.expand(cx, mitem, item, push)
46}
47
48fn show_substructure(cx: &ExtCtxt<'_>, span: Span, substr: &Substructure<'_>) -> BlockOrExpr {
49    // We want to make sure we have the ctxt set so that we can use unstable methods
50    let span = cx.with_def_site_ctxt(span);
51
52    let fmt_detail = cx.sess.opts.unstable_opts.fmt_debug;
53    if fmt_detail == FmtDebug::None {
54        return BlockOrExpr::new_expr(cx.expr_ok(span, cx.expr_tuple(span, ThinVec::new())));
55    }
56
57    let (ident, vdata, fields) = match substr.fields {
58        Struct(vdata, fields) => (substr.type_ident, *vdata, fields),
59        EnumMatching(v, fields) => (v.ident, &v.data, fields),
60        AllFieldlessEnum(enum_def) => return show_fieldless_enum(cx, span, enum_def, substr),
61        EnumDiscr(..) | StaticStruct(..) | StaticEnum(..) => {
62            cx.dcx().span_bug(span, "nonsensical .fields in `#[derive(Debug)]`")
63        }
64    };
65
66    let name = cx.expr_str(span, ident.name);
67    let fmt = substr.nonselflike_args[0].clone();
68
69    // Fieldless enums have been special-cased earlier
70    if fmt_detail == FmtDebug::Shallow {
71        let fn_path_write_str = cx.std_path(&[sym::fmt, sym::Formatter, sym::write_str]);
72        let expr = cx.expr_call_global(span, fn_path_write_str, thin_vec![fmt, name]);
73        return BlockOrExpr::new_expr(expr);
74    }
75
76    // Struct and tuples are similar enough that we use the same code for both,
77    // with some extra pieces for structs due to the field names.
78    let (is_struct, args_per_field) = match vdata {
79        ast::VariantData::Unit(..) => {
80            // Special fast path for unit variants.
81            assert!(fields.is_empty());
82            (false, 0)
83        }
84        ast::VariantData::Tuple(..) => (false, 1),
85        ast::VariantData::Struct { .. } => (true, 2),
86    };
87
88    // The number of fields that can be handled without an array.
89    const CUTOFF: usize = 5;
90
91    fn expr_for_field(
92        cx: &ExtCtxt<'_>,
93        field: &FieldInfo,
94        index: usize,
95        len: usize,
96    ) -> ast::ptr::P<ast::Expr> {
97        if index < len - 1 {
98            field.self_expr.clone()
99        } else {
100            // Unsized types need an extra indirection, but only the last field
101            // may be unsized.
102            cx.expr_addr_of(field.span, field.self_expr.clone())
103        }
104    }
105
106    if fields.is_empty() {
107        // Special case for no fields.
108        let fn_path_write_str = cx.std_path(&[sym::fmt, sym::Formatter, sym::write_str]);
109        let expr = cx.expr_call_global(span, fn_path_write_str, thin_vec![fmt, name]);
110        BlockOrExpr::new_expr(expr)
111    } else if fields.len() <= CUTOFF {
112        // Few enough fields that we can use a specific-length method.
113        let debug = if is_struct {
114            format!("debug_struct_field{}_finish", fields.len())
115        } else {
116            format!("debug_tuple_field{}_finish", fields.len())
117        };
118        let fn_path_debug = cx.std_path(&[sym::fmt, sym::Formatter, Symbol::intern(&debug)]);
119
120        let mut args = ThinVec::with_capacity(2 + fields.len() * args_per_field);
121        args.extend([fmt, name]);
122        for i in 0..fields.len() {
123            let field = &fields[i];
124            if is_struct {
125                let name = cx.expr_str(field.span, field.name.unwrap().name);
126                args.push(name);
127            }
128
129            let field = expr_for_field(cx, field, i, fields.len());
130            args.push(field);
131        }
132        let expr = cx.expr_call_global(span, fn_path_debug, args);
133        BlockOrExpr::new_expr(expr)
134    } else {
135        // Enough fields that we must use the any-length method.
136        let mut name_exprs = ThinVec::with_capacity(fields.len());
137        let mut value_exprs = ThinVec::with_capacity(fields.len());
138
139        for i in 0..fields.len() {
140            let field = &fields[i];
141            if is_struct {
142                name_exprs.push(cx.expr_str(field.span, field.name.unwrap().name));
143            }
144
145            let field = expr_for_field(cx, field, i, fields.len());
146            value_exprs.push(field);
147        }
148
149        // `let names: &'static _ = &["field1", "field2"];`
150        let names_let = is_struct.then(|| {
151            let lt_static = Some(cx.lifetime_static(span));
152            let ty_static_ref = cx.ty_ref(span, cx.ty_infer(span), lt_static, ast::Mutability::Not);
153            cx.stmt_let_ty(
154                span,
155                false,
156                Ident::new(sym::names, span),
157                Some(ty_static_ref),
158                cx.expr_array_ref(span, name_exprs),
159            )
160        });
161
162        // `let values: &[&dyn Debug] = &[&&self.field1, &&self.field2];`
163        let path_debug = cx.path_global(span, cx.std_path(&[sym::fmt, sym::Debug]));
164        let ty_dyn_debug = cx.ty(
165            span,
166            ast::TyKind::TraitObject(
167                vec![cx.trait_bound(path_debug, false)],
168                ast::TraitObjectSyntax::Dyn,
169            ),
170        );
171        let ty_slice = cx.ty(
172            span,
173            ast::TyKind::Slice(cx.ty_ref(span, ty_dyn_debug, None, ast::Mutability::Not)),
174        );
175        let values_let = cx.stmt_let_ty(
176            span,
177            false,
178            Ident::new(sym::values, span),
179            Some(cx.ty_ref(span, ty_slice, None, ast::Mutability::Not)),
180            cx.expr_array_ref(span, value_exprs),
181        );
182
183        // `fmt::Formatter::debug_struct_fields_finish(fmt, name, names, values)` or
184        // `fmt::Formatter::debug_tuple_fields_finish(fmt, name, values)`
185        let sym_debug = if is_struct {
186            sym::debug_struct_fields_finish
187        } else {
188            sym::debug_tuple_fields_finish
189        };
190        let fn_path_debug_internal = cx.std_path(&[sym::fmt, sym::Formatter, sym_debug]);
191
192        let mut args = ThinVec::with_capacity(4);
193        args.push(fmt);
194        args.push(name);
195        if is_struct {
196            args.push(cx.expr_ident(span, Ident::new(sym::names, span)));
197        }
198        args.push(cx.expr_ident(span, Ident::new(sym::values, span)));
199        let expr = cx.expr_call_global(span, fn_path_debug_internal, args);
200
201        let mut stmts = ThinVec::with_capacity(2);
202        if is_struct {
203            stmts.push(names_let.unwrap());
204        }
205        stmts.push(values_let);
206        BlockOrExpr::new_mixed(stmts, Some(expr))
207    }
208}
209
210/// Special case for enums with no fields. Builds:
211/// ```text
212/// impl ::core::fmt::Debug for A {
213///     fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
214///          ::core::fmt::Formatter::write_str(f,
215///             match self {
216///                 A::A => "A",
217///                 A::B() => "B",
218///                 A::C {} => "C",
219///             })
220///     }
221/// }
222/// ```
223fn show_fieldless_enum(
224    cx: &ExtCtxt<'_>,
225    span: Span,
226    def: &EnumDef,
227    substr: &Substructure<'_>,
228) -> BlockOrExpr {
229    let fmt = substr.nonselflike_args[0].clone();
230    let arms = def
231        .variants
232        .iter()
233        .map(|v| {
234            let variant_path = cx.path(span, vec![substr.type_ident, v.ident]);
235            let pat = match &v.data {
236                ast::VariantData::Tuple(fields, _) => {
237                    debug_assert!(fields.is_empty());
238                    cx.pat_tuple_struct(span, variant_path, ThinVec::new())
239                }
240                ast::VariantData::Struct { fields, .. } => {
241                    debug_assert!(fields.is_empty());
242                    cx.pat_struct(span, variant_path, ThinVec::new())
243                }
244                ast::VariantData::Unit(_) => cx.pat_path(span, variant_path),
245            };
246            cx.arm(span, pat, cx.expr_str(span, v.ident.name))
247        })
248        .collect::<ThinVec<_>>();
249    let name = cx.expr_match(span, cx.expr_self(span), arms);
250    let fn_path_write_str = cx.std_path(&[sym::fmt, sym::Formatter, sym::write_str]);
251    BlockOrExpr::new_expr(cx.expr_call_global(span, fn_path_write_str, thin_vec![fmt, name]))
252}
rustc_builtin_macros/deriving/debug.rs

rustc_builtin_macros/deriving/
debug.rs
