compiler/rustc_builtin_macros/src/deriving/debug.rs

   1 use crate::deriving::generic::ty::*;
   2 use crate::deriving::generic::*;
   3 use crate::deriving::path_std;
   4
   5 use ast::EnumDef;
   6 use rustc_ast::{self as ast, MetaItem};
   7 use rustc_expand::base::{Annotatable, ExtCtxt};
   8 use rustc_span::symbol::{sym, Ident, Symbol};
   9 use rustc_span::Span;
  10
  11 pub fn expand_deriving_debug(
  12     cx: &mut 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: ast::AttrVec::new(),
  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
  48 fn show_substructure(cx: &mut 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 (ident, vdata, fields) = match substr.fields {
  53         Struct(vdata, fields) => (substr.type_ident, *vdata, fields),
  54         EnumMatching(_, _, v, fields) => (v.ident, &v.data, fields),
  55         AllFieldlessEnum(enum_def) => return show_fieldless_enum(cx, span, enum_def, substr),
  56         EnumTag(..) | StaticStruct(..) | StaticEnum(..) => {
  57             cx.span_bug(span, "nonsensical .fields in `#[derive(Debug)]`")
  58         }
  59     };
  60
  61     let name = cx.expr_str(span, ident.name);
  62     let fmt = substr.nonselflike_args[0].clone();
  63
  64     // Struct and tuples are similar enough that we use the same code for both,
  65     // with some extra pieces for structs due to the field names.
  66     let (is_struct, args_per_field) = match vdata {
  67         ast::VariantData::Unit(..) => {
  68             // Special fast path for unit variants.
  69             assert!(fields.is_empty());
  70             (false, 0)
  71         }
  72         ast::VariantData::Tuple(..) => (false, 1),
  73         ast::VariantData::Struct(..) => (true, 2),
  74     };
  75
  76     // The number of fields that can be handled without an array.
  77     const CUTOFF: usize = 5;
  78
  79     if fields.is_empty() {
  80         // Special case for no fields.
  81         let fn_path_write_str = cx.std_path(&[sym::fmt, sym::Formatter, sym::write_str]);
  82         let expr = cx.expr_call_global(span, fn_path_write_str, vec![fmt, name]);
  83         BlockOrExpr::new_expr(expr)
  84     } else if fields.len() <= CUTOFF {
  85         // Few enough fields that we can use a specific-length method.
  86         let debug = if is_struct {
  87             format!("debug_struct_field{}_finish", fields.len())
  88         } else {
  89             format!("debug_tuple_field{}_finish", fields.len())
  90         };
  91         let fn_path_debug = cx.std_path(&[sym::fmt, sym::Formatter, Symbol::intern(&debug)]);
  92
  93         let mut args = Vec::with_capacity(2 + fields.len() * args_per_field);
  94         args.extend([fmt, name]);
  95         for i in 0..fields.len() {
  96             let field = &fields[i];
  97             if is_struct {
  98                 let name = cx.expr_str(field.span, field.name.unwrap().name);
  99                 args.push(name);
 100             }
 101             // Use an extra indirection to make sure this works for unsized types.
 102             let field = cx.expr_addr_of(field.span, field.self_expr.clone());
 103             args.push(field);
 104         }
 105         let expr = cx.expr_call_global(span, fn_path_debug, args);
 106         BlockOrExpr::new_expr(expr)
 107     } else {
 108         // Enough fields that we must use the any-length method.
 109         let mut name_exprs = Vec::with_capacity(fields.len());
 110         let mut value_exprs = Vec::with_capacity(fields.len());
 111
 112         for field in fields {
 113             if is_struct {
 114                 name_exprs.push(cx.expr_str(field.span, field.name.unwrap().name));
 115             }
 116
 117             // Use an extra indirection to make sure this works for unsized types.
 118             let field = cx.expr_addr_of(field.span, field.self_expr.clone());
 119             value_exprs.push(field);
 120         }
 121
 122         // `let names: &'static _ = &["field1", "field2"];`
 123         let names_let = if is_struct {
 124             let lt_static = Some(cx.lifetime_static(span));
 125             let ty_static_ref = cx.ty_ref(span, cx.ty_infer(span), lt_static, ast::Mutability::Not);
 126             Some(cx.stmt_let_ty(
 127                 span,
 128                 false,
 129                 Ident::new(sym::names, span),
 130                 Some(ty_static_ref),
 131                 cx.expr_array_ref(span, name_exprs),
 132             ))
 133         } else {
 134             None
 135         };
 136
 137         // `let values: &[&dyn Debug] = &[&&self.field1, &&self.field2];`
 138         let path_debug = cx.path_global(span, cx.std_path(&[sym::fmt, sym::Debug]));
 139         let ty_dyn_debug = cx.ty(
 140             span,
 141             ast::TyKind::TraitObject(vec![cx.trait_bound(path_debug)], ast::TraitObjectSyntax::Dyn),
 142         );
 143         let ty_slice = cx.ty(
 144             span,
 145             ast::TyKind::Slice(cx.ty_ref(span, ty_dyn_debug, None, ast::Mutability::Not)),
 146         );
 147         let values_let = cx.stmt_let_ty(
 148             span,
 149             false,
 150             Ident::new(sym::values, span),
 151             Some(cx.ty_ref(span, ty_slice, None, ast::Mutability::Not)),
 152             cx.expr_array_ref(span, value_exprs),
 153         );
 154
 155         // `fmt::Formatter::debug_struct_fields_finish(fmt, name, names, values)` or
 156         // `fmt::Formatter::debug_tuple_fields_finish(fmt, name, values)`
 157         let sym_debug = if is_struct {
 158             sym::debug_struct_fields_finish
 159         } else {
 160             sym::debug_tuple_fields_finish
 161         };
 162         let fn_path_debug_internal = cx.std_path(&[sym::fmt, sym::Formatter, sym_debug]);
 163
 164         let mut args = Vec::with_capacity(4);
 165         args.push(fmt);
 166         args.push(name);
 167         if is_struct {
 168             args.push(cx.expr_ident(span, Ident::new(sym::names, span)));
 169         }
 170         args.push(cx.expr_ident(span, Ident::new(sym::values, span)));
 171         let expr = cx.expr_call_global(span, fn_path_debug_internal, args);
 172
 173         let mut stmts = Vec::with_capacity(3);
 174         if is_struct {
 175             stmts.push(names_let.unwrap());
 176         }
 177         stmts.push(values_let);
 178         BlockOrExpr::new_mixed(stmts, Some(expr))
 179     }
 180 }
 181
 182 /// Special case for enums with no fields. Builds:
 183 /// ```text
 184 /// impl ::core::fmt::Debug for A {
 185 ///     fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
 186 ///          ::core::fmt::Formatter::write_str(f,
 187 ///             match self {
 188 ///                 A::A => "A",
 189 ///                 A::B() => "B",
 190 ///                 A::C {} => "C",
 191 ///             })
 192 ///     }
 193 /// }
 194 /// ```
 195 fn show_fieldless_enum(
 196     cx: &mut ExtCtxt<'_>,
 197     span: Span,
 198     def: &EnumDef,
 199     substr: &Substructure<'_>,
 200 ) -> BlockOrExpr {
 201     let fmt = substr.nonselflike_args[0].clone();
 202     let arms = def
 203         .variants
 204         .iter()
 205         .map(|v| {
 206             let variant_path = cx.path(span, vec![substr.type_ident, v.ident]);
 207             let pat = match &v.data {
 208                 ast::VariantData::Tuple(fields, _) => {
 209                     debug_assert!(fields.is_empty());
 210                     cx.pat_tuple_struct(span, variant_path, vec![])
 211                 }
 212                 ast::VariantData::Struct(fields, _) => {
 213                     debug_assert!(fields.is_empty());
 214                     cx.pat_struct(span, variant_path, vec![])
 215                 }
 216                 ast::VariantData::Unit(_) => cx.pat_path(span, variant_path),
 217             };
 218             cx.arm(span, pat, cx.expr_str(span, v.ident.name))
 219         })
 220         .collect::<Vec<_>>();
 221     let name = cx.expr_match(span, cx.expr_self(span), arms);
 222     let fn_path_write_str = cx.std_path(&[sym::fmt, sym::Formatter, sym::write_str]);
 223     BlockOrExpr::new_expr(cx.expr_call_global(span, fn_path_write_str, vec![fmt, name]))
 224 }