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         additional_bounds: Vec::new(),
  27         supports_unions: false,
  28         methods: vec![MethodDef {
  29             name: sym::fmt,
  30             generics: Bounds::empty(),
  31             explicit_self: true,
  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)
  39             })),
  40         }],
  41         associated_types: Vec::new(),
  42         is_const,
  43     };
  44     trait_def.expand(cx, mitem, item, push)
  45 }
  46
  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);
  50
  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)]`")
  57         }
  58     };
  59
  60     let name = cx.expr_str(span, ident.name);
  61     let fmt = substr.nonselflike_args[0].clone();
  62
  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());
  69             (false, 0)
  70         }
  71         ast::VariantData::Tuple(..) => (false, 1),
  72         ast::VariantData::Struct(..) => (true, 2),
  73     };
  74
  75     // The number of fields that can be handled without an array.
  76     const CUTOFF: usize = 5;
  77
  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())
  87         } else {
  88             format!("debug_tuple_field{}_finish", fields.len())
  89         };
  90         let fn_path_debug = cx.std_path(&[sym::fmt, sym::Formatter, Symbol::intern(&debug)]);
  91
  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];
  96             if is_struct {
  97                 let name = cx.expr_str(field.span, field.name.unwrap().name);
  98                 args.push(name);
  99             }
 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());
 102             args.push(field);
 103         }
 104         let expr = cx.expr_call_global(span, fn_path_debug, args);
 105         BlockOrExpr::new_expr(expr)
 106     } else {
 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());
 110
 111         for field in fields {
 112             if is_struct {
 113                 name_exprs.push(cx.expr_str(field.span, field.name.unwrap().name));
 114             }
 115
 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);
 119         }
 120
 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);
 125             Some(cx.stmt_let_ty(
 126                 span,
 127                 false,
 128                 Ident::new(sym::names, span),
 129                 Some(ty_static_ref),
 130                 cx.expr_array_ref(span, name_exprs),
 131             ))
 132         } else {
 133             None
 134         };
 135
 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(
 139             span,
 140             ast::TyKind::TraitObject(vec![cx.trait_bound(path_debug)], ast::TraitObjectSyntax::Dyn),
 141         );
 142         let ty_slice = cx.ty(
 143             span,
 144             ast::TyKind::Slice(cx.ty_ref(span, ty_dyn_debug, None, ast::Mutability::Not)),
 145         );
 146         let values_let = cx.stmt_let_ty(
 147             span,
 148             false,
 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),
 152         );
 153
 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
 158         } else {
 159             sym::debug_tuple_fields_finish
 160         };
 161         let fn_path_debug_internal = cx.std_path(&[sym::fmt, sym::Formatter, sym_debug]);
 162
 163         let mut args = Vec::with_capacity(4);
 164         args.push(fmt);
 165         args.push(name);
 166         if is_struct {
 167             args.push(cx.expr_ident(span, Ident::new(sym::names, span)));
 168         }
 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);
 171
 172         let mut stmts = Vec::with_capacity(3);
 173         if is_struct {
 174             stmts.push(names_let.unwrap());
 175         }
 176         stmts.push(values_let);
 177         BlockOrExpr::new_mixed(stmts, Some(expr))
 178     }
 179 }
 180
 181 /// Special case for enums with no fields. Builds:
 182 /// ```text
 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,
 186 ///             match self {
 187 ///                 A::A => "A",
 188 ///                 A::B() => "B",
 189 ///                 A::C {} => "C",
 190 ///             })
 191 ///     }
 192 /// }
 193 /// ```
 194 fn show_fieldless_enum(
 195     cx: &mut ExtCtxt<'_>,
 196     span: Span,
 197     def: &EnumDef,
 198     substr: &Substructure<'_>,
 199 ) -> BlockOrExpr {
 200     let fmt = substr.nonselflike_args[0].clone();
 201     let arms = def
 202         .variants
 203         .iter()
 204         .map(|v| {
 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![])
 210                 }
 211                 ast::VariantData::Struct(fields, _) => {
 212                     debug_assert!(fields.is_empty());
 213                     cx.pat_struct(span, variant_path, vec![])
 214                 }
 215                 ast::VariantData::Unit(_) => cx.pat_path(span, variant_path),
 216             };
 217             cx.arm(span, pat, cx.expr_str(span, v.ident.name))
 218         })
 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]))
 223 }