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 rustc_ast::{self as ast, MetaItem};
   6 use rustc_expand::base::{Annotatable, ExtCtxt};
   7 use rustc_span::symbol::{sym, Ident, Symbol};
   8 use rustc_span::Span;
   9
  10 pub fn expand_deriving_debug(
  11     cx: &mut ExtCtxt<'_>,
  12     span: Span,
  13     mitem: &MetaItem,
  14     item: &Annotatable,
  15     push: &mut dyn FnMut(Annotatable),
  16     is_const: bool,
  17 ) {
  18     // &mut ::std::fmt::Formatter
  19     let fmtr = Ref(Box::new(Path(path_std!(fmt::Formatter))), ast::Mutability::Mut);
  20
  21     let trait_def = TraitDef {
  22         span,
  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 {
  28             name: sym::fmt,
  29             generics: Bounds::empty(),
  30             explicit_self: true,
  31             nonself_args: vec![(fmtr, sym::f)],
  32             ret_ty: Path(path_std!(fmt::Result)),
  33             attributes: ast::AttrVec::new(),
  34             unify_fieldless_variants: false,
  35             combine_substructure: combine_substructure(Box::new(|a, b, c| {
  36                 show_substructure(a, b, c)
  37             })),
  38         }],
  39         associated_types: Vec::new(),
  40         is_const,
  41     };
  42     trait_def.expand(cx, mitem, item, push)
  43 }
  44
  45 fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>) -> BlockOrExpr {
  46     let (ident, vdata, fields) = match substr.fields {
  47         Struct(vdata, fields) => (substr.type_ident, *vdata, fields),
  48         EnumMatching(_, _, v, fields) => (v.ident, &v.data, fields),
  49         EnumTag(..) | StaticStruct(..) | StaticEnum(..) => {
  50             cx.span_bug(span, "nonsensical .fields in `#[derive(Debug)]`")
  51         }
  52     };
  53
  54     // We want to make sure we have the ctxt set so that we can use unstable methods
  55     let span = cx.with_def_site_ctxt(span);
  56     let name = cx.expr_str(span, ident.name);
  57     let fmt = substr.nonselflike_args[0].clone();
  58
  59     // Struct and tuples are similar enough that we use the same code for both,
  60     // with some extra pieces for structs due to the field names.
  61     let (is_struct, args_per_field) = match vdata {
  62         ast::VariantData::Unit(..) => {
  63             // Special fast path for unit variants.
  64             assert!(fields.is_empty());
  65             (false, 0)
  66         }
  67         ast::VariantData::Tuple(..) => (false, 1),
  68         ast::VariantData::Struct(..) => (true, 2),
  69     };
  70
  71     // The number of fields that can be handled without an array.
  72     const CUTOFF: usize = 5;
  73
  74     if fields.is_empty() {
  75         // Special case for no fields.
  76         let fn_path_write_str = cx.std_path(&[sym::fmt, sym::Formatter, sym::write_str]);
  77         let expr = cx.expr_call_global(span, fn_path_write_str, vec![fmt, name]);
  78         BlockOrExpr::new_expr(expr)
  79     } else if fields.len() <= CUTOFF {
  80         // Few enough fields that we can use a specific-length method.
  81         let debug = if is_struct {
  82             format!("debug_struct_field{}_finish", fields.len())
  83         } else {
  84             format!("debug_tuple_field{}_finish", fields.len())
  85         };
  86         let fn_path_debug = cx.std_path(&[sym::fmt, sym::Formatter, Symbol::intern(&debug)]);
  87
  88         let mut args = Vec::with_capacity(2 + fields.len() * args_per_field);
  89         args.extend([fmt, name]);
  90         for i in 0..fields.len() {
  91             let field = &fields[i];
  92             if is_struct {
  93                 let name = cx.expr_str(field.span, field.name.unwrap().name);
  94                 args.push(name);
  95             }
  96             // Use an extra indirection to make sure this works for unsized types.
  97             let field = cx.expr_addr_of(field.span, field.self_expr.clone());
  98             args.push(field);
  99         }
 100         let expr = cx.expr_call_global(span, fn_path_debug, args);
 101         BlockOrExpr::new_expr(expr)
 102     } else {
 103         // Enough fields that we must use the any-length method.
 104         let mut name_exprs = Vec::with_capacity(fields.len());
 105         let mut value_exprs = Vec::with_capacity(fields.len());
 106
 107         for field in fields {
 108             if is_struct {
 109                 name_exprs.push(cx.expr_str(field.span, field.name.unwrap().name));
 110             }
 111
 112             // Use an extra indirection to make sure this works for unsized types.
 113             let field = cx.expr_addr_of(field.span, field.self_expr.clone());
 114             value_exprs.push(field);
 115         }
 116
 117         // `let names: &'static _ = &["field1", "field2"];`
 118         let names_let = if is_struct {
 119             let lt_static = Some(cx.lifetime_static(span));
 120             let ty_static_ref =
 121                 cx.ty_rptr(span, cx.ty_infer(span), lt_static, ast::Mutability::Not);
 122             Some(cx.stmt_let_ty(
 123                 span,
 124                 false,
 125                 Ident::new(sym::names, span),
 126                 Some(ty_static_ref),
 127                 cx.expr_array_ref(span, name_exprs),
 128             ))
 129         } else {
 130             None
 131         };
 132
 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(
 136             span,
 137             ast::TyKind::TraitObject(vec![cx.trait_bound(path_debug)], ast::TraitObjectSyntax::Dyn),
 138         );
 139         let ty_slice = cx.ty(
 140             span,
 141             ast::TyKind::Slice(cx.ty_rptr(span, ty_dyn_debug, None, ast::Mutability::Not)),
 142         );
 143         let values_let = cx.stmt_let_ty(
 144             span,
 145             false,
 146             Ident::new(sym::values, span),
 147             Some(cx.ty_rptr(span, ty_slice, None, ast::Mutability::Not)),
 148             cx.expr_array_ref(span, value_exprs),
 149         );
 150
 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
 155         } else {
 156             sym::debug_tuple_fields_finish
 157         };
 158         let fn_path_debug_internal = cx.std_path(&[sym::fmt, sym::Formatter, sym_debug]);
 159
 160         let mut args = Vec::with_capacity(4);
 161         args.push(fmt);
 162         args.push(name);
 163         if is_struct {
 164             args.push(cx.expr_ident(span, Ident::new(sym::names, span)));
 165         }
 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);
 168
 169         let mut stmts = Vec::with_capacity(3);
 170         if is_struct {
 171             stmts.push(names_let.unwrap());
 172         }
 173         stmts.push(values_let);
 174         BlockOrExpr::new_mixed(stmts, Some(expr))
 175     }
 176 }