src/librustc_builtin_macros/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::ast::{self, Ident};
   6 use rustc_ast::ast::{Expr, MetaItem};
   7 use rustc_ast::ptr::P;
   8 use rustc_expand::base::{Annotatable, ExtCtxt};
   9 use rustc_span::symbol::sym;
  10 use rustc_span::{Span, DUMMY_SP};
  11
  12 pub fn expand_deriving_debug(
  13     cx: &mut ExtCtxt<'_>,
  14     span: Span,
  15     mitem: &MetaItem,
  16     item: &Annotatable,
  17     push: &mut dyn FnMut(Annotatable),
  18 ) {
  19     // &mut ::std::fmt::Formatter
  20     let fmtr =
  21         Ptr(Box::new(Literal(path_std!(cx, fmt::Formatter))), Borrowed(None, ast::Mutability::Mut));
  22
  23     let trait_def = TraitDef {
  24         span,
  25         attributes: Vec::new(),
  26         path: path_std!(cx, fmt::Debug),
  27         additional_bounds: Vec::new(),
  28         generics: LifetimeBounds::empty(),
  29         is_unsafe: false,
  30         supports_unions: false,
  31         methods: vec![MethodDef {
  32             name: "fmt",
  33             generics: LifetimeBounds::empty(),
  34             explicit_self: borrowed_explicit_self(),
  35             args: vec![(fmtr, "f")],
  36             ret_ty: Literal(path_std!(cx, fmt::Result)),
  37             attributes: Vec::new(),
  38             is_unsafe: false,
  39             unify_fieldless_variants: false,
  40             combine_substructure: combine_substructure(Box::new(|a, b, c| {
  41                 show_substructure(a, b, c)
  42             })),
  43         }],
  44         associated_types: Vec::new(),
  45     };
  46     trait_def.expand(cx, mitem, item, push)
  47 }
  48
  49 /// We use the debug builders to do the heavy lifting here
  50 fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>) -> P<Expr> {
  51     // build fmt.debug_struct(<name>).field(<fieldname>, &<fieldval>)....build()
  52     // or fmt.debug_tuple(<name>).field(&<fieldval>)....build()
  53     // based on the "shape".
  54     let (ident, vdata, fields) = match substr.fields {
  55         Struct(vdata, fields) => (substr.type_ident, *vdata, fields),
  56         EnumMatching(_, _, v, fields) => (v.ident, &v.data, fields),
  57         EnumNonMatchingCollapsed(..) | StaticStruct(..) | StaticEnum(..) => {
  58             cx.span_bug(span, "nonsensical .fields in `#[derive(Debug)]`")
  59         }
  60     };
  61
  62     // We want to make sure we have the ctxt set so that we can use unstable methods
  63     let span = cx.with_def_site_ctxt(span);
  64     let name = cx.expr_lit(span, ast::LitKind::Str(ident.name, ast::StrStyle::Cooked));
  65     let builder = cx.ident_of("debug_trait_builder", span);
  66     let builder_expr = cx.expr_ident(span, builder);
  67
  68     let fmt = substr.nonself_args[0].clone();
  69
  70     let mut stmts = vec![];
  71     match vdata {
  72         ast::VariantData::Tuple(..) | ast::VariantData::Unit(..) => {
  73             // tuple struct/"normal" variant
  74             let expr = cx.expr_method_call(span, fmt, cx.ident_of("debug_tuple", span), vec![name]);
  75             stmts.push(cx.stmt_let(span, true, builder, expr));
  76
  77             for field in fields {
  78                 // Use double indirection to make sure this works for unsized types
  79                 let field = cx.expr_addr_of(field.span, field.self_.clone());
  80                 let field = cx.expr_addr_of(field.span, field);
  81
  82                 let expr = cx.expr_method_call(
  83                     span,
  84                     builder_expr.clone(),
  85                     Ident::new(sym::field, span),
  86                     vec![field],
  87                 );
  88
  89                 // Use `let _ = expr;` to avoid triggering the
  90                 // unused_results lint.
  91                 stmts.push(stmt_let_undescore(cx, span, expr));
  92             }
  93         }
  94         ast::VariantData::Struct(..) => {
  95             // normal struct/struct variant
  96             let expr =
  97                 cx.expr_method_call(span, fmt, cx.ident_of("debug_struct", span), vec![name]);
  98             stmts.push(cx.stmt_let(DUMMY_SP, true, builder, expr));
  99
 100             for field in fields {
 101                 let name = cx.expr_lit(
 102                     field.span,
 103                     ast::LitKind::Str(field.name.unwrap().name, ast::StrStyle::Cooked),
 104                 );
 105
 106                 // Use double indirection to make sure this works for unsized types
 107                 let field = cx.expr_addr_of(field.span, field.self_.clone());
 108                 let field = cx.expr_addr_of(field.span, field);
 109                 let expr = cx.expr_method_call(
 110                     span,
 111                     builder_expr.clone(),
 112                     Ident::new(sym::field, span),
 113                     vec![name, field],
 114                 );
 115                 stmts.push(stmt_let_undescore(cx, span, expr));
 116             }
 117         }
 118     }
 119
 120     let expr = cx.expr_method_call(span, builder_expr, cx.ident_of("finish", span), vec![]);
 121
 122     stmts.push(cx.stmt_expr(expr));
 123     let block = cx.block(span, stmts);
 124     cx.expr_block(block)
 125 }
 126
 127 fn stmt_let_undescore(cx: &mut ExtCtxt<'_>, sp: Span, expr: P<ast::Expr>) -> ast::Stmt {
 128     let local = P(ast::Local {
 129         pat: cx.pat_wild(sp),
 130         ty: None,
 131         init: Some(expr),
 132         id: ast::DUMMY_NODE_ID,
 133         span: sp,
 134         attrs: ast::AttrVec::new(),
 135     });
 136     ast::Stmt { id: ast::DUMMY_NODE_ID, kind: ast::StmtKind::Local(local), span: sp }
 137 }