src/libsyntax_ext/deriving/debug.rs

   1 use crate::deriving::path_std;
   2 use crate::deriving::generic::*;
   3 use crate::deriving::generic::ty::*;
   4
   5 use rustc_data_structures::thin_vec::ThinVec;
   6
   7 use syntax::ast::{self, Ident};
   8 use syntax::ast::{Expr, MetaItem};
   9 use syntax::ext::base::{Annotatable, ExtCtxt};
  10 use syntax::ptr::P;
  11 use syntax::symbol::sym;
  12 use syntax_pos::{DUMMY_SP, Span};
  13
  14 pub fn expand_deriving_debug(cx: &mut ExtCtxt<'_>,
  15                              span: Span,
  16                              mitem: &MetaItem,
  17                              item: &Annotatable,
  18                              push: &mut dyn FnMut(Annotatable)) {
  19     // &mut ::std::fmt::Formatter
  20     let fmtr = Ptr(Box::new(Literal(path_std!(cx, fmt::Formatter))),
  21                    Borrowed(None, ast::Mutability::Mutable));
  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(..) |
  58         StaticStruct(..) |
  59         StaticEnum(..) => cx.span_bug(span, "nonsensical .fields in `#[derive(Debug)]`"),
  60     };
  61
  62     // We want to make sure we have the ctxt set so that we can use unstable methods
  63     let span = span.with_ctxt(cx.backtrace());
  64     let name = cx.expr_lit(span, ast::LitKind::Str(ident.name, ast::StrStyle::Cooked));
  65     let builder = Ident::from_str("debug_trait_builder").gensym();
  66     let builder_expr = cx.expr_ident(span, builder.clone());
  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 =
  75                 cx.expr_method_call(span, fmt, Ident::from_str("debug_tuple"), vec![name]);
  76             stmts.push(cx.stmt_let(DUMMY_SP, true, builder, expr));
  77
  78             for field in fields {
  79                 // Use double indirection to make sure this works for unsized types
  80                 let field = cx.expr_addr_of(field.span, field.self_.clone());
  81                 let field = cx.expr_addr_of(field.span, field);
  82
  83                 let expr = cx.expr_method_call(span,
  84                                                 builder_expr.clone(),
  85                                                 Ident::with_dummy_span(sym::field),
  86                                                 vec![field]);
  87
  88                 // Use `let _ = expr;` to avoid triggering the
  89                 // unused_results lint.
  90                 stmts.push(stmt_let_undescore(cx, span, expr));
  91             }
  92         }
  93         ast::VariantData::Struct(..) => {
  94             // normal struct/struct variant
  95             let expr =
  96                 cx.expr_method_call(span, fmt, Ident::from_str("debug_struct"), vec![name]);
  97             stmts.push(cx.stmt_let(DUMMY_SP, true, builder, expr));
  98
  99             for field in fields {
 100                 let name = cx.expr_lit(field.span,
 101                                         ast::LitKind::Str(field.name.unwrap().name,
 102                                                             ast::StrStyle::Cooked));
 103
 104                 // Use double indirection to make sure this works for unsized types
 105                 let field = cx.expr_addr_of(field.span, field.self_.clone());
 106                 let field = cx.expr_addr_of(field.span, field);
 107                 let expr = cx.expr_method_call(span,
 108                                                 builder_expr.clone(),
 109                                                 Ident::with_dummy_span(sym::field),
 110                                                 vec![name, field]);
 111                 stmts.push(stmt_let_undescore(cx, span, expr));
 112             }
 113         }
 114     }
 115
 116     let expr = cx.expr_method_call(span, builder_expr, Ident::from_str("finish"), vec![]);
 117
 118     stmts.push(cx.stmt_expr(expr));
 119     let block = cx.block(span, stmts);
 120     cx.expr_block(block)
 121 }
 122
 123 fn stmt_let_undescore(cx: &mut ExtCtxt<'_>, sp: Span, expr: P<ast::Expr>) -> ast::Stmt {
 124     let local = P(ast::Local {
 125         pat: cx.pat_wild(sp),
 126         ty: None,
 127         init: Some(expr),
 128         id: ast::DUMMY_NODE_ID,
 129         span: sp,
 130         attrs: ThinVec::new(),
 131     });
 132     ast::Stmt {
 133         id: ast::DUMMY_NODE_ID,
 134         node: ast::StmtKind::Local(local),
 135         span: sp,
 136     }
 137 }