src/libsyntax_ext/deriving/debug.rs

   1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use deriving::path_std;
  12 use deriving::generic::*;
  13 use deriving::generic::ty::*;
  14
  15 use syntax::ast::{self, Ident};
  16 use syntax::ast::{Expr, MetaItem};
  17 use syntax::ext::base::{Annotatable, ExtCtxt};
  18 use syntax::ext::build::AstBuilder;
  19 use syntax::ptr::P;
  20 use syntax_pos::{DUMMY_SP, Span};
  21
  22 pub fn expand_deriving_debug(cx: &mut ExtCtxt,
  23                              span: Span,
  24                              mitem: &MetaItem,
  25                              item: &Annotatable,
  26                              push: &mut dyn FnMut(Annotatable)) {
  27     // &mut ::std::fmt::Formatter
  28     let fmtr = Ptr(Box::new(Literal(path_std!(cx, fmt::Formatter))),
  29                    Borrowed(None, ast::Mutability::Mutable));
  30
  31     let trait_def = TraitDef {
  32         span,
  33         attributes: Vec::new(),
  34         path: path_std!(cx, fmt::Debug),
  35         additional_bounds: Vec::new(),
  36         generics: LifetimeBounds::empty(),
  37         is_unsafe: false,
  38         supports_unions: false,
  39         methods: vec![MethodDef {
  40                           name: "fmt",
  41                           generics: LifetimeBounds::empty(),
  42                           explicit_self: borrowed_explicit_self(),
  43                           args: vec![(fmtr, "f")],
  44                           ret_ty: Literal(path_std!(cx, fmt::Result)),
  45                           attributes: Vec::new(),
  46                           is_unsafe: false,
  47                           unify_fieldless_variants: false,
  48                           combine_substructure: combine_substructure(Box::new(|a, b, c| {
  49                               show_substructure(a, b, c)
  50                           })),
  51                       }],
  52         associated_types: Vec::new(),
  53     };
  54     trait_def.expand(cx, mitem, item, push)
  55 }
  56
  57 /// We use the debug builders to do the heavy lifting here
  58 fn show_substructure(cx: &mut ExtCtxt, span: Span, substr: &Substructure) -> P<Expr> {
  59     // build fmt.debug_struct(<name>).field(<fieldname>, &<fieldval>)....build()
  60     // or fmt.debug_tuple(<name>).field(&<fieldval>)....build()
  61     // based on the "shape".
  62     let (ident, is_struct) = match *substr.fields {
  63         Struct(vdata, _) => (substr.type_ident, vdata.is_struct()),
  64         EnumMatching(_, _, v, _) => (v.node.ident, v.node.data.is_struct()),
  65         EnumNonMatchingCollapsed(..) |
  66         StaticStruct(..) |
  67         StaticEnum(..) => cx.span_bug(span, "nonsensical .fields in `#[derive(Debug)]`"),
  68     };
  69
  70     // We want to make sure we have the ctxt set so that we can use unstable methods
  71     let span = span.with_ctxt(cx.backtrace());
  72     let name = cx.expr_lit(span, ast::LitKind::Str(ident.name, ast::StrStyle::Cooked));
  73     let builder = Ident::from_str("debug_trait_builder").gensym();
  74     let builder_expr = cx.expr_ident(span, builder.clone());
  75
  76     let fmt = substr.nonself_args[0].clone();
  77
  78     let mut stmts = match *substr.fields {
  79         Struct(_, ref fields) |
  80         EnumMatching(.., ref fields) => {
  81             let mut stmts = vec![];
  82             if !is_struct {
  83                 // tuple struct/"normal" variant
  84                 let expr =
  85                     cx.expr_method_call(span, fmt, Ident::from_str("debug_tuple"), vec![name]);
  86                 stmts.push(cx.stmt_let(DUMMY_SP, true, builder, expr));
  87
  88                 for field in fields {
  89                     // Use double indirection to make sure this works for unsized types
  90                     let field = cx.expr_addr_of(field.span, field.self_.clone());
  91                     let field = cx.expr_addr_of(field.span, field);
  92
  93                     let expr = cx.expr_method_call(span,
  94                                                    builder_expr.clone(),
  95                                                    Ident::from_str("field"),
  96                                                    vec![field]);
  97
  98                     // Use `let _ = expr;` to avoid triggering the
  99                     // unused_results lint.
 100                     stmts.push(stmt_let_undescore(cx, span, expr));
 101                 }
 102             } else {
 103                 // normal struct/struct variant
 104                 let expr =
 105                     cx.expr_method_call(span, fmt, Ident::from_str("debug_struct"), vec![name]);
 106                 stmts.push(cx.stmt_let(DUMMY_SP, true, builder, expr));
 107
 108                 for field in fields {
 109                     let name = cx.expr_lit(field.span,
 110                                            ast::LitKind::Str(field.name.unwrap().name,
 111                                                              ast::StrStyle::Cooked));
 112
 113                     // Use double indirection to make sure this works for unsized types
 114                     let field = cx.expr_addr_of(field.span, field.self_.clone());
 115                     let field = cx.expr_addr_of(field.span, field);
 116                     let expr = cx.expr_method_call(span,
 117                                                    builder_expr.clone(),
 118                                                    Ident::from_str("field"),
 119                                                    vec![name, field]);
 120                     stmts.push(stmt_let_undescore(cx, span, expr));
 121                 }
 122             }
 123             stmts
 124         }
 125         _ => unreachable!(),
 126     };
 127
 128     let expr = cx.expr_method_call(span, builder_expr, Ident::from_str("finish"), vec![]);
 129
 130     stmts.push(cx.stmt_expr(expr));
 131     let block = cx.block(span, stmts);
 132     cx.expr_block(block)
 133 }
 134
 135 fn stmt_let_undescore(cx: &mut ExtCtxt, sp: Span, expr: P<ast::Expr>) -> ast::Stmt {
 136     let local = P(ast::Local {
 137         pat: cx.pat_wild(sp),
 138         ty: None,
 139         init: Some(expr),
 140         id: ast::DUMMY_NODE_ID,
 141         span: sp,
 142         attrs: ast::ThinVec::new(),
 143     });
 144     ast::Stmt {
 145         id: ast::DUMMY_NODE_ID,
 146         node: ast::StmtKind::Local(local),
 147         span: sp,
 148     }
 149 }