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::generic::*;
  12 use deriving::generic::ty::*;
  13
  14 use syntax::ast::{self, Ident};
  15 use syntax::ast::{Expr, MetaItem};
  16 use syntax::ext::base::{Annotatable, ExtCtxt};
  17 use syntax::ext::build::AstBuilder;
  18 use syntax::ptr::P;
  19 use syntax_pos::{DUMMY_SP, Span};
  20
  21 pub fn expand_deriving_debug(cx: &mut ExtCtxt,
  22                              span: Span,
  23                              mitem: &MetaItem,
  24                              item: &Annotatable,
  25                              push: &mut FnMut(Annotatable)) {
  26     // &mut ::std::fmt::Formatter
  27     let fmtr = Ptr(Box::new(Literal(path_std!(cx, core::fmt::Formatter))),
  28                    Borrowed(None, ast::Mutability::Mutable));
  29
  30     let trait_def = TraitDef {
  31         span,
  32         attributes: Vec::new(),
  33         path: path_std!(cx, core::fmt::Debug),
  34         additional_bounds: Vec::new(),
  35         generics: LifetimeBounds::empty(),
  36         is_unsafe: false,
  37         supports_unions: false,
  38         methods: vec![MethodDef {
  39                           name: "fmt",
  40                           generics: LifetimeBounds::empty(),
  41                           explicit_self: borrowed_explicit_self(),
  42                           args: vec![fmtr],
  43                           ret_ty: Literal(path_std!(cx, core::fmt::Result)),
  44                           attributes: Vec::new(),
  45                           is_unsafe: false,
  46                           unify_fieldless_variants: false,
  47                           combine_substructure: combine_substructure(Box::new(|a, b, c| {
  48                               show_substructure(a, b, c)
  49                           })),
  50                       }],
  51         associated_types: Vec::new(),
  52     };
  53     trait_def.expand(cx, mitem, item, push)
  54 }
  55
  56 /// We use the debug builders to do the heavy lifting here
  57 fn show_substructure(cx: &mut ExtCtxt, span: Span, substr: &Substructure) -> P<Expr> {
  58     // build fmt.debug_struct(<name>).field(<fieldname>, &<fieldval>)....build()
  59     // or fmt.debug_tuple(<name>).field(&<fieldval>)....build()
  60     // based on the "shape".
  61     let (ident, is_struct) = match *substr.fields {
  62         Struct(vdata, _) => (substr.type_ident, vdata.is_struct()),
  63         EnumMatching(_, _, v, _) => (v.node.name, v.node.data.is_struct()),
  64         EnumNonMatchingCollapsed(..) |
  65         StaticStruct(..) |
  66         StaticEnum(..) => cx.span_bug(span, "nonsensical .fields in `#[derive(Debug)]`"),
  67     };
  68
  69     // We want to make sure we have the ctxt set so that we can use unstable methods
  70     let span = span.with_ctxt(cx.backtrace());
  71     let name = cx.expr_lit(span, ast::LitKind::Str(ident.name, ast::StrStyle::Cooked));
  72     let builder = Ident::from_str("builder");
  73     let builder_expr = cx.expr_ident(span, builder.clone());
  74
  75     let fmt = substr.nonself_args[0].clone();
  76
  77     let mut stmts = match *substr.fields {
  78         Struct(_, ref fields) |
  79         EnumMatching(.., ref fields) => {
  80             let mut stmts = vec![];
  81             if !is_struct {
  82                 // tuple struct/"normal" variant
  83                 let expr =
  84                     cx.expr_method_call(span, fmt, Ident::from_str("debug_tuple"), vec![name]);
  85                 stmts.push(cx.stmt_let(DUMMY_SP, true, builder, expr));
  86
  87                 for field in fields {
  88                     // Use double indirection to make sure this works for unsized types
  89                     let field = cx.expr_addr_of(field.span, field.self_.clone());
  90                     let field = cx.expr_addr_of(field.span, field);
  91
  92                     let expr = cx.expr_method_call(span,
  93                                                    builder_expr.clone(),
  94                                                    Ident::from_str("field"),
  95                                                    vec![field]);
  96
  97                     // Use `let _ = expr;` to avoid triggering the
  98                     // unused_results lint.
  99                     stmts.push(stmt_let_undescore(cx, span, expr));
 100                 }
 101             } else {
 102                 // normal struct/struct variant
 103                 let expr =
 104                     cx.expr_method_call(span, fmt, Ident::from_str("debug_struct"), vec![name]);
 105                 stmts.push(cx.stmt_let(DUMMY_SP, true, builder, expr));
 106
 107                 for field in fields {
 108                     let name = cx.expr_lit(field.span,
 109                                            ast::LitKind::Str(field.name.unwrap().name,
 110                                                              ast::StrStyle::Cooked));
 111
 112                     // Use double indirection to make sure this works for unsized types
 113                     let field = cx.expr_addr_of(field.span, field.self_.clone());
 114                     let field = cx.expr_addr_of(field.span, field);
 115                     let expr = cx.expr_method_call(span,
 116                                                    builder_expr.clone(),
 117                                                    Ident::from_str("field"),
 118                                                    vec![name, field]);
 119                     stmts.push(stmt_let_undescore(cx, span, expr));
 120                 }
 121             }
 122             stmts
 123         }
 124         _ => unreachable!(),
 125     };
 126
 127     let expr = cx.expr_method_call(span, builder_expr, Ident::from_str("finish"), vec![]);
 128
 129     stmts.push(cx.stmt_expr(expr));
 130     let block = cx.block(span, stmts);
 131     cx.expr_block(block)
 132 }
 133
 134 fn stmt_let_undescore(cx: &mut ExtCtxt, sp: Span, expr: P<ast::Expr>) -> ast::Stmt {
 135     let local = P(ast::Local {
 136         pat: cx.pat_wild(sp),
 137         ty: None,
 138         init: Some(expr),
 139         id: ast::DUMMY_NODE_ID,
 140         span: sp,
 141         attrs: ast::ThinVec::new(),
 142     });
 143     ast::Stmt {
 144         id: ast::DUMMY_NODE_ID,
 145         node: ast::StmtKind::Local(local),
 146         span: sp,
 147     }
 148 }