src/librustc_passes/static_recursion.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 // This compiler pass detects constants that refer to themselves
  12 // recursively.
  13
  14 use rustc::dep_graph::DepNode;
  15 use rustc::hir::map as ast_map;
  16 use rustc::session::{Session, CompileResult};
  17 use rustc::hir::def::{Def, DefMap};
  18 use rustc::util::nodemap::NodeMap;
  19
  20 use syntax::{ast};
  21 use syntax::codemap::Span;
  22 use syntax::feature_gate::{GateIssue, emit_feature_err};
  23 use rustc::hir::intravisit::{self, Visitor};
  24 use rustc::hir;
  25
  26 use std::cell::RefCell;
  27
  28 struct CheckCrateVisitor<'a, 'ast: 'a> {
  29     sess: &'a Session,
  30     def_map: &'a DefMap,
  31     ast_map: &'a ast_map::Map<'ast>,
  32     // `discriminant_map` is a cache that associates the `NodeId`s of local
  33     // variant definitions with the discriminant expression that applies to
  34     // each one. If the variant uses the default values (starting from `0`),
  35     // then `None` is stored.
  36     discriminant_map: RefCell<NodeMap<Option<&'ast hir::Expr>>>,
  37 }
  38
  39 impl<'a, 'ast: 'a> Visitor<'ast> for CheckCrateVisitor<'a, 'ast> {
  40     fn visit_item(&mut self, it: &'ast hir::Item) {
  41         match it.node {
  42             hir::ItemStatic(..) |
  43             hir::ItemConst(..) => {
  44                 let mut recursion_visitor =
  45                     CheckItemRecursionVisitor::new(self, &it.span);
  46                 recursion_visitor.visit_item(it);
  47             },
  48             hir::ItemEnum(ref enum_def, ref generics) => {
  49                 // We could process the whole enum, but handling the variants
  50                 // with discriminant expressions one by one gives more specific,
  51                 // less redundant output.
  52                 for variant in &enum_def.variants {
  53                     if let Some(_) = variant.node.disr_expr {
  54                         let mut recursion_visitor =
  55                             CheckItemRecursionVisitor::new(self, &variant.span);
  56                         recursion_visitor.populate_enum_discriminants(enum_def);
  57                         recursion_visitor.visit_variant(variant, generics, it.id);
  58                     }
  59                 }
  60             }
  61             _ => {}
  62         }
  63         intravisit::walk_item(self, it)
  64     }
  65
  66     fn visit_trait_item(&mut self, ti: &'ast hir::TraitItem) {
  67         match ti.node {
  68             hir::ConstTraitItem(_, ref default) => {
  69                 if let Some(_) = *default {
  70                     let mut recursion_visitor =
  71                         CheckItemRecursionVisitor::new(self, &ti.span);
  72                     recursion_visitor.visit_trait_item(ti);
  73                 }
  74             }
  75             _ => {}
  76         }
  77         intravisit::walk_trait_item(self, ti)
  78     }
  79
  80     fn visit_impl_item(&mut self, ii: &'ast hir::ImplItem) {
  81         match ii.node {
  82             hir::ImplItemKind::Const(..) => {
  83                 let mut recursion_visitor =
  84                     CheckItemRecursionVisitor::new(self, &ii.span);
  85                 recursion_visitor.visit_impl_item(ii);
  86             }
  87             _ => {}
  88         }
  89         intravisit::walk_impl_item(self, ii)
  90     }
  91 }
  92
  93 pub fn check_crate<'ast>(sess: &Session,
  94                          def_map: &DefMap,
  95                          ast_map: &ast_map::Map<'ast>)
  96                          -> CompileResult {
  97     let _task = ast_map.dep_graph.in_task(DepNode::CheckStaticRecursion);
  98
  99     let mut visitor = CheckCrateVisitor {
 100         sess: sess,
 101         def_map: def_map,
 102         ast_map: ast_map,
 103         discriminant_map: RefCell::new(NodeMap()),
 104     };
 105     sess.track_errors(|| {
 106         ast_map.krate().visit_all_items(&mut visitor);
 107     })
 108 }
 109
 110 struct CheckItemRecursionVisitor<'a, 'ast: 'a> {
 111     root_span: &'a Span,
 112     sess: &'a Session,
 113     ast_map: &'a ast_map::Map<'ast>,
 114     def_map: &'a DefMap,
 115     discriminant_map: &'a RefCell<NodeMap<Option<&'ast hir::Expr>>>,
 116     idstack: Vec<ast::NodeId>,
 117 }
 118
 119 impl<'a, 'ast: 'a> CheckItemRecursionVisitor<'a, 'ast> {
 120     fn new(v: &'a CheckCrateVisitor<'a, 'ast>, span: &'a Span)
 121            -> CheckItemRecursionVisitor<'a, 'ast> {
 122         CheckItemRecursionVisitor {
 123             root_span: span,
 124             sess: v.sess,
 125             ast_map: v.ast_map,
 126             def_map: v.def_map,
 127             discriminant_map: &v.discriminant_map,
 128             idstack: Vec::new(),
 129         }
 130     }
 131     fn with_item_id_pushed<F>(&mut self, id: ast::NodeId, f: F)
 132           where F: Fn(&mut Self) {
 133         if self.idstack.iter().any(|&x| x == id) {
 134             let any_static = self.idstack.iter().any(|&x| {
 135                 if let ast_map::NodeItem(item) = self.ast_map.get(x) {
 136                     if let hir::ItemStatic(..) = item.node {
 137                         true
 138                     } else {
 139                         false
 140                     }
 141                 } else {
 142                     false
 143                 }
 144             });
 145             if any_static {
 146                 if !self.sess.features.borrow().static_recursion {
 147                     emit_feature_err(&self.sess.parse_sess.span_diagnostic,
 148                                      "static_recursion",
 149                                      *self.root_span, GateIssue::Language, "recursive static");
 150                 }
 151             } else {
 152                 span_err!(self.sess, *self.root_span, E0265, "recursive constant");
 153             }
 154             return;
 155         }
 156         self.idstack.push(id);
 157         f(self);
 158         self.idstack.pop();
 159     }
 160     // If a variant has an expression specifying its discriminant, then it needs
 161     // to be checked just like a static or constant. However, if there are more
 162     // variants with no explicitly specified discriminant, those variants will
 163     // increment the same expression to get their values.
 164     //
 165     // So for every variant, we need to track whether there is an expression
 166     // somewhere in the enum definition that controls its discriminant. We do
 167     // this by starting from the end and searching backward.
 168     fn populate_enum_discriminants(&self, enum_definition: &'ast hir::EnumDef) {
 169         // Get the map, and return if we already processed this enum or if it
 170         // has no variants.
 171         let mut discriminant_map = self.discriminant_map.borrow_mut();
 172         match enum_definition.variants.first() {
 173             None => { return; }
 174             Some(variant) if discriminant_map.contains_key(&variant.node.data.id()) => {
 175                 return;
 176             }
 177             _ => {}
 178         }
 179
 180         // Go through all the variants.
 181         let mut variant_stack: Vec<ast::NodeId> = Vec::new();
 182         for variant in enum_definition.variants.iter().rev() {
 183             variant_stack.push(variant.node.data.id());
 184             // When we find an expression, every variant currently on the stack
 185             // is affected by that expression.
 186             if let Some(ref expr) = variant.node.disr_expr {
 187                 for id in &variant_stack {
 188                     discriminant_map.insert(*id, Some(expr));
 189                 }
 190                 variant_stack.clear()
 191             }
 192         }
 193         // If we are at the top, that always starts at 0, so any variant on the
 194         // stack has a default value and does not need to be checked.
 195         for id in &variant_stack {
 196             discriminant_map.insert(*id, None);
 197         }
 198     }
 199 }
 200
 201 impl<'a, 'ast: 'a> Visitor<'ast> for CheckItemRecursionVisitor<'a, 'ast> {
 202     fn visit_item(&mut self, it: &'ast hir::Item) {
 203         self.with_item_id_pushed(it.id, |v| intravisit::walk_item(v, it));
 204     }
 205
 206     fn visit_enum_def(&mut self, enum_definition: &'ast hir::EnumDef,
 207                       generics: &'ast hir::Generics, item_id: ast::NodeId, _: Span) {
 208         self.populate_enum_discriminants(enum_definition);
 209         intravisit::walk_enum_def(self, enum_definition, generics, item_id);
 210     }
 211
 212     fn visit_variant(&mut self, variant: &'ast hir::Variant,
 213                      _: &'ast hir::Generics, _: ast::NodeId) {
 214         let variant_id = variant.node.data.id();
 215         let maybe_expr;
 216         if let Some(get_expr) = self.discriminant_map.borrow().get(&variant_id) {
 217             // This is necessary because we need to let the `discriminant_map`
 218             // borrow fall out of scope, so that we can reborrow farther down.
 219             maybe_expr = (*get_expr).clone();
 220         } else {
 221             span_bug!(variant.span,
 222                       "`check_static_recursion` attempted to visit \
 223                       variant with unknown discriminant")
 224         }
 225         // If `maybe_expr` is `None`, that's because no discriminant is
 226         // specified that affects this variant. Thus, no risk of recursion.
 227         if let Some(expr) = maybe_expr {
 228             self.with_item_id_pushed(expr.id, |v| intravisit::walk_expr(v, expr));
 229         }
 230     }
 231
 232     fn visit_trait_item(&mut self, ti: &'ast hir::TraitItem) {
 233         self.with_item_id_pushed(ti.id, |v| intravisit::walk_trait_item(v, ti));
 234     }
 235
 236     fn visit_impl_item(&mut self, ii: &'ast hir::ImplItem) {
 237         self.with_item_id_pushed(ii.id, |v| intravisit::walk_impl_item(v, ii));
 238     }
 239
 240     fn visit_expr(&mut self, e: &'ast hir::Expr) {
 241         match e.node {
 242             hir::ExprPath(..) => {
 243                 match self.def_map.get(&e.id).map(|d| d.base_def) {
 244                     Some(Def::Static(def_id, _)) |
 245                     Some(Def::AssociatedConst(def_id)) |
 246                     Some(Def::Const(def_id)) => {
 247                         if let Some(node_id) = self.ast_map.as_local_node_id(def_id) {
 248                             match self.ast_map.get(node_id) {
 249                                 ast_map::NodeItem(item) =>
 250                                     self.visit_item(item),
 251                                 ast_map::NodeTraitItem(item) =>
 252                                     self.visit_trait_item(item),
 253                                 ast_map::NodeImplItem(item) =>
 254                                     self.visit_impl_item(item),
 255                                 ast_map::NodeForeignItem(_) => {},
 256                                 _ => {
 257                                     span_bug!(
 258                                         e.span,
 259                                         "expected item, found {}",
 260                                         self.ast_map.node_to_string(node_id));
 261                                 }
 262                             }
 263                         }
 264                     }
 265                     // For variants, we only want to check expressions that
 266                     // affect the specific variant used, but we need to check
 267                     // the whole enum definition to see what expression that
 268                     // might be (if any).
 269                     Some(Def::Variant(enum_id, variant_id)) => {
 270                         if let Some(enum_node_id) = self.ast_map.as_local_node_id(enum_id) {
 271                             if let hir::ItemEnum(ref enum_def, ref generics) =
 272                                 self.ast_map.expect_item(enum_node_id).node
 273                             {
 274                                 self.populate_enum_discriminants(enum_def);
 275                                 let enum_id = self.ast_map.as_local_node_id(enum_id).unwrap();
 276                                 let variant_id = self.ast_map.as_local_node_id(variant_id).unwrap();
 277                                 let variant = self.ast_map.expect_variant(variant_id);
 278                                 self.visit_variant(variant, generics, enum_id);
 279                             } else {
 280                                 span_bug!(e.span,
 281                                           "`check_static_recursion` found \
 282                                            non-enum in Def::Variant");
 283                             }
 284                         }
 285                     }
 286                     _ => ()
 287                 }
 288             },
 289             _ => ()
 290         }
 291         intravisit::walk_expr(self, e);
 292     }
 293 }