1 // Copyright 2018 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.
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.
11 use rustc_data_structures::bit_set::BitSet;
12 use rustc::hir::def_id::DefId;
13 use rustc::hir::intravisit::FnKind;
14 use rustc::hir::map::blocks::FnLikeNode;
15 use rustc::lint::builtin::UNCONDITIONAL_RECURSION;
16 use rustc::mir::{self, Mir, TerminatorKind};
17 use rustc::ty::{AssociatedItem, AssociatedItemContainer, Instance, TyCtxt, TyKind};
18 use rustc::ty::subst::Substs;
20 pub fn check(tcx: TyCtxt<'a, 'tcx, 'tcx>,
23 let node_id = tcx.hir().as_local_node_id(def_id).unwrap();
25 if let Some(fn_like_node) = FnLikeNode::from_node(tcx.hir().get(node_id)) {
26 check_fn_for_unconditional_recursion(tcx, fn_like_node.kind(), mir, def_id);
30 fn check_fn_for_unconditional_recursion(tcx: TyCtxt<'a, 'tcx, 'tcx>,
34 if let FnKind::Closure(_) = fn_kind {
35 // closures can't recur, so they don't matter.
39 //FIXME(#54444) rewrite this lint to use the dataflow framework
41 // Walk through this function (say `f`) looking to see if
42 // every possible path references itself, i.e. the function is
43 // called recursively unconditionally. This is done by trying
44 // to find a path from the entry node to the exit node that
45 // *doesn't* call `f` by traversing from the entry while
46 // pretending that calls of `f` are sinks (i.e. ignoring any
47 // exit edges from them).
49 // NB. this has an edge case with non-returning statements,
50 // like `loop {}` or `panic!()`: control flow never reaches
51 // the exit node through these, so one can have a function
52 // that never actually calls itself but is still picked up by
56 // if !cond { panic!() } // could come from `assert!(cond)`
60 // In general, functions of that form may be able to call
61 // itself a finite number of times and then diverge. The lint
62 // considers this to be an error for two reasons, (a) it is
63 // easier to implement, and (b) it seems rare to actually want
64 // to have behaviour like the above, rather than
65 // e.g. accidentally recursing after an assert.
67 let basic_blocks = mir.basic_blocks();
68 let mut reachable_without_self_call_queue = vec![mir::START_BLOCK];
69 let mut reached_exit_without_self_call = false;
70 let mut self_call_locations = vec![];
71 let mut visited = BitSet::new_empty(basic_blocks.len());
73 let param_env = tcx.param_env(def_id);
74 let trait_substs_count =
75 match tcx.opt_associated_item(def_id) {
77 container: AssociatedItemContainer::TraitContainer(trait_def_id),
79 }) => tcx.generics_of(trait_def_id).count(),
82 let caller_substs = &Substs::identity_for_item(tcx, def_id)[..trait_substs_count];
84 while let Some(bb) = reachable_without_self_call_queue.pop() {
85 if visited.contains(bb) {
92 let block = &basic_blocks[bb];
94 if let Some(ref terminator) = block.terminator {
95 match terminator.kind {
96 TerminatorKind::Call { ref func, .. } => {
97 let func_ty = func.ty(mir, tcx);
99 if let TyKind::FnDef(fn_def_id, substs) = func_ty.sty {
100 let (call_fn_id, call_substs) =
101 if let Some(instance) = Instance::resolve(tcx,
105 (instance.def_id(), instance.substs)
111 call_fn_id == def_id &&
112 &call_substs[..caller_substs.len()] == caller_substs;
115 self_call_locations.push(terminator.source_info);
117 //this is a self call so we shouldn't explore
118 //further down this path
123 TerminatorKind::Abort | TerminatorKind::Return => {
125 reached_exit_without_self_call = true;
131 for successor in terminator.successors() {
132 reachable_without_self_call_queue.push(*successor);
137 // Check the number of self calls because a function that
138 // doesn't return (e.g. calls a `-> !` function or `loop { /*
139 // no break */ }`) shouldn't be linted unless it actually
141 if !reached_exit_without_self_call && !self_call_locations.is_empty() {
142 let node_id = tcx.hir().as_local_node_id(def_id).unwrap();
143 let sp = tcx.sess.source_map().def_span(tcx.hir().span(node_id));
144 let mut db = tcx.struct_span_lint_node(UNCONDITIONAL_RECURSION,
147 "function cannot return without recursing");
148 db.span_label(sp, "cannot return without recursing");
149 // offer some help to the programmer.
150 for location in &self_call_locations {
151 db.span_label(location.span, "recursive call site");
153 db.help("a `loop` may express intention better if this is on purpose");