1 use rustc_data_structures::bit_set::BitSet;
2 use rustc::hir::def_id::DefId;
3 use rustc::hir::intravisit::FnKind;
4 use rustc::hir::map::blocks::FnLikeNode;
5 use rustc::lint::builtin::UNCONDITIONAL_RECURSION;
6 use rustc::mir::{self, Mir, TerminatorKind};
7 use rustc::ty::{AssociatedItem, AssociatedItemContainer, Instance, TyCtxt, TyKind};
8 use rustc::ty::subst::Substs;
10 pub fn check(tcx: TyCtxt<'a, 'tcx, 'tcx>,
13 let node_id = tcx.hir().as_local_node_id(def_id).unwrap();
15 if let Some(fn_like_node) = FnLikeNode::from_node(tcx.hir().get(node_id)) {
16 check_fn_for_unconditional_recursion(tcx, fn_like_node.kind(), mir, def_id);
20 fn check_fn_for_unconditional_recursion(tcx: TyCtxt<'a, 'tcx, 'tcx>,
24 if let FnKind::Closure(_) = fn_kind {
25 // closures can't recur, so they don't matter.
29 //FIXME(#54444) rewrite this lint to use the dataflow framework
31 // Walk through this function (say `f`) looking to see if
32 // every possible path references itself, i.e., the function is
33 // called recursively unconditionally. This is done by trying
34 // to find a path from the entry node to the exit node that
35 // *doesn't* call `f` by traversing from the entry while
36 // pretending that calls of `f` are sinks (i.e., ignoring any
37 // exit edges from them).
39 // NB. this has an edge case with non-returning statements,
40 // like `loop {}` or `panic!()`: control flow never reaches
41 // the exit node through these, so one can have a function
42 // that never actually calls itself but is still picked up by
46 // if !cond { panic!() } // could come from `assert!(cond)`
50 // In general, functions of that form may be able to call
51 // itself a finite number of times and then diverge. The lint
52 // considers this to be an error for two reasons, (a) it is
53 // easier to implement, and (b) it seems rare to actually want
54 // to have behaviour like the above, rather than
55 // e.g., accidentally recursing after an assert.
57 let basic_blocks = mir.basic_blocks();
58 let mut reachable_without_self_call_queue = vec![mir::START_BLOCK];
59 let mut reached_exit_without_self_call = false;
60 let mut self_call_locations = vec![];
61 let mut visited = BitSet::new_empty(basic_blocks.len());
63 let param_env = tcx.param_env(def_id);
64 let trait_substs_count =
65 match tcx.opt_associated_item(def_id) {
67 container: AssociatedItemContainer::TraitContainer(trait_def_id),
69 }) => tcx.generics_of(trait_def_id).count(),
72 let caller_substs = &Substs::identity_for_item(tcx, def_id)[..trait_substs_count];
74 while let Some(bb) = reachable_without_self_call_queue.pop() {
75 if visited.contains(bb) {
82 let block = &basic_blocks[bb];
84 if let Some(ref terminator) = block.terminator {
85 match terminator.kind {
86 TerminatorKind::Call { ref func, .. } => {
87 let func_ty = func.ty(mir, tcx);
89 if let TyKind::FnDef(fn_def_id, substs) = func_ty.sty {
90 let (call_fn_id, call_substs) =
91 if let Some(instance) = Instance::resolve(tcx,
95 (instance.def_id(), instance.substs)
101 call_fn_id == def_id &&
102 &call_substs[..caller_substs.len()] == caller_substs;
105 self_call_locations.push(terminator.source_info);
107 //this is a self call so we shouldn't explore
108 //further down this path
113 TerminatorKind::Abort | TerminatorKind::Return => {
115 reached_exit_without_self_call = true;
121 for successor in terminator.successors() {
122 reachable_without_self_call_queue.push(*successor);
127 // Check the number of self calls because a function that
128 // doesn't return (e.g., calls a `-> !` function or `loop { /*
129 // no break */ }`) shouldn't be linted unless it actually
131 if !reached_exit_without_self_call && !self_call_locations.is_empty() {
132 let node_id = tcx.hir().as_local_node_id(def_id).unwrap();
133 let sp = tcx.sess.source_map().def_span(tcx.hir().span(node_id));
134 let mut db = tcx.struct_span_lint_node(UNCONDITIONAL_RECURSION,
137 "function cannot return without recursing");
138 db.span_label(sp, "cannot return without recursing");
139 // offer some help to the programmer.
140 for location in &self_call_locations {
141 db.span_label(location.span, "recursive call site");
143 db.help("a `loop` may express intention better if this is on purpose");