1 use rustc_data_structures::graph::iterate::{
2 NodeStatus, TriColorDepthFirstSearch, TriColorVisitor,
4 use rustc_hir::intravisit::FnKind;
5 use rustc_middle::mir::{BasicBlock, Body, Operand, TerminatorKind};
6 use rustc_middle::ty::subst::{GenericArg, InternalSubsts};
7 use rustc_middle::ty::{self, AssocItem, AssocItemContainer, Instance, TyCtxt};
8 use rustc_session::lint::builtin::UNCONDITIONAL_RECURSION;
10 use std::ops::ControlFlow;
12 crate fn check<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
13 let def_id = body.source.def_id().expect_local();
15 if let Some(fn_kind) = tcx.hir().get_by_def_id(def_id).fn_kind() {
16 if let FnKind::Closure = fn_kind {
17 // closures can't recur, so they don't matter.
21 // If this is trait/impl method, extract the trait's substs.
22 let trait_substs = match tcx.opt_associated_item(def_id.to_def_id()) {
24 container: AssocItemContainer::TraitContainer(trait_def_id), ..
26 let trait_substs_count = tcx.generics_of(*trait_def_id).count();
27 &InternalSubsts::identity_for_item(tcx, def_id.to_def_id())[..trait_substs_count]
32 let mut vis = Search { tcx, body, reachable_recursive_calls: vec![], trait_substs };
33 if let Some(NonRecursive) = TriColorDepthFirstSearch::new(&body).run_from_start(&mut vis) {
37 vis.reachable_recursive_calls.sort();
39 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
40 let sp = tcx.sess.source_map().guess_head_span(tcx.hir().span_with_body(hir_id));
41 tcx.struct_span_lint_hir(UNCONDITIONAL_RECURSION, hir_id, sp, |lint| {
42 let mut db = lint.build("function cannot return without recursing");
43 db.span_label(sp, "cannot return without recursing");
44 // offer some help to the programmer.
45 for call_span in vis.reachable_recursive_calls {
46 db.span_label(call_span, "recursive call site");
48 db.help("a `loop` may express intention better if this is on purpose");
56 struct Search<'mir, 'tcx> {
58 body: &'mir Body<'tcx>,
59 trait_substs: &'tcx [GenericArg<'tcx>],
61 reachable_recursive_calls: Vec<Span>,
64 impl<'mir, 'tcx> Search<'mir, 'tcx> {
65 /// Returns `true` if `func` refers to the function we are searching in.
66 fn is_recursive_call(&self, func: &Operand<'tcx>) -> bool {
67 let Search { tcx, body, trait_substs, .. } = *self;
68 let caller = body.source.def_id();
69 let param_env = tcx.param_env(caller);
71 let func_ty = func.ty(body, tcx);
72 if let ty::FnDef(callee, substs) = *func_ty.kind() {
73 let normalized_substs = tcx.normalize_erasing_regions(param_env, substs);
74 let (callee, call_substs) = if let Ok(Some(instance)) =
75 Instance::resolve(tcx, param_env, callee, normalized_substs)
77 (instance.def_id(), instance.substs)
79 (callee, normalized_substs)
82 // FIXME(#57965): Make this work across function boundaries
84 // If this is a trait fn, the substs on the trait have to match, or we might be
85 // calling into an entirely different method (for example, a call from the default
86 // method in the trait to `<A as Trait<B>>::method`, where `A` and/or `B` are
88 return callee == caller && &call_substs[..trait_substs.len()] == trait_substs;
95 impl<'mir, 'tcx> TriColorVisitor<&'mir Body<'tcx>> for Search<'mir, 'tcx> {
96 type BreakVal = NonRecursive;
101 prior_status: Option<NodeStatus>,
102 ) -> ControlFlow<Self::BreakVal> {
103 // Back-edge in the CFG (loop).
104 if let Some(NodeStatus::Visited) = prior_status {
105 return ControlFlow::Break(NonRecursive);
108 match self.body[bb].terminator().kind {
109 // These terminators return control flow to the caller.
110 TerminatorKind::Abort
111 | TerminatorKind::GeneratorDrop
112 | TerminatorKind::Resume
113 | TerminatorKind::Return
114 | TerminatorKind::Unreachable
115 | TerminatorKind::Yield { .. } => ControlFlow::Break(NonRecursive),
117 // A diverging InlineAsm is treated as non-recursing
118 TerminatorKind::InlineAsm { destination, .. } => {
119 if destination.is_some() {
120 ControlFlow::CONTINUE
122 ControlFlow::Break(NonRecursive)
127 TerminatorKind::Assert { .. }
128 | TerminatorKind::Call { .. }
129 | TerminatorKind::Drop { .. }
130 | TerminatorKind::DropAndReplace { .. }
131 | TerminatorKind::FalseEdge { .. }
132 | TerminatorKind::FalseUnwind { .. }
133 | TerminatorKind::Goto { .. }
134 | TerminatorKind::SwitchInt { .. } => ControlFlow::CONTINUE,
138 fn node_settled(&mut self, bb: BasicBlock) -> ControlFlow<Self::BreakVal> {
139 // When we examine a node for the last time, remember it if it is a recursive call.
140 let terminator = self.body[bb].terminator();
141 if let TerminatorKind::Call { func, .. } = &terminator.kind {
142 if self.is_recursive_call(func) {
143 self.reachable_recursive_calls.push(terminator.source_info.span);
147 ControlFlow::CONTINUE
150 fn ignore_edge(&mut self, bb: BasicBlock, target: BasicBlock) -> bool {
151 // Don't traverse successors of recursive calls or false CFG edges.
152 match self.body[bb].terminator().kind {
153 TerminatorKind::Call { ref func, .. } => self.is_recursive_call(func),
155 TerminatorKind::FalseUnwind { unwind: Some(imaginary_target), .. }
156 | TerminatorKind::FalseEdge { imaginary_target, .. } => imaginary_target == target,