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) {
36 if vis.reachable_recursive_calls.is_empty() {
40 vis.reachable_recursive_calls.sort();
42 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
43 let sp = tcx.sess.source_map().guess_head_span(tcx.hir().span_with_body(hir_id));
44 tcx.struct_span_lint_hir(UNCONDITIONAL_RECURSION, hir_id, sp, |lint| {
45 let mut db = lint.build("function cannot return without recursing");
46 db.span_label(sp, "cannot return without recursing");
47 // offer some help to the programmer.
48 for call_span in vis.reachable_recursive_calls {
49 db.span_label(call_span, "recursive call site");
51 db.help("a `loop` may express intention better if this is on purpose");
59 struct Search<'mir, 'tcx> {
61 body: &'mir Body<'tcx>,
62 trait_substs: &'tcx [GenericArg<'tcx>],
64 reachable_recursive_calls: Vec<Span>,
67 impl<'mir, 'tcx> Search<'mir, 'tcx> {
68 /// Returns `true` if `func` refers to the function we are searching in.
69 fn is_recursive_call(&self, func: &Operand<'tcx>) -> bool {
70 let Search { tcx, body, trait_substs, .. } = *self;
71 let caller = body.source.def_id();
72 let param_env = tcx.param_env(caller);
74 let func_ty = func.ty(body, tcx);
75 if let ty::FnDef(callee, substs) = *func_ty.kind() {
76 let normalized_substs = tcx.normalize_erasing_regions(param_env, substs);
77 let (callee, call_substs) = if let Ok(Some(instance)) =
78 Instance::resolve(tcx, param_env, callee, normalized_substs)
80 (instance.def_id(), instance.substs)
82 (callee, normalized_substs)
85 // FIXME(#57965): Make this work across function boundaries
87 // If this is a trait fn, the substs on the trait have to match, or we might be
88 // calling into an entirely different method (for example, a call from the default
89 // method in the trait to `<A as Trait<B>>::method`, where `A` and/or `B` are
91 return callee == caller && &call_substs[..trait_substs.len()] == trait_substs;
98 impl<'mir, 'tcx> TriColorVisitor<&'mir Body<'tcx>> for Search<'mir, 'tcx> {
99 type BreakVal = NonRecursive;
104 prior_status: Option<NodeStatus>,
105 ) -> ControlFlow<Self::BreakVal> {
106 // Back-edge in the CFG (loop).
107 if let Some(NodeStatus::Visited) = prior_status {
108 return ControlFlow::Break(NonRecursive);
111 match self.body[bb].terminator().kind {
112 // These terminators return control flow to the caller.
113 TerminatorKind::Abort
114 | TerminatorKind::GeneratorDrop
115 | TerminatorKind::Resume
116 | TerminatorKind::Return
117 | TerminatorKind::Unreachable
118 | TerminatorKind::Yield { .. } => ControlFlow::Break(NonRecursive),
120 // A diverging InlineAsm is treated as non-recursing
121 TerminatorKind::InlineAsm { destination, .. } => {
122 if destination.is_some() {
123 ControlFlow::CONTINUE
125 ControlFlow::Break(NonRecursive)
130 TerminatorKind::Assert { .. }
131 | TerminatorKind::Call { .. }
132 | TerminatorKind::Drop { .. }
133 | TerminatorKind::DropAndReplace { .. }
134 | TerminatorKind::FalseEdge { .. }
135 | TerminatorKind::FalseUnwind { .. }
136 | TerminatorKind::Goto { .. }
137 | TerminatorKind::SwitchInt { .. } => ControlFlow::CONTINUE,
141 fn node_settled(&mut self, bb: BasicBlock) -> ControlFlow<Self::BreakVal> {
142 // When we examine a node for the last time, remember it if it is a recursive call.
143 let terminator = self.body[bb].terminator();
144 if let TerminatorKind::Call { func, .. } = &terminator.kind {
145 if self.is_recursive_call(func) {
146 self.reachable_recursive_calls.push(terminator.source_info.span);
150 ControlFlow::CONTINUE
153 fn ignore_edge(&mut self, bb: BasicBlock, target: BasicBlock) -> bool {
154 let terminator = self.body[bb].terminator();
155 if terminator.unwind() == Some(&Some(target)) && terminator.successors().count() > 1 {
158 // Don't traverse successors of recursive calls or false CFG edges.
159 match self.body[bb].terminator().kind {
160 TerminatorKind::Call { ref func, .. } => self.is_recursive_call(func),
161 TerminatorKind::FalseEdge { imaginary_target, .. } => imaginary_target == target,