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();
14 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
16 if let Some(fn_kind) = tcx.hir().get(hir_id).fn_kind() {
17 if let FnKind::Closure = fn_kind {
18 // closures can't recur, so they don't matter.
22 // If this is trait/impl method, extract the trait's substs.
23 let trait_substs = match tcx.opt_associated_item(def_id.to_def_id()) {
25 container: AssocItemContainer::TraitContainer(trait_def_id), ..
27 let trait_substs_count = tcx.generics_of(*trait_def_id).count();
28 &InternalSubsts::identity_for_item(tcx, def_id.to_def_id())[..trait_substs_count]
33 let mut vis = Search { tcx, body, reachable_recursive_calls: vec![], trait_substs };
34 if let Some(NonRecursive) = TriColorDepthFirstSearch::new(&body).run_from_start(&mut vis) {
38 vis.reachable_recursive_calls.sort();
40 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
41 let sp = tcx.sess.source_map().guess_head_span(tcx.hir().span_with_body(hir_id));
42 tcx.struct_span_lint_hir(UNCONDITIONAL_RECURSION, hir_id, sp, |lint| {
43 let mut db = lint.build("function cannot return without recursing");
44 db.span_label(sp, "cannot return without recursing");
45 // offer some help to the programmer.
46 for call_span in vis.reachable_recursive_calls {
47 db.span_label(call_span, "recursive call site");
49 db.help("a `loop` may express intention better if this is on purpose");
57 struct Search<'mir, 'tcx> {
59 body: &'mir Body<'tcx>,
60 trait_substs: &'tcx [GenericArg<'tcx>],
62 reachable_recursive_calls: Vec<Span>,
65 impl<'mir, 'tcx> Search<'mir, 'tcx> {
66 /// Returns `true` if `func` refers to the function we are searching in.
67 fn is_recursive_call(&self, func: &Operand<'tcx>) -> bool {
68 let Search { tcx, body, trait_substs, .. } = *self;
69 let caller = body.source.def_id();
70 let param_env = tcx.param_env(caller);
72 let func_ty = func.ty(body, tcx);
73 if let ty::FnDef(callee, substs) = *func_ty.kind() {
74 let normalized_substs = tcx.normalize_erasing_regions(param_env, substs);
75 let (callee, call_substs) = if let Ok(Some(instance)) =
76 Instance::resolve(tcx, param_env, callee, normalized_substs)
78 (instance.def_id(), instance.substs)
80 (callee, normalized_substs)
83 // FIXME(#57965): Make this work across function boundaries
85 // If this is a trait fn, the substs on the trait have to match, or we might be
86 // calling into an entirely different method (for example, a call from the default
87 // method in the trait to `<A as Trait<B>>::method`, where `A` and/or `B` are
89 return callee == caller && &call_substs[..trait_substs.len()] == trait_substs;
96 impl<'mir, 'tcx> TriColorVisitor<&'mir Body<'tcx>> for Search<'mir, 'tcx> {
97 type BreakVal = NonRecursive;
102 prior_status: Option<NodeStatus>,
103 ) -> ControlFlow<Self::BreakVal> {
104 // Back-edge in the CFG (loop).
105 if let Some(NodeStatus::Visited) = prior_status {
106 return ControlFlow::Break(NonRecursive);
109 match self.body[bb].terminator().kind {
110 // These terminators return control flow to the caller.
111 TerminatorKind::Abort
112 | TerminatorKind::GeneratorDrop
113 | TerminatorKind::Resume
114 | TerminatorKind::Return
115 | TerminatorKind::Unreachable
116 | TerminatorKind::Yield { .. } => ControlFlow::Break(NonRecursive),
118 // A diverging InlineAsm is treated as non-recursing
119 TerminatorKind::InlineAsm { destination, .. } => {
120 if destination.is_some() {
121 ControlFlow::CONTINUE
123 ControlFlow::Break(NonRecursive)
128 TerminatorKind::Assert { .. }
129 | TerminatorKind::Call { .. }
130 | TerminatorKind::Drop { .. }
131 | TerminatorKind::DropAndReplace { .. }
132 | TerminatorKind::FalseEdge { .. }
133 | TerminatorKind::FalseUnwind { .. }
134 | TerminatorKind::Goto { .. }
135 | TerminatorKind::SwitchInt { .. } => ControlFlow::CONTINUE,
139 fn node_settled(&mut self, bb: BasicBlock) -> ControlFlow<Self::BreakVal> {
140 // When we examine a node for the last time, remember it if it is a recursive call.
141 let terminator = self.body[bb].terminator();
142 if let TerminatorKind::Call { func, .. } = &terminator.kind {
143 if self.is_recursive_call(func) {
144 self.reachable_recursive_calls.push(terminator.source_info.span);
148 ControlFlow::CONTINUE
151 fn ignore_edge(&mut self, bb: BasicBlock, target: BasicBlock) -> bool {
152 // Don't traverse successors of recursive calls or false CFG edges.
153 match self.body[bb].terminator().kind {
154 TerminatorKind::Call { ref func, .. } => self.is_recursive_call(func),
156 TerminatorKind::FalseUnwind { unwind: Some(imaginary_target), .. }
157 | TerminatorKind::FalseEdge { imaginary_target, .. } => imaginary_target == target,