| use rustc::hir::map::blocks::FnLikeNode; |
| use rustc::lint::builtin::UNCONDITIONAL_RECURSION; |
| use rustc::mir::{self, Body, TerminatorKind}; |
| use rustc::ty::subst::InternalSubsts; |
| use rustc::ty::{self, AssocItem, AssocItemContainer, Instance, TyCtxt}; |
| use rustc_hir::def_id::DefId; |
| use rustc_hir::intravisit::FnKind; |
| use rustc_index::bit_set::BitSet; |
| |
| crate fn check<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'tcx>, def_id: DefId) { |
| let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap(); |
| |
| if let Some(fn_like_node) = FnLikeNode::from_node(tcx.hir().get(hir_id)) { |
| check_fn_for_unconditional_recursion(tcx, fn_like_node.kind(), body, def_id); |
| } |
| } |
| |
| fn check_fn_for_unconditional_recursion<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| fn_kind: FnKind<'_>, |
| body: &Body<'tcx>, |
| def_id: DefId, |
| ) { |
| if let FnKind::Closure(_) = fn_kind { |
| // closures can't recur, so they don't matter. |
| return; |
| } |
| |
| //FIXME(#54444) rewrite this lint to use the dataflow framework |
| |
| // Walk through this function (say `f`) looking to see if |
| // every possible path references itself, i.e., the function is |
| // called recursively unconditionally. This is done by trying |
| // to find a path from the entry node to the exit node that |
| // *doesn't* call `f` by traversing from the entry while |
| // pretending that calls of `f` are sinks (i.e., ignoring any |
| // exit edges from them). |
| // |
| // NB. this has an edge case with non-returning statements, |
| // like `loop {}` or `panic!()`: control flow never reaches |
| // the exit node through these, so one can have a function |
| // that never actually calls itself but is still picked up by |
| // this lint: |
| // |
| // fn f(cond: bool) { |
| // if !cond { panic!() } // could come from `assert!(cond)` |
| // f(false) |
| // } |
| // |
| // In general, functions of that form may be able to call |
| // itself a finite number of times and then diverge. The lint |
| // considers this to be an error for two reasons, (a) it is |
| // easier to implement, and (b) it seems rare to actually want |
| // to have behaviour like the above, rather than |
| // e.g., accidentally recursing after an assert. |
| |
| let basic_blocks = body.basic_blocks(); |
| let mut reachable_without_self_call_queue = vec![mir::START_BLOCK]; |
| let mut reached_exit_without_self_call = false; |
| let mut self_call_locations = vec![]; |
| let mut visited = BitSet::new_empty(basic_blocks.len()); |
| |
| let param_env = tcx.param_env(def_id); |
| let trait_substs_count = match tcx.opt_associated_item(def_id) { |
| Some(AssocItem { container: AssocItemContainer::TraitContainer(trait_def_id), .. }) => { |
| tcx.generics_of(trait_def_id).count() |
| } |
| _ => 0, |
| }; |
| let caller_substs = &InternalSubsts::identity_for_item(tcx, def_id)[..trait_substs_count]; |
| |
| while let Some(bb) = reachable_without_self_call_queue.pop() { |
| if !visited.insert(bb) { |
| //already done |
| continue; |
| } |
| |
| let block = &basic_blocks[bb]; |
| |
| if let Some(ref terminator) = block.terminator { |
| match terminator.kind { |
| TerminatorKind::Call { ref func, .. } => { |
| let func_ty = func.ty(body, tcx); |
| |
| if let ty::FnDef(fn_def_id, substs) = func_ty.kind { |
| let (call_fn_id, call_substs) = if let Some(instance) = |
| Instance::resolve(tcx, param_env, fn_def_id, substs) |
| { |
| (instance.def_id(), instance.substs) |
| } else { |
| (fn_def_id, substs) |
| }; |
| |
| let is_self_call = call_fn_id == def_id |
| && &call_substs[..caller_substs.len()] == caller_substs; |
| |
| if is_self_call { |
| self_call_locations.push(terminator.source_info); |
| |
| //this is a self call so we shouldn't explore |
| //further down this path |
| continue; |
| } |
| } |
| } |
| TerminatorKind::Abort | TerminatorKind::Return => { |
| //found a path! |
| reached_exit_without_self_call = true; |
| break; |
| } |
| _ => {} |
| } |
| |
| for successor in terminator.successors() { |
| reachable_without_self_call_queue.push(*successor); |
| } |
| } |
| } |
| |
| // Check the number of self calls because a function that |
| // doesn't return (e.g., calls a `-> !` function or `loop { /* |
| // no break */ }`) shouldn't be linted unless it actually |
| // recurs. |
| if !reached_exit_without_self_call && !self_call_locations.is_empty() { |
| let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap(); |
| let sp = tcx.sess.source_map().def_span(tcx.hir().span(hir_id)); |
| tcx.struct_span_lint_hir(UNCONDITIONAL_RECURSION, hir_id, sp, |lint| { |
| let mut db = lint.build("function cannot return without recursing"); |
| db.span_label(sp, "cannot return without recursing"); |
| // offer some help to the programmer. |
| for location in &self_call_locations { |
| db.span_label(location.span, "recursive call site"); |
| } |
| db.help("a `loop` may express intention better if this is on purpose"); |
| db.emit(); |
| }); |
| } |
| } |