use middle::ty::{self, Ty};
use middle::{def, pat_util, stability};
use middle::const_eval::{eval_const_expr_partial, const_int, const_uint};
+use middle::cfg;
use util::ppaux::{ty_to_string};
use util::nodemap::{FnvHashMap, NodeSet};
-use lint::{Context, LintPass, LintArray, Lint};
+use lint::{Level, Context, LintPass, LintArray, Lint};
+use std::collections::BitvSet;
use std::collections::hash_map::Entry::{Occupied, Vacant};
use std::num::SignedInt;
use std::{cmp, slice};
}
}
+declare_lint! {
+ pub UNCONDITIONAL_RECURSION,
+ Warn,
+ "functions that cannot return without calling themselves"
+}
+
+#[derive(Copy)]
+pub struct UnconditionalRecursion;
+
+
+impl LintPass for UnconditionalRecursion {
+ fn get_lints(&self) -> LintArray {
+ lint_array![UNCONDITIONAL_RECURSION]
+ }
+
+ fn check_fn(&mut self, cx: &Context, fn_kind: visit::FnKind, _: &ast::FnDecl,
+ blk: &ast::Block, sp: Span, id: ast::NodeId) {
+ type F = for<'tcx> fn(&ty::ctxt<'tcx>,
+ ast::NodeId, ast::NodeId, ast::Ident, ast::NodeId) -> bool;
+
+ let (name, checker) = match fn_kind {
+ visit::FkItemFn(name, _, _, _) => (name, id_refers_to_this_fn as F),
+ visit::FkMethod(name, _, _) => (name, id_refers_to_this_method as F),
+ // closures can't recur, so they don't matter.
+ visit::FkFnBlock => return
+ };
+
+ let impl_def_id = ty::impl_of_method(cx.tcx, ast_util::local_def(id))
+ .unwrap_or(ast_util::local_def(ast::DUMMY_NODE_ID));
+ assert!(ast_util::is_local(impl_def_id));
+ let impl_node_id = impl_def_id.node;
+
+ // 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 itselfs 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 recurring after an assert.
+
+ let cfg = cfg::CFG::new(cx.tcx, blk);
+
+ let mut work_queue = vec![cfg.entry];
+ let mut reached_exit_without_self_call = false;
+ let mut self_call_spans = vec![];
+ let mut visited = BitvSet::new();
+
+ while let Some(idx) = work_queue.pop() {
+ let cfg_id = idx.node_id();
+ if idx == cfg.exit {
+ // found a path!
+ reached_exit_without_self_call = true;
+ break
+ } else if visited.contains(&cfg_id) {
+ // already done
+ continue
+ }
+ visited.insert(cfg_id);
+ let node_id = cfg.graph.node_data(idx).id;
+
+ // is this a recursive call?
+ if node_id != ast::DUMMY_NODE_ID && checker(cx.tcx, impl_node_id, id, name, node_id) {
+
+ self_call_spans.push(cx.tcx.map.span(node_id));
+ // this is a self call, so we shouldn't explore past
+ // this node in the CFG.
+ continue
+ }
+ // add the successors of this node to explore the graph further.
+ cfg.graph.each_outgoing_edge(idx, |_, edge| {
+ let target_idx = edge.target();
+ let target_cfg_id = target_idx.node_id();
+ if !visited.contains(&target_cfg_id) {
+ work_queue.push(target_idx)
+ }
+ true
+ });
+ }
+
+ // check the number of sell 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_spans.len() > 0 {
+ cx.span_lint(UNCONDITIONAL_RECURSION, sp,
+ "function cannot return without recurring");
+
+ // FIXME #19668: these could be span_lint_note's instead of this manual guard.
+ if cx.current_level(UNCONDITIONAL_RECURSION) != Level::Allow {
+ let sess = cx.sess();
+ // offer some help to the programmer.
+ for call in self_call_spans.iter() {
+ sess.span_note(*call, "recursive call site")
+ }
+ sess.span_help(sp, "a `loop` may express intention better if this is on purpose")
+ }
+ }
+
+ // all done
+ return;
+
+ // Functions for identifying if the given NodeId `id`
+ // represents a call to the function `fn_id`/method
+ // `method_id`.
+
+ fn id_refers_to_this_fn<'tcx>(tcx: &ty::ctxt<'tcx>,
+ _: ast::NodeId,
+ fn_id: ast::NodeId,
+ _: ast::Ident,
+ id: ast::NodeId) -> bool {
+ tcx.def_map.borrow().get(&id)
+ .map_or(false, |def| {
+ let did = def.def_id();
+ ast_util::is_local(did) && did.node == fn_id
+ })
+ }
+
+ // check if the method call `id` refers to method `method_id`
+ // (with name `method_name` contained in impl `impl_id`).
+ fn id_refers_to_this_method<'tcx>(tcx: &ty::ctxt<'tcx>,
+ impl_id: ast::NodeId,
+ method_id: ast::NodeId,
+ method_name: ast::Ident,
+ id: ast::NodeId) -> bool {
+ let did = match tcx.method_map.borrow().get(&ty::MethodCall::expr(id)) {
+ None => return false,
+ Some(m) => match m.origin {
+ // There's no way to know if a method call via a
+ // vtable is recursion, so we assume it's not.
+ ty::MethodTraitObject(_) => return false,
+
+ // This `did` refers directly to the method definition.
+ ty::MethodStatic(did) | ty::MethodStaticUnboxedClosure(did) => did,
+
+ // MethodTypeParam are methods from traits:
+
+ // The `impl ... for ...` of this method call
+ // isn't known, e.g. it might be a default method
+ // in a trait, so we get the def-id of the trait
+ // method instead.
+ ty::MethodTypeParam(
+ ty::MethodParam { ref trait_ref, method_num, impl_def_id: None, }) => {
+ ty::trait_item(tcx, trait_ref.def_id, method_num).def_id()
+ }
+
+ // The `impl` is known, so we check that with a
+ // special case:
+ ty::MethodTypeParam(
+ ty::MethodParam { impl_def_id: Some(impl_def_id), .. }) => {
+
+ let name = match tcx.map.expect_expr(id).node {
+ ast::ExprMethodCall(ref sp_ident, _, _) => sp_ident.node,
+ _ => tcx.sess.span_bug(
+ tcx.map.span(id),
+ "non-method call expr behaving like a method call?")
+ };
+ // it matches if it comes from the same impl,
+ // and has the same method name.
+ return ast_util::is_local(impl_def_id)
+ && impl_def_id.node == impl_id
+ && method_name.name == name.name
+ }
+ }
+ };
+
+ ast_util::is_local(did) && did.node == method_id
+ }
+ }
+}
+
declare_lint! {
pub UNUSED_IMPORTS,
Warn,
projects / rust.git / commitdiff