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Rollup merge of #39009 - canndrew:default-unit-warnings, r=nikomatsakis

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Add warning for () to ! switch

With feature(never_type) enabled diverging type variables will default to `!` instead of `()`. This can cause breakages where a trait is resolved on such a type.

This PR emits a future-compatibility warning when it sees this happen.
This commit is contained in:
Corey Farwell 2017-02-05 09:14:39 -05:00 • committed by GitHub
commit 4f8ce9efb9
56 changed files with 249 additions and 106 deletions
Download patch file Download diff file Expand all files Collapse all files

8
src/librustc/lint/builtin.rs
View file

@ -192,6 +192,13 @@ declare_lint! {
"lifetimes or labels named `'_` were erroneously allowed"
}
declare_lint! {
pub RESOLVE_TRAIT_ON_DEFAULTED_UNIT,
Warn,
"attempt to resolve a trait on an expression whose type cannot be inferred but which \
currently defaults to ()"
}
declare_lint! {
pub SAFE_EXTERN_STATICS,
Warn,
@ -272,6 +279,7 @@ impl LintPass for HardwiredLints {
SUPER_OR_SELF_IN_GLOBAL_PATH,
HR_LIFETIME_IN_ASSOC_TYPE,
LIFETIME_UNDERSCORE,
RESOLVE_TRAIT_ON_DEFAULTED_UNIT,
SAFE_EXTERN_STATICS,
PATTERNS_IN_FNS_WITHOUT_BODY,
EXTRA_REQUIREMENT_IN_IMPL,

2
src/librustc/middle/mem_categorization.rs
View file

@ -1199,7 +1199,7 @@ impl<'a, 'gcx, 'tcx> MemCategorizationContext<'a, 'gcx, 'tcx> {
PatKind::Tuple(ref subpats, ddpos) => {
// (p1, ..., pN)
let expected_len = match self.pat_ty(&pat)?.sty {
ty::TyTuple(ref tys) => tys.len(),
ty::TyTuple(ref tys, _) => tys.len(),
ref ty => span_bug!(pat.span, "tuple pattern unexpected type {:?}", ty),
};
for (i, subpat) in subpats.iter().enumerate_and_adjust(expected_len, ddpos) {

5
src/librustc/mir/tcx.rs
View file

@ -163,7 +163,7 @@ impl<'tcx> Rvalue<'tcx> {
let lhs_ty = lhs.ty(mir, tcx);
let rhs_ty = rhs.ty(mir, tcx);
let ty = op.ty(tcx, lhs_ty, rhs_ty);
let ty = tcx.intern_tup(&[ty, tcx.types.bool]);
let ty = tcx.intern_tup(&[ty, tcx.types.bool], false);
Some(ty)
}
&Rvalue::UnaryOp(_, ref operand) => {
@ -184,7 +184,8 @@ impl<'tcx> Rvalue<'tcx> {
}
AggregateKind::Tuple => {
Some(tcx.mk_tup(
ops.iter().map(|op| op.ty(mir, tcx))
ops.iter().map(|op| op.ty(mir, tcx)),
false
))
}
AggregateKind::Adt(def, _, substs, _) => {

60
src/librustc/traits/select.rs
View file

@ -52,6 +52,7 @@ use std::mem;
use std::rc::Rc;
use syntax::abi::Abi;
use hir;
use lint;
use util::nodemap::FxHashMap;
struct InferredObligationsSnapshotVecDelegate<'tcx> {
@ -407,19 +408,62 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
debug!("select({:?})", obligation);
assert!(!obligation.predicate.has_escaping_regions());
let tcx = self.tcx();
let dep_node = obligation.predicate.dep_node();
let _task = self.tcx().dep_graph.in_task(dep_node);
let _task = tcx.dep_graph.in_task(dep_node);
let stack = self.push_stack(TraitObligationStackList::empty(), obligation);
match self.candidate_from_obligation(&stack)? {
None => Ok(None),
let ret = match self.candidate_from_obligation(&stack)? {
None => None,
Some(candidate) => {
let mut candidate = self.confirm_candidate(obligation, candidate)?;
let inferred_obligations = (*self.inferred_obligations).into_iter().cloned();
candidate.nested_obligations_mut().extend(inferred_obligations);
Ok(Some(candidate))
Some(candidate)
},
};
// Test whether this is a `()` which was produced by defaulting a
// diverging type variable with `!` disabled. If so, we may need
// to raise a warning.
if obligation.predicate.skip_binder().self_ty().is_defaulted_unit() {
let mut raise_warning = true;
// Don't raise a warning if the trait is implemented for ! and only
// permits a trivial implementation for !. This stops us warning
// about (for example) `(): Clone` becoming `!: Clone` because such
// a switch can't cause code to stop compiling or execute
// differently.
let mut never_obligation = obligation.clone();
let def_id = never_obligation.predicate.skip_binder().trait_ref.def_id;
never_obligation.predicate = never_obligation.predicate.map_bound(|mut trait_pred| {
// Swap out () with ! so we can check if the trait is impld for !
{
let mut trait_ref = &mut trait_pred.trait_ref;
let unit_substs = trait_ref.substs;
let mut never_substs = Vec::with_capacity(unit_substs.len());
never_substs.push(From::from(tcx.types.never));
never_substs.extend(&unit_substs[1..]);
trait_ref.substs = tcx.intern_substs(&never_substs);
}
trait_pred
});
if let Ok(Some(..)) = self.select(&never_obligation) {
if !tcx.trait_relevant_for_never(def_id) {
// The trait is also implemented for ! and the resulting
// implementation cannot actually be invoked in any way.
raise_warning = false;
}
}
if raise_warning {
tcx.sess.add_lint(lint::builtin::RESOLVE_TRAIT_ON_DEFAULTED_UNIT,
obligation.cause.body_id,
obligation.cause.span,
format!("code relies on type inference rules which are likely \
to change"));
}
}
Ok(ret)
}
///////////////////////////////////////////////////////////////////////////
@ -1744,7 +1788,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
ty::TyStr | ty::TySlice(_) | ty::TyDynamic(..) => Never,
ty::TyTuple(tys) => {
ty::TyTuple(tys, _) => {
Where(ty::Binder(tys.last().into_iter().cloned().collect()))
}
@ -1752,7 +1796,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
let sized_crit = def.sized_constraint(self.tcx());
// (*) binder moved here
Where(ty::Binder(match sized_crit.sty {
ty::TyTuple(tys) => tys.to_vec().subst(self.tcx(), substs),
ty::TyTuple(tys, _) => tys.to_vec().subst(self.tcx(), substs),
ty::TyBool => vec![],
_ => vec![sized_crit.subst(self.tcx(), substs)]
}))
@ -1799,7 +1843,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
Where(ty::Binder(vec![element_ty]))
}
ty::TyTuple(tys) => {
ty::TyTuple(tys, _) => {
// (*) binder moved here
Where(ty::Binder(tys.to_vec()))
}
@ -1874,7 +1918,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
vec![element_ty]
}
ty::TyTuple(ref tys) => {
ty::TyTuple(ref tys, _) => {
// (T1, ..., Tn) -- meets any bound that all of T1...Tn meet
tys.to_vec()
}

2
src/librustc/traits/util.rs
View file

@ -489,7 +489,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
let arguments_tuple = match tuple_arguments {
TupleArgumentsFlag::No => sig.skip_binder().inputs()[0],
TupleArgumentsFlag::Yes =>
self.intern_tup(sig.skip_binder().inputs()),
self.intern_tup(sig.skip_binder().inputs(), false),
};
let trait_ref = ty::TraitRef {
def_id: fn_trait_def_id,

2
src/librustc/ty/contents.rs
View file

@ -201,7 +201,7 @@ impl<'a, 'tcx> ty::TyS<'tcx> {
|ty| tc_ty(tcx, &ty, cache))
}
ty::TyTuple(ref tys) => {
ty::TyTuple(ref tys, _) => {
TypeContents::union(&tys[..],
|ty| tc_ty(tcx, *ty, cache))
}

13
src/librustc/ty/context.rs
View file

@ -1384,23 +1384,24 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
self.mk_ty(TySlice(ty))
}
pub fn intern_tup(self, ts: &[Ty<'tcx>]) -> Ty<'tcx> {
self.mk_ty(TyTuple(self.intern_type_list(ts)))
pub fn intern_tup(self, ts: &[Ty<'tcx>], defaulted: bool) -> Ty<'tcx> {
self.mk_ty(TyTuple(self.intern_type_list(ts), defaulted))
}
pub fn mk_tup<I: InternAs<[Ty<'tcx>], Ty<'tcx>>>(self, iter: I) -> I::Output {
iter.intern_with(|ts| self.mk_ty(TyTuple(self.intern_type_list(ts))))
pub fn mk_tup<I: InternAs<[Ty<'tcx>], Ty<'tcx>>>(self, iter: I,
defaulted: bool) -> I::Output {
iter.intern_with(|ts| self.mk_ty(TyTuple(self.intern_type_list(ts), defaulted)))
}
pub fn mk_nil(self) -> Ty<'tcx> {
self.intern_tup(&[])
self.intern_tup(&[], false)
}
pub fn mk_diverging_default(self) -> Ty<'tcx> {
if self.sess.features.borrow().never_type {
self.types.never
} else {
self.mk_nil()
self.intern_tup(&[], true)
}
}

4
src/librustc/ty/error.rs
View file

@ -178,7 +178,7 @@ impl<'a, 'gcx, 'lcx, 'tcx> ty::TyS<'tcx> {
match self.sty {
ty::TyBool | ty::TyChar | ty::TyInt(_) |
ty::TyUint(_) | ty::TyFloat(_) | ty::TyStr | ty::TyNever => self.to_string(),
ty::TyTuple(ref tys) if tys.is_empty() => self.to_string(),
ty::TyTuple(ref tys, _) if tys.is_empty() => self.to_string(),
ty::TyAdt(def, _) => format!("{} `{}`", def.descr(), tcx.item_path_str(def.did)),
ty::TyArray(_, n) => format!("array of {} elements", n),
@ -209,7 +209,7 @@ impl<'a, 'gcx, 'lcx, 'tcx> ty::TyS<'tcx> {
|p| format!("trait {}", tcx.item_path_str(p.def_id())))
}
ty::TyClosure(..) => "closure".to_string(),
ty::TyTuple(_) => "tuple".to_string(),
ty::TyTuple(..) => "tuple".to_string(),
ty::TyInfer(ty::TyVar(_)) => "inferred type".to_string(),
ty::TyInfer(ty::IntVar(_)) => "integral variable".to_string(),
ty::TyInfer(ty::FloatVar(_)) => "floating-point variable".to_string(),

2
src/librustc/ty/fast_reject.rs
View file

@ -72,7 +72,7 @@ pub fn simplify_type<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
Some(ClosureSimplifiedType(def_id))
}
ty::TyNever => Some(NeverSimplifiedType),
ty::TyTuple(ref tys) => {
ty::TyTuple(ref tys, _) => {
Some(TupleSimplifiedType(tys.len()))
}
ty::TyFnDef(.., ref f) | ty::TyFnPtr(ref f) => {

2
src/librustc/ty/flags.rs
View file

@ -151,7 +151,7 @@ impl FlagComputation {
self.add_ty(m.ty);
}
&ty::TyTuple(ref ts) => {
&ty::TyTuple(ref ts, _) => {
self.add_tys(&ts[..]);
}

2
src/librustc/ty/inhabitedness/mod.rs
View file

@ -178,7 +178,7 @@ impl<'a, 'gcx, 'tcx> TyS<'tcx> {
},
TyNever => DefIdForest::full(tcx),
TyTuple(ref tys) => {
TyTuple(ref tys, _) => {
DefIdForest::union(tcx, tys.iter().map(|ty| {
ty.uninhabited_from(visited, tcx)
}))

6
src/librustc/ty/item_path.rs
View file

@ -319,9 +319,9 @@ pub fn characteristic_def_id_of_type(ty: Ty) -> Option<DefId> {
ty::TyRawPtr(mt) |
ty::TyRef(_, mt) => characteristic_def_id_of_type(mt.ty),
ty::TyTuple(ref tys) => tys.iter()
.filter_map(|ty| characteristic_def_id_of_type(ty))
.next(),
ty::TyTuple(ref tys, _) => tys.iter()
.filter_map(|ty| characteristic_def_id_of_type(ty))
.next(),
ty::TyFnDef(def_id, ..) |
ty::TyClosure(def_id, _) => Some(def_id),

4
src/librustc/ty/layout.rs
View file

@ -791,7 +791,7 @@ impl<'a, 'gcx, 'tcx> Struct {
Some(&variant.memory_index[..]))
}
// Can we use one of the fields in this tuple?
(&Univariant { ref variant, .. }, &ty::TyTuple(tys)) => {
(&Univariant { ref variant, .. }, &ty::TyTuple(tys, _)) => {
Struct::non_zero_field_paths(infcx, tys.iter().cloned(),
Some(&variant.memory_index[..]))
}
@ -1157,7 +1157,7 @@ impl<'a, 'gcx, 'tcx> Layout {
Univariant { variant: st, non_zero: false }
}
ty::TyTuple(tys) => {
ty::TyTuple(tys, _) => {
// FIXME(camlorn): if we ever allow unsized tuples, this needs to be checked.
// See the univariant case below to learn how.
let st = Struct::new(dl,

23
src/librustc/ty/mod.rs
View file

@ -197,6 +197,17 @@ impl AssociatedItem {
AssociatedKind::Type => Def::AssociatedTy(self.def_id),
}
}
/// Tests whether the associated item admits a non-trivial implementation
/// for !
pub fn relevant_for_never<'tcx>(&self) -> bool {
match self.kind {
AssociatedKind::Const => true,
AssociatedKind::Type => true,
// FIXME(canndrew): Be more thorough here, check if any argument is uninhabited.
AssociatedKind::Method => !self.method_has_self_argument,
}
}
}
#[derive(Clone, Debug, PartialEq, Eq, Copy, RustcEncodable, RustcDecodable)]
@ -1603,7 +1614,7 @@ impl<'a, 'gcx, 'tcx> AdtDef {
_ if tys.references_error() => tcx.types.err,
0 => tcx.types.bool,
1 => tys[0],
_ => tcx.intern_tup(&tys[..])
_ => tcx.intern_tup(&tys[..], false)
};
let old = tcx.adt_sized_constraint.borrow().get(&self.did).cloned();
@ -1638,7 +1649,7 @@ impl<'a, 'gcx, 'tcx> AdtDef {
vec![ty]
}
TyTuple(ref tys) => {
TyTuple(ref tys, _) => {
match tys.last() {
None => vec![],
Some(ty) => self.sized_constraint_for_ty(tcx, stack, ty)
@ -1652,7 +1663,7 @@ impl<'a, 'gcx, 'tcx> AdtDef {
.subst(tcx, substs);
debug!("sized_constraint_for_ty({:?}) intermediate = {:?}",
ty, adt_ty);
if let ty::TyTuple(ref tys) = adt_ty.sty {
if let ty::TyTuple(ref tys, _) = adt_ty.sty {
tys.iter().flat_map(|ty| {
self.sized_constraint_for_ty(tcx, stack, ty)
}).collect()
@ -2010,6 +2021,12 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
}
}
pub fn trait_relevant_for_never(self, did: DefId) -> bool {
self.associated_items(did).any(|item| {
item.relevant_for_never()
})
}
pub fn custom_coerce_unsized_kind(self, did: DefId) -> adjustment::CustomCoerceUnsized {
self.custom_coerce_unsized_kinds.memoize(did, || {
let (kind, src) = if did.krate != LOCAL_CRATE {

5
src/librustc/ty/relate.rs
View file

@ -447,10 +447,11 @@ pub fn super_relate_tys<'a, 'gcx, 'tcx, R>(relation: &mut R,
Ok(tcx.mk_slice(t))
}
(&ty::TyTuple(as_), &ty::TyTuple(bs)) =>
(&ty::TyTuple(as_, a_defaulted), &ty::TyTuple(bs, b_defaulted)) =>
{
if as_.len() == bs.len() {
Ok(tcx.mk_tup(as_.iter().zip(bs).map(|(a, b)| relation.relate(a, b)))?)
let defaulted = a_defaulted || b_defaulted;
Ok(tcx.mk_tup(as_.iter().zip(bs).map(|(a, b)| relation.relate(a, b)), defaulted)?)
} else if !(as_.is_empty() || bs.is_empty()) {
Err(TypeError::TupleSize(
expected_found(relation, &as_.len(), &bs.len())))

4
src/librustc/ty/structural_impls.rs
View file

@ -474,7 +474,7 @@ impl<'tcx> TypeFoldable<'tcx> for Ty<'tcx> {
ty::TyAdt(tid, substs) => ty::TyAdt(tid, substs.fold_with(folder)),
ty::TyDynamic(ref trait_ty, ref region) =>
ty::TyDynamic(trait_ty.fold_with(folder), region.fold_with(folder)),
ty::TyTuple(ts) => ty::TyTuple(ts.fold_with(folder)),
ty::TyTuple(ts, defaulted) => ty::TyTuple(ts.fold_with(folder), defaulted),
ty::TyFnDef(def_id, substs, f) => {
ty::TyFnDef(def_id,
substs.fold_with(folder),
@ -511,7 +511,7 @@ impl<'tcx> TypeFoldable<'tcx> for Ty<'tcx> {
ty::TyAdt(_, substs) => substs.visit_with(visitor),
ty::TyDynamic(ref trait_ty, ref reg) =>
trait_ty.visit_with(visitor) || reg.visit_with(visitor),
ty::TyTuple(ts) => ts.visit_with(visitor),
ty::TyTuple(ts, _) => ts.visit_with(visitor),
ty::TyFnDef(_, substs, ref f) => {
substs.visit_with(visitor) || f.visit_with(visitor)
}

19
src/librustc/ty/sty.rs
View file

@ -151,7 +151,11 @@ pub enum TypeVariants<'tcx> {
TyNever,
/// A tuple type. For example, `(i32, bool)`.
TyTuple(&'tcx Slice<Ty<'tcx>>),
/// The bool indicates whether this is a unit tuple and was created by
/// defaulting a diverging type variable with feature(never_type) disabled.
/// It's only purpose is for raising future-compatibility warnings for when
/// diverging type variables start defaulting to ! instead of ().
TyTuple(&'tcx Slice<Ty<'tcx>>, bool),
/// The projection of an associated type. For example,
/// `<T as Trait<..>>::N`.
@ -961,7 +965,7 @@ impl<'a, 'gcx, 'tcx> TyS<'tcx> {
pub fn is_nil(&self) -> bool {
match self.sty {
TyTuple(ref tys) => tys.is_empty(),
TyTuple(ref tys, _) => tys.is_empty(),
_ => false
}
}
@ -973,6 +977,15 @@ impl<'a, 'gcx, 'tcx> TyS<'tcx> {
}
}
// Test whether this is a `()` which was produced by defaulting a
// diverging type variable with feature(never_type) disabled.
pub fn is_defaulted_unit(&self) -> bool {
match self.sty {
TyTuple(_, true) => true,
_ => false,
}
}
/// Checks whether a type is visibly uninhabited from a particular module.
/// # Example
/// ```rust
@ -1355,7 +1368,7 @@ impl<'a, 'gcx, 'tcx> TyS<'tcx> {
TySlice(_) |
TyRawPtr(_) |
TyNever |
TyTuple(_) |
TyTuple(..) |
TyParam(_) |
TyInfer(_) |
TyError => {

7
src/librustc/ty/util.rs
View file

@ -207,7 +207,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
// Don't use `struct_variant`, this may be a univariant enum.
adt.variants[0].fields.get(i).map(|f| f.ty(self, substs))
}
(&TyTuple(ref v), None) => v.get(i).cloned(),
(&TyTuple(ref v, _), None) => v.get(i).cloned(),
_ => None
}
}
@ -466,8 +466,9 @@ impl<'a, 'gcx, 'tcx, W> TypeVisitor<'tcx> for TypeIdHasher<'a, 'gcx, 'tcx, W>
self.def_id(d);
}
}
TyTuple(tys) => {
TyTuple(tys, defaulted) => {
self.hash(tys.len());
self.hash(defaulted);
}
TyParam(p) => {
self.hash(p.idx);
@ -675,7 +676,7 @@ impl<'a, 'tcx> ty::TyS<'tcx> {
seen: &mut Vec<Ty<'tcx>>, ty: Ty<'tcx>)
-> Representability {
match ty.sty {
TyTuple(ref ts) => {
TyTuple(ref ts, _) => {
find_nonrepresentable(tcx, sp, seen, ts.iter().cloned())
}
// Fixed-length vectors.

2
src/librustc/ty/walk.rs
View file

@ -112,7 +112,7 @@ fn push_subtypes<'tcx>(stack: &mut TypeWalkerStack<'tcx>, parent_ty: Ty<'tcx>) {
ty::TyClosure(_, ref substs) => {
stack.extend(substs.substs.types().rev());
}
ty::TyTuple(ts) => {
ty::TyTuple(ts, _) => {
stack.extend(ts.iter().cloned().rev());
}
ty::TyFnDef(_, substs, ref ft) => {

2
src/librustc/ty/wf.rs
View file

@ -315,7 +315,7 @@ impl<'a, 'gcx, 'tcx> WfPredicates<'a, 'gcx, 'tcx> {
self.require_sized(subty, traits::SliceOrArrayElem);
}
ty::TyTuple(ref tys) => {
ty::TyTuple(ref tys, _) => {
if let Some((_last, rest)) = tys.split_last() {
for elem in rest {
self.require_sized(elem, traits::TupleElem);

4
src/librustc/util/ppaux.rs
View file

@ -156,7 +156,7 @@ pub fn parameterized(f: &mut fmt::Formatter,
if !verbose && fn_trait_kind.is_some() && projections.len() == 1 {
let projection_ty = projections[0].ty;
if let TyTuple(ref args) = substs.type_at(1).sty {
if let TyTuple(ref args, _) = substs.type_at(1).sty {
return fn_sig(f, args, false, projection_ty);
}
}
@ -724,7 +724,7 @@ impl<'tcx> fmt::Display for ty::TypeVariants<'tcx> {
write!(f, "{}", tm)
}
TyNever => write!(f, "!"),
TyTuple(ref tys) => {
TyTuple(ref tys, _) => {
write!(f, "(")?;
let mut tys = tys.iter();
if let Some(&ty) = tys.next() {