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Remove all unstable feature support in the missing_const_for_fn lint
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@oli-obk
oli-obk committed Sep 26, 2020
1 parent a6fda14 commit 7072e45
Showing 1 changed file with 25 additions and 97 deletions.
122 changes: 25 additions & 97 deletions clippy_lints/src/utils/qualify_min_const_fn.rs
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Expand Up @@ -3,22 +3,14 @@ use rustc_hir::def_id::DefId;
use rustc_middle::mir::*;
use rustc_middle::ty::subst::GenericArgKind;
use rustc_middle::ty::{self, adjustment::PointerCast, Ty, TyCtxt};
use rustc_span::symbol::{sym, Symbol};
use rustc_span::symbol::{sym};
use rustc_span::Span;
use rustc_target::spec::abi::Abi::RustIntrinsic;
use std::borrow::Cow;

type McfResult = Result<(), (Span, Cow<'static, str>)>;

pub fn is_min_const_fn(tcx: TyCtxt<'tcx>, def_id: DefId, body: &'a Body<'tcx>) -> McfResult {
// Prevent const trait methods from being annotated as `stable`.
if tcx.features().staged_api {
let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
if rustc_mir::const_eval::is_parent_const_impl_raw(tcx, hir_id) {
return Err((body.span, "trait methods cannot be stable const fn".into()));
}
}

let mut current = def_id;
loop {
let predicates = tcx.predicates_of(current);
Expand All @@ -40,19 +32,12 @@ pub fn is_min_const_fn(tcx: TyCtxt<'tcx>, def_id: DefId, body: &'a Body<'tcx>) -
ty::PredicateAtom::Subtype(_) => {
panic!("subtype predicate on function: {:#?}", predicate)
}
ty::PredicateAtom::Trait(pred, constness) => {
ty::PredicateAtom::Trait(pred, _) => {
if Some(pred.def_id()) == tcx.lang_items().sized_trait() {
continue;
}
match pred.self_ty().kind() {
ty::Param(ref p) => {
// Allow `T: ?const Trait`
if constness == hir::Constness::NotConst
&& feature_allowed(tcx, def_id, sym::const_trait_bound_opt_out)
{
continue;
}

let generics = tcx.generics_of(current);
let def = generics.type_param(p, tcx);
let span = tcx.def_span(def.def_id);
Expand All @@ -77,26 +62,25 @@ pub fn is_min_const_fn(tcx: TyCtxt<'tcx>, def_id: DefId, body: &'a Body<'tcx>) -
}

for local in &body.local_decls {
check_ty(tcx, local.ty, local.source_info.span, def_id)?;
check_ty(tcx, local.ty, local.source_info.span)?;
}
// impl trait is gone in MIR, so check the return type manually
check_ty(
tcx,
tcx.fn_sig(def_id).output().skip_binder(),
body.local_decls.iter().next().unwrap().source_info.span,
def_id,
)?;

for bb in body.basic_blocks() {
check_terminator(tcx, body, def_id, bb.terminator())?;
check_terminator(tcx, body, bb.terminator())?;
for stmt in &bb.statements {
check_statement(tcx, body, def_id, stmt)?;
}
}
Ok(())
}

fn check_ty(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, span: Span, fn_def_id: DefId) -> McfResult {
fn check_ty(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, span: Span) -> McfResult {
for arg in ty.walk() {
let ty = match arg.unpack() {
GenericArgKind::Type(ty) => ty,
Expand All @@ -108,15 +92,11 @@ fn check_ty(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, span: Span, fn_def_id: DefId) -> Mc

match ty.kind() {
ty::Ref(_, _, hir::Mutability::Mut) => {
if !feature_allowed(tcx, fn_def_id, sym::const_mut_refs) {
return Err((span, "mutable references in const fn are unstable".into()));
}
}
ty::Opaque(..) => return Err((span, "`impl Trait` in const fn is unstable".into())),
ty::FnPtr(..) => {
if !tcx.const_fn_is_allowed_fn_ptr(fn_def_id) {
return Err((span, "function pointers in const fn are unstable".into()));
}
}
ty::Dynamic(preds, _) => {
for pred in preds.iter() {
Expand Down Expand Up @@ -161,12 +141,12 @@ fn check_rvalue(
Err((span, "cannot access thread local storage in const fn".into()))
}
Rvalue::Repeat(operand, _) | Rvalue::Use(operand) => {
check_operand(tcx, operand, span, def_id, body)
check_operand(tcx, operand, span, body)
}
Rvalue::Len(place)
| Rvalue::Discriminant(place)
| Rvalue::Ref(_, _, place)
| Rvalue::AddressOf(_, place) => check_place(tcx, *place, span, def_id, body),
| Rvalue::AddressOf(_, place) => check_place(tcx, *place, span, body),
Rvalue::Cast(CastKind::Misc, operand, cast_ty) => {
use rustc_middle::ty::cast::CastTy;
let cast_in = CastTy::from_ty(operand.ty(body, tcx)).expect("bad input type for cast");
Expand All @@ -175,14 +155,14 @@ fn check_rvalue(
(CastTy::Ptr(_) | CastTy::FnPtr, CastTy::Int(_)) => {
Err((span, "casting pointers to ints is unstable in const fn".into()))
}
_ => check_operand(tcx, operand, span, def_id, body),
_ => check_operand(tcx, operand, span, body),
}
}
Rvalue::Cast(
CastKind::Pointer(PointerCast::MutToConstPointer | PointerCast::ArrayToPointer),
operand,
_,
) => check_operand(tcx, operand, span, def_id, body),
) => check_operand(tcx, operand, span, body),
Rvalue::Cast(
CastKind::Pointer(
PointerCast::UnsafeFnPointer
Expand All @@ -204,7 +184,7 @@ fn check_rvalue(
};
let unsized_ty = tcx.struct_tail_erasing_lifetimes(pointee_ty, tcx.param_env(def_id));
if let ty::Slice(_) | ty::Str = unsized_ty.kind() {
check_operand(tcx, op, span, def_id, body)?;
check_operand(tcx, op, span, body)?;
// Casting/coercing things to slices is fine.
Ok(())
} else {
Expand All @@ -214,8 +194,8 @@ fn check_rvalue(
}
// binops are fine on integers
Rvalue::BinaryOp(_, lhs, rhs) | Rvalue::CheckedBinaryOp(_, lhs, rhs) => {
check_operand(tcx, lhs, span, def_id, body)?;
check_operand(tcx, rhs, span, def_id, body)?;
check_operand(tcx, lhs, span, body)?;
check_operand(tcx, rhs, span, body)?;
let ty = lhs.ty(body, tcx);
if ty.is_integral() || ty.is_bool() || ty.is_char() {
Ok(())
Expand All @@ -230,14 +210,14 @@ fn check_rvalue(
Rvalue::UnaryOp(_, operand) => {
let ty = operand.ty(body, tcx);
if ty.is_integral() || ty.is_bool() {
check_operand(tcx, operand, span, def_id, body)
check_operand(tcx, operand, span, body)
} else {
Err((span, "only int and `bool` operations are stable in const fn".into()))
}
}
Rvalue::Aggregate(_, operands) => {
for operand in operands {
check_operand(tcx, operand, span, def_id, body)?;
check_operand(tcx, operand, span, body)?;
}
Ok(())
}
Expand All @@ -253,15 +233,15 @@ fn check_statement(
let span = statement.source_info.span;
match &statement.kind {
StatementKind::Assign(box (place, rval)) => {
check_place(tcx, *place, span, def_id, body)?;
check_place(tcx, *place, span, body)?;
check_rvalue(tcx, body, def_id, rval, span)
}

StatementKind::FakeRead(_, place) => check_place(tcx, **place, span, def_id, body),
StatementKind::FakeRead(_, place) => check_place(tcx, **place, span, body),

// just an assignment
StatementKind::SetDiscriminant { place, .. } => {
check_place(tcx, **place, span, def_id, body)
check_place(tcx, **place, span, body)
}

StatementKind::LlvmInlineAsm { .. } => {
Expand All @@ -282,11 +262,10 @@ fn check_operand(
tcx: TyCtxt<'tcx>,
operand: &Operand<'tcx>,
span: Span,
def_id: DefId,
body: &Body<'tcx>,
) -> McfResult {
match operand {
Operand::Move(place) | Operand::Copy(place) => check_place(tcx, *place, span, def_id, body),
Operand::Move(place) | Operand::Copy(place) => check_place(tcx, *place, span, body),
Operand::Constant(c) => match c.check_static_ptr(tcx) {
Some(_) => Err((span, "cannot access `static` items in const fn".into())),
None => Ok(()),
Expand All @@ -298,7 +277,6 @@ fn check_place(
tcx: TyCtxt<'tcx>,
place: Place<'tcx>,
span: Span,
def_id: DefId,
body: &Body<'tcx>,
) -> McfResult {
let mut cursor = place.projection.as_ref();
Expand All @@ -310,9 +288,7 @@ fn check_place(
if let Some(def) = base_ty.ty_adt_def() {
// No union field accesses in `const fn`
if def.is_union() {
if !feature_allowed(tcx, def_id, sym::const_fn_union) {
return Err((span, "accessing union fields is unstable".into()));
}
}
}
}
Expand All @@ -327,48 +303,9 @@ fn check_place(
Ok(())
}

/// Returns `true` if the given feature gate is allowed within the function with the given `DefId`.
fn feature_allowed(tcx: TyCtxt<'tcx>, def_id: DefId, feature_gate: Symbol) -> bool {
// All features require that the corresponding gate be enabled,
// even if the function has `#[allow_internal_unstable(the_gate)]`.
if !tcx.features().enabled(feature_gate) {
return false;
}

// If this crate is not using stability attributes, or this function is not claiming to be a
// stable `const fn`, that is all that is required.
if !tcx.features().staged_api || tcx.has_attr(def_id, sym::rustc_const_unstable) {
return true;
}

// However, we cannot allow stable `const fn`s to use unstable features without an explicit
// opt-in via `allow_internal_unstable`.
rustc_mir::transform::check_consts::allow_internal_unstable(tcx, def_id, feature_gate)
}

/// Returns `true` if the given library feature gate is allowed within the function with the given `DefId`.
pub fn lib_feature_allowed(tcx: TyCtxt<'tcx>, def_id: DefId, feature_gate: Symbol) -> bool {
// All features require that the corresponding gate be enabled,
// even if the function has `#[allow_internal_unstable(the_gate)]`.
if !tcx.features().declared_lib_features.iter().any(|&(sym, _)| sym == feature_gate) {
return false;
}

// If this crate is not using stability attributes, or this function is not claiming to be a
// stable `const fn`, that is all that is required.
if !tcx.features().staged_api || tcx.has_attr(def_id, sym::rustc_const_unstable) {
return true;
}

// However, we cannot allow stable `const fn`s to use unstable features without an explicit
// opt-in via `allow_internal_unstable`.
rustc_mir::transform::check_consts::allow_internal_unstable(tcx, def_id, feature_gate)
}

fn check_terminator(
tcx: TyCtxt<'tcx>,
body: &'a Body<'tcx>,
def_id: DefId,
terminator: &Terminator<'tcx>,
) -> McfResult {
let span = terminator.source_info.span;
Expand All @@ -380,14 +317,14 @@ fn check_terminator(
| TerminatorKind::Resume
| TerminatorKind::Unreachable => Ok(()),

TerminatorKind::Drop { place, .. } => check_place(tcx, *place, span, def_id, body),
TerminatorKind::Drop { place, .. } => check_place(tcx, *place, span, body),
TerminatorKind::DropAndReplace { place, value, .. } => {
check_place(tcx, *place, span, def_id, body)?;
check_operand(tcx, value, span, def_id, body)
check_place(tcx, *place, span, body)?;
check_operand(tcx, value, span, body)
}

TerminatorKind::SwitchInt { discr, switch_ty: _, values: _, targets: _ } => {
check_operand(tcx, discr, span, def_id, body)
check_operand(tcx, discr, span, body)
}

TerminatorKind::Abort => Err((span, "abort is not stable in const fn".into())),
Expand All @@ -405,15 +342,7 @@ fn check_terminator(
} => {
let fn_ty = func.ty(body, tcx);
if let ty::FnDef(fn_def_id, _) = *fn_ty.kind() {
// Allow unstable const if we opt in by using #[allow_internal_unstable]
// on function or macro declaration.
if !rustc_mir::const_eval::is_min_const_fn(tcx, fn_def_id)
&& !rustc_mir::const_eval::is_unstable_const_fn(tcx, fn_def_id)
.map(|feature| {
span.allows_unstable(feature)
|| lib_feature_allowed(tcx, def_id, feature)
})
.unwrap_or(false)
{
return Err((
span,
Expand All @@ -432,18 +361,17 @@ fn check_terminator(
// transmutes in const fn before we add more hacks to this.
if tcx.fn_sig(fn_def_id).abi() == RustIntrinsic
&& tcx.item_name(fn_def_id) == sym::transmute
&& !feature_allowed(tcx, def_id, sym::const_fn_transmute)
{
return Err((
span,
"can only call `transmute` from const items, not `const fn`".into(),
));
}

check_operand(tcx, func, span, fn_def_id, body)?;
check_operand(tcx, func, span, body)?;

for arg in args {
check_operand(tcx, arg, span, fn_def_id, body)?;
check_operand(tcx, arg, span, body)?;
}
Ok(())
} else {
Expand All @@ -452,7 +380,7 @@ fn check_terminator(
}

TerminatorKind::Assert { cond, expected: _, msg: _, target: _, cleanup: _ } => {
check_operand(tcx, cond, span, def_id, body)
check_operand(tcx, cond, span, body)
}

TerminatorKind::InlineAsm { .. } => {
Expand Down

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