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Rollup merge of #84547 - RalfJung:max_const_fn, r=oli-obk
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Get rid of is_min_const_fn

This removes the last trace of the min_const_fn mechanism by making the unsafety checker agnostic about whether something is a min or "non-min" const fn. It seems this distinction was used to disallow some features inside `const fn`, but that is the responsibility of the const checker, not of the unsafety checker. No test seems to even notice this change in the unsafety checker so I guess we are good...

r? `@oli-obk`
Cc #84510
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@Dylan-DPC
Dylan-DPC authored Apr 25, 2021
2 parents 25508eb + 588530d commit 000a630
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Showing 11 changed files with 102 additions and 142 deletions.
4 changes: 1 addition & 3 deletions compiler/rustc_middle/src/mir/query.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -19,10 +19,8 @@ use super::{Field, SourceInfo};

#[derive(Copy, Clone, PartialEq, TyEncodable, TyDecodable, HashStable, Debug)]
pub enum UnsafetyViolationKind {
/// Only permitted in regular `fn`s, prohibited in `const fn`s.
/// Unsafe operation outside `unsafe`.
General,
/// Permitted both in `const fn`s and regular `fn`s.
GeneralAndConstFn,
/// Unsafe operation in an `unsafe fn` but outside an `unsafe` block.
/// Has to be handled as a lint for backwards compatibility.
UnsafeFn,
Expand Down
49 changes: 0 additions & 49 deletions compiler/rustc_mir/src/const_eval/fn_queries.rs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,3 @@
use rustc_attr as attr;
use rustc_hir as hir;
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_middle::hir::map::blocks::FnLikeNode;
Expand Down Expand Up @@ -34,54 +33,6 @@ pub fn is_unstable_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Symbol> {
}
}

/// Returns `true` if this function must conform to `min_const_fn`
pub fn is_min_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
// Bail out if the signature doesn't contain `const`
if !tcx.is_const_fn_raw(def_id) {
return false;
}

if tcx.features().staged_api {
// In order for a libstd function to be considered min_const_fn
// it needs to be stable and have no `rustc_const_unstable` attribute.
match tcx.lookup_const_stability(def_id) {
// `rustc_const_unstable` functions don't need to conform.
Some(&attr::ConstStability { ref level, .. }) if level.is_unstable() => false,
None => {
if let Some(stab) = tcx.lookup_stability(def_id) {
if stab.level.is_stable() {
tcx.sess.delay_span_bug(
tcx.def_span(def_id),
"stable const functions must have either `rustc_const_stable` or \
`rustc_const_unstable` attribute",
);
// While we errored above, because we don't know if we need to conform, we
// err on the "safe" side and require min_const_fn.
true
} else {
// Unstable functions need not conform to min_const_fn.
false
}
} else {
// Internal functions are forced to conform to min_const_fn.
// Annotate the internal function with a const stability attribute if
// you need to use unstable features.
// Note: this is an arbitrary choice that does not affect stability or const
// safety or anything, it just changes whether we need to annotate some
// internal functions with `rustc_const_stable` or with `rustc_const_unstable`
true
}
}
// Everything else needs to conform, because it would be callable from
// other `min_const_fn` functions.
_ => true,
}
} else {
// users enabling the `const_fn` feature gate can do what they want
!tcx.features().const_fn
}
}

pub fn is_parent_const_impl_raw(tcx: TyCtxt<'_>, hir_id: hir::HirId) -> bool {
let parent_id = tcx.hir().get_parent_did(hir_id);
if !parent_id.is_top_level_module() { is_const_impl_raw(tcx, parent_id) } else { false }
Expand Down
67 changes: 17 additions & 50 deletions compiler/rustc_mir/src/transform/check_unsafety.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -15,13 +15,10 @@ use rustc_session::lint::Level;

use std::ops::Bound;

use crate::const_eval::is_min_const_fn;

pub struct UnsafetyChecker<'a, 'tcx> {
body: &'a Body<'tcx>,
body_did: LocalDefId,
const_context: bool,
min_const_fn: bool,
violations: Vec<UnsafetyViolation>,
source_info: SourceInfo,
tcx: TyCtxt<'tcx>,
Expand All @@ -34,21 +31,15 @@ pub struct UnsafetyChecker<'a, 'tcx> {
impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
fn new(
const_context: bool,
min_const_fn: bool,
body: &'a Body<'tcx>,
body_did: LocalDefId,
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
) -> Self {
// sanity check
if min_const_fn {
assert!(const_context);
}
Self {
body,
body_did,
const_context,
min_const_fn,
violations: vec![],
source_info: SourceInfo::outermost(body.span),
tcx,
Expand Down Expand Up @@ -84,7 +75,7 @@ impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
let sig = func_ty.fn_sig(self.tcx);
if let hir::Unsafety::Unsafe = sig.unsafety() {
self.require_unsafe(
UnsafetyViolationKind::GeneralAndConstFn,
UnsafetyViolationKind::General,
UnsafetyViolationDetails::CallToUnsafeFunction,
)
}
Expand Down Expand Up @@ -134,7 +125,7 @@ impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
match self.tcx.layout_scalar_valid_range(def.did) {
(Bound::Unbounded, Bound::Unbounded) => {}
_ => self.require_unsafe(
UnsafetyViolationKind::GeneralAndConstFn,
UnsafetyViolationKind::General,
UnsafetyViolationDetails::InitializingTypeWith,
),
}
Expand Down Expand Up @@ -213,7 +204,7 @@ impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
let base_ty = base.ty(self.body, self.tcx).ty;
if base_ty.is_unsafe_ptr() {
self.require_unsafe(
UnsafetyViolationKind::GeneralAndConstFn,
UnsafetyViolationKind::General,
UnsafetyViolationDetails::DerefOfRawPointer,
)
}
Expand Down Expand Up @@ -258,15 +249,15 @@ impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
);
if !nodrop {
self.require_unsafe(
UnsafetyViolationKind::GeneralAndConstFn,
UnsafetyViolationKind::General,
UnsafetyViolationDetails::AssignToDroppingUnionField,
);
} else {
// write to non-drop union field, safe
}
} else {
self.require_unsafe(
UnsafetyViolationKind::GeneralAndConstFn,
UnsafetyViolationKind::General,
UnsafetyViolationDetails::AccessToUnionField,
)
}
Expand All @@ -277,6 +268,9 @@ impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {

impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
fn require_unsafe(&mut self, kind: UnsafetyViolationKind, details: UnsafetyViolationDetails) {
// Violations can turn out to be `UnsafeFn` during analysis, but they should not start out as such.
assert_ne!(kind, UnsafetyViolationKind::UnsafeFn);

let source_info = self.source_info;
let lint_root = self.body.source_scopes[self.source_info.scope]
.local_data
Expand Down Expand Up @@ -304,8 +298,7 @@ impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
Safety::Safe => {
for violation in violations {
match violation.kind {
UnsafetyViolationKind::GeneralAndConstFn
| UnsafetyViolationKind::General => {}
UnsafetyViolationKind::General => {}
UnsafetyViolationKind::UnsafeFn => {
bug!("`UnsafetyViolationKind::UnsafeFn` in an `Safe` context")
}
Expand Down Expand Up @@ -334,29 +327,6 @@ impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
if !violations.is_empty() {
self.used_unsafe.insert(hir_id);
}
// only some unsafety is allowed in const fn
if self.min_const_fn {
for violation in violations {
match violation.kind {
// these unsafe things are stable in const fn
UnsafetyViolationKind::GeneralAndConstFn => {}
// these things are forbidden in const fns
UnsafetyViolationKind::General => {
let mut violation = *violation;
// const fns don't need to be backwards compatible and can
// emit these violations as a hard error instead of a backwards
// compat lint
violation.kind = UnsafetyViolationKind::General;
if !self.violations.contains(&violation) {
self.violations.push(violation)
}
}
UnsafetyViolationKind::UnsafeFn => bug!(
"`UnsafetyViolationKind::UnsafeFn` in an `ExplicitUnsafe` context"
),
}
}
}
true
}
};
Expand Down Expand Up @@ -394,7 +364,7 @@ impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
} else {
continue;
};
self.require_unsafe(UnsafetyViolationKind::GeneralAndConstFn, details);
self.require_unsafe(UnsafetyViolationKind::General, details);
}
}
}
Expand All @@ -412,7 +382,7 @@ impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
// Is `callee_features` a subset of `calling_features`?
if !callee_features.iter().all(|feature| self_features.contains(feature)) {
self.require_unsafe(
UnsafetyViolationKind::GeneralAndConstFn,
UnsafetyViolationKind::General,
UnsafetyViolationDetails::CallToFunctionWith,
)
}
Expand Down Expand Up @@ -494,15 +464,12 @@ fn unsafety_check_result<'tcx>(
let param_env = tcx.param_env(def.did);

let id = tcx.hir().local_def_id_to_hir_id(def.did);
let (const_context, min_const_fn) = match tcx.hir().body_owner_kind(id) {
hir::BodyOwnerKind::Closure => (false, false),
hir::BodyOwnerKind::Fn => {
(tcx.is_const_fn_raw(def.did.to_def_id()), is_min_const_fn(tcx, def.did.to_def_id()))
}
hir::BodyOwnerKind::Const | hir::BodyOwnerKind::Static(_) => (true, false),
let const_context = match tcx.hir().body_owner_kind(id) {
hir::BodyOwnerKind::Closure => false,
hir::BodyOwnerKind::Fn => tcx.is_const_fn_raw(def.did.to_def_id()),
hir::BodyOwnerKind::Const | hir::BodyOwnerKind::Static(_) => true,
};
let mut checker =
UnsafetyChecker::new(const_context, min_const_fn, body, def.did, tcx, param_env);
let mut checker = UnsafetyChecker::new(const_context, body, def.did, tcx, param_env);
checker.visit_body(&body);

check_unused_unsafe(tcx, def.did, &checker.used_unsafe, &mut checker.inherited_blocks);
Expand Down Expand Up @@ -577,7 +544,7 @@ pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: LocalDefId) {
if unsafe_op_in_unsafe_fn_allowed(tcx, lint_root) { " function or" } else { "" };

match kind {
UnsafetyViolationKind::GeneralAndConstFn | UnsafetyViolationKind::General => {
UnsafetyViolationKind::General => {
// once
struct_span_err!(
tcx.sess,
Expand Down
14 changes: 4 additions & 10 deletions library/alloc/src/raw_vec.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -53,17 +53,11 @@ pub struct RawVec<T, A: Allocator = Global> {
}

impl<T> RawVec<T, Global> {
/// HACK(Centril): This exists because `#[unstable]` `const fn`s needn't conform
/// to `min_const_fn` and so they cannot be called in `min_const_fn`s either.
/// HACK(Centril): This exists because stable `const fn` can only call stable `const fn`, so
/// they cannot call `Self::new()`.
///
/// If you change `RawVec<T>::new` or dependencies, please take care to not
/// introduce anything that would truly violate `min_const_fn`.
///
/// NOTE: We could avoid this hack and check conformance with some
/// `#[rustc_force_min_const_fn]` attribute which requires conformance
/// with `min_const_fn` but does not necessarily allow calling it in
/// `stable(...) const fn` / user code not enabling `foo` when
/// `#[rustc_const_unstable(feature = "foo", issue = "01234")]` is present.
/// If you change `RawVec<T>::new` or dependencies, please take care to not introduce anything
/// that would truly const-call something unstable.
pub const NEW: Self = Self::new();

/// Creates the biggest possible `RawVec` (on the system heap)
Expand Down
3 changes: 1 addition & 2 deletions src/librustdoc/clean/inline.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,6 @@ use rustc_hir::def_id::DefId;
use rustc_hir::Mutability;
use rustc_metadata::creader::LoadedMacro;
use rustc_middle::ty::{self, TyCtxt};
use rustc_mir::const_eval::is_min_const_fn;
use rustc_span::hygiene::MacroKind;
use rustc_span::symbol::{kw, sym, Symbol};
use rustc_span::Span;
Expand Down Expand Up @@ -210,7 +209,7 @@ fn build_external_function(cx: &mut DocContext<'_>, did: DefId) -> clean::Functi
let sig = cx.tcx.fn_sig(did);

let constness =
if is_min_const_fn(cx.tcx, did) { hir::Constness::Const } else { hir::Constness::NotConst };
if cx.tcx.is_const_fn_raw(did) { hir::Constness::Const } else { hir::Constness::NotConst };
let asyncness = cx.tcx.asyncness(did);
let predicates = cx.tcx.predicates_of(did);
let (generics, decl) = clean::enter_impl_trait(cx, |cx| {
Expand Down
4 changes: 2 additions & 2 deletions src/librustdoc/clean/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -22,7 +22,7 @@ use rustc_middle::middle::resolve_lifetime as rl;
use rustc_middle::ty::fold::TypeFolder;
use rustc_middle::ty::subst::{InternalSubsts, Subst};
use rustc_middle::ty::{self, AdtKind, Lift, Ty, TyCtxt};
use rustc_mir::const_eval::{is_const_fn, is_min_const_fn, is_unstable_const_fn};
use rustc_mir::const_eval::{is_const_fn, is_unstable_const_fn};
use rustc_span::hygiene::{AstPass, MacroKind};
use rustc_span::symbol::{kw, sym, Ident, Symbol};
use rustc_span::{self, ExpnKind};
Expand Down Expand Up @@ -1048,7 +1048,7 @@ impl Clean<Item> for ty::AssocItem {
ty::TraitContainer(_) => self.defaultness.has_value(),
};
if provided {
let constness = if is_min_const_fn(tcx, self.def_id) {
let constness = if tcx.is_const_fn_raw(self.def_id) {
hir::Constness::Const
} else {
hir::Constness::NotConst
Expand Down
22 changes: 18 additions & 4 deletions src/test/ui/cast/cast-ptr-to-int-const.rs
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Original file line number Diff line number Diff line change
@@ -1,11 +1,25 @@
// gate-test-const_raw_ptr_to_usize_cast
// revisions: with_feature without_feature

#![cfg_attr(with_feature, feature(const_raw_ptr_to_usize_cast))]

fn main() {
const X: u32 = unsafe {
main as u32 //~ ERROR casting pointers to integers in constants is unstable
const X: usize = unsafe {
main as usize //[without_feature]~ ERROR casting pointers to integers in constants is unstable
};
const Y: u32 = 0;
const Z: u32 = unsafe {
&Y as *const u32 as u32 //~ ERROR is unstable
const Z: usize = unsafe {
&Y as *const u32 as usize //[without_feature]~ ERROR is unstable
};
// Cast in `const` without `unsafe` block
const SAFE: usize = {
&Y as *const u32 as usize //[without_feature]~ ERROR is unstable
//[with_feature]~^ ERROR cast of pointer to int is unsafe and requires unsafe
};
}

// Cast in `const fn` without `unsafe` block
const fn test() -> usize {
&0 as *const i32 as usize //[without_feature]~ ERROR is unstable
//[with_feature]~^ ERROR cast of pointer to int is unsafe and requires unsafe
}
21 changes: 0 additions & 21 deletions src/test/ui/cast/cast-ptr-to-int-const.stderr
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This file was deleted.

19 changes: 19 additions & 0 deletions src/test/ui/cast/cast-ptr-to-int-const.with_feature.stderr
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Original file line number Diff line number Diff line change
@@ -0,0 +1,19 @@
error[E0133]: cast of pointer to int is unsafe and requires unsafe function or block
--> $DIR/cast-ptr-to-int-const.rs:16:9
|
LL | &Y as *const u32 as usize
| ^^^^^^^^^^^^^^^^^^^^^^^^^ cast of pointer to int
|
= note: casting pointers to integers in constants

error[E0133]: cast of pointer to int is unsafe and requires unsafe function or block
--> $DIR/cast-ptr-to-int-const.rs:23:5
|
LL | &0 as *const i32 as usize
| ^^^^^^^^^^^^^^^^^^^^^^^^^ cast of pointer to int
|
= note: casting pointers to integers in constants

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0133`.
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