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Use explicit promotion for constants in repeat expressions #70042

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Use explicit promotion for constants in repeat expressions #70042

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44e8a9a
Fix ui test blessing when a test has an empty stderr file after havin…
oli-obk Mar 16, 2020
85e2c32
Rename `Item` to `ConstCx`.
oli-obk Mar 23, 2020
77345cc
Use ConstCx in more places
oli-obk Apr 2, 2020
ee868e0
Use ConstCx in the promoted collector
oli-obk Apr 2, 2020
29aebf4
Use `ConstCx` for `validate_candidates`
oli-obk Apr 2, 2020
a4e551e
Use explicit promotion for repeat expression elements if the type is …
oli-obk Apr 2, 2020
f7b89da
Catch and fix explicit promotions that fail to actually promote
oli-obk Apr 6, 2020
1530fe0
Rustfmt
oli-obk Apr 7, 2020
d41c8d3
Add test for passing promotion but failing compilation
oli-obk Apr 7, 2020
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16 changes: 11 additions & 5 deletions src/librustc_mir/borrow_check/type_check/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -42,7 +42,10 @@ use rustc_trait_selection::traits::{self, ObligationCause, PredicateObligations}
use crate::dataflow::move_paths::MoveData;
use crate::dataflow::MaybeInitializedPlaces;
use crate::dataflow::ResultsCursor;
use crate::transform::promote_consts::should_suggest_const_in_array_repeat_expressions_attribute;
use crate::transform::{
check_consts::ConstCx,
promote_consts::should_suggest_const_in_array_repeat_expressions_attribute,
};

use crate::borrow_check::{
borrow_set::BorrowSet,
Expand Down Expand Up @@ -1997,14 +2000,17 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
let span = body.source_info(location).span;
let ty = operand.ty(*body, tcx);
if !self.infcx.type_is_copy_modulo_regions(self.param_env, ty, span) {
let ccx = ConstCx::new_with_param_env(
tcx,
self.mir_def_id,
body,
self.param_env,
);
// To determine if `const_in_array_repeat_expressions` feature gate should
// be mentioned, need to check if the rvalue is promotable.
let should_suggest =
should_suggest_const_in_array_repeat_expressions_attribute(
tcx,
self.mir_def_id,
body,
operand,
&ccx, operand,
);
debug!("check_rvalue: should_suggest={:?}", should_suggest);

Expand Down
15 changes: 12 additions & 3 deletions src/librustc_mir/transform/check_consts/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -20,24 +20,33 @@ pub mod validation;

/// Information about the item currently being const-checked, as well as a reference to the global
/// context.
pub struct Item<'mir, 'tcx> {
pub struct ConstCx<'mir, 'tcx> {
pub body: mir::ReadOnlyBodyAndCache<'mir, 'tcx>,
pub tcx: TyCtxt<'tcx>,
pub def_id: DefId,
pub param_env: ty::ParamEnv<'tcx>,
pub const_kind: Option<ConstKind>,
}

impl Item<'mir, 'tcx> {
impl ConstCx<'mir, 'tcx> {
pub fn new(
tcx: TyCtxt<'tcx>,
def_id: DefId,
body: mir::ReadOnlyBodyAndCache<'mir, 'tcx>,
) -> Self {
let param_env = tcx.param_env(def_id);
Self::new_with_param_env(tcx, def_id, body, param_env)
}

pub fn new_with_param_env(
tcx: TyCtxt<'tcx>,
def_id: DefId,
body: mir::ReadOnlyBodyAndCache<'mir, 'tcx>,
param_env: ty::ParamEnv<'tcx>,
) -> Self {
let const_kind = ConstKind::for_item(tcx, def_id);

Item { body, tcx, def_id, param_env, const_kind }
ConstCx { body, tcx, def_id, param_env, const_kind }
}

/// Returns the kind of const context this `Item` represents (`const`, `static`, etc.).
Expand Down
124 changes: 62 additions & 62 deletions src/librustc_mir/transform/check_consts/ops.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@ use rustc_session::parse::feature_err;
use rustc_span::symbol::sym;
use rustc_span::{Span, Symbol};

use super::{ConstKind, Item};
use super::{ConstCx, ConstKind};

/// An operation that is not *always* allowed in a const context.
pub trait NonConstOp: std::fmt::Debug {
Expand All @@ -27,19 +27,19 @@ pub trait NonConstOp: std::fmt::Debug {
///
/// By default, it returns `true` if and only if this operation has a corresponding feature
/// gate and that gate is enabled.
fn is_allowed_in_item(&self, item: &Item<'_, '_>) -> bool {
Self::feature_gate().map_or(false, |gate| item.tcx.features().enabled(gate))
fn is_allowed_in_item(&self, ccx: &ConstCx<'_, '_>) -> bool {
Self::feature_gate().map_or(false, |gate| ccx.tcx.features().enabled(gate))
}

fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
let mut err = struct_span_err!(
item.tcx.sess,
ccx.tcx.sess,
span,
E0019,
"{} contains unimplemented expression type",
item.const_kind()
ccx.const_kind()
);
if item.tcx.sess.teach(&err.get_code().unwrap()) {
if ccx.tcx.sess.teach(&err.get_code().unwrap()) {
err.note(
"A function call isn't allowed in the const's initialization expression \
because the expression's value must be known at compile-time.",
Expand All @@ -66,9 +66,9 @@ impl NonConstOp for Downcast {
#[derive(Debug)]
pub struct FnCallIndirect;
impl NonConstOp for FnCallIndirect {
fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
let mut err =
item.tcx.sess.struct_span_err(span, "function pointers are not allowed in const fn");
ccx.tcx.sess.struct_span_err(span, "function pointers are not allowed in const fn");
err.emit();
}
}
Expand All @@ -77,14 +77,14 @@ impl NonConstOp for FnCallIndirect {
#[derive(Debug)]
pub struct FnCallNonConst(pub DefId);
impl NonConstOp for FnCallNonConst {
fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
let mut err = struct_span_err!(
item.tcx.sess,
ccx.tcx.sess,
span,
E0015,
"calls in {}s are limited to constant functions, \
tuple structs and tuple variants",
item.const_kind(),
ccx.const_kind(),
);
err.emit();
}
Expand All @@ -106,12 +106,12 @@ impl NonConstOp for FnCallOther {
#[derive(Debug)]
pub struct FnCallUnstable(pub DefId, pub Symbol);
impl NonConstOp for FnCallUnstable {
fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
let FnCallUnstable(def_id, feature) = *self;

let mut err = item.tcx.sess.struct_span_err(
let mut err = ccx.tcx.sess.struct_span_err(
span,
&format!("`{}` is not yet stable as a const fn", item.tcx.def_path_str(def_id)),
&format!("`{}` is not yet stable as a const fn", ccx.tcx.def_path_str(def_id)),
);
if nightly_options::is_nightly_build() {
err.help(&format!("add `#![feature({})]` to the crate attributes to enable", feature));
Expand All @@ -125,16 +125,16 @@ pub struct HeapAllocation;
impl NonConstOp for HeapAllocation {
const IS_SUPPORTED_IN_MIRI: bool = false;

fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
let mut err = struct_span_err!(
item.tcx.sess,
ccx.tcx.sess,
span,
E0010,
"allocations are not allowed in {}s",
item.const_kind()
ccx.const_kind()
);
err.span_label(span, format!("allocation not allowed in {}s", item.const_kind()));
if item.tcx.sess.teach(&err.get_code().unwrap()) {
err.span_label(span, format!("allocation not allowed in {}s", ccx.const_kind()));
if ccx.tcx.sess.teach(&err.get_code().unwrap()) {
err.note(
"The value of statics and constants must be known at compile time, \
and they live for the entire lifetime of a program. Creating a boxed \
Expand All @@ -153,23 +153,23 @@ impl NonConstOp for IfOrMatch {
Some(sym::const_if_match)
}

fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
// This should be caught by the HIR const-checker.
item.tcx.sess.delay_span_bug(span, "complex control flow is forbidden in a const context");
ccx.tcx.sess.delay_span_bug(span, "complex control flow is forbidden in a const context");
}
}

#[derive(Debug)]
pub struct LiveDrop;
impl NonConstOp for LiveDrop {
fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
struct_span_err!(
item.tcx.sess,
ccx.tcx.sess,
span,
E0493,
"destructors cannot be evaluated at compile-time"
)
.span_label(span, format!("{}s cannot evaluate destructors", item.const_kind()))
.span_label(span, format!("{}s cannot evaluate destructors", ccx.const_kind()))
.emit();
}
}
Expand All @@ -181,18 +181,18 @@ impl NonConstOp for Loop {
Some(sym::const_loop)
}

fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
// This should be caught by the HIR const-checker.
item.tcx.sess.delay_span_bug(span, "complex control flow is forbidden in a const context");
ccx.tcx.sess.delay_span_bug(span, "complex control flow is forbidden in a const context");
}
}

#[derive(Debug)]
pub struct CellBorrow;
impl NonConstOp for CellBorrow {
fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
struct_span_err!(
item.tcx.sess,
ccx.tcx.sess,
span,
E0492,
"cannot borrow a constant which may contain \
Expand All @@ -209,19 +209,19 @@ impl NonConstOp for MutBorrow {
Some(sym::const_mut_refs)
}

fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
let mut err = feature_err(
&item.tcx.sess.parse_sess,
&ccx.tcx.sess.parse_sess,
sym::const_mut_refs,
span,
&format!(
"references in {}s may only refer \
to immutable values",
item.const_kind()
ccx.const_kind()
),
);
err.span_label(span, format!("{}s require immutable values", item.const_kind()));
if item.tcx.sess.teach(&err.get_code().unwrap()) {
err.span_label(span, format!("{}s require immutable values", ccx.const_kind()));
if ccx.tcx.sess.teach(&err.get_code().unwrap()) {
err.note(
"References in statics and constants may only refer \
to immutable values.\n\n\
Expand All @@ -244,12 +244,12 @@ impl NonConstOp for MutAddressOf {
Some(sym::const_mut_refs)
}

fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
feature_err(
&item.tcx.sess.parse_sess,
&ccx.tcx.sess.parse_sess,
sym::const_mut_refs,
span,
&format!("`&raw mut` is not allowed in {}s", item.const_kind()),
&format!("`&raw mut` is not allowed in {}s", ccx.const_kind()),
)
.emit();
}
Expand All @@ -270,12 +270,12 @@ impl NonConstOp for Panic {
Some(sym::const_panic)
}

fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
feature_err(
&item.tcx.sess.parse_sess,
&ccx.tcx.sess.parse_sess,
sym::const_panic,
span,
&format!("panicking in {}s is unstable", item.const_kind()),
&format!("panicking in {}s is unstable", ccx.const_kind()),
)
.emit();
}
Expand All @@ -288,12 +288,12 @@ impl NonConstOp for RawPtrComparison {
Some(sym::const_compare_raw_pointers)
}

fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
feature_err(
&item.tcx.sess.parse_sess,
&ccx.tcx.sess.parse_sess,
sym::const_compare_raw_pointers,
span,
&format!("comparing raw pointers inside {}", item.const_kind()),
&format!("comparing raw pointers inside {}", ccx.const_kind()),
)
.emit();
}
Expand All @@ -306,12 +306,12 @@ impl NonConstOp for RawPtrDeref {
Some(sym::const_raw_ptr_deref)
}

fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
feature_err(
&item.tcx.sess.parse_sess,
&ccx.tcx.sess.parse_sess,
sym::const_raw_ptr_deref,
span,
&format!("dereferencing raw pointers in {}s is unstable", item.const_kind(),),
&format!("dereferencing raw pointers in {}s is unstable", ccx.const_kind(),),
)
.emit();
}
Expand All @@ -324,12 +324,12 @@ impl NonConstOp for RawPtrToIntCast {
Some(sym::const_raw_ptr_to_usize_cast)
}

fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
feature_err(
&item.tcx.sess.parse_sess,
&ccx.tcx.sess.parse_sess,
sym::const_raw_ptr_to_usize_cast,
span,
&format!("casting pointers to integers in {}s is unstable", item.const_kind(),),
&format!("casting pointers to integers in {}s is unstable", ccx.const_kind(),),
)
.emit();
}
Expand All @@ -339,22 +339,22 @@ impl NonConstOp for RawPtrToIntCast {
#[derive(Debug)]
pub struct StaticAccess;
impl NonConstOp for StaticAccess {
fn is_allowed_in_item(&self, item: &Item<'_, '_>) -> bool {
item.const_kind().is_static()
fn is_allowed_in_item(&self, ccx: &ConstCx<'_, '_>) -> bool {
ccx.const_kind().is_static()
}

fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
let mut err = struct_span_err!(
item.tcx.sess,
ccx.tcx.sess,
span,
E0013,
"{}s cannot refer to statics",
item.const_kind()
ccx.const_kind()
);
err.help(
"consider extracting the value of the `static` to a `const`, and referring to that",
);
if item.tcx.sess.teach(&err.get_code().unwrap()) {
if ccx.tcx.sess.teach(&err.get_code().unwrap()) {
err.note(
"`static` and `const` variables can refer to other `const` variables. \
A `const` variable, however, cannot refer to a `static` variable.",
Expand All @@ -371,9 +371,9 @@ pub struct ThreadLocalAccess;
impl NonConstOp for ThreadLocalAccess {
const IS_SUPPORTED_IN_MIRI: bool = false;

fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
struct_span_err!(
item.tcx.sess,
ccx.tcx.sess,
span,
E0625,
"thread-local statics cannot be \
Expand All @@ -386,19 +386,19 @@ impl NonConstOp for ThreadLocalAccess {
#[derive(Debug)]
pub struct UnionAccess;
impl NonConstOp for UnionAccess {
fn is_allowed_in_item(&self, item: &Item<'_, '_>) -> bool {
fn is_allowed_in_item(&self, ccx: &ConstCx<'_, '_>) -> bool {
// Union accesses are stable in all contexts except `const fn`.
item.const_kind() != ConstKind::ConstFn
|| item.tcx.features().enabled(Self::feature_gate().unwrap())
ccx.const_kind() != ConstKind::ConstFn
|| ccx.tcx.features().enabled(Self::feature_gate().unwrap())
}

fn feature_gate() -> Option<Symbol> {
Some(sym::const_fn_union)
}

fn emit_error(&self, item: &Item<'_, '_>, span: Span) {
fn emit_error(&self, ccx: &ConstCx<'_, '_>, span: Span) {
feature_err(
&item.tcx.sess.parse_sess,
&ccx.tcx.sess.parse_sess,
sym::const_fn_union,
span,
"unions in const fn are unstable",
Expand Down
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