Get rid of HIR const checker
This commit is contained in:
Michael Goulet
parent
75703c1a78
commit
01ff36a6b9
38 changed files with 151 additions and 604 deletions
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@ -1,236 +0,0 @@
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//! This pass checks HIR bodies that may be evaluated at compile-time (e.g., `const`, `static`,
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//! `const fn`) for structured control flow (e.g. `if`, `while`), which is forbidden in a const
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//! context.
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//!
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//! By the time the MIR const-checker runs, these high-level constructs have been lowered to
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//! control-flow primitives (e.g., `Goto`, `SwitchInt`), making it tough to properly attribute
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//! errors. We still look for those primitives in the MIR const-checker to ensure nothing slips
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//! through, but errors for structured control flow in a `const` should be emitted here.
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use rustc_hir::def_id::{LocalDefId, LocalModDefId};
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use rustc_hir::intravisit::{self, Visitor};
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use rustc_middle::hir::nested_filter;
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use rustc_middle::query::Providers;
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use rustc_middle::span_bug;
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use rustc_middle::ty::TyCtxt;
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use rustc_session::parse::feature_err;
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use rustc_span::{Span, Symbol, sym};
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use {rustc_attr as attr, rustc_hir as hir};
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use crate::errors::SkippingConstChecks;
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/// An expression that is not *always* legal in a const context.
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#[derive(Clone, Copy)]
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enum NonConstExpr {
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Loop(hir::LoopSource),
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Match(hir::MatchSource),
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}
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impl NonConstExpr {
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fn name(self) -> String {
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match self {
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Self::Loop(src) => format!("`{}`", src.name()),
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Self::Match(src) => format!("`{}`", src.name()),
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}
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}
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fn required_feature_gates(self) -> Option<&'static [Symbol]> {
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use hir::LoopSource::*;
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use hir::MatchSource::*;
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let gates: &[_] = match self {
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Self::Match(AwaitDesugar) => {
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return None;
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}
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Self::Loop(ForLoop) | Self::Match(ForLoopDesugar) => &[sym::const_for],
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Self::Match(TryDesugar(_)) => &[sym::const_try],
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// All other expressions are allowed.
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Self::Loop(Loop | While) | Self::Match(Normal | Postfix | FormatArgs) => &[],
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};
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Some(gates)
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}
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}
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fn check_mod_const_bodies(tcx: TyCtxt<'_>, module_def_id: LocalModDefId) {
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let mut vis = CheckConstVisitor::new(tcx);
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tcx.hir().visit_item_likes_in_module(module_def_id, &mut vis);
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}
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pub(crate) fn provide(providers: &mut Providers) {
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*providers = Providers { check_mod_const_bodies, ..*providers };
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}
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#[derive(Copy, Clone)]
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struct CheckConstVisitor<'tcx> {
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tcx: TyCtxt<'tcx>,
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const_kind: Option<hir::ConstContext>,
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def_id: Option<LocalDefId>,
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}
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impl<'tcx> CheckConstVisitor<'tcx> {
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fn new(tcx: TyCtxt<'tcx>) -> Self {
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CheckConstVisitor { tcx, const_kind: None, def_id: None }
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}
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/// Emits an error when an unsupported expression is found in a const context.
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#[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
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fn const_check_violated(&self, expr: NonConstExpr, span: Span) {
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let Self { tcx, def_id, const_kind } = *self;
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let features = tcx.features();
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let required_gates = expr.required_feature_gates();
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let is_feature_allowed = |feature_gate| {
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// All features require that the corresponding gate be enabled,
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// even if the function has `#[rustc_allow_const_fn_unstable(the_gate)]`.
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if !tcx.features().enabled(feature_gate) {
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return false;
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}
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// If `def_id` is `None`, we don't need to consider stability attributes.
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let def_id = match def_id {
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Some(x) => x,
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None => return true,
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};
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// If the function belongs to a trait, then it must enable the const_trait_impl
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// feature to use that trait function (with a const default body).
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if tcx.trait_of_item(def_id.to_def_id()).is_some() {
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return true;
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}
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// If this crate is not using stability attributes, or this function is not claiming to be a
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// stable `const fn`, that is all that is required.
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if !tcx.features().staged_api() || tcx.has_attr(def_id, sym::rustc_const_unstable) {
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return true;
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}
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// However, we cannot allow stable `const fn`s to use unstable features without an explicit
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// opt-in via `rustc_allow_const_fn_unstable`.
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let attrs = tcx.hir().attrs(tcx.local_def_id_to_hir_id(def_id));
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attr::rustc_allow_const_fn_unstable(tcx.sess, attrs).any(|name| name == feature_gate)
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};
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match required_gates {
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// Don't emit an error if the user has enabled the requisite feature gates.
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Some(gates) if gates.iter().copied().all(is_feature_allowed) => return,
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// `-Zunleash-the-miri-inside-of-you` only works for expressions that don't have a
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// corresponding feature gate. This encourages nightly users to use feature gates when
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// possible.
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None if tcx.sess.opts.unstable_opts.unleash_the_miri_inside_of_you => {
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tcx.dcx().emit_warn(SkippingConstChecks { span });
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return;
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}
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_ => {}
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}
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let const_kind =
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const_kind.expect("`const_check_violated` may only be called inside a const context");
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let required_gates = required_gates.unwrap_or(&[]);
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let missing_gates: Vec<_> =
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required_gates.iter().copied().filter(|&g| !features.enabled(g)).collect();
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match missing_gates.as_slice() {
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[] => {
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span_bug!(
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span,
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"we should not have reached this point, since `.await` is denied earlier"
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);
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}
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[missing_primary, ref missing_secondary @ ..] => {
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let msg =
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format!("{} is not allowed in a `{}`", expr.name(), const_kind.keyword_name());
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let mut err = feature_err(&tcx.sess, *missing_primary, span, msg);
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// If multiple feature gates would be required to enable this expression, include
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// them as help messages. Don't emit a separate error for each missing feature gate.
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//
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// FIXME(ecstaticmorse): Maybe this could be incorporated into `feature_err`? This
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// is a pretty narrow case, however.
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tcx.disabled_nightly_features(
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&mut err,
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def_id.map(|id| tcx.local_def_id_to_hir_id(id)),
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missing_secondary.into_iter().map(|gate| (String::new(), *gate)),
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);
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err.emit();
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}
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}
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}
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/// Saves the parent `const_kind` before calling `f` and restores it afterwards.
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fn recurse_into(
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&mut self,
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kind: Option<hir::ConstContext>,
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def_id: Option<LocalDefId>,
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f: impl FnOnce(&mut Self),
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) {
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let parent_def_id = self.def_id;
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let parent_kind = self.const_kind;
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self.def_id = def_id;
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self.const_kind = kind;
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f(self);
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self.def_id = parent_def_id;
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self.const_kind = parent_kind;
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}
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}
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impl<'tcx> Visitor<'tcx> for CheckConstVisitor<'tcx> {
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type NestedFilter = nested_filter::OnlyBodies;
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fn nested_visit_map(&mut self) -> Self::Map {
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self.tcx.hir()
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}
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fn visit_anon_const(&mut self, anon: &'tcx hir::AnonConst) {
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let kind = Some(hir::ConstContext::Const { inline: false });
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self.recurse_into(kind, None, |this| intravisit::walk_anon_const(this, anon));
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}
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fn visit_inline_const(&mut self, block: &'tcx hir::ConstBlock) {
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let kind = Some(hir::ConstContext::Const { inline: true });
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self.recurse_into(kind, None, |this| intravisit::walk_inline_const(this, block));
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}
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fn visit_body(&mut self, body: &hir::Body<'tcx>) {
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let owner = self.tcx.hir().body_owner_def_id(body.id());
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let kind = self.tcx.hir().body_const_context(owner);
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self.recurse_into(kind, Some(owner), |this| intravisit::walk_body(this, body));
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}
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fn visit_expr(&mut self, e: &'tcx hir::Expr<'tcx>) {
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match &e.kind {
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// Skip the following checks if we are not currently in a const context.
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_ if self.const_kind.is_none() => {}
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hir::ExprKind::Loop(_, _, source, _) => {
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self.const_check_violated(NonConstExpr::Loop(*source), e.span);
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}
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hir::ExprKind::Match(_, _, source) => {
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let non_const_expr = match source {
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// These are handled by `ExprKind::Loop` above.
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hir::MatchSource::ForLoopDesugar => None,
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_ => Some(NonConstExpr::Match(*source)),
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};
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if let Some(expr) = non_const_expr {
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self.const_check_violated(expr, e.span);
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}
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}
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_ => {}
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}
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intravisit::walk_expr(self, e);
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}
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}
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@ -1670,13 +1670,6 @@ pub(crate) struct ProcMacroBadSig {
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pub kind: ProcMacroKind,
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}
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#[derive(Diagnostic)]
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#[diag(passes_skipping_const_checks)]
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pub(crate) struct SkippingConstChecks {
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#[primary_span]
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pub span: Span,
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}
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#[derive(LintDiagnostic)]
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#[diag(passes_unreachable_due_to_uninhabited)]
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pub(crate) struct UnreachableDueToUninhabited<'desc, 'tcx> {
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@ -19,7 +19,6 @@ use rustc_middle::query::Providers;
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pub mod abi_test;
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mod check_attr;
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mod check_const;
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pub mod dead;
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mod debugger_visualizer;
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mod diagnostic_items;
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@ -43,7 +42,6 @@ rustc_fluent_macro::fluent_messages! { "../messages.ftl" }
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pub fn provide(providers: &mut Providers) {
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check_attr::provide(providers);
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check_const::provide(providers);
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dead::provide(providers);
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debugger_visualizer::provide(providers);
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diagnostic_items::provide(providers);
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