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Diffstat (limited to 'compiler/rustc_passes/src/check_const.rs')
| -rw-r--r-- | compiler/rustc_passes/src/check_const.rs | 236 |
1 files changed, 0 insertions, 236 deletions
diff --git a/compiler/rustc_passes/src/check_const.rs b/compiler/rustc_passes/src/check_const.rs deleted file mode 100644 index f5ece513956..00000000000 --- a/compiler/rustc_passes/src/check_const.rs +++ /dev/null @@ -1,236 +0,0 @@ -//! This pass checks HIR bodies that may be evaluated at compile-time (e.g., `const`, `static`, -//! `const fn`) for structured control flow (e.g. `if`, `while`), which is forbidden in a const -//! context. -//! -//! By the time the MIR const-checker runs, these high-level constructs have been lowered to -//! control-flow primitives (e.g., `Goto`, `SwitchInt`), making it tough to properly attribute -//! errors. We still look for those primitives in the MIR const-checker to ensure nothing slips -//! through, but errors for structured control flow in a `const` should be emitted here. - -use rustc_hir::def_id::{LocalDefId, LocalModDefId}; -use rustc_hir::intravisit::{self, Visitor}; -use rustc_middle::hir::nested_filter; -use rustc_middle::query::Providers; -use rustc_middle::span_bug; -use rustc_middle::ty::TyCtxt; -use rustc_session::parse::feature_err; -use rustc_span::{Span, Symbol, sym}; -use {rustc_attr as attr, rustc_hir as hir}; - -use crate::errors::SkippingConstChecks; - -/// An expression that is not *always* legal in a const context. -#[derive(Clone, Copy)] -enum NonConstExpr { - Loop(hir::LoopSource), - Match(hir::MatchSource), -} - -impl NonConstExpr { - fn name(self) -> String { - match self { - Self::Loop(src) => format!("`{}`", src.name()), - Self::Match(src) => format!("`{}`", src.name()), - } - } - - fn required_feature_gates(self) -> Option<&'static [Symbol]> { - use hir::LoopSource::*; - use hir::MatchSource::*; - - let gates: &[_] = match self { - Self::Match(AwaitDesugar) => { - return None; - } - - Self::Loop(ForLoop) | Self::Match(ForLoopDesugar) => &[sym::const_for], - - Self::Match(TryDesugar(_)) => &[sym::const_try], - - // All other expressions are allowed. - Self::Loop(Loop | While) | Self::Match(Normal | Postfix | FormatArgs) => &[], - }; - - Some(gates) - } -} - -fn check_mod_const_bodies(tcx: TyCtxt<'_>, module_def_id: LocalModDefId) { - let mut vis = CheckConstVisitor::new(tcx); - tcx.hir().visit_item_likes_in_module(module_def_id, &mut vis); -} - -pub(crate) fn provide(providers: &mut Providers) { - *providers = Providers { check_mod_const_bodies, ..*providers }; -} - -#[derive(Copy, Clone)] -struct CheckConstVisitor<'tcx> { - tcx: TyCtxt<'tcx>, - const_kind: Option<hir::ConstContext>, - def_id: Option<LocalDefId>, -} - -impl<'tcx> CheckConstVisitor<'tcx> { - fn new(tcx: TyCtxt<'tcx>) -> Self { - CheckConstVisitor { tcx, const_kind: None, def_id: None } - } - - /// Emits an error when an unsupported expression is found in a const context. - #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable - fn const_check_violated(&self, expr: NonConstExpr, span: Span) { - let Self { tcx, def_id, const_kind } = *self; - - let features = tcx.features(); - let required_gates = expr.required_feature_gates(); - - let is_feature_allowed = |feature_gate| { - // All features require that the corresponding gate be enabled, - // even if the function has `#[rustc_allow_const_fn_unstable(the_gate)]`. - if !tcx.features().enabled(feature_gate) { - return false; - } - - // If `def_id` is `None`, we don't need to consider stability attributes. - let def_id = match def_id { - Some(x) => x, - None => return true, - }; - - // If the function belongs to a trait, then it must enable the const_trait_impl - // feature to use that trait function (with a const default body). - if tcx.trait_of_item(def_id.to_def_id()).is_some() { - return true; - } - - // 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 `rustc_allow_const_fn_unstable`. - let attrs = tcx.hir().attrs(tcx.local_def_id_to_hir_id(def_id)); - attr::rustc_allow_const_fn_unstable(tcx.sess, attrs).any(|name| name == feature_gate) - }; - - match required_gates { - // Don't emit an error if the user has enabled the requisite feature gates. - Some(gates) if gates.iter().copied().all(is_feature_allowed) => return, - - // `-Zunleash-the-miri-inside-of-you` only works for expressions that don't have a - // corresponding feature gate. This encourages nightly users to use feature gates when - // possible. - None if tcx.sess.opts.unstable_opts.unleash_the_miri_inside_of_you => { - tcx.dcx().emit_warn(SkippingConstChecks { span }); - return; - } - - _ => {} - } - - let const_kind = - const_kind.expect("`const_check_violated` may only be called inside a const context"); - - let required_gates = required_gates.unwrap_or(&[]); - let missing_gates: Vec<_> = - required_gates.iter().copied().filter(|&g| !features.enabled(g)).collect(); - - match missing_gates.as_slice() { - [] => { - span_bug!( - span, - "we should not have reached this point, since `.await` is denied earlier" - ); - } - - [missing_primary, ref missing_secondary @ ..] => { - let msg = - format!("{} is not allowed in a `{}`", expr.name(), const_kind.keyword_name()); - let mut err = feature_err(&tcx.sess, *missing_primary, span, msg); - - // If multiple feature gates would be required to enable this expression, include - // them as help messages. Don't emit a separate error for each missing feature gate. - // - // FIXME(ecstaticmorse): Maybe this could be incorporated into `feature_err`? This - // is a pretty narrow case, however. - tcx.disabled_nightly_features( - &mut err, - def_id.map(|id| tcx.local_def_id_to_hir_id(id)), - missing_secondary.into_iter().map(|gate| (String::new(), *gate)), - ); - - err.emit(); - } - } - } - - /// Saves the parent `const_kind` before calling `f` and restores it afterwards. - fn recurse_into( - &mut self, - kind: Option<hir::ConstContext>, - def_id: Option<LocalDefId>, - f: impl FnOnce(&mut Self), - ) { - let parent_def_id = self.def_id; - let parent_kind = self.const_kind; - self.def_id = def_id; - self.const_kind = kind; - f(self); - self.def_id = parent_def_id; - self.const_kind = parent_kind; - } -} - -impl<'tcx> Visitor<'tcx> for CheckConstVisitor<'tcx> { - type NestedFilter = nested_filter::OnlyBodies; - - fn nested_visit_map(&mut self) -> Self::Map { - self.tcx.hir() - } - - fn visit_anon_const(&mut self, anon: &'tcx hir::AnonConst) { - let kind = Some(hir::ConstContext::Const { inline: false }); - self.recurse_into(kind, None, |this| intravisit::walk_anon_const(this, anon)); - } - - fn visit_inline_const(&mut self, block: &'tcx hir::ConstBlock) { - let kind = Some(hir::ConstContext::Const { inline: true }); - self.recurse_into(kind, None, |this| intravisit::walk_inline_const(this, block)); - } - - fn visit_body(&mut self, body: &hir::Body<'tcx>) { - let owner = self.tcx.hir().body_owner_def_id(body.id()); - let kind = self.tcx.hir().body_const_context(owner); - self.recurse_into(kind, Some(owner), |this| intravisit::walk_body(this, body)); - } - - fn visit_expr(&mut self, e: &'tcx hir::Expr<'tcx>) { - match &e.kind { - // Skip the following checks if we are not currently in a const context. - _ if self.const_kind.is_none() => {} - - hir::ExprKind::Loop(_, _, source, _) => { - self.const_check_violated(NonConstExpr::Loop(*source), e.span); - } - - hir::ExprKind::Match(_, _, source) => { - let non_const_expr = match source { - // These are handled by `ExprKind::Loop` above. - hir::MatchSource::ForLoopDesugar => None, - - _ => Some(NonConstExpr::Match(*source)), - }; - - if let Some(expr) = non_const_expr { - self.const_check_violated(expr, e.span); - } - } - - _ => {} - } - - intravisit::walk_expr(self, e); - } -} |