From 5363f350887b1e5b5dd21a86f88c8af9d7fea6da Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Wed, 17 Apr 2024 14:18:25 +0200 Subject: Merging upstream version 1.67.1+dfsg1. Signed-off-by: Daniel Baumann --- .../src/traits/const_evaluatable.rs | 354 ++++++++------------- 1 file changed, 137 insertions(+), 217 deletions(-) (limited to 'compiler/rustc_trait_selection/src/traits/const_evaluatable.rs') diff --git a/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs b/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs index 84038625f..7c9fde274 100644 --- a/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs +++ b/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs @@ -8,164 +8,30 @@ //! In this case we try to build an abstract representation of this constant using //! `thir_abstract_const` which can then be checked for structural equality with other //! generic constants mentioned in the `caller_bounds` of the current environment. -use rustc_errors::ErrorGuaranteed; +use rustc_hir::def::DefKind; use rustc_infer::infer::InferCtxt; use rustc_middle::mir::interpret::ErrorHandled; -use rustc_middle::ty::abstract_const::{ - walk_abstract_const, AbstractConst, FailureKind, Node, NotConstEvaluatable, -}; -use rustc_middle::ty::{self, TyCtxt, TypeVisitable}; -use rustc_span::Span; - -use std::iter; -use std::ops::ControlFlow; - -pub struct ConstUnifyCtxt<'tcx> { - pub tcx: TyCtxt<'tcx>, - pub param_env: ty::ParamEnv<'tcx>, -} - -impl<'tcx> ConstUnifyCtxt<'tcx> { - // Substitutes generics repeatedly to allow AbstractConsts to unify where a - // ConstKind::Unevaluated could be turned into an AbstractConst that would unify e.g. - // Param(N) should unify with Param(T), substs: [Unevaluated("T2", [Unevaluated("T3", [Param(N)])])] - #[inline] - #[instrument(skip(self), level = "debug")] - fn try_replace_substs_in_root( - &self, - mut abstr_const: AbstractConst<'tcx>, - ) -> Option> { - while let Node::Leaf(ct) = abstr_const.root(self.tcx) { - match AbstractConst::from_const(self.tcx, ct) { - Ok(Some(act)) => abstr_const = act, - Ok(None) => break, - Err(_) => return None, - } - } - - Some(abstr_const) - } - /// Tries to unify two abstract constants using structural equality. - #[instrument(skip(self), level = "debug")] - pub fn try_unify(&self, a: AbstractConst<'tcx>, b: AbstractConst<'tcx>) -> bool { - let a = if let Some(a) = self.try_replace_substs_in_root(a) { - a - } else { - return true; - }; - - let b = if let Some(b) = self.try_replace_substs_in_root(b) { - b - } else { - return true; - }; - - let a_root = a.root(self.tcx); - let b_root = b.root(self.tcx); - debug!(?a_root, ?b_root); - - match (a_root, b_root) { - (Node::Leaf(a_ct), Node::Leaf(b_ct)) => { - let a_ct = a_ct.eval(self.tcx, self.param_env); - debug!("a_ct evaluated: {:?}", a_ct); - let b_ct = b_ct.eval(self.tcx, self.param_env); - debug!("b_ct evaluated: {:?}", b_ct); - - if a_ct.ty() != b_ct.ty() { - return false; - } +use rustc_middle::traits::ObligationCause; +use rustc_middle::ty::abstract_const::NotConstEvaluatable; +use rustc_middle::ty::{self, TyCtxt, TypeVisitable, TypeVisitor}; - match (a_ct.kind(), b_ct.kind()) { - // We can just unify errors with everything to reduce the amount of - // emitted errors here. - (ty::ConstKind::Error(_), _) | (_, ty::ConstKind::Error(_)) => true, - (ty::ConstKind::Param(a_param), ty::ConstKind::Param(b_param)) => { - a_param == b_param - } - (ty::ConstKind::Value(a_val), ty::ConstKind::Value(b_val)) => a_val == b_val, - // If we have `fn a() -> [u8; N + 1]` and `fn b() -> [u8; 1 + M]` - // we do not want to use `assert_eq!(a(), b())` to infer that `N` and `M` have to be `1`. This - // means that we only allow inference variables if they are equal. - (ty::ConstKind::Infer(a_val), ty::ConstKind::Infer(b_val)) => a_val == b_val, - // We expand generic anonymous constants at the start of this function, so this - // branch should only be taking when dealing with associated constants, at - // which point directly comparing them seems like the desired behavior. - // - // FIXME(generic_const_exprs): This isn't actually the case. - // We also take this branch for concrete anonymous constants and - // expand generic anonymous constants with concrete substs. - (ty::ConstKind::Unevaluated(a_uv), ty::ConstKind::Unevaluated(b_uv)) => { - a_uv == b_uv - } - // FIXME(generic_const_exprs): We may want to either actually try - // to evaluate `a_ct` and `b_ct` if they are fully concrete or something like - // this, for now we just return false here. - _ => false, - } - } - (Node::Binop(a_op, al, ar), Node::Binop(b_op, bl, br)) if a_op == b_op => { - self.try_unify(a.subtree(al), b.subtree(bl)) - && self.try_unify(a.subtree(ar), b.subtree(br)) - } - (Node::UnaryOp(a_op, av), Node::UnaryOp(b_op, bv)) if a_op == b_op => { - self.try_unify(a.subtree(av), b.subtree(bv)) - } - (Node::FunctionCall(a_f, a_args), Node::FunctionCall(b_f, b_args)) - if a_args.len() == b_args.len() => - { - self.try_unify(a.subtree(a_f), b.subtree(b_f)) - && iter::zip(a_args, b_args) - .all(|(&an, &bn)| self.try_unify(a.subtree(an), b.subtree(bn))) - } - (Node::Cast(a_kind, a_operand, a_ty), Node::Cast(b_kind, b_operand, b_ty)) - if (a_ty == b_ty) && (a_kind == b_kind) => - { - self.try_unify(a.subtree(a_operand), b.subtree(b_operand)) - } - // use this over `_ => false` to make adding variants to `Node` less error prone - (Node::Cast(..), _) - | (Node::FunctionCall(..), _) - | (Node::UnaryOp(..), _) - | (Node::Binop(..), _) - | (Node::Leaf(..), _) => false, - } - } -} - -#[instrument(skip(tcx), level = "debug")] -pub fn try_unify_abstract_consts<'tcx>( - tcx: TyCtxt<'tcx>, - (a, b): (ty::UnevaluatedConst<'tcx>, ty::UnevaluatedConst<'tcx>), - param_env: ty::ParamEnv<'tcx>, -) -> bool { - (|| { - if let Some(a) = AbstractConst::new(tcx, a)? { - if let Some(b) = AbstractConst::new(tcx, b)? { - let const_unify_ctxt = ConstUnifyCtxt { tcx, param_env }; - return Ok(const_unify_ctxt.try_unify(a, b)); - } - } +use rustc_span::Span; +use std::ops::ControlFlow; - Ok(false) - })() - .unwrap_or_else(|_: ErrorGuaranteed| true) - // FIXME(generic_const_exprs): We should instead have this - // method return the resulting `ty::Const` and return `ConstKind::Error` - // on `ErrorGuaranteed`. -} +use crate::traits::ObligationCtxt; /// Check if a given constant can be evaluated. #[instrument(skip(infcx), level = "debug")] pub fn is_const_evaluatable<'tcx>( infcx: &InferCtxt<'tcx>, - ct: ty::Const<'tcx>, + unexpanded_ct: ty::Const<'tcx>, param_env: ty::ParamEnv<'tcx>, span: Span, ) -> Result<(), NotConstEvaluatable> { let tcx = infcx.tcx; - let uv = match ct.kind() { - ty::ConstKind::Unevaluated(uv) => uv, + match tcx.expand_abstract_consts(unexpanded_ct).kind() { + ty::ConstKind::Unevaluated(_) | ty::ConstKind::Expr(_) => (), ty::ConstKind::Param(_) | ty::ConstKind::Bound(_, _) | ty::ConstKind::Placeholder(_) @@ -175,40 +41,59 @@ pub fn is_const_evaluatable<'tcx>( }; if tcx.features().generic_const_exprs { - if let Some(ct) = AbstractConst::new(tcx, uv)? { - if satisfied_from_param_env(tcx, ct, param_env)? { + let ct = tcx.expand_abstract_consts(unexpanded_ct); + + let is_anon_ct = if let ty::ConstKind::Unevaluated(uv) = ct.kind() { + tcx.def_kind(uv.def.did) == DefKind::AnonConst + } else { + false + }; + + if !is_anon_ct { + if satisfied_from_param_env(tcx, infcx, ct, param_env) { return Ok(()); } - match ct.unify_failure_kind(tcx) { - FailureKind::MentionsInfer => { - return Err(NotConstEvaluatable::MentionsInfer); - } - FailureKind::MentionsParam => { - return Err(NotConstEvaluatable::MentionsParam); - } - // returned below - FailureKind::Concrete => {} + if ct.has_non_region_infer() { + return Err(NotConstEvaluatable::MentionsInfer); + } else if ct.has_non_region_param() { + return Err(NotConstEvaluatable::MentionsParam); } } - let concrete = infcx.const_eval_resolve(param_env, uv, Some(span)); - match concrete { - Err(ErrorHandled::TooGeneric) => { - Err(NotConstEvaluatable::Error(infcx.tcx.sess.delay_span_bug( + + match unexpanded_ct.kind() { + ty::ConstKind::Expr(_) => { + // FIXME(generic_const_exprs): we have a `ConstKind::Expr` which is fully concrete, but + // currently it is not possible to evaluate `ConstKind::Expr` so we are unable to tell if it + // is evaluatable or not. For now we just ICE until this is implemented. + Err(NotConstEvaluatable::Error(tcx.sess.delay_span_bug( span, - format!("Missing value for constant, but no error reported?"), + "evaluating `ConstKind::Expr` is not currently supported", ))) } - Err(ErrorHandled::Linted) => { - let reported = infcx - .tcx - .sess - .delay_span_bug(span, "constant in type had error reported as lint"); - Err(NotConstEvaluatable::Error(reported)) + ty::ConstKind::Unevaluated(uv) => { + let concrete = infcx.const_eval_resolve(param_env, uv, Some(span)); + match concrete { + Err(ErrorHandled::TooGeneric) => { + Err(NotConstEvaluatable::Error(infcx.tcx.sess.delay_span_bug( + span, + "Missing value for constant, but no error reported?", + ))) + } + Err(ErrorHandled::Reported(e)) => Err(NotConstEvaluatable::Error(e)), + Ok(_) => Ok(()), + } } - Err(ErrorHandled::Reported(e)) => Err(NotConstEvaluatable::Error(e)), - Ok(_) => Ok(()), + _ => bug!("unexpected constkind in `is_const_evalautable: {unexpanded_ct:?}`"), } } else { + let uv = match unexpanded_ct.kind() { + ty::ConstKind::Unevaluated(uv) => uv, + ty::ConstKind::Expr(_) => { + bug!("`ConstKind::Expr` without `feature(generic_const_exprs)` enabled") + } + _ => bug!("unexpected constkind in `is_const_evalautable: {unexpanded_ct:?}`"), + }; + // FIXME: We should only try to evaluate a given constant here if it is fully concrete // as we don't want to allow things like `[u8; std::mem::size_of::<*mut T>()]`. // @@ -218,28 +103,33 @@ pub fn is_const_evaluatable<'tcx>( // // See #74595 for more details about this. let concrete = infcx.const_eval_resolve(param_env, uv, Some(span)); - match concrete { - // If we're evaluating a foreign constant, under a nightly compiler without generic - // const exprs, AND it would've passed if that expression had been evaluated with - // generic const exprs, then suggest using generic const exprs. - Err(_) if tcx.sess.is_nightly_build() - && let Ok(Some(ct)) = AbstractConst::new(tcx, uv) - && satisfied_from_param_env(tcx, ct, param_env) == Ok(true) => { - tcx.sess - .struct_span_fatal( - // Slightly better span than just using `span` alone - if span == rustc_span::DUMMY_SP { tcx.def_span(uv.def.did) } else { span }, - "failed to evaluate generic const expression", - ) - .note("the crate this constant originates from uses `#![feature(generic_const_exprs)]`") - .span_suggestion_verbose( - rustc_span::DUMMY_SP, - "consider enabling this feature", - "#![feature(generic_const_exprs)]\n", - rustc_errors::Applicability::MaybeIncorrect, - ) - .emit() + // If we're evaluating a generic foreign constant, under a nightly compiler while + // the current crate does not enable `feature(generic_const_exprs)`, abort + // compilation with a useful error. + Err(_) + if tcx.sess.is_nightly_build() + && satisfied_from_param_env( + tcx, + infcx, + tcx.expand_abstract_consts(unexpanded_ct), + param_env, + ) => + { + tcx.sess + .struct_span_fatal( + // Slightly better span than just using `span` alone + if span == rustc_span::DUMMY_SP { tcx.def_span(uv.def.did) } else { span }, + "failed to evaluate generic const expression", + ) + .note("the crate this constant originates from uses `#![feature(generic_const_exprs)]`") + .span_suggestion_verbose( + rustc_span::DUMMY_SP, + "consider enabling this feature", + "#![feature(generic_const_exprs)]\n", + rustc_errors::Applicability::MaybeIncorrect, + ) + .emit() } Err(ErrorHandled::TooGeneric) => { @@ -248,16 +138,14 @@ pub fn is_const_evaluatable<'tcx>( } else if uv.has_non_region_param() { NotConstEvaluatable::MentionsParam } else { - let guar = infcx.tcx.sess.delay_span_bug(span, format!("Missing value for constant, but no error reported?")); + let guar = infcx.tcx.sess.delay_span_bug( + span, + format!("Missing value for constant, but no error reported?"), + ); NotConstEvaluatable::Error(guar) }; Err(err) - }, - Err(ErrorHandled::Linted) => { - let reported = - infcx.tcx.sess.delay_span_bug(span, "constant in type had error reported as lint"); - Err(NotConstEvaluatable::Error(reported)) } Err(ErrorHandled::Reported(e)) => Err(NotConstEvaluatable::Error(e)), Ok(_) => Ok(()), @@ -265,37 +153,69 @@ pub fn is_const_evaluatable<'tcx>( } } -#[instrument(skip(tcx), level = "debug")] +#[instrument(skip(infcx, tcx), level = "debug")] fn satisfied_from_param_env<'tcx>( tcx: TyCtxt<'tcx>, - ct: AbstractConst<'tcx>, + infcx: &InferCtxt<'tcx>, + ct: ty::Const<'tcx>, param_env: ty::ParamEnv<'tcx>, -) -> Result { +) -> bool { + // Try to unify with each subtree in the AbstractConst to allow for + // `N + 1` being const evaluatable even if theres only a `ConstEvaluatable` + // predicate for `(N + 1) * 2` + struct Visitor<'a, 'tcx> { + ct: ty::Const<'tcx>, + param_env: ty::ParamEnv<'tcx>, + + infcx: &'a InferCtxt<'tcx>, + } + impl<'a, 'tcx> TypeVisitor<'tcx> for Visitor<'a, 'tcx> { + type BreakTy = (); + fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow { + debug!("is_const_evaluatable: candidate={:?}", c); + if let Ok(()) = self.infcx.commit_if_ok(|_| { + let ocx = ObligationCtxt::new_in_snapshot(self.infcx); + if let Ok(()) = ocx.eq(&ObligationCause::dummy(), self.param_env, c.ty(), self.ct.ty()) + && let Ok(()) = ocx.eq(&ObligationCause::dummy(), self.param_env, c, self.ct) + && ocx.select_all_or_error().is_empty() + { + Ok(()) + } else { + Err(()) + } + }) { + ControlFlow::BREAK + } else if let ty::ConstKind::Expr(e) = c.kind() { + e.visit_with(self) + } else { + // FIXME(generic_const_exprs): This doesn't recurse into `>::ASSOC`'s substs. + // This is currently unobservable as `>::ASSOC` creates an anon const + // with its own `ConstEvaluatable` bound in the param env which we will visit separately. + // + // If we start allowing directly writing `ConstKind::Expr` without an intermediate anon const + // this will be incorrect. It might be worth investigating making `predicates_of` elaborate + // all of the `ConstEvaluatable` bounds rather than having a visitor here. + ControlFlow::CONTINUE + } + } + } + for pred in param_env.caller_bounds() { match pred.kind().skip_binder() { - ty::PredicateKind::ConstEvaluatable(uv) => { - if let Some(b_ct) = AbstractConst::from_const(tcx, uv)? { - let const_unify_ctxt = ConstUnifyCtxt { tcx, param_env }; - - // Try to unify with each subtree in the AbstractConst to allow for - // `N + 1` being const evaluatable even if theres only a `ConstEvaluatable` - // predicate for `(N + 1) * 2` - let result = walk_abstract_const(tcx, b_ct, |b_ct| { - match const_unify_ctxt.try_unify(ct, b_ct) { - true => ControlFlow::BREAK, - false => ControlFlow::CONTINUE, - } - }); - - if let ControlFlow::Break(()) = result { - debug!("is_const_evaluatable: abstract_const ~~> ok"); - return Ok(true); - } + ty::PredicateKind::ConstEvaluatable(ce) => { + let b_ct = tcx.expand_abstract_consts(ce); + let mut v = Visitor { ct, infcx, param_env }; + let result = b_ct.visit_with(&mut v); + + if let ControlFlow::Break(()) = result { + debug!("is_const_evaluatable: yes"); + return true; } } _ => {} // don't care } } - Ok(false) + debug!("is_const_evaluatable: no"); + false } -- cgit v1.2.3