| //! Checking that constant values used in types can be successfully evaluated. |
| //! |
| //! For concrete constants, this is fairly simple as we can just try and evaluate it. |
| //! |
| //! When dealing with polymorphic constants, for example `std::mem::size_of::<T>() - 1`, |
| //! this is not as easy. |
| //! |
| //! In this case we try to build an abstract representation of this constant using |
| //! `mir_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::ErrorReported; |
| use rustc_hir::def::DefKind; |
| use rustc_index::bit_set::BitSet; |
| use rustc_index::vec::IndexVec; |
| use rustc_infer::infer::InferCtxt; |
| use rustc_middle::mir::abstract_const::{Node, NodeId, NotConstEvaluatable}; |
| use rustc_middle::mir::interpret::ErrorHandled; |
| use rustc_middle::mir::{self, Rvalue, StatementKind, TerminatorKind}; |
| use rustc_middle::ty::subst::{Subst, SubstsRef}; |
| use rustc_middle::ty::{self, TyCtxt, TypeFoldable}; |
| use rustc_session::lint; |
| use rustc_span::def_id::LocalDefId; |
| use rustc_span::Span; |
| |
| use std::cmp; |
| use std::iter; |
| use std::ops::ControlFlow; |
| |
| /// Check if a given constant can be evaluated. |
| pub fn is_const_evaluatable<'cx, 'tcx>( |
| infcx: &InferCtxt<'cx, 'tcx>, |
| uv: ty::Unevaluated<'tcx, ()>, |
| param_env: ty::ParamEnv<'tcx>, |
| span: Span, |
| ) -> Result<(), NotConstEvaluatable> { |
| debug!("is_const_evaluatable({:?})", uv); |
| if infcx.tcx.features().generic_const_exprs { |
| let tcx = infcx.tcx; |
| match AbstractConst::new(tcx, uv)? { |
| // We are looking at a generic abstract constant. |
| Some(ct) => { |
| for pred in param_env.caller_bounds() { |
| match pred.kind().skip_binder() { |
| ty::PredicateKind::ConstEvaluatable(uv) => { |
| if let Some(b_ct) = AbstractConst::new(tcx, uv)? { |
| // 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 try_unify(tcx, ct, b_ct) { |
| true => ControlFlow::BREAK, |
| false => ControlFlow::CONTINUE, |
| } |
| }); |
| |
| if let ControlFlow::Break(()) = result { |
| debug!("is_const_evaluatable: abstract_const ~~> ok"); |
| return Ok(()); |
| } |
| } |
| } |
| _ => {} // don't care |
| } |
| } |
| |
| // We were unable to unify the abstract constant with |
| // a constant found in the caller bounds, there are |
| // now three possible cases here. |
| #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)] |
| enum FailureKind { |
| /// The abstract const still references an inference |
| /// variable, in this case we return `TooGeneric`. |
| MentionsInfer, |
| /// The abstract const references a generic parameter, |
| /// this means that we emit an error here. |
| MentionsParam, |
| /// The substs are concrete enough that we can simply |
| /// try and evaluate the given constant. |
| Concrete, |
| } |
| let mut failure_kind = FailureKind::Concrete; |
| walk_abstract_const::<!, _>(tcx, ct, |node| match node.root() { |
| Node::Leaf(leaf) => { |
| let leaf = leaf.subst(tcx, ct.substs); |
| if leaf.has_infer_types_or_consts() { |
| failure_kind = FailureKind::MentionsInfer; |
| } else if leaf.definitely_has_param_types_or_consts(tcx) { |
| failure_kind = cmp::min(failure_kind, FailureKind::MentionsParam); |
| } |
| |
| ControlFlow::CONTINUE |
| } |
| Node::Cast(_, _, ty) => { |
| let ty = ty.subst(tcx, ct.substs); |
| if ty.has_infer_types_or_consts() { |
| failure_kind = FailureKind::MentionsInfer; |
| } else if ty.definitely_has_param_types_or_consts(tcx) { |
| failure_kind = cmp::min(failure_kind, FailureKind::MentionsParam); |
| } |
| |
| ControlFlow::CONTINUE |
| } |
| Node::Binop(_, _, _) | Node::UnaryOp(_, _) | Node::FunctionCall(_, _) => { |
| ControlFlow::CONTINUE |
| } |
| }); |
| |
| match failure_kind { |
| FailureKind::MentionsInfer => { |
| return Err(NotConstEvaluatable::MentionsInfer); |
| } |
| FailureKind::MentionsParam => { |
| return Err(NotConstEvaluatable::MentionsParam); |
| } |
| FailureKind::Concrete => { |
| // Dealt with below by the same code which handles this |
| // without the feature gate. |
| } |
| } |
| } |
| None => { |
| // If we are dealing with a concrete constant, we can |
| // reuse the old code path and try to evaluate |
| // the constant. |
| } |
| } |
| } |
| |
| let future_compat_lint = || { |
| if let Some(local_def_id) = uv.def.did.as_local() { |
| infcx.tcx.struct_span_lint_hir( |
| lint::builtin::CONST_EVALUATABLE_UNCHECKED, |
| infcx.tcx.hir().local_def_id_to_hir_id(local_def_id), |
| span, |
| |err| { |
| err.build("cannot use constants which depend on generic parameters in types") |
| .emit(); |
| }, |
| ); |
| } |
| }; |
| |
| // 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>()]`. |
| // |
| // We previously did not check this, so we only emit a future compat warning if |
| // const evaluation succeeds and the given constant is still polymorphic for now |
| // and hopefully soon change this to an error. |
| // |
| // See #74595 for more details about this. |
| let concrete = infcx.const_eval_resolve(param_env, uv.expand(), Some(span)); |
| |
| if concrete.is_ok() && uv.substs(infcx.tcx).definitely_has_param_types_or_consts(infcx.tcx) { |
| match infcx.tcx.def_kind(uv.def.did) { |
| DefKind::AnonConst => { |
| let mir_body = infcx.tcx.mir_for_ctfe_opt_const_arg(uv.def); |
| |
| if mir_body.is_polymorphic { |
| future_compat_lint(); |
| } |
| } |
| _ => future_compat_lint(), |
| } |
| } |
| |
| debug!(?concrete, "is_const_evaluatable"); |
| match concrete { |
| Err(ErrorHandled::TooGeneric) => Err(match uv.has_infer_types_or_consts() { |
| true => NotConstEvaluatable::MentionsInfer, |
| false => NotConstEvaluatable::MentionsParam, |
| }), |
| Err(ErrorHandled::Linted) => { |
| infcx.tcx.sess.delay_span_bug(span, "constant in type had error reported as lint"); |
| Err(NotConstEvaluatable::Error(ErrorReported)) |
| } |
| Err(ErrorHandled::Reported(e)) => Err(NotConstEvaluatable::Error(e)), |
| Ok(_) => Ok(()), |
| } |
| } |
| |
| /// A tree representing an anonymous constant. |
| /// |
| /// This is only able to represent a subset of `MIR`, |
| /// and should not leak any information about desugarings. |
| #[derive(Debug, Clone, Copy)] |
| pub struct AbstractConst<'tcx> { |
| // FIXME: Consider adding something like `IndexSlice` |
| // and use this here. |
| pub inner: &'tcx [Node<'tcx>], |
| pub substs: SubstsRef<'tcx>, |
| } |
| |
| impl<'tcx> AbstractConst<'tcx> { |
| pub fn new( |
| tcx: TyCtxt<'tcx>, |
| uv: ty::Unevaluated<'tcx, ()>, |
| ) -> Result<Option<AbstractConst<'tcx>>, ErrorReported> { |
| let inner = tcx.mir_abstract_const_opt_const_arg(uv.def)?; |
| debug!("AbstractConst::new({:?}) = {:?}", uv, inner); |
| Ok(inner.map(|inner| AbstractConst { inner, substs: uv.substs(tcx) })) |
| } |
| |
| pub fn from_const( |
| tcx: TyCtxt<'tcx>, |
| ct: &ty::Const<'tcx>, |
| ) -> Result<Option<AbstractConst<'tcx>>, ErrorReported> { |
| match ct.val { |
| ty::ConstKind::Unevaluated(uv) => AbstractConst::new(tcx, uv.shrink()), |
| ty::ConstKind::Error(_) => Err(ErrorReported), |
| _ => Ok(None), |
| } |
| } |
| |
| #[inline] |
| pub fn subtree(self, node: NodeId) -> AbstractConst<'tcx> { |
| AbstractConst { inner: &self.inner[..=node.index()], substs: self.substs } |
| } |
| |
| #[inline] |
| pub fn root(self) -> Node<'tcx> { |
| self.inner.last().copied().unwrap() |
| } |
| } |
| |
| #[derive(Debug, Clone, Copy, PartialEq, Eq)] |
| struct WorkNode<'tcx> { |
| node: Node<'tcx>, |
| span: Span, |
| used: bool, |
| } |
| |
| struct AbstractConstBuilder<'a, 'tcx> { |
| tcx: TyCtxt<'tcx>, |
| body: &'a mir::Body<'tcx>, |
| /// The current WIP node tree. |
| /// |
| /// We require all nodes to be used in the final abstract const, |
| /// so we store this here. Note that we also consider nodes as used |
| /// if they are mentioned in an assert, so some used nodes are never |
| /// actually reachable by walking the [`AbstractConst`]. |
| nodes: IndexVec<NodeId, WorkNode<'tcx>>, |
| locals: IndexVec<mir::Local, NodeId>, |
| /// We only allow field accesses if they access |
| /// the result of a checked operation. |
| checked_op_locals: BitSet<mir::Local>, |
| } |
| |
| impl<'a, 'tcx> AbstractConstBuilder<'a, 'tcx> { |
| fn error(&mut self, span: Option<Span>, msg: &str) -> Result<!, ErrorReported> { |
| self.tcx |
| .sess |
| .struct_span_err(self.body.span, "overly complex generic constant") |
| .span_label(span.unwrap_or(self.body.span), msg) |
| .help("consider moving this anonymous constant into a `const` function") |
| .emit(); |
| |
| Err(ErrorReported) |
| } |
| |
| fn new( |
| tcx: TyCtxt<'tcx>, |
| body: &'a mir::Body<'tcx>, |
| ) -> Result<Option<AbstractConstBuilder<'a, 'tcx>>, ErrorReported> { |
| let mut builder = AbstractConstBuilder { |
| tcx, |
| body, |
| nodes: IndexVec::new(), |
| locals: IndexVec::from_elem(NodeId::MAX, &body.local_decls), |
| checked_op_locals: BitSet::new_empty(body.local_decls.len()), |
| }; |
| |
| // We don't have to look at concrete constants, as we |
| // can just evaluate them. |
| if !body.is_polymorphic { |
| return Ok(None); |
| } |
| |
| // We only allow consts without control flow, so |
| // we check for cycles here which simplifies the |
| // rest of this implementation. |
| if body.is_cfg_cyclic() { |
| builder.error(None, "cyclic anonymous constants are forbidden")?; |
| } |
| |
| Ok(Some(builder)) |
| } |
| |
| fn add_node(&mut self, node: Node<'tcx>, span: Span) -> NodeId { |
| // Mark used nodes. |
| match node { |
| Node::Leaf(_) => (), |
| Node::Binop(_, lhs, rhs) => { |
| self.nodes[lhs].used = true; |
| self.nodes[rhs].used = true; |
| } |
| Node::UnaryOp(_, input) => { |
| self.nodes[input].used = true; |
| } |
| Node::FunctionCall(func, nodes) => { |
| self.nodes[func].used = true; |
| nodes.iter().for_each(|&n| self.nodes[n].used = true); |
| } |
| Node::Cast(_, operand, _) => { |
| self.nodes[operand].used = true; |
| } |
| } |
| |
| // Nodes start as unused. |
| self.nodes.push(WorkNode { node, span, used: false }) |
| } |
| |
| fn place_to_local( |
| &mut self, |
| span: Span, |
| p: &mir::Place<'tcx>, |
| ) -> Result<mir::Local, ErrorReported> { |
| const ZERO_FIELD: mir::Field = mir::Field::from_usize(0); |
| // Do not allow any projections. |
| // |
| // One exception are field accesses on the result of checked operations, |
| // which are required to support things like `1 + 2`. |
| if let Some(p) = p.as_local() { |
| debug_assert!(!self.checked_op_locals.contains(p)); |
| Ok(p) |
| } else if let &[mir::ProjectionElem::Field(ZERO_FIELD, _)] = p.projection.as_ref() { |
| // Only allow field accesses if the given local |
| // contains the result of a checked operation. |
| if self.checked_op_locals.contains(p.local) { |
| Ok(p.local) |
| } else { |
| self.error(Some(span), "unsupported projection")?; |
| } |
| } else { |
| self.error(Some(span), "unsupported projection")?; |
| } |
| } |
| |
| fn operand_to_node( |
| &mut self, |
| span: Span, |
| op: &mir::Operand<'tcx>, |
| ) -> Result<NodeId, ErrorReported> { |
| debug!("operand_to_node: op={:?}", op); |
| match op { |
| mir::Operand::Copy(p) | mir::Operand::Move(p) => { |
| let local = self.place_to_local(span, p)?; |
| Ok(self.locals[local]) |
| } |
| mir::Operand::Constant(ct) => match ct.literal { |
| mir::ConstantKind::Ty(ct) => Ok(self.add_node(Node::Leaf(ct), span)), |
| mir::ConstantKind::Val(..) => self.error(Some(span), "unsupported constant")?, |
| }, |
| } |
| } |
| |
| /// We do not allow all binary operations in abstract consts, so filter disallowed ones. |
| fn check_binop(op: mir::BinOp) -> bool { |
| use mir::BinOp::*; |
| match op { |
| Add | Sub | Mul | Div | Rem | BitXor | BitAnd | BitOr | Shl | Shr | Eq | Lt | Le |
| | Ne | Ge | Gt => true, |
| Offset => false, |
| } |
| } |
| |
| /// While we currently allow all unary operations, we still want to explicitly guard against |
| /// future changes here. |
| fn check_unop(op: mir::UnOp) -> bool { |
| use mir::UnOp::*; |
| match op { |
| Not | Neg => true, |
| } |
| } |
| |
| fn build_statement(&mut self, stmt: &mir::Statement<'tcx>) -> Result<(), ErrorReported> { |
| debug!("AbstractConstBuilder: stmt={:?}", stmt); |
| let span = stmt.source_info.span; |
| match stmt.kind { |
| StatementKind::Assign(box (ref place, ref rvalue)) => { |
| let local = self.place_to_local(span, place)?; |
| match *rvalue { |
| Rvalue::Use(ref operand) => { |
| self.locals[local] = self.operand_to_node(span, operand)?; |
| Ok(()) |
| } |
| Rvalue::BinaryOp(op, box (ref lhs, ref rhs)) if Self::check_binop(op) => { |
| let lhs = self.operand_to_node(span, lhs)?; |
| let rhs = self.operand_to_node(span, rhs)?; |
| self.locals[local] = self.add_node(Node::Binop(op, lhs, rhs), span); |
| if op.is_checkable() { |
| bug!("unexpected unchecked checkable binary operation"); |
| } else { |
| Ok(()) |
| } |
| } |
| Rvalue::CheckedBinaryOp(op, box (ref lhs, ref rhs)) |
| if Self::check_binop(op) => |
| { |
| let lhs = self.operand_to_node(span, lhs)?; |
| let rhs = self.operand_to_node(span, rhs)?; |
| self.locals[local] = self.add_node(Node::Binop(op, lhs, rhs), span); |
| self.checked_op_locals.insert(local); |
| Ok(()) |
| } |
| Rvalue::UnaryOp(op, ref operand) if Self::check_unop(op) => { |
| let operand = self.operand_to_node(span, operand)?; |
| self.locals[local] = self.add_node(Node::UnaryOp(op, operand), span); |
| Ok(()) |
| } |
| Rvalue::Cast(cast_kind, ref operand, ty) => { |
| let operand = self.operand_to_node(span, operand)?; |
| self.locals[local] = |
| self.add_node(Node::Cast(cast_kind, operand, ty), span); |
| Ok(()) |
| } |
| _ => self.error(Some(span), "unsupported rvalue")?, |
| } |
| } |
| // These are not actually relevant for us here, so we can ignore them. |
| StatementKind::AscribeUserType(..) |
| | StatementKind::StorageLive(_) |
| | StatementKind::StorageDead(_) => Ok(()), |
| _ => self.error(Some(stmt.source_info.span), "unsupported statement")?, |
| } |
| } |
| |
| /// Possible return values: |
| /// |
| /// - `None`: unsupported terminator, stop building |
| /// - `Some(None)`: supported terminator, finish building |
| /// - `Some(Some(block))`: support terminator, build `block` next |
| fn build_terminator( |
| &mut self, |
| terminator: &mir::Terminator<'tcx>, |
| ) -> Result<Option<mir::BasicBlock>, ErrorReported> { |
| debug!("AbstractConstBuilder: terminator={:?}", terminator); |
| match terminator.kind { |
| TerminatorKind::Goto { target } => Ok(Some(target)), |
| TerminatorKind::Return => Ok(None), |
| TerminatorKind::Call { |
| ref func, |
| ref args, |
| destination: Some((ref place, target)), |
| // We do not care about `cleanup` here. Any branch which |
| // uses `cleanup` will fail const-eval and they therefore |
| // do not matter when checking for const evaluatability. |
| // |
| // Do note that even if `panic::catch_unwind` is made const, |
| // we still do not have to care about this, as we do not look |
| // into functions. |
| cleanup: _, |
| // Do not allow overloaded operators for now, |
| // we probably do want to allow this in the future. |
| // |
| // This is currently fairly irrelevant as it requires `const Trait`s. |
| from_hir_call: true, |
| fn_span, |
| } => { |
| let local = self.place_to_local(fn_span, place)?; |
| let func = self.operand_to_node(fn_span, func)?; |
| let args = self.tcx.arena.alloc_from_iter( |
| args.iter() |
| .map(|arg| self.operand_to_node(terminator.source_info.span, arg)) |
| .collect::<Result<Vec<NodeId>, _>>()?, |
| ); |
| self.locals[local] = self.add_node(Node::FunctionCall(func, args), fn_span); |
| Ok(Some(target)) |
| } |
| TerminatorKind::Assert { ref cond, expected: false, target, .. } => { |
| let p = match cond { |
| mir::Operand::Copy(p) | mir::Operand::Move(p) => p, |
| mir::Operand::Constant(_) => bug!("unexpected assert"), |
| }; |
| |
| const ONE_FIELD: mir::Field = mir::Field::from_usize(1); |
| debug!("proj: {:?}", p.projection); |
| if let Some(p) = p.as_local() { |
| debug_assert!(!self.checked_op_locals.contains(p)); |
| // Mark locals directly used in asserts as used. |
| // |
| // This is needed because division does not use `CheckedBinop` but instead |
| // adds an explicit assert for `divisor != 0`. |
| self.nodes[self.locals[p]].used = true; |
| return Ok(Some(target)); |
| } else if let &[mir::ProjectionElem::Field(ONE_FIELD, _)] = p.projection.as_ref() { |
| // Only allow asserts checking the result of a checked operation. |
| if self.checked_op_locals.contains(p.local) { |
| return Ok(Some(target)); |
| } |
| } |
| |
| self.error(Some(terminator.source_info.span), "unsupported assertion")?; |
| } |
| _ => self.error(Some(terminator.source_info.span), "unsupported terminator")?, |
| } |
| } |
| |
| /// Builds the abstract const by walking the mir from start to finish |
| /// and bailing out when encountering an unsupported operation. |
| fn build(mut self) -> Result<&'tcx [Node<'tcx>], ErrorReported> { |
| let mut block = &self.body.basic_blocks()[mir::START_BLOCK]; |
| // We checked for a cyclic cfg above, so this should terminate. |
| loop { |
| debug!("AbstractConstBuilder: block={:?}", block); |
| for stmt in block.statements.iter() { |
| self.build_statement(stmt)?; |
| } |
| |
| if let Some(next) = self.build_terminator(block.terminator())? { |
| block = &self.body.basic_blocks()[next]; |
| } else { |
| break; |
| } |
| } |
| |
| assert_eq!(self.locals[mir::RETURN_PLACE], self.nodes.last().unwrap()); |
| for n in self.nodes.iter() { |
| if let Node::Leaf(ty::Const { val: ty::ConstKind::Unevaluated(ct), ty: _ }) = n.node { |
| // `AbstractConst`s should not contain any promoteds as they require references which |
| // are not allowed. |
| assert_eq!(ct.promoted, None); |
| } |
| } |
| |
| self.nodes[self.locals[mir::RETURN_PLACE]].used = true; |
| if let Some(&unused) = self.nodes.iter().find(|n| !n.used) { |
| self.error(Some(unused.span), "dead code")?; |
| } |
| |
| Ok(self.tcx.arena.alloc_from_iter(self.nodes.into_iter().map(|n| n.node))) |
| } |
| } |
| |
| /// Builds an abstract const, do not use this directly, but use `AbstractConst::new` instead. |
| pub(super) fn mir_abstract_const<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| def: ty::WithOptConstParam<LocalDefId>, |
| ) -> Result<Option<&'tcx [mir::abstract_const::Node<'tcx>]>, ErrorReported> { |
| if tcx.features().generic_const_exprs { |
| match tcx.def_kind(def.did) { |
| // FIXME(generic_const_exprs): We currently only do this for anonymous constants, |
| // meaning that we do not look into associated constants. I(@lcnr) am not yet sure whether |
| // we want to look into them or treat them as opaque projections. |
| // |
| // Right now we do neither of that and simply always fail to unify them. |
| DefKind::AnonConst => (), |
| _ => return Ok(None), |
| } |
| let body = tcx.mir_const(def).borrow(); |
| AbstractConstBuilder::new(tcx, &body)?.map(AbstractConstBuilder::build).transpose() |
| } else { |
| Ok(None) |
| } |
| } |
| |
| pub(super) fn try_unify_abstract_consts<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| (a, b): (ty::Unevaluated<'tcx, ()>, ty::Unevaluated<'tcx, ()>), |
| ) -> bool { |
| (|| { |
| if let Some(a) = AbstractConst::new(tcx, a)? { |
| if let Some(b) = AbstractConst::new(tcx, b)? { |
| return Ok(try_unify(tcx, a, b)); |
| } |
| } |
| |
| Ok(false) |
| })() |
| .unwrap_or_else(|ErrorReported| true) |
| // FIXME(generic_const_exprs): We should instead have this |
| // method return the resulting `ty::Const` and return `ConstKind::Error` |
| // on `ErrorReported`. |
| } |
| |
| pub fn walk_abstract_const<'tcx, R, F>( |
| tcx: TyCtxt<'tcx>, |
| ct: AbstractConst<'tcx>, |
| mut f: F, |
| ) -> ControlFlow<R> |
| where |
| F: FnMut(AbstractConst<'tcx>) -> ControlFlow<R>, |
| { |
| fn recurse<'tcx, R>( |
| tcx: TyCtxt<'tcx>, |
| ct: AbstractConst<'tcx>, |
| f: &mut dyn FnMut(AbstractConst<'tcx>) -> ControlFlow<R>, |
| ) -> ControlFlow<R> { |
| f(ct)?; |
| let root = ct.root(); |
| match root { |
| Node::Leaf(_) => ControlFlow::CONTINUE, |
| Node::Binop(_, l, r) => { |
| recurse(tcx, ct.subtree(l), f)?; |
| recurse(tcx, ct.subtree(r), f) |
| } |
| Node::UnaryOp(_, v) => recurse(tcx, ct.subtree(v), f), |
| Node::FunctionCall(func, args) => { |
| recurse(tcx, ct.subtree(func), f)?; |
| args.iter().try_for_each(|&arg| recurse(tcx, ct.subtree(arg), f)) |
| } |
| Node::Cast(_, operand, _) => recurse(tcx, ct.subtree(operand), f), |
| } |
| } |
| |
| recurse(tcx, ct, &mut f) |
| } |
| |
| /// Tries to unify two abstract constants using structural equality. |
| pub(super) fn try_unify<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| mut a: AbstractConst<'tcx>, |
| mut b: AbstractConst<'tcx>, |
| ) -> bool { |
| // We substitute generics repeatedly to allow AbstractConsts to unify where a |
| // ConstKind::Unevalated 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)])])] |
| while let Node::Leaf(a_ct) = a.root() { |
| let a_ct = a_ct.subst(tcx, a.substs); |
| match AbstractConst::from_const(tcx, a_ct) { |
| Ok(Some(a_act)) => a = a_act, |
| Ok(None) => break, |
| Err(_) => return true, |
| } |
| } |
| while let Node::Leaf(b_ct) = b.root() { |
| let b_ct = b_ct.subst(tcx, b.substs); |
| match AbstractConst::from_const(tcx, b_ct) { |
| Ok(Some(b_act)) => b = b_act, |
| Ok(None) => break, |
| Err(_) => return true, |
| } |
| } |
| |
| match (a.root(), b.root()) { |
| (Node::Leaf(a_ct), Node::Leaf(b_ct)) => { |
| let a_ct = a_ct.subst(tcx, a.substs); |
| let b_ct = b_ct.subst(tcx, b.substs); |
| if a_ct.ty != b_ct.ty { |
| return false; |
| } |
| |
| match (a_ct.val, b_ct.val) { |
| // 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<const N: usize>() -> [u8; N + 1]` and `fn b<const M: usize>() -> [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 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 => { |
| try_unify(tcx, a.subtree(al), b.subtree(bl)) |
| && try_unify(tcx, a.subtree(ar), b.subtree(br)) |
| } |
| (Node::UnaryOp(a_op, av), Node::UnaryOp(b_op, bv)) if a_op == b_op => { |
| try_unify(tcx, 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() => |
| { |
| try_unify(tcx, a.subtree(a_f), b.subtree(b_f)) |
| && iter::zip(a_args, b_args) |
| .all(|(&an, &bn)| try_unify(tcx, a.subtree(an), b.subtree(bn))) |
| } |
| (Node::Cast(a_cast_kind, a_operand, a_ty), Node::Cast(b_cast_kind, b_operand, b_ty)) |
| if (a_ty == b_ty) && (a_cast_kind == b_cast_kind) => |
| { |
| try_unify(tcx, a.subtree(a_operand), b.subtree(b_operand)) |
| } |
| _ => false, |
| } |
| } |
