// Copyright 2012-2015 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 or the MIT license // , at your // option. This file may not be copied, modified, or distributed // except according to those terms. //#![allow(non_camel_case_types)] use self::ConstVal::*; use self::ErrKind::*; use self::EvalHint::*; use front::map as ast_map; use front::map::blocks::FnLikeNode; use middle::cstore::{self, CrateStore, InlinedItem}; use middle::{infer, subst, traits}; use middle::def::Def; use middle::subst::Subst; use middle::def_id::DefId; use middle::pat_util::def_to_path; use middle::ty::{self, Ty}; use middle::astconv_util::ast_ty_to_prim_ty; use util::num::ToPrimitive; use util::nodemap::NodeMap; use session::Session; use graphviz::IntoCow; use syntax::ast; use rustc_front::hir::Expr; use rustc_front::hir; use rustc_front::intravisit::FnKind; use syntax::codemap::Span; use syntax::parse::token::InternedString; use syntax::ptr::P; use syntax::codemap; use std::borrow::Cow; use std::cmp::Ordering; use std::collections::hash_map::Entry::Vacant; use std::hash; use std::mem::transmute; use std::{i8, i16, i32, i64, u8, u16, u32, u64}; use std::rc::Rc; fn lookup_variant_by_id<'a>(tcx: &'a ty::ctxt, enum_def: DefId, variant_def: DefId) -> Option<&'a Expr> { fn variant_expr<'a>(variants: &'a [hir::Variant], id: ast::NodeId) -> Option<&'a Expr> { for variant in variants { if variant.node.data.id() == id { return variant.node.disr_expr.as_ref().map(|e| &**e); } } None } if let Some(enum_node_id) = tcx.map.as_local_node_id(enum_def) { let variant_node_id = tcx.map.as_local_node_id(variant_def).unwrap(); match tcx.map.find(enum_node_id) { None => None, Some(ast_map::NodeItem(it)) => match it.node { hir::ItemEnum(hir::EnumDef { ref variants }, _) => { variant_expr(variants, variant_node_id) } _ => None }, Some(_) => None } } else { None } } /// * `def_id` is the id of the constant. /// * `maybe_ref_id` is the id of the expr referencing the constant. /// * `param_substs` is the monomorphization substitution for the expression. /// /// `maybe_ref_id` and `param_substs` are optional and are used for /// finding substitutions in associated constants. This generally /// happens in late/trans const evaluation. pub fn lookup_const_by_id<'a, 'tcx: 'a>(tcx: &'a ty::ctxt<'tcx>, def_id: DefId, maybe_ref_id: Option, param_substs: Option<&'tcx subst::Substs<'tcx>>) -> Option<&'tcx Expr> { if let Some(node_id) = tcx.map.as_local_node_id(def_id) { match tcx.map.find(node_id) { None => None, Some(ast_map::NodeItem(it)) => match it.node { hir::ItemConst(_, ref const_expr) => { Some(&*const_expr) } _ => None }, Some(ast_map::NodeTraitItem(ti)) => match ti.node { hir::ConstTraitItem(_, _) => { match maybe_ref_id { // If we have a trait item, and we know the expression // that's the source of the obligation to resolve it, // `resolve_trait_associated_const` will select an impl // or the default. Some(ref_id) => { let trait_id = tcx.trait_of_item(def_id) .unwrap(); let mut substs = tcx.node_id_item_substs(ref_id) .substs; if let Some(param_substs) = param_substs { substs = substs.subst(tcx, param_substs); } resolve_trait_associated_const(tcx, ti, trait_id, substs) } // Technically, without knowing anything about the // expression that generates the obligation, we could // still return the default if there is one. However, // it's safer to return `None` than to return some value // that may differ from what you would get from // correctly selecting an impl. None => None } } _ => None }, Some(ast_map::NodeImplItem(ii)) => match ii.node { hir::ImplItemKind::Const(_, ref expr) => { Some(&*expr) } _ => None }, Some(_) => None } } else { match tcx.extern_const_statics.borrow().get(&def_id) { Some(&ast::DUMMY_NODE_ID) => return None, Some(&expr_id) => { return Some(tcx.map.expect_expr(expr_id)); } None => {} } let mut used_ref_id = false; let expr_id = match tcx.sess.cstore.maybe_get_item_ast(tcx, def_id) { cstore::FoundAst::Found(&InlinedItem::Item(ref item)) => match item.node { hir::ItemConst(_, ref const_expr) => Some(const_expr.id), _ => None }, cstore::FoundAst::Found(&InlinedItem::TraitItem(trait_id, ref ti)) => match ti.node { hir::ConstTraitItem(_, _) => { used_ref_id = true; match maybe_ref_id { // As mentioned in the comments above for in-crate // constants, we only try to find the expression for // a trait-associated const if the caller gives us // the expression that refers to it. Some(ref_id) => { let mut substs = tcx.node_id_item_substs(ref_id) .substs; if let Some(param_substs) = param_substs { substs = substs.subst(tcx, param_substs); } resolve_trait_associated_const(tcx, ti, trait_id, substs).map(|e| e.id) } None => None } } _ => None }, cstore::FoundAst::Found(&InlinedItem::ImplItem(_, ref ii)) => match ii.node { hir::ImplItemKind::Const(_, ref expr) => Some(expr.id), _ => None }, _ => None }; // If we used the reference expression, particularly to choose an impl // of a trait-associated const, don't cache that, because the next // lookup with the same def_id may yield a different result. if !used_ref_id { tcx.extern_const_statics .borrow_mut().insert(def_id, expr_id.unwrap_or(ast::DUMMY_NODE_ID)); } expr_id.map(|id| tcx.map.expect_expr(id)) } } fn inline_const_fn_from_external_crate(tcx: &ty::ctxt, def_id: DefId) -> Option { match tcx.extern_const_fns.borrow().get(&def_id) { Some(&ast::DUMMY_NODE_ID) => return None, Some(&fn_id) => return Some(fn_id), None => {} } if !tcx.sess.cstore.is_const_fn(def_id) { tcx.extern_const_fns.borrow_mut().insert(def_id, ast::DUMMY_NODE_ID); return None; } let fn_id = match tcx.sess.cstore.maybe_get_item_ast(tcx, def_id) { cstore::FoundAst::Found(&InlinedItem::Item(ref item)) => Some(item.id), cstore::FoundAst::Found(&InlinedItem::ImplItem(_, ref item)) => Some(item.id), _ => None }; tcx.extern_const_fns.borrow_mut().insert(def_id, fn_id.unwrap_or(ast::DUMMY_NODE_ID)); fn_id } pub fn lookup_const_fn_by_id<'tcx>(tcx: &ty::ctxt<'tcx>, def_id: DefId) -> Option> { let fn_id = if let Some(node_id) = tcx.map.as_local_node_id(def_id) { node_id } else { if let Some(fn_id) = inline_const_fn_from_external_crate(tcx, def_id) { fn_id } else { return None; } }; let fn_like = match FnLikeNode::from_node(tcx.map.get(fn_id)) { Some(fn_like) => fn_like, None => return None }; match fn_like.kind() { FnKind::ItemFn(_, _, _, hir::Constness::Const, _, _) => { Some(fn_like) } FnKind::Method(_, m, _) => { if m.constness == hir::Constness::Const { Some(fn_like) } else { None } } _ => None } } #[derive(Clone, Debug, RustcEncodable, RustcDecodable)] pub enum ConstVal { Float(f64), Int(i64), Uint(u64), Str(InternedString), ByteStr(Rc>), Bool(bool), Struct(ast::NodeId), Tuple(ast::NodeId), Function(DefId), Array(ast::NodeId, u64), Repeat(ast::NodeId, u64), } impl hash::Hash for ConstVal { fn hash(&self, state: &mut H) { match *self { Float(a) => unsafe { transmute::<_,u64>(a) }.hash(state), Int(a) => a.hash(state), Uint(a) => a.hash(state), Str(ref a) => a.hash(state), ByteStr(ref a) => a.hash(state), Bool(a) => a.hash(state), Struct(a) => a.hash(state), Tuple(a) => a.hash(state), Function(a) => a.hash(state), Array(a, n) => { a.hash(state); n.hash(state) }, Repeat(a, n) => { a.hash(state); n.hash(state) }, } } } /// Note that equality for `ConstVal` means that the it is the same /// constant, not that the rust values are equal. In particular, `NaN /// == NaN` (at least if it's the same NaN; distinct encodings for NaN /// are considering unequal). impl PartialEq for ConstVal { fn eq(&self, other: &ConstVal) -> bool { match (self, other) { (&Float(a), &Float(b)) => unsafe{transmute::<_,u64>(a) == transmute::<_,u64>(b)}, (&Int(a), &Int(b)) => a == b, (&Uint(a), &Uint(b)) => a == b, (&Str(ref a), &Str(ref b)) => a == b, (&ByteStr(ref a), &ByteStr(ref b)) => a == b, (&Bool(a), &Bool(b)) => a == b, (&Struct(a), &Struct(b)) => a == b, (&Tuple(a), &Tuple(b)) => a == b, (&Function(a), &Function(b)) => a == b, (&Array(a, an), &Array(b, bn)) => (a == b) && (an == bn), (&Repeat(a, an), &Repeat(b, bn)) => (a == b) && (an == bn), _ => false, } } } impl Eq for ConstVal { } impl ConstVal { pub fn description(&self) -> &'static str { match *self { Float(_) => "float", Int(i) if i < 0 => "negative integer", Int(_) => "positive integer", Uint(_) => "unsigned integer", Str(_) => "string literal", ByteStr(_) => "byte string literal", Bool(_) => "boolean", Struct(_) => "struct", Tuple(_) => "tuple", Function(_) => "function definition", Array(..) => "array", Repeat(..) => "repeat", } } } pub fn const_expr_to_pat(tcx: &ty::ctxt, expr: &Expr, span: Span) -> P { let pat = match expr.node { hir::ExprTup(ref exprs) => hir::PatTup(exprs.iter().map(|expr| const_expr_to_pat(tcx, &**expr, span)).collect()), hir::ExprCall(ref callee, ref args) => { let def = *tcx.def_map.borrow().get(&callee.id).unwrap(); if let Vacant(entry) = tcx.def_map.borrow_mut().entry(expr.id) { entry.insert(def); } let path = match def.full_def() { Def::Struct(def_id) => def_to_path(tcx, def_id), Def::Variant(_, variant_did) => def_to_path(tcx, variant_did), Def::Fn(..) => return P(hir::Pat { id: expr.id, node: hir::PatLit(P(expr.clone())), span: span, }), _ => unreachable!() }; let pats = args.iter().map(|expr| const_expr_to_pat(tcx, &**expr, span)).collect(); hir::PatEnum(path, Some(pats)) } hir::ExprStruct(ref path, ref fields, None) => { let field_pats = fields.iter().map(|field| codemap::Spanned { span: codemap::DUMMY_SP, node: hir::FieldPat { name: field.name.node, pat: const_expr_to_pat(tcx, &*field.expr, span), is_shorthand: false, }, }).collect(); hir::PatStruct(path.clone(), field_pats, false) } hir::ExprVec(ref exprs) => { let pats = exprs.iter().map(|expr| const_expr_to_pat(tcx, &**expr, span)).collect(); hir::PatVec(pats, None, hir::HirVec::new()) } hir::ExprPath(_, ref path) => { let opt_def = tcx.def_map.borrow().get(&expr.id).map(|d| d.full_def()); match opt_def { Some(Def::Struct(..)) => hir::PatStruct(path.clone(), hir::HirVec::new(), false), Some(Def::Variant(..)) => hir::PatEnum(path.clone(), None), Some(Def::Const(def_id)) | Some(Def::AssociatedConst(def_id)) => { let expr = lookup_const_by_id(tcx, def_id, Some(expr.id), None).unwrap(); return const_expr_to_pat(tcx, expr, span); }, _ => unreachable!(), } } _ => hir::PatLit(P(expr.clone())) }; P(hir::Pat { id: expr.id, node: pat, span: span }) } pub fn eval_const_expr(tcx: &ty::ctxt, e: &Expr) -> ConstVal { match eval_const_expr_partial(tcx, e, ExprTypeChecked, None) { Ok(r) => r, Err(s) => tcx.sess.span_fatal(s.span, &s.description()) } } pub type FnArgMap<'a> = Option<&'a NodeMap>; #[derive(Clone)] pub struct ConstEvalErr { pub span: Span, pub kind: ErrKind, } #[derive(Clone)] pub enum ErrKind { CannotCast, CannotCastTo(&'static str), InvalidOpForInts(hir::BinOp_), InvalidOpForUInts(hir::BinOp_), InvalidOpForBools(hir::BinOp_), InvalidOpForFloats(hir::BinOp_), InvalidOpForIntUint(hir::BinOp_), InvalidOpForUintInt(hir::BinOp_), NegateOn(ConstVal), NotOn(ConstVal), CallOn(ConstVal), NegateWithOverflow(i64), AddiWithOverflow(i64, i64), SubiWithOverflow(i64, i64), MuliWithOverflow(i64, i64), AdduWithOverflow(u64, u64), SubuWithOverflow(u64, u64), MuluWithOverflow(u64, u64), DivideByZero, DivideWithOverflow, ModuloByZero, ModuloWithOverflow, ShiftLeftWithOverflow, ShiftRightWithOverflow, MissingStructField, NonConstPath, UnimplementedConstVal(&'static str), UnresolvedPath, ExpectedConstTuple, ExpectedConstStruct, TupleIndexOutOfBounds, IndexedNonVec, IndexNegative, IndexNotInt, IndexOutOfBounds, RepeatCountNotNatural, RepeatCountNotInt, MiscBinaryOp, MiscCatchAll, IndexOpFeatureGated, } impl ConstEvalErr { pub fn description(&self) -> Cow { use self::ErrKind::*; match self.kind { CannotCast => "can't cast this type".into_cow(), CannotCastTo(s) => format!("can't cast this type to {}", s).into_cow(), InvalidOpForInts(_) => "can't do this op on signed integrals".into_cow(), InvalidOpForUInts(_) => "can't do this op on unsigned integrals".into_cow(), InvalidOpForBools(_) => "can't do this op on bools".into_cow(), InvalidOpForFloats(_) => "can't do this op on floats".into_cow(), InvalidOpForIntUint(..) => "can't do this op on an isize and usize".into_cow(), InvalidOpForUintInt(..) => "can't do this op on a usize and isize".into_cow(), NegateOn(ref const_val) => format!("negate on {}", const_val.description()).into_cow(), NotOn(ref const_val) => format!("not on {}", const_val.description()).into_cow(), CallOn(ref const_val) => format!("call on {}", const_val.description()).into_cow(), NegateWithOverflow(..) => "attempted to negate with overflow".into_cow(), AddiWithOverflow(..) => "attempted to add with overflow".into_cow(), SubiWithOverflow(..) => "attempted to sub with overflow".into_cow(), MuliWithOverflow(..) => "attempted to mul with overflow".into_cow(), AdduWithOverflow(..) => "attempted to add with overflow".into_cow(), SubuWithOverflow(..) => "attempted to sub with overflow".into_cow(), MuluWithOverflow(..) => "attempted to mul with overflow".into_cow(), DivideByZero => "attempted to divide by zero".into_cow(), DivideWithOverflow => "attempted to divide with overflow".into_cow(), ModuloByZero => "attempted remainder with a divisor of zero".into_cow(), ModuloWithOverflow => "attempted remainder with overflow".into_cow(), ShiftLeftWithOverflow => "attempted left shift with overflow".into_cow(), ShiftRightWithOverflow => "attempted right shift with overflow".into_cow(), MissingStructField => "nonexistent struct field".into_cow(), NonConstPath => "non-constant path in constant expression".into_cow(), UnimplementedConstVal(what) => format!("unimplemented constant expression: {}", what).into_cow(), UnresolvedPath => "unresolved path in constant expression".into_cow(), ExpectedConstTuple => "expected constant tuple".into_cow(), ExpectedConstStruct => "expected constant struct".into_cow(), TupleIndexOutOfBounds => "tuple index out of bounds".into_cow(), IndexedNonVec => "indexing is only supported for arrays".into_cow(), IndexNegative => "indices must be non-negative integers".into_cow(), IndexNotInt => "indices must be integers".into_cow(), IndexOutOfBounds => "array index out of bounds".into_cow(), RepeatCountNotNatural => "repeat count must be a natural number".into_cow(), RepeatCountNotInt => "repeat count must be integers".into_cow(), MiscBinaryOp => "bad operands for binary".into_cow(), MiscCatchAll => "unsupported constant expr".into_cow(), IndexOpFeatureGated => "the index operation on const values is unstable".into_cow(), } } } pub type EvalResult = Result; pub type CastResult = Result; // FIXME: Long-term, this enum should go away: trying to evaluate // an expression which hasn't been type-checked is a recipe for // disaster. That said, it's not clear how to fix ast_ty_to_ty // to avoid the ordering issue. /// Hint to determine how to evaluate constant expressions which /// might not be type-checked. #[derive(Copy, Clone, Debug)] pub enum EvalHint<'tcx> { /// We have a type-checked expression. ExprTypeChecked, /// We have an expression which hasn't been type-checked, but we have /// an idea of what the type will be because of the context. For example, /// the length of an array is always `usize`. (This is referred to as /// a hint because it isn't guaranteed to be consistent with what /// type-checking would compute.) UncheckedExprHint(Ty<'tcx>), /// We have an expression which has not yet been type-checked, and /// and we have no clue what the type will be. UncheckedExprNoHint, } impl<'tcx> EvalHint<'tcx> { fn erase_hint(&self) -> EvalHint<'tcx> { match *self { ExprTypeChecked => ExprTypeChecked, UncheckedExprHint(_) | UncheckedExprNoHint => UncheckedExprNoHint, } } fn checked_or(&self, ty: Ty<'tcx>) -> EvalHint<'tcx> { match *self { ExprTypeChecked => ExprTypeChecked, _ => UncheckedExprHint(ty), } } } #[derive(Copy, Clone, PartialEq, Debug)] pub enum IntTy { I8, I16, I32, I64 } #[derive(Copy, Clone, PartialEq, Debug)] pub enum UintTy { U8, U16, U32, U64 } impl IntTy { pub fn from(tcx: &ty::ctxt, t: ast::IntTy) -> IntTy { let t = if let ast::TyIs = t { tcx.sess.target.int_type } else { t }; match t { ast::TyIs => unreachable!(), ast::TyI8 => IntTy::I8, ast::TyI16 => IntTy::I16, ast::TyI32 => IntTy::I32, ast::TyI64 => IntTy::I64, } } } impl UintTy { pub fn from(tcx: &ty::ctxt, t: ast::UintTy) -> UintTy { let t = if let ast::TyUs = t { tcx.sess.target.uint_type } else { t }; match t { ast::TyUs => unreachable!(), ast::TyU8 => UintTy::U8, ast::TyU16 => UintTy::U16, ast::TyU32 => UintTy::U32, ast::TyU64 => UintTy::U64, } } } macro_rules! signal { ($e:expr, $exn:expr) => { return Err(ConstEvalErr { span: $e.span, kind: $exn }) } } // The const_{int,uint}_checked_{neg,add,sub,mul,div,shl,shr} family // of functions catch and signal overflow errors during constant // evaluation. // // They all take the operator's arguments (`a` and `b` if binary), the // overall expression (`e`) and, if available, whole expression's // concrete type (`opt_ety`). // // If the whole expression's concrete type is None, then this is a // constant evaluation happening before type check (e.g. in the check // to confirm that a pattern range's left-side is not greater than its // right-side). We do not do arithmetic modulo the type's bitwidth in // such a case; we just do 64-bit arithmetic and assume that later // passes will do it again with the type information, and thus do the // overflow checks then. pub fn const_int_checked_neg<'a>( a: i64, e: &'a Expr, opt_ety: Option) -> EvalResult { let (min,max) = match opt_ety { // (-i8::MIN is itself not an i8, etc, but this is an easy way // to allow literals to pass the check. Of course that does // not work for i64::MIN.) Some(IntTy::I8) => (-(i8::MAX as i64), -(i8::MIN as i64)), Some(IntTy::I16) => (-(i16::MAX as i64), -(i16::MIN as i64)), Some(IntTy::I32) => (-(i32::MAX as i64), -(i32::MIN as i64)), None | Some(IntTy::I64) => (-i64::MAX, -(i64::MIN+1)), }; let oflo = a < min || a > max; if oflo { signal!(e, NegateWithOverflow(a)); } else { Ok(Int(-a)) } } pub fn const_uint_checked_neg<'a>( a: u64, _e: &'a Expr, _opt_ety: Option) -> EvalResult { // This always succeeds, and by definition, returns `(!a)+1`. Ok(Uint((!a).wrapping_add(1))) } fn const_uint_not(a: u64, opt_ety: Option) -> ConstVal { let mask = match opt_ety { Some(UintTy::U8) => u8::MAX as u64, Some(UintTy::U16) => u16::MAX as u64, Some(UintTy::U32) => u32::MAX as u64, None | Some(UintTy::U64) => u64::MAX, }; Uint(!a & mask) } macro_rules! overflow_checking_body { ($a:ident, $b:ident, $ety:ident, $overflowing_op:ident, lhs: $to_8_lhs:ident $to_16_lhs:ident $to_32_lhs:ident, rhs: $to_8_rhs:ident $to_16_rhs:ident $to_32_rhs:ident $to_64_rhs:ident, $EnumTy:ident $T8: ident $T16: ident $T32: ident $T64: ident, $result_type: ident) => { { let (a,b,opt_ety) = ($a,$b,$ety); match opt_ety { Some($EnumTy::$T8) => match (a.$to_8_lhs(), b.$to_8_rhs()) { (Some(a), Some(b)) => { let (a, oflo) = a.$overflowing_op(b); (a as $result_type, oflo) } (None, _) | (_, None) => (0, true) }, Some($EnumTy::$T16) => match (a.$to_16_lhs(), b.$to_16_rhs()) { (Some(a), Some(b)) => { let (a, oflo) = a.$overflowing_op(b); (a as $result_type, oflo) } (None, _) | (_, None) => (0, true) }, Some($EnumTy::$T32) => match (a.$to_32_lhs(), b.$to_32_rhs()) { (Some(a), Some(b)) => { let (a, oflo) = a.$overflowing_op(b); (a as $result_type, oflo) } (None, _) | (_, None) => (0, true) }, None | Some($EnumTy::$T64) => match b.$to_64_rhs() { Some(b) => a.$overflowing_op(b), None => (0, true), } } } } } macro_rules! int_arith_body { ($a:ident, $b:ident, $ety:ident, $overflowing_op:ident) => { overflow_checking_body!( $a, $b, $ety, $overflowing_op, lhs: to_i8 to_i16 to_i32, rhs: to_i8 to_i16 to_i32 to_i64, IntTy I8 I16 I32 I64, i64) } } macro_rules! uint_arith_body { ($a:ident, $b:ident, $ety:ident, $overflowing_op:ident) => { overflow_checking_body!( $a, $b, $ety, $overflowing_op, lhs: to_u8 to_u16 to_u32, rhs: to_u8 to_u16 to_u32 to_u64, UintTy U8 U16 U32 U64, u64) } } macro_rules! int_shift_body { ($a:ident, $b:ident, $ety:ident, $overflowing_op:ident) => { overflow_checking_body!( $a, $b, $ety, $overflowing_op, lhs: to_i8 to_i16 to_i32, rhs: to_u32 to_u32 to_u32 to_u32, IntTy I8 I16 I32 I64, i64) } } macro_rules! uint_shift_body { ($a:ident, $b:ident, $ety:ident, $overflowing_op:ident) => { overflow_checking_body!( $a, $b, $ety, $overflowing_op, lhs: to_u8 to_u16 to_u32, rhs: to_u32 to_u32 to_u32 to_u32, UintTy U8 U16 U32 U64, u64) } } macro_rules! pub_fn_checked_op { {$fn_name:ident ($a:ident : $a_ty:ty, $b:ident : $b_ty:ty,.. $WhichTy:ident) { $ret_oflo_body:ident $overflowing_op:ident $const_ty:ident $signal_exn:expr }} => { pub fn $fn_name<'a>($a: $a_ty, $b: $b_ty, e: &'a Expr, opt_ety: Option<$WhichTy>) -> EvalResult { let (ret, oflo) = $ret_oflo_body!($a, $b, opt_ety, $overflowing_op); if !oflo { Ok($const_ty(ret)) } else { signal!(e, $signal_exn) } } } } pub_fn_checked_op!{ const_int_checked_add(a: i64, b: i64,.. IntTy) { int_arith_body overflowing_add Int AddiWithOverflow(a, b) }} pub_fn_checked_op!{ const_int_checked_sub(a: i64, b: i64,.. IntTy) { int_arith_body overflowing_sub Int SubiWithOverflow(a, b) }} pub_fn_checked_op!{ const_int_checked_mul(a: i64, b: i64,.. IntTy) { int_arith_body overflowing_mul Int MuliWithOverflow(a, b) }} pub fn const_int_checked_div<'a>( a: i64, b: i64, e: &'a Expr, opt_ety: Option) -> EvalResult { if b == 0 { signal!(e, DivideByZero); } let (ret, oflo) = int_arith_body!(a, b, opt_ety, overflowing_div); if !oflo { Ok(Int(ret)) } else { signal!(e, DivideWithOverflow) } } pub fn const_int_checked_rem<'a>( a: i64, b: i64, e: &'a Expr, opt_ety: Option) -> EvalResult { if b == 0 { signal!(e, ModuloByZero); } let (ret, oflo) = int_arith_body!(a, b, opt_ety, overflowing_rem); if !oflo { Ok(Int(ret)) } else { signal!(e, ModuloWithOverflow) } } pub_fn_checked_op!{ const_int_checked_shl(a: i64, b: i64,.. IntTy) { int_shift_body overflowing_shl Int ShiftLeftWithOverflow }} pub_fn_checked_op!{ const_int_checked_shl_via_uint(a: i64, b: u64,.. IntTy) { int_shift_body overflowing_shl Int ShiftLeftWithOverflow }} pub_fn_checked_op!{ const_int_checked_shr(a: i64, b: i64,.. IntTy) { int_shift_body overflowing_shr Int ShiftRightWithOverflow }} pub_fn_checked_op!{ const_int_checked_shr_via_uint(a: i64, b: u64,.. IntTy) { int_shift_body overflowing_shr Int ShiftRightWithOverflow }} pub_fn_checked_op!{ const_uint_checked_add(a: u64, b: u64,.. UintTy) { uint_arith_body overflowing_add Uint AdduWithOverflow(a, b) }} pub_fn_checked_op!{ const_uint_checked_sub(a: u64, b: u64,.. UintTy) { uint_arith_body overflowing_sub Uint SubuWithOverflow(a, b) }} pub_fn_checked_op!{ const_uint_checked_mul(a: u64, b: u64,.. UintTy) { uint_arith_body overflowing_mul Uint MuluWithOverflow(a, b) }} pub fn const_uint_checked_div<'a>( a: u64, b: u64, e: &'a Expr, opt_ety: Option) -> EvalResult { if b == 0 { signal!(e, DivideByZero); } let (ret, oflo) = uint_arith_body!(a, b, opt_ety, overflowing_div); if !oflo { Ok(Uint(ret)) } else { signal!(e, DivideWithOverflow) } } pub fn const_uint_checked_rem<'a>( a: u64, b: u64, e: &'a Expr, opt_ety: Option) -> EvalResult { if b == 0 { signal!(e, ModuloByZero); } let (ret, oflo) = uint_arith_body!(a, b, opt_ety, overflowing_rem); if !oflo { Ok(Uint(ret)) } else { signal!(e, ModuloWithOverflow) } } pub_fn_checked_op!{ const_uint_checked_shl(a: u64, b: u64,.. UintTy) { uint_shift_body overflowing_shl Uint ShiftLeftWithOverflow }} pub_fn_checked_op!{ const_uint_checked_shl_via_int(a: u64, b: i64,.. UintTy) { uint_shift_body overflowing_shl Uint ShiftLeftWithOverflow }} pub_fn_checked_op!{ const_uint_checked_shr(a: u64, b: u64,.. UintTy) { uint_shift_body overflowing_shr Uint ShiftRightWithOverflow }} pub_fn_checked_op!{ const_uint_checked_shr_via_int(a: u64, b: i64,.. UintTy) { uint_shift_body overflowing_shr Uint ShiftRightWithOverflow }} /// Evaluate a constant expression in a context where the expression isn't /// guaranteed to be evaluatable. `ty_hint` is usually ExprTypeChecked, /// but a few places need to evaluate constants during type-checking, like /// computing the length of an array. (See also the FIXME above EvalHint.) pub fn eval_const_expr_partial<'tcx>(tcx: &ty::ctxt<'tcx>, e: &Expr, ty_hint: EvalHint<'tcx>, fn_args: FnArgMap) -> EvalResult { // Try to compute the type of the expression based on the EvalHint. // (See also the definition of EvalHint, and the FIXME above EvalHint.) let ety = match ty_hint { ExprTypeChecked => { // After type-checking, expr_ty is guaranteed to succeed. Some(tcx.expr_ty(e)) } UncheckedExprHint(ty) => { // Use the type hint; it's not guaranteed to be right, but it's // usually good enough. Some(ty) } UncheckedExprNoHint => { // This expression might not be type-checked, and we have no hint. // Try to query the context for a type anyway; we might get lucky // (for example, if the expression was imported from another crate). tcx.expr_ty_opt(e) } }; // If type of expression itself is int or uint, normalize in these // bindings so that isize/usize is mapped to a type with an // inherently known bitwidth. let expr_int_type = ety.and_then(|ty| { if let ty::TyInt(t) = ty.sty { Some(IntTy::from(tcx, t)) } else { None } }); let expr_uint_type = ety.and_then(|ty| { if let ty::TyUint(t) = ty.sty { Some(UintTy::from(tcx, t)) } else { None } }); let result = match e.node { hir::ExprUnary(hir::UnNeg, ref inner) => { match try!(eval_const_expr_partial(tcx, &**inner, ty_hint, fn_args)) { Float(f) => Float(-f), Int(n) => try!(const_int_checked_neg(n, e, expr_int_type)), Uint(i) => { try!(const_uint_checked_neg(i, e, expr_uint_type)) } const_val => signal!(e, NegateOn(const_val)), } } hir::ExprUnary(hir::UnNot, ref inner) => { match try!(eval_const_expr_partial(tcx, &**inner, ty_hint, fn_args)) { Int(i) => Int(!i), Uint(i) => const_uint_not(i, expr_uint_type), Bool(b) => Bool(!b), const_val => signal!(e, NotOn(const_val)), } } hir::ExprBinary(op, ref a, ref b) => { let b_ty = match op.node { hir::BiShl | hir::BiShr => ty_hint.checked_or(tcx.types.usize), _ => ty_hint }; match (try!(eval_const_expr_partial(tcx, &**a, ty_hint, fn_args)), try!(eval_const_expr_partial(tcx, &**b, b_ty, fn_args))) { (Float(a), Float(b)) => { match op.node { hir::BiAdd => Float(a + b), hir::BiSub => Float(a - b), hir::BiMul => Float(a * b), hir::BiDiv => Float(a / b), hir::BiRem => Float(a % b), hir::BiEq => Bool(a == b), hir::BiLt => Bool(a < b), hir::BiLe => Bool(a <= b), hir::BiNe => Bool(a != b), hir::BiGe => Bool(a >= b), hir::BiGt => Bool(a > b), _ => signal!(e, InvalidOpForFloats(op.node)), } } (Int(a), Int(b)) => { match op.node { hir::BiAdd => try!(const_int_checked_add(a,b,e,expr_int_type)), hir::BiSub => try!(const_int_checked_sub(a,b,e,expr_int_type)), hir::BiMul => try!(const_int_checked_mul(a,b,e,expr_int_type)), hir::BiDiv => try!(const_int_checked_div(a,b,e,expr_int_type)), hir::BiRem => try!(const_int_checked_rem(a,b,e,expr_int_type)), hir::BiBitAnd => Int(a & b), hir::BiBitOr => Int(a | b), hir::BiBitXor => Int(a ^ b), hir::BiShl => try!(const_int_checked_shl(a,b,e,expr_int_type)), hir::BiShr => try!(const_int_checked_shr(a,b,e,expr_int_type)), hir::BiEq => Bool(a == b), hir::BiLt => Bool(a < b), hir::BiLe => Bool(a <= b), hir::BiNe => Bool(a != b), hir::BiGe => Bool(a >= b), hir::BiGt => Bool(a > b), _ => signal!(e, InvalidOpForInts(op.node)), } } (Uint(a), Uint(b)) => { match op.node { hir::BiAdd => try!(const_uint_checked_add(a,b,e,expr_uint_type)), hir::BiSub => try!(const_uint_checked_sub(a,b,e,expr_uint_type)), hir::BiMul => try!(const_uint_checked_mul(a,b,e,expr_uint_type)), hir::BiDiv => try!(const_uint_checked_div(a,b,e,expr_uint_type)), hir::BiRem => try!(const_uint_checked_rem(a,b,e,expr_uint_type)), hir::BiBitAnd => Uint(a & b), hir::BiBitOr => Uint(a | b), hir::BiBitXor => Uint(a ^ b), hir::BiShl => try!(const_uint_checked_shl(a,b,e,expr_uint_type)), hir::BiShr => try!(const_uint_checked_shr(a,b,e,expr_uint_type)), hir::BiEq => Bool(a == b), hir::BiLt => Bool(a < b), hir::BiLe => Bool(a <= b), hir::BiNe => Bool(a != b), hir::BiGe => Bool(a >= b), hir::BiGt => Bool(a > b), _ => signal!(e, InvalidOpForUInts(op.node)), } } // shifts can have any integral type as their rhs (Int(a), Uint(b)) => { match op.node { hir::BiShl => try!(const_int_checked_shl_via_uint(a,b,e,expr_int_type)), hir::BiShr => try!(const_int_checked_shr_via_uint(a,b,e,expr_int_type)), _ => signal!(e, InvalidOpForIntUint(op.node)), } } (Uint(a), Int(b)) => { match op.node { hir::BiShl => try!(const_uint_checked_shl_via_int(a,b,e,expr_uint_type)), hir::BiShr => try!(const_uint_checked_shr_via_int(a,b,e,expr_uint_type)), _ => signal!(e, InvalidOpForUintInt(op.node)), } } (Bool(a), Bool(b)) => { Bool(match op.node { hir::BiAnd => a && b, hir::BiOr => a || b, hir::BiBitXor => a ^ b, hir::BiBitAnd => a & b, hir::BiBitOr => a | b, hir::BiEq => a == b, hir::BiNe => a != b, _ => signal!(e, InvalidOpForBools(op.node)), }) } _ => signal!(e, MiscBinaryOp), } } hir::ExprCast(ref base, ref target_ty) => { let ety = ety.or_else(|| ast_ty_to_prim_ty(tcx, &**target_ty)) .unwrap_or_else(|| { tcx.sess.span_fatal(target_ty.span, "target type not found for const cast") }); let base_hint = if let ExprTypeChecked = ty_hint { ExprTypeChecked } else { // FIXME (#23833): the type-hint can cause problems, // e.g. `(i8::MAX + 1_i8) as u32` feeds in `u32` as result // type to the sum, and thus no overflow is signaled. match tcx.expr_ty_opt(&base) { Some(t) => UncheckedExprHint(t), None => ty_hint } }; let val = try!(eval_const_expr_partial(tcx, &**base, base_hint, fn_args)); match cast_const(tcx, val, ety) { Ok(val) => val, Err(kind) => return Err(ConstEvalErr { span: e.span, kind: kind }), } } hir::ExprPath(..) => { let opt_def = if let Some(def) = tcx.def_map.borrow().get(&e.id) { // After type-checking, def_map contains definition of the // item referred to by the path. During type-checking, it // can contain the raw output of path resolution, which // might be a partially resolved path. // FIXME: There's probably a better way to make sure we don't // panic here. if def.depth != 0 { signal!(e, UnresolvedPath); } Some(def.full_def()) } else { None }; let (const_expr, const_ty) = match opt_def { Some(Def::Const(def_id)) => { if let Some(node_id) = tcx.map.as_local_node_id(def_id) { match tcx.map.find(node_id) { Some(ast_map::NodeItem(it)) => match it.node { hir::ItemConst(ref ty, ref expr) => { (Some(&**expr), Some(&**ty)) } _ => (None, None) }, _ => (None, None) } } else { (lookup_const_by_id(tcx, def_id, Some(e.id), None), None) } } Some(Def::AssociatedConst(def_id)) => { if let Some(node_id) = tcx.map.as_local_node_id(def_id) { match tcx.impl_or_trait_item(def_id).container() { ty::TraitContainer(trait_id) => match tcx.map.find(node_id) { Some(ast_map::NodeTraitItem(ti)) => match ti.node { hir::ConstTraitItem(ref ty, _) => { if let ExprTypeChecked = ty_hint { let substs = tcx.node_id_item_substs(e.id).substs; (resolve_trait_associated_const(tcx, ti, trait_id, substs), Some(&**ty)) } else { (None, None) } } _ => (None, None) }, _ => (None, None) }, ty::ImplContainer(_) => match tcx.map.find(node_id) { Some(ast_map::NodeImplItem(ii)) => match ii.node { hir::ImplItemKind::Const(ref ty, ref expr) => { (Some(&**expr), Some(&**ty)) } _ => (None, None) }, _ => (None, None) }, } } else { (lookup_const_by_id(tcx, def_id, Some(e.id), None), None) } } Some(Def::Variant(enum_def, variant_def)) => { (lookup_variant_by_id(tcx, enum_def, variant_def), None) } Some(Def::Struct(..)) => { return Ok(ConstVal::Struct(e.id)) } Some(Def::Local(_, id)) => { debug!("Def::Local({:?}): {:?}", id, fn_args); if let Some(val) = fn_args.and_then(|args| args.get(&id)) { return Ok(val.clone()); } else { (None, None) } }, Some(Def::Method(id)) | Some(Def::Fn(id)) => return Ok(Function(id)), _ => (None, None) }; let const_expr = match const_expr { Some(actual_e) => actual_e, None => signal!(e, NonConstPath) }; let item_hint = if let UncheckedExprNoHint = ty_hint { match const_ty { Some(ty) => match ast_ty_to_prim_ty(tcx, ty) { Some(ty) => UncheckedExprHint(ty), None => UncheckedExprNoHint }, None => UncheckedExprNoHint } } else { ty_hint }; try!(eval_const_expr_partial(tcx, const_expr, item_hint, fn_args)) } hir::ExprCall(ref callee, ref args) => { let sub_ty_hint = ty_hint.erase_hint(); let callee_val = try!(eval_const_expr_partial(tcx, callee, sub_ty_hint, fn_args)); let did = match callee_val { Function(did) => did, callee => signal!(e, CallOn(callee)), }; let (decl, result) = if let Some(fn_like) = lookup_const_fn_by_id(tcx, did) { (fn_like.decl(), &fn_like.body().expr) } else { signal!(e, NonConstPath) }; let result = result.as_ref().expect("const fn has no result expression"); assert_eq!(decl.inputs.len(), args.len()); let mut call_args = NodeMap(); for (arg, arg_expr) in decl.inputs.iter().zip(args.iter()) { let arg_val = try!(eval_const_expr_partial( tcx, arg_expr, sub_ty_hint, fn_args )); debug!("const call arg: {:?}", arg); let old = call_args.insert(arg.pat.id, arg_val); assert!(old.is_none()); } debug!("const call({:?})", call_args); try!(eval_const_expr_partial(tcx, &**result, ty_hint, Some(&call_args))) }, hir::ExprLit(ref lit) => lit_to_const(tcx.sess, e.span, &**lit, ety), hir::ExprBlock(ref block) => { match block.expr { Some(ref expr) => try!(eval_const_expr_partial(tcx, &**expr, ty_hint, fn_args)), None => unreachable!(), } } hir::ExprType(ref e, _) => try!(eval_const_expr_partial(tcx, &**e, ty_hint, fn_args)), hir::ExprTup(_) => Tuple(e.id), hir::ExprStruct(..) => Struct(e.id), hir::ExprIndex(ref arr, ref idx) => { if !tcx.sess.features.borrow().const_indexing { signal!(e, IndexOpFeatureGated); } let arr_hint = ty_hint.erase_hint(); let arr = try!(eval_const_expr_partial(tcx, arr, arr_hint, fn_args)); let idx_hint = ty_hint.checked_or(tcx.types.usize); let idx = match try!(eval_const_expr_partial(tcx, idx, idx_hint, fn_args)) { Int(i) if i >= 0 => i as u64, Int(_) => signal!(idx, IndexNegative), Uint(i) => i, _ => signal!(idx, IndexNotInt), }; match arr { Array(_, n) if idx >= n => signal!(e, IndexOutOfBounds), Array(v, _) => if let hir::ExprVec(ref v) = tcx.map.expect_expr(v).node { try!(eval_const_expr_partial(tcx, &*v[idx as usize], ty_hint, fn_args)) } else { unreachable!() }, Repeat(_, n) if idx >= n => signal!(e, IndexOutOfBounds), Repeat(elem, _) => try!(eval_const_expr_partial( tcx, &*tcx.map.expect_expr(elem), ty_hint, fn_args, )), ByteStr(ref data) if idx as usize >= data.len() => signal!(e, IndexOutOfBounds), ByteStr(data) => Uint(data[idx as usize] as u64), Str(ref s) if idx as usize >= s.len() => signal!(e, IndexOutOfBounds), Str(_) => unimplemented!(), // there's no const_char type _ => signal!(e, IndexedNonVec), } } hir::ExprVec(ref v) => Array(e.id, v.len() as u64), hir::ExprRepeat(_, ref n) => { let len_hint = ty_hint.checked_or(tcx.types.usize); Repeat( e.id, match try!(eval_const_expr_partial(tcx, &**n, len_hint, fn_args)) { Int(i) if i >= 0 => i as u64, Int(_) => signal!(e, RepeatCountNotNatural), Uint(i) => i, _ => signal!(e, RepeatCountNotInt), }, ) }, hir::ExprTupField(ref base, index) => { let base_hint = ty_hint.erase_hint(); let c = try!(eval_const_expr_partial(tcx, base, base_hint, fn_args)); if let Tuple(tup_id) = c { if let hir::ExprTup(ref fields) = tcx.map.expect_expr(tup_id).node { if index.node < fields.len() { return eval_const_expr_partial(tcx, &fields[index.node], base_hint, fn_args) } else { signal!(e, TupleIndexOutOfBounds); } } else { unreachable!() } } else { signal!(base, ExpectedConstTuple); } } hir::ExprField(ref base, field_name) => { let base_hint = ty_hint.erase_hint(); // Get the base expression if it is a struct and it is constant let c = try!(eval_const_expr_partial(tcx, base, base_hint, fn_args)); if let Struct(struct_id) = c { if let hir::ExprStruct(_, ref fields, _) = tcx.map.expect_expr(struct_id).node { // Check that the given field exists and evaluate it // if the idents are compared run-pass/issue-19244 fails if let Some(f) = fields.iter().find(|f| f.name.node == field_name.node) { return eval_const_expr_partial(tcx, &*f.expr, base_hint, fn_args) } else { signal!(e, MissingStructField); } } else { unreachable!() } } else { signal!(base, ExpectedConstStruct); } } _ => signal!(e, MiscCatchAll) }; Ok(result) } fn resolve_trait_associated_const<'a, 'tcx: 'a>(tcx: &'a ty::ctxt<'tcx>, ti: &'tcx hir::TraitItem, trait_id: DefId, rcvr_substs: subst::Substs<'tcx>) -> Option<&'tcx Expr> { let trait_ref = ty::Binder( rcvr_substs.erase_regions().to_trait_ref(tcx, trait_id) ); debug!("resolve_trait_associated_const: trait_ref={:?}", trait_ref); tcx.populate_implementations_for_trait_if_necessary(trait_ref.def_id()); let infcx = infer::new_infer_ctxt(tcx, &tcx.tables, None); let mut selcx = traits::SelectionContext::new(&infcx); let obligation = traits::Obligation::new(traits::ObligationCause::dummy(), trait_ref.to_poly_trait_predicate()); let selection = match selcx.select(&obligation) { Ok(Some(vtable)) => vtable, // Still ambiguous, so give up and let the caller decide whether this // expression is really needed yet. Some associated constant values // can't be evaluated until monomorphization is done in trans. Ok(None) => { return None } Err(_) => { return None } }; match selection { traits::VtableImpl(ref impl_data) => { match tcx.associated_consts(impl_data.impl_def_id) .iter().find(|ic| ic.name == ti.name) { Some(ic) => lookup_const_by_id(tcx, ic.def_id, None, None), None => match ti.node { hir::ConstTraitItem(_, Some(ref expr)) => Some(&*expr), _ => None, }, } } _ => { tcx.sess.span_bug( ti.span, "resolve_trait_associated_const: unexpected vtable type") } } } fn cast_const<'tcx>(tcx: &ty::ctxt<'tcx>, val: ConstVal, ty: Ty) -> CastResult { macro_rules! convert_val { ($intermediate_ty:ty, $const_type:ident, $target_ty:ty) => { match val { Bool(b) => Ok($const_type(b as u64 as $intermediate_ty as $target_ty)), Uint(u) => Ok($const_type(u as $intermediate_ty as $target_ty)), Int(i) => Ok($const_type(i as $intermediate_ty as $target_ty)), Float(f) => Ok($const_type(f as $intermediate_ty as $target_ty)), _ => Err(ErrKind::CannotCastTo(stringify!($const_type))), } } } // Issue #23890: If isize/usize, then dispatch to appropriate target representation type match (&ty.sty, tcx.sess.target.int_type, tcx.sess.target.uint_type) { (&ty::TyInt(ast::TyIs), ast::TyI32, _) => return convert_val!(i32, Int, i64), (&ty::TyInt(ast::TyIs), ast::TyI64, _) => return convert_val!(i64, Int, i64), (&ty::TyInt(ast::TyIs), _, _) => panic!("unexpected target.int_type"), (&ty::TyUint(ast::TyUs), _, ast::TyU32) => return convert_val!(u32, Uint, u64), (&ty::TyUint(ast::TyUs), _, ast::TyU64) => return convert_val!(u64, Uint, u64), (&ty::TyUint(ast::TyUs), _, _) => panic!("unexpected target.uint_type"), _ => {} } match ty.sty { ty::TyInt(ast::TyIs) => unreachable!(), ty::TyUint(ast::TyUs) => unreachable!(), ty::TyInt(ast::TyI8) => convert_val!(i8, Int, i64), ty::TyInt(ast::TyI16) => convert_val!(i16, Int, i64), ty::TyInt(ast::TyI32) => convert_val!(i32, Int, i64), ty::TyInt(ast::TyI64) => convert_val!(i64, Int, i64), ty::TyUint(ast::TyU8) => convert_val!(u8, Uint, u64), ty::TyUint(ast::TyU16) => convert_val!(u16, Uint, u64), ty::TyUint(ast::TyU32) => convert_val!(u32, Uint, u64), ty::TyUint(ast::TyU64) => convert_val!(u64, Uint, u64), ty::TyFloat(ast::TyF32) => convert_val!(f32, Float, f64), ty::TyFloat(ast::TyF64) => convert_val!(f64, Float, f64), _ => Err(ErrKind::CannotCast), } } fn lit_to_const(sess: &Session, span: Span, lit: &ast::Lit, ty_hint: Option) -> ConstVal { match lit.node { ast::LitStr(ref s, _) => Str((*s).clone()), ast::LitByteStr(ref data) => { ByteStr(data.clone()) } ast::LitByte(n) => Uint(n as u64), ast::LitChar(n) => Uint(n as u64), ast::LitInt(n, ast::SignedIntLit(_, ast::Plus)) => Int(n as i64), ast::LitInt(n, ast::UnsuffixedIntLit(ast::Plus)) => { match ty_hint.map(|ty| &ty.sty) { Some(&ty::TyUint(_)) => Uint(n), _ => Int(n as i64) } } ast::LitInt(n, ast::SignedIntLit(_, ast::Minus)) | ast::LitInt(n, ast::UnsuffixedIntLit(ast::Minus)) => Int(-(n as i64)), ast::LitInt(n, ast::UnsignedIntLit(_)) => Uint(n), ast::LitFloat(ref n, _) | ast::LitFloatUnsuffixed(ref n) => { if let Ok(x) = n.parse::() { Float(x) } else { // FIXME(#31407) this is only necessary because float parsing is buggy sess.span_bug(span, "could not evaluate float literal (see issue #31407)"); } } ast::LitBool(b) => Bool(b) } } pub fn compare_const_vals(a: &ConstVal, b: &ConstVal) -> Option { Some(match (a, b) { (&Int(a), &Int(b)) => a.cmp(&b), (&Uint(a), &Uint(b)) => a.cmp(&b), (&Float(a), &Float(b)) => { // This is pretty bad but it is the existing behavior. if a == b { Ordering::Equal } else if a < b { Ordering::Less } else { Ordering::Greater } } (&Str(ref a), &Str(ref b)) => a.cmp(b), (&Bool(a), &Bool(b)) => a.cmp(&b), (&ByteStr(ref a), &ByteStr(ref b)) => a.cmp(b), _ => return None }) } pub fn compare_lit_exprs<'tcx>(tcx: &ty::ctxt<'tcx>, a: &Expr, b: &Expr) -> Option { let a = match eval_const_expr_partial(tcx, a, ExprTypeChecked, None) { Ok(a) => a, Err(e) => { tcx.sess.span_err(a.span, &e.description()); return None; } }; let b = match eval_const_expr_partial(tcx, b, ExprTypeChecked, None) { Ok(b) => b, Err(e) => { tcx.sess.span_err(b.span, &e.description()); return None; } }; compare_const_vals(&a, &b) }