1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Code for type-checking cast expressions.
13 //! A cast `e as U` is valid if one of the following holds:
14 //! * `e` has type `T` and `T` coerces to `U`; *coercion-cast*
15 //! * `e` has type `*T`, `U` is `*U_0`, and either `U_0: Sized` or
16 //! unsize_kind(`T`) = unsize_kind(`U_0`); *ptr-ptr-cast*
17 //! * `e` has type `*T` and `U` is a numeric type, while `T: Sized`; *ptr-addr-cast*
18 //! * `e` is an integer and `U` is `*U_0`, while `U_0: Sized`; *addr-ptr-cast*
19 //! * `e` has type `T` and `T` and `U` are any numeric types; *numeric-cast*
20 //! * `e` is a C-like enum and `U` is an integer type; *enum-cast*
21 //! * `e` has type `bool` or `char` and `U` is an integer; *prim-int-cast*
22 //! * `e` has type `u8` and `U` is `char`; *u8-char-cast*
23 //! * `e` has type `&[T; n]` and `U` is `*const T`; *array-ptr-cast*
24 //! * `e` is a function pointer type and `U` has type `*T`,
25 //! while `T: Sized`; *fptr-ptr-cast*
26 //! * `e` is a function pointer type and `U` is an integer; *fptr-addr-cast*
28 //! where `&.T` and `*T` are references of either mutability,
29 //! and where unsize_kind(`T`) is the kind of the unsize info
30 //! in `T` - the vtable for a trait definition (e.g. `fmt::Display` or
31 //! `Iterator`, not `Iterator<Item=u8>`) or a length (or `()` if `T: Sized`).
33 //! Note that lengths are not adjusted when casting raw slices -
34 //! `T: *const [u16] as *const [u8]` creates a slice that only includes
35 //! half of the original memory.
37 //! Casting is not transitive, that is, even if `e as U1 as U2` is a valid
38 //! expression, `e as U2` is not necessarily so (in fact it will only be valid if
39 //! `U1` coerces to `U2`).
44 use super::structurally_resolved_type;
47 use middle::cast::{CastKind, CastTy};
48 use middle::ty::{self, Ty, HasTypeFlags};
50 use syntax::ast::UintTy::{TyU8};
51 use syntax::codemap::Span;
53 /// Reifies a cast check to be checked once we have full type information for
54 /// a function context.
55 pub struct CastCheck<'tcx> {
62 /// The kind of the unsize info (length or vtable) - we only allow casts between
63 /// fat pointers if their unsize-infos have the same kind.
64 #[derive(Copy, Clone, PartialEq, Eq)]
65 enum UnsizeKind<'tcx> {
68 /// The unsize info of this projection
69 OfProjection(&'tcx ty::ProjectionTy<'tcx>),
70 /// The unsize info of this parameter
71 OfParam(&'tcx ty::ParamTy)
74 /// Returns the kind of unsize information of t, or None
75 /// if t is sized or it is unknown.
76 fn unsize_kind<'a,'tcx>(fcx: &FnCtxt<'a, 'tcx>,
78 -> Option<UnsizeKind<'tcx>> {
80 ty::TySlice(_) | ty::TyStr => Some(UnsizeKind::Length),
81 ty::TyTrait(ref tty) => Some(UnsizeKind::Vtable(tty.principal_def_id())),
82 ty::TyStruct(def, substs) => {
83 // FIXME(arielb1): do some kind of normalization
84 match def.struct_variant().fields.last() {
86 Some(f) => unsize_kind(fcx, f.ty(fcx.tcx(), substs))
89 // We should really try to normalize here.
90 ty::TyProjection(ref pi) => Some(UnsizeKind::OfProjection(pi)),
91 ty::TyParam(ref p) => Some(UnsizeKind::OfParam(p)),
96 #[derive(Copy, Clone)]
109 impl<'tcx> CastCheck<'tcx> {
110 pub fn new(expr: ast::Expr, expr_ty: Ty<'tcx>, cast_ty: Ty<'tcx>, span: Span)
120 fn report_cast_error<'a>(&self, fcx: &FnCtxt<'a, 'tcx>,
123 CastError::NeedViaPtr |
124 CastError::NeedViaThinPtr |
125 CastError::NeedViaInt |
126 CastError::NeedViaUsize => {
127 fcx.type_error_message(self.span, |actual| {
128 format!("casting `{}` as `{}` is invalid",
130 fcx.infcx().ty_to_string(self.cast_ty))
131 }, self.expr_ty, None);
132 fcx.ccx.tcx.sess.fileline_help(self.span,
133 &format!("cast through {} first", match e {
134 CastError::NeedViaPtr => "a raw pointer",
135 CastError::NeedViaThinPtr => "a thin pointer",
136 CastError::NeedViaInt => "an integer",
137 CastError::NeedViaUsize => "a usize",
141 CastError::CastToBool => {
142 span_err!(fcx.tcx().sess, self.span, E0054, "cannot cast as `bool`");
143 fcx.ccx.tcx.sess.fileline_help(self.span, "compare with zero instead");
145 CastError::CastToChar => {
146 fcx.type_error_message(self.span, |actual| {
147 format!("only `u8` can be cast as `char`, not `{}`", actual)
148 }, self.expr_ty, None);
150 CastError::NonScalar => {
151 fcx.type_error_message(self.span, |actual| {
152 format!("non-scalar cast: `{}` as `{}`",
154 fcx.infcx().ty_to_string(self.cast_ty))
155 }, self.expr_ty, None);
157 CastError::IllegalCast => {
158 fcx.type_error_message(self.span, |actual| {
159 format!("casting `{}` as `{}` is invalid",
161 fcx.infcx().ty_to_string(self.cast_ty))
162 }, self.expr_ty, None);
164 CastError::DifferingKinds => {
165 fcx.type_error_message(self.span, |actual| {
166 format!("casting `{}` as `{}` is invalid",
168 fcx.infcx().ty_to_string(self.cast_ty))
169 }, self.expr_ty, None);
170 fcx.ccx.tcx.sess.fileline_note(self.span, "vtable kinds may not match");
175 fn trivial_cast_lint<'a>(&self, fcx: &FnCtxt<'a, 'tcx>) {
176 let t_cast = self.cast_ty;
177 let t_expr = self.expr_ty;
178 if t_cast.is_numeric() && t_expr.is_numeric() {
179 fcx.tcx().sess.add_lint(lint::builtin::TRIVIAL_NUMERIC_CASTS,
182 format!("trivial numeric cast: `{}` as `{}`. Cast can be \
183 replaced by coercion, this might require type \
184 ascription or a temporary variable",
185 fcx.infcx().ty_to_string(t_expr),
186 fcx.infcx().ty_to_string(t_cast)));
188 fcx.tcx().sess.add_lint(lint::builtin::TRIVIAL_CASTS,
191 format!("trivial cast: `{}` as `{}`. Cast can be \
192 replaced by coercion, this might require type \
193 ascription or a temporary variable",
194 fcx.infcx().ty_to_string(t_expr),
195 fcx.infcx().ty_to_string(t_cast)));
200 pub fn check<'a>(mut self, fcx: &FnCtxt<'a, 'tcx>) {
201 self.expr_ty = structurally_resolved_type(fcx, self.span, self.expr_ty);
202 self.cast_ty = structurally_resolved_type(fcx, self.span, self.cast_ty);
204 debug!("check_cast({}, {:?} as {:?})", self.expr.id, self.expr_ty,
207 if self.expr_ty.references_error() || self.cast_ty.references_error() {
208 // No sense in giving duplicate error messages
209 } else if self.try_coercion_cast(fcx) {
210 self.trivial_cast_lint(fcx);
211 debug!(" -> CoercionCast");
212 fcx.tcx().cast_kinds.borrow_mut().insert(self.expr.id,
213 CastKind::CoercionCast);
214 } else { match self.do_check(fcx) {
216 debug!(" -> {:?}", k);
217 fcx.tcx().cast_kinds.borrow_mut().insert(self.expr.id, k);
219 Err(e) => self.report_cast_error(fcx, e)
223 /// Check a cast, and report an error if one exists. In some cases, this
224 /// can return Ok and create type errors in the fcx rather than returning
225 /// directly. coercion-cast is handled in check instead of here.
226 fn do_check<'a>(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<CastKind, CastError> {
227 use middle::cast::IntTy::*;
228 use middle::cast::CastTy::*;
230 let (t_from, t_cast) = match (CastTy::from_ty(self.expr_ty),
231 CastTy::from_ty(self.cast_ty)) {
232 (Some(t_from), Some(t_cast)) => (t_from, t_cast),
234 return Err(CastError::NonScalar)
238 match (t_from, t_cast) {
239 // These types have invariants! can't cast into them.
240 (_, RPtr(_)) | (_, Int(CEnum)) | (_, FnPtr) => Err(CastError::NonScalar),
243 (_, Int(Bool)) => Err(CastError::CastToBool),
246 (Int(U(ast::TyU8)), Int(Char)) => Ok(CastKind::U8CharCast), // u8-char-cast
247 (_, Int(Char)) => Err(CastError::CastToChar),
250 (Int(Bool), Float) | (Int(CEnum), Float) | (Int(Char), Float)
251 => Err(CastError::NeedViaInt),
252 (Int(Bool), Ptr(_)) | (Int(CEnum), Ptr(_)) | (Int(Char), Ptr(_))
253 => Err(CastError::NeedViaUsize),
256 (Ptr(m_e), Ptr(m_c)) => self.check_ptr_ptr_cast(fcx, m_e, m_c), // ptr-ptr-cast
257 (Ptr(m_expr), Int(_)) => self.check_ptr_addr_cast(fcx, m_expr), // ptr-addr-cast
258 (Ptr(_), Float) | (FnPtr, Float) => Err(CastError::NeedViaUsize),
259 (FnPtr, Int(_)) => Ok(CastKind::FnPtrAddrCast),
260 (RPtr(_), Int(_)) | (RPtr(_), Float) => Err(CastError::NeedViaPtr),
262 (Int(_), Ptr(mt)) => self.check_addr_ptr_cast(fcx, mt), // addr-ptr-cast
263 (FnPtr, Ptr(mt)) => self.check_fptr_ptr_cast(fcx, mt),
264 (Float, Ptr(_)) => Err(CastError::NeedViaUsize),
265 (RPtr(rmt), Ptr(mt)) => self.check_ref_cast(fcx, rmt, mt), // array-ptr-cast
268 (Int(CEnum), Int(_)) => Ok(CastKind::EnumCast),
269 (Int(Char), Int(_)) | (Int(Bool), Int(_)) => Ok(CastKind::PrimIntCast),
274 (Float, Float) => Ok(CastKind::NumericCast),
279 fn check_ptr_ptr_cast<'a>(&self,
280 fcx: &FnCtxt<'a, 'tcx>,
281 m_expr: &'tcx ty::TypeAndMut<'tcx>,
282 m_cast: &'tcx ty::TypeAndMut<'tcx>)
283 -> Result<CastKind, CastError>
285 debug!("check_ptr_ptr_cast m_expr={:?} m_cast={:?}",
287 // ptr-ptr cast. vtables must match.
289 // Cast to sized is OK
290 if fcx.type_is_known_to_be_sized(m_cast.ty, self.span) {
291 return Ok(CastKind::PtrPtrCast);
294 // sized -> unsized? report invalid cast (don't complain about vtable kinds)
295 if fcx.type_is_known_to_be_sized(m_expr.ty, self.span) {
296 return Err(CastError::IllegalCast);
299 // vtable kinds must match
300 match (unsize_kind(fcx, m_cast.ty), unsize_kind(fcx, m_expr.ty)) {
301 (Some(a), Some(b)) if a == b => Ok(CastKind::PtrPtrCast),
302 _ => Err(CastError::DifferingKinds)
306 fn check_fptr_ptr_cast<'a>(&self,
307 fcx: &FnCtxt<'a, 'tcx>,
308 m_cast: &'tcx ty::TypeAndMut<'tcx>)
309 -> Result<CastKind, CastError>
311 // fptr-ptr cast. must be to sized ptr
313 if fcx.type_is_known_to_be_sized(m_cast.ty, self.span) {
314 Ok(CastKind::FnPtrPtrCast)
316 Err(CastError::IllegalCast)
320 fn check_ptr_addr_cast<'a>(&self,
321 fcx: &FnCtxt<'a, 'tcx>,
322 m_expr: &'tcx ty::TypeAndMut<'tcx>)
323 -> Result<CastKind, CastError>
325 // ptr-addr cast. must be from sized ptr
327 if fcx.type_is_known_to_be_sized(m_expr.ty, self.span) {
328 Ok(CastKind::PtrAddrCast)
330 Err(CastError::NeedViaThinPtr)
334 fn check_ref_cast<'a>(&self,
335 fcx: &FnCtxt<'a, 'tcx>,
336 m_expr: &'tcx ty::TypeAndMut<'tcx>,
337 m_cast: &'tcx ty::TypeAndMut<'tcx>)
338 -> Result<CastKind, CastError>
342 if m_expr.mutbl == ast::MutImmutable && m_cast.mutbl == ast::MutImmutable {
343 if let ty::TyArray(ety, _) = m_expr.ty.sty {
344 // Due to the limitations of LLVM global constants,
345 // region pointers end up pointing at copies of
346 // vector elements instead of the original values.
347 // To allow raw pointers to work correctly, we
348 // need to special-case obtaining a raw pointer
349 // from a region pointer to a vector.
351 // this will report a type mismatch if needed
352 demand::eqtype(fcx, self.span, ety, m_cast.ty);
353 return Ok(CastKind::ArrayPtrCast);
357 Err(CastError::IllegalCast)
360 fn check_addr_ptr_cast<'a>(&self,
361 fcx: &FnCtxt<'a, 'tcx>,
362 m_cast: &'tcx ty::TypeAndMut<'tcx>)
363 -> Result<CastKind, CastError>
365 // ptr-addr cast. pointer must be thin.
366 if fcx.type_is_known_to_be_sized(m_cast.ty, self.span) {
367 Ok(CastKind::AddrPtrCast)
369 Err(CastError::IllegalCast)
373 fn try_coercion_cast<'a>(&self, fcx: &FnCtxt<'a, 'tcx>) -> bool {
374 if let Ok(()) = coercion::mk_assignty(fcx,