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(did, substs) => {
83 match fcx.tcx().struct_fields(did, substs).pop() {
85 Some(f) => unsize_kind(fcx, f.mt.ty)
88 // We should really try to normalize here.
89 ty::TyProjection(ref pi) => Some(UnsizeKind::OfProjection(pi)),
90 ty::TyParam(ref p) => Some(UnsizeKind::OfParam(p)),
95 #[derive(Copy, Clone)]
107 impl<'tcx> CastCheck<'tcx> {
108 pub fn new(expr: ast::Expr, expr_ty: Ty<'tcx>, cast_ty: Ty<'tcx>, span: Span)
118 fn report_cast_error<'a>(&self, fcx: &FnCtxt<'a, 'tcx>,
121 CastError::NeedViaPtr |
122 CastError::NeedViaInt |
123 CastError::NeedViaUsize => {
124 fcx.type_error_message(self.span, |actual| {
125 format!("casting `{}` as `{}` is invalid",
127 fcx.infcx().ty_to_string(self.cast_ty))
128 }, self.expr_ty, None);
129 fcx.ccx.tcx.sess.fileline_help(self.span,
130 &format!("cast through {} first", match e {
131 CastError::NeedViaPtr => "a raw pointer",
132 CastError::NeedViaInt => "an integer",
133 CastError::NeedViaUsize => "a usize",
137 CastError::CastToBool => {
138 span_err!(fcx.tcx().sess, self.span, E0054, "cannot cast as `bool`");
139 fcx.ccx.tcx.sess.fileline_help(self.span, "compare with zero instead");
141 CastError::CastToChar => {
142 fcx.type_error_message(self.span, |actual| {
143 format!("only `u8` can be cast as `char`, not `{}`", actual)
144 }, self.expr_ty, None);
146 CastError::NonScalar => {
147 fcx.type_error_message(self.span, |actual| {
148 format!("non-scalar cast: `{}` as `{}`",
150 fcx.infcx().ty_to_string(self.cast_ty))
151 }, self.expr_ty, None);
153 CastError::IllegalCast => {
154 fcx.type_error_message(self.span, |actual| {
155 format!("casting `{}` as `{}` is invalid",
157 fcx.infcx().ty_to_string(self.cast_ty))
158 }, self.expr_ty, None);
160 CastError::DifferingKinds => {
161 fcx.type_error_message(self.span, |actual| {
162 format!("casting `{}` as `{}` is invalid",
164 fcx.infcx().ty_to_string(self.cast_ty))
165 }, self.expr_ty, None);
166 fcx.ccx.tcx.sess.fileline_note(self.span, "vtable kinds may not match");
171 fn trivial_cast_lint<'a>(&self, fcx: &FnCtxt<'a, 'tcx>) {
172 let t_cast = self.cast_ty;
173 let t_expr = self.expr_ty;
174 if t_cast.is_numeric() && t_expr.is_numeric() {
175 fcx.tcx().sess.add_lint(lint::builtin::TRIVIAL_NUMERIC_CASTS,
178 format!("trivial numeric cast: `{}` as `{}`. Cast can be \
179 replaced by coercion, this might require type \
180 ascription or a temporary variable",
181 fcx.infcx().ty_to_string(t_expr),
182 fcx.infcx().ty_to_string(t_cast)));
184 fcx.tcx().sess.add_lint(lint::builtin::TRIVIAL_CASTS,
187 format!("trivial cast: `{}` as `{}`. Cast can be \
188 replaced by coercion, this might require type \
189 ascription or a temporary variable",
190 fcx.infcx().ty_to_string(t_expr),
191 fcx.infcx().ty_to_string(t_cast)));
196 pub fn check<'a>(mut self, fcx: &FnCtxt<'a, 'tcx>) {
197 self.expr_ty = structurally_resolved_type(fcx, self.span, self.expr_ty);
198 self.cast_ty = structurally_resolved_type(fcx, self.span, self.cast_ty);
200 debug!("check_cast({}, {:?} as {:?})", self.expr.id, self.expr_ty,
203 if self.expr_ty.references_error() || self.cast_ty.references_error() {
204 // No sense in giving duplicate error messages
205 } else if self.try_coercion_cast(fcx) {
206 self.trivial_cast_lint(fcx);
207 debug!(" -> CoercionCast");
208 fcx.tcx().cast_kinds.borrow_mut().insert(self.expr.id,
209 CastKind::CoercionCast);
210 } else { match self.do_check(fcx) {
212 debug!(" -> {:?}", k);
213 fcx.tcx().cast_kinds.borrow_mut().insert(self.expr.id, k);
215 Err(e) => self.report_cast_error(fcx, e)
219 /// Check a cast, and report an error if one exists. In some cases, this
220 /// can return Ok and create type errors in the fcx rather than returning
221 /// directly. coercion-cast is handled in check instead of here.
222 fn do_check<'a>(&self, fcx: &FnCtxt<'a, 'tcx>) -> Result<CastKind, CastError> {
223 use middle::cast::IntTy::*;
224 use middle::cast::CastTy::*;
226 let (t_from, t_cast) = match (CastTy::from_ty(fcx.tcx(), self.expr_ty),
227 CastTy::from_ty(fcx.tcx(), self.cast_ty)) {
228 (Some(t_from), Some(t_cast)) => (t_from, t_cast),
230 return Err(CastError::NonScalar)
234 match (t_from, t_cast) {
235 // These types have invariants! can't cast into them.
236 (_, RPtr(_)) | (_, Int(CEnum)) | (_, FnPtr) => Err(CastError::NonScalar),
239 (_, Int(Bool)) => Err(CastError::CastToBool),
242 (Int(U(ast::TyU8)), Int(Char)) => Ok(CastKind::U8CharCast), // u8-char-cast
243 (_, Int(Char)) => Err(CastError::CastToChar),
246 (Int(Bool), Float) | (Int(CEnum), Float) | (Int(Char), Float)
247 => Err(CastError::NeedViaInt),
248 (Int(Bool), Ptr(_)) | (Int(CEnum), Ptr(_)) | (Int(Char), Ptr(_))
249 => Err(CastError::NeedViaUsize),
252 (Ptr(m_e), Ptr(m_c)) => self.check_ptr_ptr_cast(fcx, m_e, m_c), // ptr-ptr-cast
253 (Ptr(m_expr), Int(_)) => self.check_ptr_addr_cast(fcx, m_expr), // ptr-addr-cast
254 (Ptr(_), Float) | (FnPtr, Float) => Err(CastError::NeedViaUsize),
255 (FnPtr, Int(_)) => Ok(CastKind::FnPtrAddrCast),
256 (RPtr(_), Int(_)) | (RPtr(_), Float) => Err(CastError::NeedViaPtr),
258 (Int(_), Ptr(mt)) => self.check_addr_ptr_cast(fcx, mt), // addr-ptr-cast
259 (FnPtr, Ptr(mt)) => self.check_fptr_ptr_cast(fcx, mt),
260 (Float, Ptr(_)) => Err(CastError::NeedViaUsize),
261 (RPtr(rmt), Ptr(mt)) => self.check_ref_cast(fcx, rmt, mt), // array-ptr-cast
264 (Int(CEnum), Int(_)) => Ok(CastKind::EnumCast),
265 (Int(Char), Int(_)) | (Int(Bool), Int(_)) => Ok(CastKind::PrimIntCast),
270 (Float, Float) => Ok(CastKind::NumericCast),
275 fn check_ptr_ptr_cast<'a>(&self,
276 fcx: &FnCtxt<'a, 'tcx>,
277 m_expr: &'tcx ty::TypeAndMut<'tcx>,
278 m_cast: &'tcx ty::TypeAndMut<'tcx>)
279 -> Result<CastKind, CastError>
281 debug!("check_ptr_ptr_cast m_expr={:?} m_cast={:?}",
283 // ptr-ptr cast. vtables must match.
285 // Cast to sized is OK
286 if fcx.type_is_known_to_be_sized(m_cast.ty, self.span) {
287 return Ok(CastKind::PtrPtrCast);
290 // sized -> unsized? report invalid cast (don't complain about vtable kinds)
291 if fcx.type_is_known_to_be_sized(m_expr.ty, self.span) {
292 return Err(CastError::IllegalCast);
295 // vtable kinds must match
296 match (unsize_kind(fcx, m_cast.ty), unsize_kind(fcx, m_expr.ty)) {
297 (Some(a), Some(b)) if a == b => Ok(CastKind::PtrPtrCast),
298 _ => Err(CastError::DifferingKinds)
302 fn check_fptr_ptr_cast<'a>(&self,
303 fcx: &FnCtxt<'a, 'tcx>,
304 m_cast: &'tcx ty::TypeAndMut<'tcx>)
305 -> Result<CastKind, CastError>
307 // fptr-ptr cast. must be to sized ptr
309 if fcx.type_is_known_to_be_sized(m_cast.ty, self.span) {
310 Ok(CastKind::FnPtrPtrCast)
312 Err(CastError::IllegalCast)
316 fn check_ptr_addr_cast<'a>(&self,
317 fcx: &FnCtxt<'a, 'tcx>,
318 m_expr: &'tcx ty::TypeAndMut<'tcx>)
319 -> Result<CastKind, CastError>
321 // ptr-addr cast. must be from sized ptr
323 if fcx.type_is_known_to_be_sized(m_expr.ty, self.span) {
324 Ok(CastKind::PtrAddrCast)
326 Err(CastError::NeedViaPtr)
330 fn check_ref_cast<'a>(&self,
331 fcx: &FnCtxt<'a, 'tcx>,
332 m_expr: &'tcx ty::TypeAndMut<'tcx>,
333 m_cast: &'tcx ty::TypeAndMut<'tcx>)
334 -> Result<CastKind, CastError>
338 if m_expr.mutbl == ast::MutImmutable && m_cast.mutbl == ast::MutImmutable {
339 if let ty::TyArray(ety, _) = m_expr.ty.sty {
340 // Due to the limitations of LLVM global constants,
341 // region pointers end up pointing at copies of
342 // vector elements instead of the original values.
343 // To allow raw pointers to work correctly, we
344 // need to special-case obtaining a raw pointer
345 // from a region pointer to a vector.
347 // this will report a type mismatch if needed
348 demand::eqtype(fcx, self.span, ety, m_cast.ty);
349 return Ok(CastKind::ArrayPtrCast);
353 Err(CastError::IllegalCast)
356 fn check_addr_ptr_cast<'a>(&self,
357 fcx: &FnCtxt<'a, 'tcx>,
358 m_cast: &'tcx ty::TypeAndMut<'tcx>)
359 -> Result<CastKind, CastError>
361 // ptr-addr cast. pointer must be thin.
362 if fcx.type_is_known_to_be_sized(m_cast.ty, self.span) {
363 Ok(CastKind::AddrPtrCast)
365 Err(CastError::IllegalCast)
369 fn try_coercion_cast<'a>(&self, fcx: &FnCtxt<'a, 'tcx>) -> bool {
370 if let Ok(()) = coercion::mk_assignty(fcx,