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librustc: Don't try to perform the magical

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vector-reference-to-unsafe-pointer-to-element cast if the type to be
casted to is not fully specified.

This is a conservative change to fix the user-visible symptoms of the
issue. A more flexible treatment would delay cast checks to after
function typechecking.

This can break code that did:

    let x: *u8 = &([0, 0]) as *_;

Change this code to:

    let x: *u8 = &([0, 0]) as *u8;

Closes #14893.

[breaking-change]
This commit is contained in:
Patrick Walton 2014-06-24 18:22:21 -07:00
parent 7a93beef7f
commit 315f2a7054
2 changed files with 191 additions and 129 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

289
src/librustc/middle/typeck/check/mod.rs
View File

@ -1060,6 +1060,164 @@ fn compare_impl_method(tcx: &ty::ctxt,
}
}
fn check_cast(fcx: &FnCtxt,
e: &ast::Expr,
t: &ast::Ty,
id: ast::NodeId,
span: Span) {
// Find the type of `e`. Supply hints based on the type we are casting to,
// if appropriate.
let t_1 = fcx.to_ty(t);
let t_1 = structurally_resolved_type(fcx, span, t_1);
if ty::type_is_scalar(t_1) {
// Supply the type as a hint so as to influence integer
// literals and other things that might care.
check_expr_with_hint(fcx, e, t_1)
} else {
check_expr(fcx, e)
}
let t_e = fcx.expr_ty(e);
debug!("t_1={}", fcx.infcx().ty_to_str(t_1));
debug!("t_e={}", fcx.infcx().ty_to_str(t_e));
if ty::type_is_error(t_e) {
fcx.write_error(id);
return
}
if ty::type_is_bot(t_e) {
fcx.write_bot(id);
return
}
if ty::type_is_trait(t_1) {
// This will be looked up later on.
fcx.write_ty(id, t_1);
return
}
let t_1 = structurally_resolved_type(fcx, span, t_1);
let t_e = structurally_resolved_type(fcx, span, t_e);
if ty::type_is_nil(t_e) {
fcx.type_error_message(span, |actual| {
format!("cast from nil: `{}` as `{}`",
actual,
fcx.infcx().ty_to_str(t_1))
}, t_e, None);
} else if ty::type_is_nil(t_1) {
fcx.type_error_message(span, |actual| {
format!("cast to nil: `{}` as `{}`",
actual,
fcx.infcx().ty_to_str(t_1))
}, t_e, None);
}
let t_1_is_scalar = ty::type_is_scalar(t_1);
let t_1_is_char = ty::type_is_char(t_1);
let t_1_is_bare_fn = ty::type_is_bare_fn(t_1);
let t_1_is_float = ty::type_is_floating_point(t_1);
// casts to scalars other than `char` and `bare fn` are trivial
let t_1_is_trivial = t_1_is_scalar && !t_1_is_char && !t_1_is_bare_fn;
if ty::type_is_c_like_enum(fcx.tcx(), t_e) && t_1_is_trivial {
if t_1_is_float {
fcx.type_error_message(span, |actual| {
format!("illegal cast; cast through an \
integer first: `{}` as `{}`",
actual,
fcx.infcx().ty_to_str(t_1))
}, t_e, None);
}
// casts from C-like enums are allowed
} else if t_1_is_char {
let t_e = fcx.infcx().resolve_type_vars_if_possible(t_e);
if ty::get(t_e).sty != ty::ty_uint(ast::TyU8) {
fcx.type_error_message(span, |actual| {
format!("only `u8` can be cast as \
`char`, not `{}`", actual)
}, t_e, None);
}
} else if ty::get(t_1).sty == ty::ty_bool {
fcx.tcx()
.sess
.span_err(span,
"cannot cast as `bool`, compare with zero instead");
} else if ty::type_is_region_ptr(t_e) && ty::type_is_unsafe_ptr(t_1) {
fn is_vec(t: ty::t) -> bool {
match ty::get(t).sty {
ty::ty_vec(..) => true,
ty::ty_ptr(ty::mt{ty: t, ..}) |
ty::ty_rptr(_, ty::mt{ty: t, ..}) |
ty::ty_box(t) |
ty::ty_uniq(t) => {
match ty::get(t).sty {
ty::ty_vec(_, None) => true,
_ => false,
}
}
_ => false
}
}
fn types_compatible(fcx: &FnCtxt, sp: Span,
t1: ty::t, t2: ty::t) -> bool {
if !is_vec(t1) {
// If the type being casted from is not a vector, this special
// case does not apply.
return false
}
if ty::type_needs_infer(t2) {
// This prevents this special case from going off when casting
// to a type that isn't fully specified; e.g. `as *_`. (Issue
// #14893.)
return false
}
let el = ty::sequence_element_type(fcx.tcx(), t1);
infer::mk_eqty(fcx.infcx(),
false,
infer::Misc(sp),
el,
t2).is_ok()
}
// Due to the limitations of LLVM global constants,
// region pointers end up pointing at copies of
// vector elements instead of the original values.
// To allow unsafe pointers to work correctly, we
// need to special-case obtaining an unsafe pointer
// from a region pointer to a vector.
/* this cast is only allowed from &[T] to *T or
&T to *T. */
match (&ty::get(t_e).sty, &ty::get(t_1).sty) {
(&ty::ty_rptr(_, ty::mt { ty: mt1, mutbl: ast::MutImmutable }),
&ty::ty_ptr(ty::mt { ty: mt2, mutbl: ast::MutImmutable }))
if types_compatible(fcx, e.span, mt1, mt2) => {
/* this case is allowed */
}
_ => {
demand::coerce(fcx, e.span, t_1, &*e);
}
}
} else if !(ty::type_is_scalar(t_e) && t_1_is_trivial) {
/*
If more type combinations should be supported than are
supported here, then file an enhancement issue and
record the issue number in this comment.
*/
fcx.type_error_message(span, |actual| {
format!("non-scalar cast: `{}` as `{}`",
actual,
fcx.infcx().ty_to_str(t_1))
}, t_e, None);
}
fcx.write_ty(id, t_1);
}
impl<'a> AstConv for FnCtxt<'a> {
fn tcx<'a>(&'a self) -> &'a ty::ctxt { self.ccx.tcx }
@ -3049,11 +3207,8 @@ fn check_expr_with_unifier(fcx: &FnCtxt,
fcx.write_bot(id);
}
}
ast::ExprCast(expr_from, t) => {
let ty_to = fcx.to_ty(t);
debug!("ExprCast ty_to={}", fcx.infcx().ty_to_str(ty_to));
check_cast(fcx, expr_from, ty_to);
fcx.write_ty(id, ty_to);
ast::ExprCast(ref e, ref t) => {
check_cast(fcx, &**e, &**t, id, expr.span);
}
ast::ExprVec(ref args) => {
let t: ty::t = fcx.infcx().next_ty_var();
@ -3248,130 +3403,6 @@ impl Repr for Expectation {
}
}
fn check_cast(fcx: &FnCtxt, expr_from: Gc<ast::Expr>, ty_to: ty::t) {
// Find the type of `expr_from`. Supply hints based on the type
// we are casting to, if appropriate.
let ty_to = structurally_resolved_type(fcx, expr_from.span, ty_to);
if ty::type_is_scalar(ty_to) {
// Supply the type as a hint so as to influence integer
// literals and other things that might care.
check_expr_with_hint(fcx, expr_from, ty_to)
} else {
check_expr(fcx, expr_from)
}
let ty_from = fcx.expr_ty(expr_from);
// Object creation is checked during the vtable phase.
if ty::type_is_trait(ty_to) {
check_expr(fcx, expr_from);
return;
}
let ty_from = fcx.infcx().resolve_type_vars_if_possible(ty_from);
if ty::type_is_nil(ty_from) {
fcx.type_error_message(expr_from.span, |actual| {
format!("cast from nil: `{}` as `{}`", actual,
fcx.infcx().ty_to_str(ty_to))
}, ty_from, None);
return;
}
if ty::type_is_nil(ty_to) {
fcx.type_error_message(expr_from.span, |actual| {
format!("cast to nil: `{}` as `{}`", actual,
fcx.infcx().ty_to_str(ty_to))
}, ty_from, None);
return;
}
let t_e = structurally_resolved_type(fcx, expr_from.span, ty_from);
let t_1 = structurally_resolved_type(fcx, expr_from.span, ty_to);
let to_is_scalar = ty::type_is_scalar(t_1);
let to_is_float = ty::type_is_floating_point(t_1);
let to_is_char = ty::type_is_char(t_1);
let to_is_bare_fn = ty::type_is_bare_fn(t_1);
// casts to scalars other than `char` and `bare fn` are trivial
let to_is_trivial = to_is_scalar &&
!to_is_char && !to_is_bare_fn;
if ty::type_is_c_like_enum(fcx.tcx(), t_e) && to_is_trivial {
if to_is_float {
fcx.type_error_message(expr_from.span, |actual| {
format!("illegal cast; cast through an integer first: `{}` \
as `{}`",
actual,
fcx.infcx().ty_to_str(t_1))
}, ty_from, None);
}
// casts from C-like enums are allowed
} else if to_is_char {
if ty::get(ty_from).sty != ty::ty_uint(ast::TyU8) {
fcx.type_error_message(expr_from.span, |actual| {
format!("only `u8` can be cast as `char`, not `{}`", actual)
}, ty_from, None);
}
} else if ty::type_is_bool(t_1) {
fcx.tcx().sess.span_err(expr_from.span,
"cannot cast as `bool`, compare with zero instead");
} else if ty::type_is_region_ptr(t_e) && ty::type_is_unsafe_ptr(t_1) {
fn is_vec(t: ty::t) -> bool {
match ty::get(t).sty {
ty::ty_vec(..) => true,
ty::ty_ptr(ty::mt{ty: t, ..}) |
ty::ty_rptr(_, ty::mt{ty: t, ..}) |
ty::ty_box(t) |
ty::ty_uniq(t) => match ty::get(t).sty {
ty::ty_vec(_, None) => true,
_ => false,
},
_ => false
}
}
fn types_compatible(fcx: &FnCtxt, sp: Span,
t1: ty::t, t2: ty::t) -> bool {
if !is_vec(t1) {
false
} else {
let el = ty::sequence_element_type(fcx.tcx(),
t1);
infer::mk_eqty(fcx.infcx(), false,
infer::Misc(sp), el, t2).is_ok()
}
}
// Due to the limitations of LLVM global constants,
// region pointers end up pointing at copies of
// vector elements instead of the original values.
// To allow unsafe pointers to work correctly, we
// need to special-case obtaining an unsafe pointer
// from a region pointer to a vector.
/* this cast is only allowed from &[T] to *T or
&T to *T. */
match (&ty::get(t_e).sty, &ty::get(t_1).sty) {
(&ty::ty_rptr(_, ty::mt { ty: mt1, mutbl: ast::MutImmutable }),
&ty::ty_ptr(ty::mt { ty: mt2, mutbl: ast::MutImmutable }))
if types_compatible(fcx, expr_from.span, mt1, mt2) => {
/* this case is allowed */
}
_ => {
demand::coerce(fcx, expr_from.span, ty_to, expr_from);
}
}
} else if !(ty::type_is_scalar(t_e) && to_is_trivial) {
// If more type combinations should be supported than are
// supported here, then file an enhancement issue and
// record the issue number in this comment.
fcx.type_error_message(expr_from.span, |actual| {
format!("non-scalar cast: `{}` as `{}`", actual,
fcx.infcx().ty_to_str(ty_to))
}, ty_from, None);
}
}
pub fn require_uint(fcx: &FnCtxt, sp: Span, t: ty::t) {
if !type_is_uint(fcx, sp, t) {
fcx.type_error_message(sp, |actual| {

31
src/test/compile-fail/vector-cast-weirdness.rs Normal file
View File

@ -0,0 +1,31 @@
// Copyright 2012 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 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// Issue #14893. Tests that casts from vectors don't behave strangely in the
// presence of the `_` type shorthand notation.
struct X {
y: [u8, ..2],
}
fn main() {
let x1 = X { y: [0, 0] };
let p1: *u8 = &x1.y as *_; //~ ERROR mismatched types
let t1: *[u8, ..2] = &x1.y as *_;
let h1: *[u8, ..2] = &x1.y as *[u8, ..2];
let mut x1 = X { y: [0, 0] };
let p1: *mut u8 = &mut x1.y as *mut _; //~ ERROR mismatched types
let t1: *mut [u8, ..2] = &mut x1.y as *mut _;
let h1: *mut [u8, ..2] = &mut x1.y as *mut [u8, ..2];
}