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mir-borrowck: Autoderef values followed by a constant index, and fix reported lvalue for constant index

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Previously the constant index was reported as `[x of y]` or `[-x of y]` where
`x` was the offset and `y` the minimum length of the slice. The minus sign
wasn't in the right case since for `&[_, x, .., _, _]`, the error reported was
`[-1 of 4]`, and for `&[_, _, .., x, _]`, the error reported was `[2 of 4]`.
This commit fixes the sign so that the indexes 1 and -2 are reported, and
remove the ` of y` part of the message to make it more succinct.
This commit is contained in:
Basile Desloges 2017-10-05 11:03:32 +02:00
parent 456e12ec38
commit ef2f42d04a
2 changed files with 43 additions and 4 deletions
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12
src/librustc_mir/borrow_check.rs
View file

@ -1090,10 +1090,14 @@ impl<'c, 'b, 'a: 'b+'c, 'gcx, 'tcx: 'a> MirBorrowckCtxt<'c, 'b, 'a, 'gcx, 'tcx>
autoderef = true;
("", format!(""), Some(index))
},
ProjectionElem::ConstantIndex { offset, min_length, from_end: true } =>
("", format!("[{} of {}]", offset, min_length), None),
ProjectionElem::ConstantIndex { offset, min_length, from_end: false } =>
("", format!("[-{} of {}]", offset, min_length), None),
ProjectionElem::ConstantIndex { offset, from_end: false, .. } => {
autoderef = true;
("", format!("[{}]", offset), None)
},
ProjectionElem::ConstantIndex { offset, from_end: true, .. } => {
autoderef = true;
("", format!("[-{}]", offset), None)
},
ProjectionElem::Subslice { from, to: 0 } =>
("", format!("[{}:]", from), None),
ProjectionElem::Subslice { from: 0, to } =>

35
src/test/compile-fail/borrowck/borrowck-describe-lvalue.rs
View file

@ -11,6 +11,8 @@
// revisions: ast mir
//[mir]compile-flags: -Z emit-end-regions -Z borrowck-mir
#![feature(advanced_slice_patterns)]
pub struct Foo {
x: u32
}
@ -163,4 +165,37 @@ fn main() {
//[mir]~^ ERROR cannot use `u.a` because it was mutably borrowed (Ast)
//[mir]~| ERROR cannot use `u.a` because it was mutably borrowed (Mir)
}
// Constant index
{
let mut v = &[1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
let _v = &mut v;
match v {
&[x, _, .., _, _] => println!("{}", x),
//[ast]~^ ERROR cannot use `v[..]` because it was mutably borrowed
//[mir]~^^ ERROR cannot use `v[..]` because it was mutably borrowed (Ast)
//[mir]~| ERROR cannot use `v[0]` because it was mutably borrowed (Mir)
_ => panic!("other case"),
}
match v {
&[_, x, .., _, _] => println!("{}", x),
//[ast]~^ ERROR cannot use `v[..]` because it was mutably borrowed
//[mir]~^^ ERROR cannot use `v[..]` because it was mutably borrowed (Ast)
//[mir]~| ERROR cannot use `v[1]` because it was mutably borrowed (Mir)
_ => panic!("other case"),
}
match v {
&[_, _, .., x, _] => println!("{}", x),
//[ast]~^ ERROR cannot use `v[..]` because it was mutably borrowed
//[mir]~^^ ERROR cannot use `v[..]` because it was mutably borrowed (Ast)
//[mir]~| ERROR cannot use `v[-2]` because it was mutably borrowed (Mir)
_ => panic!("other case"),
}
match v {
&[_, _, .., _, x] => println!("{}", x),
//[ast]~^ ERROR cannot use `v[..]` because it was mutably borrowed
//[mir]~^^ ERROR cannot use `v[..]` because it was mutably borrowed (Ast)
//[mir]~| ERROR cannot use `v[-1]` because it was mutably borrowed (Mir)
_ => panic!("other case"),
}
}
}