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Improve mutability error suggestions.

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This commit improves mutability error suggestions by suggesting the
removal of `&mut` where a mutable borrow is being taken of a `&mut self`
or a `self: &mut Self`.
This commit is contained in:
David Wood 2018-10-01 19:20:57 +02:00
parent 43b5d725d0
commit 2be306939d
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GPG key ID: 01760B4F9F53F154
4 changed files with 74 additions and 26 deletions
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35
src/librustc_mir/borrow_check/mutability_errors.rs
View file

@ -16,6 +16,7 @@ use rustc::mir::TerminatorKind;
use rustc::ty::{self, Const, DefIdTree, TyS, TyKind, TyCtxt};
use rustc_data_structures::indexed_vec::Idx;
use syntax_pos::Span;
use syntax_pos::symbol::keywords;
use dataflow::move_paths::InitLocation;
use borrow_check::MirBorrowckCtxt;
@ -217,6 +218,40 @@ impl<'a, 'gcx, 'tcx> MirBorrowckCtxt<'a, 'gcx, 'tcx> {
debug!("report_mutability_error: act={:?}, acted_on={:?}", act, acted_on);
match the_place_err {
// Suggest removing a `&mut` from the use of a mutable reference.
Place::Local(local)
if {
self.mir.local_decls.get(*local).map(|local_decl| {
if let ClearCrossCrate::Set(
mir::BindingForm::ImplicitSelf(kind)
) = local_decl.is_user_variable.as_ref().unwrap() {
// Check if the user variable is a `&mut self` and we can therefore
// suggest removing the `&mut`.
//
// Deliberately fall into this case for all implicit self types,
// so that we don't fall in to the next case with them.
*kind == mir::ImplicitSelfKind::MutRef
} else if Some(keywords::SelfValue.name()) == local_decl.name {
// Otherwise, check if the name is the self kewyord - in which case
// we have an explicit self. Do the same thing in this case and check
// for a `self: &mut Self` to suggest removing the `&mut`.
if let ty::TyKind::Ref(
_, _, hir::Mutability::MutMutable
) = local_decl.ty.sty {
true
} else {
false
}
} else {
false
}
}).unwrap_or(false)
} =>
{
err.span_label(span, format!("cannot {ACT}", ACT = act));
err.span_label(span, "try removing `&mut` here");
},
// We want to suggest users use `let mut` for local (user
// variable) mutations...
Place::Local(local) if self.mir.local_decls[*local].can_be_made_mutable() => {

12
src/test/ui/did_you_mean/issue-31424.nll.stderr
View file

@ -2,15 +2,19 @@ error[E0596]: cannot borrow `self` as mutable, as it is not declared as mutable
--> $DIR/issue-31424.rs:17:9
|
LL | (&mut self).bar(); //~ ERROR cannot borrow
| ^^^^^^^^^^^ cannot borrow as mutable
| ^^^^^^^^^^^
| |
| cannot borrow as mutable
| try removing `&mut` here
error[E0596]: cannot borrow `self` as mutable, as it is not declared as mutable
--> $DIR/issue-31424.rs:23:9
|
LL | fn bar(self: &mut Self) {
| ---- help: consider changing this to be mutable: `mut self`
LL | (&mut self).bar(); //~ ERROR cannot borrow
| ^^^^^^^^^^^ cannot borrow as mutable
| ^^^^^^^^^^^
| |
| cannot borrow as mutable
| try removing `&mut` here
error: aborting due to 2 previous errors

11
src/test/ui/nll/issue-51191.rs
View file

@ -14,11 +14,13 @@ struct Struct;
impl Struct {
fn bar(self: &mut Self) {
(&mut self).bar(); //~ ERROR cannot borrow
(&mut self).bar();
//~^ ERROR cannot borrow `self` as mutable, as it is not declared as mutable [E0596]
}
fn imm(self) {
(&mut self).bar(); //~ ERROR cannot borrow
(&mut self).bar();
//~^ ERROR cannot borrow `self` as mutable, as it is not declared as mutable [E0596]
}
fn mtbl(mut self) {
@ -26,11 +28,14 @@ impl Struct {
}
fn immref(&self) {
(&mut self).bar(); //~ ERROR cannot borrow
(&mut self).bar();
//~^ ERROR cannot borrow `self` as mutable, as it is not declared as mutable [E0596]
//~^^ ERROR cannot borrow data in a `&` reference as mutable [E0596]
}
fn mtblref(&mut self) {
(&mut self).bar();
//~^ ERROR cannot borrow `self` as mutable, as it is not declared as mutable [E0596]
}
}

42
src/test/ui/nll/issue-51191.stderr
View file

@ -1,37 +1,41 @@
error[E0596]: cannot borrow `self` as mutable, as it is not declared as mutable
--> $DIR/issue-51191.rs:17:9
|
LL | fn bar(self: &mut Self) {
| ---- help: consider changing this to be mutable: `mut self`
LL | (&mut self).bar(); //~ ERROR cannot borrow
| ^^^^^^^^^^^ cannot borrow as mutable
LL | (&mut self).bar();
| ^^^^^^^^^^^
| |
| cannot borrow as mutable
| try removing `&mut` here
error[E0596]: cannot borrow `self` as mutable, as it is not declared as mutable
--> $DIR/issue-51191.rs:21:9
--> $DIR/issue-51191.rs:22:9
|
LL | fn imm(self) {
| ---- help: consider changing this to be mutable: `mut self`
LL | (&mut self).bar(); //~ ERROR cannot borrow
LL | (&mut self).bar();
| ^^^^^^^^^^^ cannot borrow as mutable
error[E0596]: cannot borrow `self` as mutable, as it is not declared as mutable
--> $DIR/issue-51191.rs:29:9
|
LL | (&mut self).bar(); //~ ERROR cannot borrow
| ^^^^^^^^^^^ cannot borrow as mutable
error[E0596]: cannot borrow data in a `&` reference as mutable
--> $DIR/issue-51191.rs:29:9
|
LL | (&mut self).bar(); //~ ERROR cannot borrow
| ^^^^^^^^^^^ cannot borrow as mutable
error[E0596]: cannot borrow `self` as mutable, as it is not declared as mutable
--> $DIR/issue-51191.rs:33:9
--> $DIR/issue-51191.rs:31:9
|
LL | (&mut self).bar();
| ^^^^^^^^^^^ cannot borrow as mutable
error[E0596]: cannot borrow data in a `&` reference as mutable
--> $DIR/issue-51191.rs:31:9
|
LL | (&mut self).bar();
| ^^^^^^^^^^^ cannot borrow as mutable
error[E0596]: cannot borrow `self` as mutable, as it is not declared as mutable
--> $DIR/issue-51191.rs:37:9
|
LL | (&mut self).bar();
| ^^^^^^^^^^^
| |
| cannot borrow as mutable
| try removing `&mut` here
error: aborting due to 5 previous errors
For more information about this error, try `rustc --explain E0596`.