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rust/tests/ui/borrowck/suggest-local-var-double-mut.stderr

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Suggest using a temporary variable to fix borrowck errors In Rust, nesting method calls with both require `&mut` access to `self` produces a borrow-check error: error[E0499]: cannot borrow `*self` as mutable more than once at a time --> src/lib.rs:7:14 | 7 | self.foo(self.bar()); | ---------^^^^^^^^^^- | | | | | | | second mutable borrow occurs here | | first borrow later used by call | first mutable borrow occurs here That's because Rust has a left-to-right evaluation order, and the method receiver is passed first. Thus, the argument to the method cannot then mutate `self`. There's an easy solution to this error: just extract a local variable for the inner argument: let tmp = self.bar(); self.foo(tmp); However, the error doesn't give any suggestion of how to solve the problem. As a result, new users may assume that it's impossible to express their code correctly and get stuck. This commit adds a (non-structured) suggestion to extract a local variable for the inner argument to solve the error. The suggestion uses heuristics that eliminate most false positives, though there are a few false negatives (cases where the suggestion should be emitted but is not). Those other cases can be implemented in a future change.
2021-03-15 17:09:06 -05:00
error[E0499]: cannot borrow `*self` as mutable more than once at a time
--> $DIR/suggest-local-var-double-mut.rs:12:22
|
LL | self.foo(self.bar());
Do not set up wrong span for adjustments
2023-06-22 15:30:23 -05:00
| ---- --- ^^^^ second mutable borrow occurs here
| | |
Suggest using a temporary variable to fix borrowck errors In Rust, nesting method calls with both require `&mut` access to `self` produces a borrow-check error: error[E0499]: cannot borrow `*self` as mutable more than once at a time --> src/lib.rs:7:14 | 7 | self.foo(self.bar()); | ---------^^^^^^^^^^- | | | | | | | second mutable borrow occurs here | | first borrow later used by call | first mutable borrow occurs here That's because Rust has a left-to-right evaluation order, and the method receiver is passed first. Thus, the argument to the method cannot then mutate `self`. There's an easy solution to this error: just extract a local variable for the inner argument: let tmp = self.bar(); self.foo(tmp); However, the error doesn't give any suggestion of how to solve the problem. As a result, new users may assume that it's impossible to express their code correctly and get stuck. This commit adds a (non-structured) suggestion to extract a local variable for the inner argument to solve the error. The suggestion uses heuristics that eliminate most false positives, though there are a few false negatives (cases where the suggestion should be emitted but is not). Those other cases can be implemented in a future change.
2021-03-15 17:09:06 -05:00
| | first borrow later used by call
| first mutable borrow occurs here
|
help: try adding a local storing this argument...
--> $DIR/suggest-local-var-double-mut.rs:12:22
|
LL | self.foo(self.bar());
| ^^^^^^^^^^
help: ...and then using that local as the argument to this call
--> $DIR/suggest-local-var-double-mut.rs:12:13
|
LL | self.foo(self.bar());
| ^^^^^^^^^^^^^^^^^^^^
error[E0499]: cannot borrow `*self` as mutable more than once at a time
--> $DIR/suggest-local-var-double-mut.rs:24:39
|
LL | Self::foo(self, Self::bar(self));
| --------- ---- ^^^^ second mutable borrow occurs here
| | |
| | first mutable borrow occurs here
| first borrow later used by call
|
help: try adding a local storing this argument...
--> $DIR/suggest-local-var-double-mut.rs:24:29
|
LL | Self::foo(self, Self::bar(self));
| ^^^^^^^^^^^^^^^
help: ...and then using that local as the argument to this call
--> $DIR/suggest-local-var-double-mut.rs:24:13
|
LL | Self::foo(self, Self::bar(self));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: aborting due to 2 previous errors
For more information about this error, try `rustc --explain E0499`.
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