Field pattern shorthand can be interpreted as an item reference #42876
Comments
Mark-Simulacrum
added
the
T-lang
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Nominating for @rust-lang/lang. I don't think changing things here at this point is going to be easy (feature is stable) but perhaps we could do a warning cycle if we wanted to not allow this. |
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I don't think this is a bug, just the shorthand desugaring and "existing entity vs fresh binding" disambiguation working orthogonally and as expected. (I.e. a perfect behavior for a corner case with near-zero practical impact.)
The wording for the "local-global shadowing" error is misleading, it's actually a "can't disambiguate between existing entity and fresh binding" error, not shadowing error (and it's reported more often than strictly necessary, I was planning to fix it, but still never got to this). If we can force |
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I don't see what this has to do with the shorthand? If the pattern is |
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Is there no warning on the field name of |
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I'm of the opinion that (a) hence I'd prefer to have a lint targeting this case specifically. |
Mark-Simulacrum
added
C-bug
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+1 for having this a lint |
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Triage: not aware of any movement on this issue. |
When encountering an Item in a pat context, point at the item def
```
error[E0308]: mismatched types
--> $DIR/const-in-struct-pat.rs:8:17
|
LL | struct foo;
| ----------- `foo` defined here
...
LL | let Thing { foo } = t;
| ^^^ expected struct `std::string::String`, found struct `foo`
|
= note: `foo` is interpreted as a unit struct, not a new binding
help: you can bind the struct field to a different name
|
LL | let Thing { foo: other_foo } = t;
| ^^^^^^^^^^^^^^
```
```
error[E0308]: mismatched types
--> $DIR/const.rs:14:9
|
LL | const FOO: Foo = Foo{bar: 5};
| ----------------------------- constant defined here
...
LL | FOO => {},
| ^^^
| |
| expected `&Foo`, found struct `Foo`
| `FOO` is interpreted as a constant, not a new binding
| help: use different name to introduce a new binding: `other_foo`
```
Fix rust-lang#55631, fix rust-lang#48062, cc rust-lang#42876.
When encountering an Item in a pat context, point at the item def
```
error[E0308]: mismatched types
--> $DIR/const-in-struct-pat.rs:8:17
|
LL | struct foo;
| ----------- `foo` defined here
...
LL | let Thing { foo } = t;
| ^^^ expected struct `std::string::String`, found struct `foo`
|
= note: `foo` is interpreted as a unit struct, not a new binding
help: you can bind the struct field to a different name
|
LL | let Thing { foo: other_foo } = t;
| ^^^^^^^^^^^^^^
```
```
error[E0308]: mismatched types
--> $DIR/const.rs:14:9
|
LL | const FOO: Foo = Foo{bar: 5};
| ----------------------------- constant defined here
...
LL | FOO => {},
| ^^^
| |
| expected `&Foo`, found struct `Foo`
| `FOO` is interpreted as a constant, not a new binding
| help: use different name to introduce a new binding: `other_foo`
```
Fix rust-lang#55631, fix rust-lang#48062, cc rust-lang#42876.
B { X }is a shorthand forB { X: X }andXhere can be intepreted as an item reference, rather than a binding. I don't know if this is actually a bug or not. Possible fixes are:Xbe interpreted as a binding and let it fail to compile (due to local-global shadowing).Bar!is printed.rustc 1.20.0-nightly (ab5bec255 2017-06-22)The text was updated successfully, but these errors were encountered: