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Initial implementation of `#[feature(default_field_values]`, proposed in https://github.com/rust-lang/rfcs/pull/3681. Support default fields in enum struct variant Allow default values in an enum struct variant definition: ```rust pub enum Bar { Foo { bar: S = S, baz: i32 = 42 + 3, } } ``` Allow using `..` without a base on an enum struct variant ```rust Bar::Foo { .. } ``` `#[derive(Default)]` doesn't account for these as it is still gating `#[default]` only being allowed on unit variants. Support `#[derive(Default)]` on enum struct variants with all defaulted fields ```rust pub enum Bar { #[default] Foo { bar: S = S, baz: i32 = 42 + 3, } } ``` Check for missing fields in typeck instead of mir_build. Expand test with `const` param case (needs `generic_const_exprs` enabled). Properly instantiate MIR const The following works: ```rust struct S<A> { a: Vec<A> = Vec::new(), } S::<i32> { .. } ``` Add lint for default fields that will always fail const-eval We *allow* this to happen for API writers that might want to rely on users' getting a compile error when using the default field, different to the error that they would get when the field isn't default. We could change this to *always* error instead of being a lint, if we wanted. This will *not* catch errors for partially evaluated consts, like when the expression relies on a const parameter. Suggestions when encountering `Foo { .. }` without `#[feature(default_field_values)]`: - Suggest adding a base expression if there are missing fields. - Suggest enabling the feature if all the missing fields have optional values. - Suggest removing `..` if there are no missing fields.
55 lines
1.8 KiB
Plaintext
55 lines
1.8 KiB
Plaintext
error: expected identifier, found reserved identifier `_`
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--> $DIR/struct_destructure_fail.rs:11:17
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LL | Struct { a, _ } = Struct { a: 1, b: 2 };
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| ------ ^ expected identifier, found reserved identifier
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| |
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| while parsing this struct
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error: functional record updates are not allowed in destructuring assignments
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--> $DIR/struct_destructure_fail.rs:13:19
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LL | Struct { a, ..d } = Struct { a: 1, b: 2 };
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| ^ help: consider removing the trailing pattern
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error[E0026]: struct `Struct` does not have a field named `c`
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--> $DIR/struct_destructure_fail.rs:10:20
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LL | Struct { a, b, c } = Struct { a: 0, b: 1 };
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| ^ struct `Struct` does not have this field
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error[E0027]: pattern does not mention field `b`
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--> $DIR/struct_destructure_fail.rs:11:5
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LL | Struct { a, _ } = Struct { a: 1, b: 2 };
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| ^^^^^^^^^^^^^^^ missing field `b`
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help: include the missing field in the pattern
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LL | Struct { a, b } = Struct { a: 1, b: 2 };
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| ~~~~~
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help: if you don't care about this missing field, you can explicitly ignore it
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LL | Struct { a, b: _ } = Struct { a: 1, b: 2 };
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| ~~~~~~~~
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help: or always ignore missing fields here
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LL | Struct { a, .. } = Struct { a: 1, b: 2 };
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| ~~~~~~
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error[E0797]: base expression required after `..`
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--> $DIR/struct_destructure_fail.rs:15:19
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LL | Struct { a, .. };
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| ^
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help: add a base expression here
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LL | Struct { a, ../* expr */ };
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| ++++++++++
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error: aborting due to 5 previous errors
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Some errors have detailed explanations: E0026, E0027, E0797.
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For more information about an error, try `rustc --explain E0026`.
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