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9ac95c10c0
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.
35 lines
1.2 KiB
Rust
35 lines
1.2 KiB
Rust
#![allow(dead_code)]
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enum E {
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A,
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}
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struct S {
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field1: i32 = 42, //~ ERROR default values on `struct` fields aren't supported
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field2: E = E::A, //~ ERROR default values on `struct` fields aren't supported
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field3: i32 = 1 + 2, //~ ERROR default values on `struct` fields aren't supported
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field4: i32 = { 1 + 2 }, //~ ERROR default values on `struct` fields aren't supported
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field5: E = foo(42), //~ ERROR default values on `struct` fields aren't supported
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field6: E = { foo(42) }, //~ ERROR default values on `struct` fields aren't supported
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}
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struct S1 {
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field1: i32 //~ ERROR expected `,`, or `}`, found `field2`
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field2: E //~ ERROR expected `,`, or `}`, found `field3`
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field3: i32 = 1 + 2, //~ ERROR default values on `struct` fields aren't supported
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field4: i32 = { 1 + 2 }, //~ ERROR default values on `struct` fields aren't supported
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field5: E = foo(42), //~ ERROR default values on `struct` fields aren't supported
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field6: E = { foo(42) }, //~ ERROR default values on `struct` fields aren't supported
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}
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struct S2 {
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field1 = i32, //~ ERROR expected `:`, found `=`
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field2; E, //~ ERROR expected `:`, found `;`
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}
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const fn foo(_: i32) -> E {
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E::A
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}
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fn main() {}
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