From 9ac95c10c09faf50cc22eb97b6e1c59d64053c28 Mon Sep 17 00:00:00 2001 From: Esteban Küber Date: Sat, 24 Aug 2024 17:22:48 +0000 Subject: Introduce `default_field_values` feature 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: Vec = Vec::new(), } S:: { .. } ``` 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. --- compiler/rustc_parse/src/parser/expr.rs | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'compiler/rustc_parse/src/parser/expr.rs') diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs index 3a9e9b480ec..eeb83a85e59 100644 --- a/compiler/rustc_parse/src/parser/expr.rs +++ b/compiler/rustc_parse/src/parser/expr.rs @@ -3533,7 +3533,7 @@ impl<'a> Parser<'a> { let exp_span = self.prev_token.span; // We permit `.. }` on the left-hand side of a destructuring assignment. if self.check(&token::CloseDelim(close_delim)) { - base = ast::StructRest::Rest(self.prev_token.span.shrink_to_hi()); + base = ast::StructRest::Rest(self.prev_token.span); break; } match self.parse_expr() { -- cgit 1.4.1-3-g733a5