59392bec75
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.
70 lines
2.1 KiB
Rust
70 lines
2.1 KiB
Rust
use clippy_utils::diagnostics::span_lint;
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use rustc_hir::{Expr, ExprKind, StructTailExpr};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::ty;
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use rustc_session::declare_lint_pass;
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for needlessly including a base struct on update
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/// when all fields are changed anyway.
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///
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/// This lint is not applied to structs marked with
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/// [non_exhaustive](https://doc.rust-lang.org/reference/attributes/type_system.html).
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///
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/// ### Why is this bad?
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/// This will cost resources (because the base has to be
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/// somewhere), and make the code less readable.
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///
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/// ### Example
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/// ```no_run
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/// # struct Point {
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/// # x: i32,
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/// # y: i32,
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/// # z: i32,
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/// # }
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/// # let zero_point = Point { x: 0, y: 0, z: 0 };
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/// Point {
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/// x: 1,
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/// y: 1,
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/// z: 1,
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/// ..zero_point
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/// };
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/// ```
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///
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/// Use instead:
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/// ```rust,ignore
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/// // Missing field `z`
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/// Point {
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/// x: 1,
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/// y: 1,
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/// ..zero_point
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/// };
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/// ```
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#[clippy::version = "pre 1.29.0"]
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pub NEEDLESS_UPDATE,
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complexity,
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"using `Foo { ..base }` when there are no missing fields"
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}
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declare_lint_pass!(NeedlessUpdate => [NEEDLESS_UPDATE]);
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impl<'tcx> LateLintPass<'tcx> for NeedlessUpdate {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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if let ExprKind::Struct(_, fields, StructTailExpr::Base(base)) = expr.kind {
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let ty = cx.typeck_results().expr_ty(expr);
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if let ty::Adt(def, _) = ty.kind() {
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if fields.len() == def.non_enum_variant().fields.len()
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&& !def.variant(0_usize.into()).is_field_list_non_exhaustive()
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{
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span_lint(
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cx,
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NEEDLESS_UPDATE,
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base.span,
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"struct update has no effect, all the fields in the struct have already been specified",
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);
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}
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}
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}
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}
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}
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