71 lines
2.1 KiB
Rust
71 lines
2.1 KiB
Rust
use clippy_utils::diagnostics::span_lint;
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use rustc_hir::{Expr, ExprKind};
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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, Some(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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