50 lines
1.4 KiB
Rust
50 lines
1.4 KiB
Rust
use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
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use rustc::ty;
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use rustc::hir::{Expr, ExprStruct};
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use utils::span_lint;
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/// **What it does:** 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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/// **Why is this bad?** 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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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// Point { x: 1, y: 0, ..zero_point }
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/// ```
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declare_lint! {
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pub NEEDLESS_UPDATE,
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Warn,
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"using `Foo { ..base }` when there are no missing fields"
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}
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#[derive(Copy, Clone)]
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pub struct Pass;
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impl LintPass for Pass {
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fn get_lints(&self) -> LintArray {
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lint_array!(NEEDLESS_UPDATE)
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
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if let ExprStruct(_, ref fields, Some(ref base)) = expr.node {
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let ty = cx.tables.expr_ty(expr);
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if let ty::TyAdt(def, _) = ty.sty {
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if fields.len() == def.non_enum_variant().fields.len() {
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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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