rust-clippy/clippy_lints/src/needless_update.rs
2018-07-19 00:53:23 -07:00

50 lines
1.5 KiB
Rust

use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use rustc::{declare_lint, lint_array};
use rustc::ty;
use rustc::hir::{Expr, ExprKind};
use crate::utils::span_lint;
/// **What it does:** Checks for needlessly including a base struct on update
/// when all fields are changed anyway.
///
/// **Why is this bad?** This will cost resources (because the base has to be
/// somewhere), and make the code less readable.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// Point { x: 1, y: 0, ..zero_point }
/// ```
declare_clippy_lint! {
pub NEEDLESS_UPDATE,
complexity,
"using `Foo { ..base }` when there are no missing fields"
}
#[derive(Copy, Clone)]
pub struct Pass;
impl LintPass for Pass {
fn get_lints(&self) -> LintArray {
lint_array!(NEEDLESS_UPDATE)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if let ExprKind::Struct(_, ref fields, Some(ref base)) = expr.node {
let ty = cx.tables.expr_ty(expr);
if let ty::TyAdt(def, _) = ty.sty {
if fields.len() == def.non_enum_variant().fields.len() {
span_lint(
cx,
NEEDLESS_UPDATE,
base.span,
"struct update has no effect, all the fields in the struct have already been specified",
);
}
}
}
}
}