use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use rustc::ty::TyStruct;
use rustc::hir::{Expr, ExprStruct};
use utils::span_lint;
declare_lint! {
pub NEEDLESS_UPDATE,
Warn,
"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 LateLintPass for Pass {
fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
if let ExprStruct(_, ref fields, Some(ref base)) = expr.node {
let ty = cx.tcx.expr_ty(expr);
if let TyStruct(def, _) = ty.sty {
if fields.len() == def.struct_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");
}
}
}
}
}