1 use crate::utils::{is_adjusted, span_lint};
2 use rustc_hir::def::{DefKind, Res};
3 use rustc_hir::{Expr, ExprKind};
4 use rustc_lint::{LateContext, LateLintPass};
5 use rustc_session::{declare_lint_pass, declare_tool_lint};
8 /// **What it does:** Checks for construction of a structure or tuple just to
9 /// assign a value in it.
11 /// **Why is this bad?** Readability. If the structure is only created to be
12 /// updated, why not write the structure you want in the first place?
14 /// **Known problems:** None.
20 pub TEMPORARY_ASSIGNMENT,
22 "assignments to temporaries"
25 fn is_temporary(cx: &LateContext<'_, '_>, expr: &Expr<'_>) -> bool {
27 ExprKind::Struct(..) | ExprKind::Tup(..) => true,
28 ExprKind::Path(qpath) => {
29 if let Res::Def(DefKind::Const, ..) = cx.tables.qpath_res(qpath, expr.hir_id) {
39 declare_lint_pass!(TemporaryAssignment => [TEMPORARY_ASSIGNMENT]);
41 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TemporaryAssignment {
42 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
43 if let ExprKind::Assign(target, ..) = &expr.kind {
44 let mut base = target;
45 while let ExprKind::Field(f, _) | ExprKind::Index(f, _) = &base.kind {
48 if is_temporary(cx, base) && !is_adjusted(cx, base) {
49 span_lint(cx, TEMPORARY_ASSIGNMENT, expr.span, "assignment to temporary");