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