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