1 use crate::utils::{get_parent_expr, implements_trait, snippet, span_lint_and_sugg};
2 use if_chain::if_chain;
3 use rustc_ast::util::parser::{ExprPrecedence, PREC_POSTFIX, PREC_PREFIX};
4 use rustc_errors::Applicability;
5 use rustc_hir::{Expr, ExprKind};
6 use rustc_lint::{LateContext, LateLintPass};
7 use rustc_session::{declare_lint_pass, declare_tool_lint};
8 use rustc_span::source_map::Span;
10 declare_clippy_lint! {
11 /// **What it does:** Checks for explicit `deref()` or `deref_mut()` method calls.
13 /// **Why is this bad?** Dereferencing by `&*x` or `&mut *x` is clearer and more concise,
14 /// when not part of a method chain.
18 /// use std::ops::Deref;
19 /// let a: &mut String = &mut String::from("foo");
20 /// let b: &str = a.deref();
22 /// Could be written as:
24 /// let a: &mut String = &mut String::from("foo");
28 /// This lint excludes
30 /// let _ = d.unwrap().deref();
32 pub EXPLICIT_DEREF_METHODS,
34 "Explicit use of deref or deref_mut method while not in a method chain."
37 declare_lint_pass!(Dereferencing => [
38 EXPLICIT_DEREF_METHODS
41 impl<'tcx> LateLintPass<'tcx> for Dereferencing {
42 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
44 if !expr.span.from_expansion();
45 if let ExprKind::MethodCall(ref method_name, _, ref args, _) = &expr.kind;
49 if let Some(parent_expr) = get_parent_expr(cx, expr) {
50 // Check if we have the whole call chain here
51 if let ExprKind::MethodCall(..) = parent_expr.kind {
54 // Check for Expr that we don't want to be linted
55 let precedence = parent_expr.precedence();
57 // Lint a Call is ok though
58 ExprPrecedence::Call | ExprPrecedence::AddrOf => (),
60 if precedence.order() >= PREC_PREFIX && precedence.order() <= PREC_POSTFIX {
66 let name = method_name.ident.as_str();
67 lint_deref(cx, &*name, &args[0], args[0].span, expr.span);
73 fn lint_deref(cx: &LateContext<'_>, method_name: &str, call_expr: &Expr<'_>, var_span: Span, expr_span: Span) {
76 let impls_deref_trait = cx.tcx.lang_items().deref_trait().map_or(false, |id| {
77 implements_trait(cx, cx.typeck_results().expr_ty(&call_expr), id, &[])
79 if impls_deref_trait {
82 EXPLICIT_DEREF_METHODS,
84 "explicit deref method call",
86 format!("&*{}", &snippet(cx, var_span, "..")),
87 Applicability::MachineApplicable,
92 let impls_deref_mut_trait = cx.tcx.lang_items().deref_mut_trait().map_or(false, |id| {
93 implements_trait(cx, cx.typeck_results().expr_ty(&call_expr), id, &[])
95 if impls_deref_mut_trait {
98 EXPLICIT_DEREF_METHODS,
100 "explicit deref_mut method call",
102 format!("&mut *{}", &snippet(cx, var_span, "..")),
103 Applicability::MachineApplicable,