1 use crate::consts::{constant, Constant};
2 use crate::utils::usage::mutated_variables;
4 eq_expr_value, get_inner_attr, higher, match_def_path, meets_msrv, multispan_sugg, paths, qpath_res, snippet,
8 use if_chain::if_chain;
9 use rustc_ast::ast::{Attribute, LitKind};
10 use rustc_hir::def::Res;
11 use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
12 use rustc_hir::BinOpKind;
13 use rustc_hir::{BorrowKind, Expr, ExprKind};
14 use rustc_lint::{LateContext, LateLintPass, LintContext};
15 use rustc_middle::hir::map::Map;
17 use rustc_session::{declare_tool_lint, impl_lint_pass};
18 use rustc_span::source_map::Spanned;
20 use semver::{Version, VersionReq};
22 const MANUAL_STRIP_MSRV: Version = Version {
30 declare_clippy_lint! {
32 /// Suggests using `strip_{prefix,suffix}` over `str::{starts,ends}_with` and slicing using
33 /// the pattern's length.
35 /// **Why is this bad?**
36 /// Using `str:strip_{prefix,suffix}` is safer and may have better performance as there is no
37 /// slicing which may panic and the compiler does not need to insert this panic code. It is
38 /// also sometimes more readable as it removes the need for duplicating or storing the pattern
39 /// used by `str::{starts,ends}_with` and in the slicing.
41 /// **Known problems:**
47 /// let s = "hello, world!";
48 /// if s.starts_with("hello, ") {
49 /// assert_eq!(s["hello, ".len()..].to_uppercase(), "WORLD!");
54 /// let s = "hello, world!";
55 /// if let Some(end) = s.strip_prefix("hello, ") {
56 /// assert_eq!(end.to_uppercase(), "WORLD!");
61 "suggests using `strip_{prefix,suffix}` over `str::{starts,ends}_with` and slicing"
64 pub struct ManualStrip {
65 msrv: Option<VersionReq>,
70 pub fn new(msrv: Option<VersionReq>) -> Self {
75 impl_lint_pass!(ManualStrip => [MANUAL_STRIP]);
77 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
83 impl<'tcx> LateLintPass<'tcx> for ManualStrip {
84 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
85 if !meets_msrv(self.msrv.as_ref(), &MANUAL_STRIP_MSRV) {
90 if let Some((cond, then, _)) = higher::if_block(&expr);
91 if let ExprKind::MethodCall(_, _, [target_arg, pattern], _) = cond.kind;
92 if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(cond.hir_id);
93 if let ExprKind::Path(target_path) = &target_arg.kind;
95 let strip_kind = if match_def_path(cx, method_def_id, &paths::STR_STARTS_WITH) {
97 } else if match_def_path(cx, method_def_id, &paths::STR_ENDS_WITH) {
102 let target_res = qpath_res(cx, &target_path, target_arg.hir_id);
103 if target_res == Res::Err {
108 if let Res::Local(hir_id) = target_res;
109 if let Some(used_mutably) = mutated_variables(then, cx);
110 if used_mutably.contains(&hir_id);
116 let strippings = find_stripping(cx, strip_kind, target_res, pattern, then);
117 if !strippings.is_empty() {
119 let kind_word = match strip_kind {
120 StripKind::Prefix => "prefix",
121 StripKind::Suffix => "suffix",
124 let test_span = expr.span.until(then.span);
125 span_lint_and_then(cx, MANUAL_STRIP, strippings[0], &format!("stripping a {} manually", kind_word), |diag| {
126 diag.span_note(test_span, &format!("the {} was tested here", kind_word));
129 &format!("try using the `strip_{}` method", kind_word),
131 format!("if let Some(<stripped>) = {}.strip_{}({}) ",
132 snippet(cx, target_arg.span, ".."),
134 snippet(cx, pattern.span, "..")))]
135 .into_iter().chain(strippings.into_iter().map(|span| (span, "<stripped>".into()))),
143 extract_msrv_attr!(LateContext);
146 // Returns `Some(arg)` if `expr` matches `arg.len()` and `None` otherwise.
147 fn len_arg<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
149 if let ExprKind::MethodCall(_, _, [arg], _) = expr.kind;
150 if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
151 if match_def_path(cx, method_def_id, &paths::STR_LEN);
160 // Returns the length of the `expr` if it's a constant string or char.
161 fn constant_length(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<u128> {
162 let (value, _) = constant(cx, cx.typeck_results(), expr)?;
164 Constant::Str(value) => Some(value.len() as u128),
165 Constant::Char(value) => Some(value.len_utf8() as u128),
170 // Tests if `expr` equals the length of the pattern.
171 fn eq_pattern_length<'tcx>(cx: &LateContext<'tcx>, pattern: &Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
172 if let ExprKind::Lit(Spanned {
173 node: LitKind::Int(n, _),
177 constant_length(cx, pattern).map_or(false, |length| length == n)
179 len_arg(cx, expr).map_or(false, |arg| eq_expr_value(cx, pattern, arg))
183 // Tests if `expr` is a `&str`.
184 fn is_ref_str(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
185 match cx.typeck_results().expr_ty_adjusted(&expr).kind() {
186 ty::Ref(_, ty, _) => ty.is_str(),
191 // Removes the outer `AddrOf` expression if needed.
192 fn peel_ref<'a>(expr: &'a Expr<'_>) -> &'a Expr<'a> {
193 if let ExprKind::AddrOf(BorrowKind::Ref, _, unref) = &expr.kind {
200 // Find expressions where `target` is stripped using the length of `pattern`.
201 // We'll suggest replacing these expressions with the result of the `strip_{prefix,suffix}`
203 fn find_stripping<'tcx>(
204 cx: &LateContext<'tcx>,
205 strip_kind: StripKind,
207 pattern: &'tcx Expr<'_>,
208 expr: &'tcx Expr<'_>,
210 struct StrippingFinder<'a, 'tcx> {
211 cx: &'a LateContext<'tcx>,
212 strip_kind: StripKind,
214 pattern: &'tcx Expr<'tcx>,
218 impl<'a, 'tcx> Visitor<'tcx> for StrippingFinder<'a, 'tcx> {
219 type Map = Map<'tcx>;
220 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
221 NestedVisitorMap::None
224 fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
226 if is_ref_str(self.cx, ex);
227 let unref = peel_ref(ex);
228 if let ExprKind::Index(indexed, index) = &unref.kind;
229 if let Some(range) = higher::range(index);
230 if let higher::Range { start, end, .. } = range;
231 if let ExprKind::Path(path) = &indexed.kind;
232 if qpath_res(self.cx, path, ex.hir_id) == self.target;
234 match (self.strip_kind, start, end) {
235 (StripKind::Prefix, Some(start), None) => {
236 if eq_pattern_length(self.cx, self.pattern, start) {
237 self.results.push(ex.span);
241 (StripKind::Suffix, None, Some(end)) => {
243 if let ExprKind::Binary(Spanned { node: BinOpKind::Sub, .. }, left, right) = end.kind;
244 if let Some(left_arg) = len_arg(self.cx, left);
245 if let ExprKind::Path(left_path) = &left_arg.kind;
246 if qpath_res(self.cx, left_path, left_arg.hir_id) == self.target;
247 if eq_pattern_length(self.cx, self.pattern, right);
249 self.results.push(ex.span);
263 let mut finder = StrippingFinder {
270 walk_expr(&mut finder, expr);