1 use crate::consts::{constant, Constant};
2 use clippy_utils::diagnostics::{multispan_sugg, span_lint_and_then};
3 use clippy_utils::source::snippet;
4 use clippy_utils::usage::mutated_variables;
5 use clippy_utils::{eq_expr_value, higher, match_def_path, meets_msrv, paths};
6 use if_chain::if_chain;
7 use rustc_ast::ast::LitKind;
8 use rustc_hir::def::Res;
9 use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
10 use rustc_hir::BinOpKind;
11 use rustc_hir::{BorrowKind, Expr, ExprKind};
12 use rustc_lint::{LateContext, LateLintPass, LintContext};
13 use rustc_middle::hir::map::Map;
15 use rustc_semver::RustcVersion;
16 use rustc_session::{declare_tool_lint, impl_lint_pass};
17 use rustc_span::source_map::Spanned;
20 const MANUAL_STRIP_MSRV: RustcVersion = RustcVersion::new(1, 45, 0);
22 declare_clippy_lint! {
24 /// Suggests using `strip_{prefix,suffix}` over `str::{starts,ends}_with` and slicing using
25 /// the pattern's length.
27 /// **Why is this bad?**
28 /// Using `str:strip_{prefix,suffix}` is safer and may have better performance as there is no
29 /// slicing which may panic and the compiler does not need to insert this panic code. It is
30 /// also sometimes more readable as it removes the need for duplicating or storing the pattern
31 /// used by `str::{starts,ends}_with` and in the slicing.
33 /// **Known problems:**
39 /// let s = "hello, world!";
40 /// if s.starts_with("hello, ") {
41 /// assert_eq!(s["hello, ".len()..].to_uppercase(), "WORLD!");
46 /// let s = "hello, world!";
47 /// if let Some(end) = s.strip_prefix("hello, ") {
48 /// assert_eq!(end.to_uppercase(), "WORLD!");
53 "suggests using `strip_{prefix,suffix}` over `str::{starts,ends}_with` and slicing"
56 pub struct ManualStrip {
57 msrv: Option<RustcVersion>,
62 pub fn new(msrv: Option<RustcVersion>) -> Self {
67 impl_lint_pass!(ManualStrip => [MANUAL_STRIP]);
69 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
75 impl<'tcx> LateLintPass<'tcx> for ManualStrip {
76 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
77 if !meets_msrv(self.msrv.as_ref(), &MANUAL_STRIP_MSRV) {
82 if let ExprKind::If(cond, then, _) = &expr.kind;
83 if let ExprKind::MethodCall(_, _, [target_arg, pattern], _) = cond.kind;
84 if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(cond.hir_id);
85 if let ExprKind::Path(target_path) = &target_arg.kind;
87 let strip_kind = if match_def_path(cx, method_def_id, &paths::STR_STARTS_WITH) {
89 } else if match_def_path(cx, method_def_id, &paths::STR_ENDS_WITH) {
94 let target_res = cx.qpath_res(target_path, target_arg.hir_id);
95 if target_res == Res::Err {
100 if let Res::Local(hir_id) = target_res;
101 if let Some(used_mutably) = mutated_variables(then, cx);
102 if used_mutably.contains(&hir_id);
108 let strippings = find_stripping(cx, strip_kind, target_res, pattern, then);
109 if !strippings.is_empty() {
111 let kind_word = match strip_kind {
112 StripKind::Prefix => "prefix",
113 StripKind::Suffix => "suffix",
116 let test_span = expr.span.until(then.span);
117 span_lint_and_then(cx, MANUAL_STRIP, strippings[0], &format!("stripping a {} manually", kind_word), |diag| {
118 diag.span_note(test_span, &format!("the {} was tested here", kind_word));
121 &format!("try using the `strip_{}` method", kind_word),
123 format!("if let Some(<stripped>) = {}.strip_{}({}) ",
124 snippet(cx, target_arg.span, ".."),
126 snippet(cx, pattern.span, "..")))]
127 .into_iter().chain(strippings.into_iter().map(|span| (span, "<stripped>".into()))),
135 extract_msrv_attr!(LateContext);
138 // Returns `Some(arg)` if `expr` matches `arg.len()` and `None` otherwise.
139 fn len_arg<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
141 if let ExprKind::MethodCall(_, _, [arg], _) = expr.kind;
142 if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
143 if match_def_path(cx, method_def_id, &paths::STR_LEN);
152 // Returns the length of the `expr` if it's a constant string or char.
153 fn constant_length(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<u128> {
154 let (value, _) = constant(cx, cx.typeck_results(), expr)?;
156 Constant::Str(value) => Some(value.len() as u128),
157 Constant::Char(value) => Some(value.len_utf8() as u128),
162 // Tests if `expr` equals the length of the pattern.
163 fn eq_pattern_length<'tcx>(cx: &LateContext<'tcx>, pattern: &Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
164 if let ExprKind::Lit(Spanned {
165 node: LitKind::Int(n, _),
169 constant_length(cx, pattern).map_or(false, |length| length == n)
171 len_arg(cx, expr).map_or(false, |arg| eq_expr_value(cx, pattern, arg))
175 // Tests if `expr` is a `&str`.
176 fn is_ref_str(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
177 match cx.typeck_results().expr_ty_adjusted(expr).kind() {
178 ty::Ref(_, ty, _) => ty.is_str(),
183 // Removes the outer `AddrOf` expression if needed.
184 fn peel_ref<'a>(expr: &'a Expr<'_>) -> &'a Expr<'a> {
185 if let ExprKind::AddrOf(BorrowKind::Ref, _, unref) = &expr.kind {
192 // Find expressions where `target` is stripped using the length of `pattern`.
193 // We'll suggest replacing these expressions with the result of the `strip_{prefix,suffix}`
195 fn find_stripping<'tcx>(
196 cx: &LateContext<'tcx>,
197 strip_kind: StripKind,
199 pattern: &'tcx Expr<'_>,
200 expr: &'tcx Expr<'_>,
202 struct StrippingFinder<'a, 'tcx> {
203 cx: &'a LateContext<'tcx>,
204 strip_kind: StripKind,
206 pattern: &'tcx Expr<'tcx>,
210 impl<'a, 'tcx> Visitor<'tcx> for StrippingFinder<'a, 'tcx> {
211 type Map = Map<'tcx>;
212 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
213 NestedVisitorMap::None
216 fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
218 if is_ref_str(self.cx, ex);
219 let unref = peel_ref(ex);
220 if let ExprKind::Index(indexed, index) = &unref.kind;
221 if let Some(higher::Range { start, end, .. }) = higher::range(index);
222 if let ExprKind::Path(path) = &indexed.kind;
223 if self.cx.qpath_res(path, ex.hir_id) == self.target;
225 match (self.strip_kind, start, end) {
226 (StripKind::Prefix, Some(start), None) => {
227 if eq_pattern_length(self.cx, self.pattern, start) {
228 self.results.push(ex.span);
232 (StripKind::Suffix, None, Some(end)) => {
234 if let ExprKind::Binary(Spanned { node: BinOpKind::Sub, .. }, left, right) = end.kind;
235 if let Some(left_arg) = len_arg(self.cx, left);
236 if let ExprKind::Path(left_path) = &left_arg.kind;
237 if self.cx.qpath_res(left_path, left_arg.hir_id) == self.target;
238 if eq_pattern_length(self.cx, self.pattern, right);
240 self.results.push(ex.span);
254 let mut finder = StrippingFinder {
261 walk_expr(&mut finder, expr);