clippy_lints/src/manual_strip.rs

   1 use clippy_utils::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, msrvs, 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, Visitor};
  10 use rustc_hir::BinOpKind;
  11 use rustc_hir::{BorrowKind, Expr, ExprKind};
  12 use rustc_lint::{LateContext, LateLintPass};
  13 use rustc_middle::ty;
  14 use rustc_semver::RustcVersion;
  15 use rustc_session::{declare_tool_lint, impl_lint_pass};
  16 use rustc_span::source_map::Spanned;
  17 use rustc_span::Span;
  18
  19 declare_clippy_lint! {
  20     /// ### What it does
  21     /// Suggests using `strip_{prefix,suffix}` over `str::{starts,ends}_with` and slicing using
  22     /// the pattern's length.
  23     ///
  24     /// ### Why is this bad?
  25     /// Using `str:strip_{prefix,suffix}` is safer and may have better performance as there is no
  26     /// slicing which may panic and the compiler does not need to insert this panic code. It is
  27     /// also sometimes more readable as it removes the need for duplicating or storing the pattern
  28     /// used by `str::{starts,ends}_with` and in the slicing.
  29     ///
  30     /// ### Example
  31     /// ```rust
  32     /// let s = "hello, world!";
  33     /// if s.starts_with("hello, ") {
  34     ///     assert_eq!(s["hello, ".len()..].to_uppercase(), "WORLD!");
  35     /// }
  36     /// ```
  37     /// Use instead:
  38     /// ```rust
  39     /// let s = "hello, world!";
  40     /// if let Some(end) = s.strip_prefix("hello, ") {
  41     ///     assert_eq!(end.to_uppercase(), "WORLD!");
  42     /// }
  43     /// ```
  44     #[clippy::version = "1.48.0"]
  45     pub MANUAL_STRIP,
  46     complexity,
  47     "suggests using `strip_{prefix,suffix}` over `str::{starts,ends}_with` and slicing"
  48 }
  49
  50 pub struct ManualStrip {
  51     msrv: Option<RustcVersion>,
  52 }
  53
  54 impl ManualStrip {
  55     #[must_use]
  56     pub fn new(msrv: Option<RustcVersion>) -> Self {
  57         Self { msrv }
  58     }
  59 }
  60
  61 impl_lint_pass!(ManualStrip => [MANUAL_STRIP]);
  62
  63 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
  64 enum StripKind {
  65     Prefix,
  66     Suffix,
  67 }
  68
  69 impl<'tcx> LateLintPass<'tcx> for ManualStrip {
  70     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  71         if !meets_msrv(self.msrv, msrvs::STR_STRIP_PREFIX) {
  72             return;
  73         }
  74
  75         if_chain! {
  76             if let Some(higher::If { cond, then, .. }) = higher::If::hir(expr);
  77             if let ExprKind::MethodCall(_, [target_arg, pattern], _) = cond.kind;
  78             if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(cond.hir_id);
  79             if let ExprKind::Path(target_path) = &target_arg.kind;
  80             then {
  81                 let strip_kind = if match_def_path(cx, method_def_id, &paths::STR_STARTS_WITH) {
  82                     StripKind::Prefix
  83                 } else if match_def_path(cx, method_def_id, &paths::STR_ENDS_WITH) {
  84                     StripKind::Suffix
  85                 } else {
  86                     return;
  87                 };
  88                 let target_res = cx.qpath_res(target_path, target_arg.hir_id);
  89                 if target_res == Res::Err {
  90                     return;
  91                 };
  92
  93                 if_chain! {
  94                     if let Res::Local(hir_id) = target_res;
  95                     if let Some(used_mutably) = mutated_variables(then, cx);
  96                     if used_mutably.contains(&hir_id);
  97                     then {
  98                         return;
  99                     }
 100                 }
 101
 102                 let strippings = find_stripping(cx, strip_kind, target_res, pattern, then);
 103                 if !strippings.is_empty() {
 104
 105                     let kind_word = match strip_kind {
 106                         StripKind::Prefix => "prefix",
 107                         StripKind::Suffix => "suffix",
 108                     };
 109
 110                     let test_span = expr.span.until(then.span);
 111                     span_lint_and_then(cx, MANUAL_STRIP, strippings[0], &format!("stripping a {} manually", kind_word), |diag| {
 112                         diag.span_note(test_span, &format!("the {} was tested here", kind_word));
 113                         multispan_sugg(
 114                             diag,
 115                             &format!("try using the `strip_{}` method", kind_word),
 116                             vec![(test_span,
 117                                   format!("if let Some(<stripped>) = {}.strip_{}({}) ",
 118                                           snippet(cx, target_arg.span, ".."),
 119                                           kind_word,
 120                                           snippet(cx, pattern.span, "..")))]
 121                             .into_iter().chain(strippings.into_iter().map(|span| (span, "<stripped>".into()))),
 122                         );
 123                     });
 124                 }
 125             }
 126         }
 127     }
 128
 129     extract_msrv_attr!(LateContext);
 130 }
 131
 132 // Returns `Some(arg)` if `expr` matches `arg.len()` and `None` otherwise.
 133 fn len_arg<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
 134     if_chain! {
 135         if let ExprKind::MethodCall(_, [arg], _) = expr.kind;
 136         if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
 137         if match_def_path(cx, method_def_id, &paths::STR_LEN);
 138         then {
 139             Some(arg)
 140         } else {
 141             None
 142         }
 143     }
 144 }
 145
 146 // Returns the length of the `expr` if it's a constant string or char.
 147 fn constant_length(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<u128> {
 148     let (value, _) = constant(cx, cx.typeck_results(), expr)?;
 149     match value {
 150         Constant::Str(value) => Some(value.len() as u128),
 151         Constant::Char(value) => Some(value.len_utf8() as u128),
 152         _ => None,
 153     }
 154 }
 155
 156 // Tests if `expr` equals the length of the pattern.
 157 fn eq_pattern_length<'tcx>(cx: &LateContext<'tcx>, pattern: &Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
 158     if let ExprKind::Lit(Spanned {
 159         node: LitKind::Int(n, _),
 160         ..
 161     }) = expr.kind
 162     {
 163         constant_length(cx, pattern).map_or(false, |length| length == n)
 164     } else {
 165         len_arg(cx, expr).map_or(false, |arg| eq_expr_value(cx, pattern, arg))
 166     }
 167 }
 168
 169 // Tests if `expr` is a `&str`.
 170 fn is_ref_str(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
 171     match cx.typeck_results().expr_ty_adjusted(expr).kind() {
 172         ty::Ref(_, ty, _) => ty.is_str(),
 173         _ => false,
 174     }
 175 }
 176
 177 // Removes the outer `AddrOf` expression if needed.
 178 fn peel_ref<'a>(expr: &'a Expr<'_>) -> &'a Expr<'a> {
 179     if let ExprKind::AddrOf(BorrowKind::Ref, _, unref) = &expr.kind {
 180         unref
 181     } else {
 182         expr
 183     }
 184 }
 185
 186 // Find expressions where `target` is stripped using the length of `pattern`.
 187 // We'll suggest replacing these expressions with the result of the `strip_{prefix,suffix}`
 188 // method.
 189 fn find_stripping<'tcx>(
 190     cx: &LateContext<'tcx>,
 191     strip_kind: StripKind,
 192     target: Res,
 193     pattern: &'tcx Expr<'_>,
 194     expr: &'tcx Expr<'_>,
 195 ) -> Vec<Span> {
 196     struct StrippingFinder<'a, 'tcx> {
 197         cx: &'a LateContext<'tcx>,
 198         strip_kind: StripKind,
 199         target: Res,
 200         pattern: &'tcx Expr<'tcx>,
 201         results: Vec<Span>,
 202     }
 203
 204     impl<'a, 'tcx> Visitor<'tcx> for StrippingFinder<'a, 'tcx> {
 205         fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
 206             if_chain! {
 207                 if is_ref_str(self.cx, ex);
 208                 let unref = peel_ref(ex);
 209                 if let ExprKind::Index(indexed, index) = &unref.kind;
 210                 if let Some(higher::Range { start, end, .. }) = higher::Range::hir(index);
 211                 if let ExprKind::Path(path) = &indexed.kind;
 212                 if self.cx.qpath_res(path, ex.hir_id) == self.target;
 213                 then {
 214                     match (self.strip_kind, start, end) {
 215                         (StripKind::Prefix, Some(start), None) => {
 216                             if eq_pattern_length(self.cx, self.pattern, start) {
 217                                 self.results.push(ex.span);
 218                                 return;
 219                             }
 220                         },
 221                         (StripKind::Suffix, None, Some(end)) => {
 222                             if_chain! {
 223                                 if let ExprKind::Binary(Spanned { node: BinOpKind::Sub, .. }, left, right) = end.kind;
 224                                 if let Some(left_arg) = len_arg(self.cx, left);
 225                                 if let ExprKind::Path(left_path) = &left_arg.kind;
 226                                 if self.cx.qpath_res(left_path, left_arg.hir_id) == self.target;
 227                                 if eq_pattern_length(self.cx, self.pattern, right);
 228                                 then {
 229                                     self.results.push(ex.span);
 230                                     return;
 231                                 }
 232                             }
 233                         },
 234                         _ => {}
 235                     }
 236                 }
 237             }
 238
 239             walk_expr(self, ex);
 240         }
 241     }
 242
 243     let mut finder = StrippingFinder {
 244         cx,
 245         strip_kind,
 246         target,
 247         pattern,
 248         results: vec![],
 249     };
 250     walk_expr(&mut finder, expr);
 251     finder.results
 252 }