src/tools/clippy/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, 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;
  14 use rustc_middle::ty;
  15 use rustc_semver::RustcVersion;
  16 use rustc_session::{declare_tool_lint, impl_lint_pass};
  17 use rustc_span::source_map::Spanned;
  18 use rustc_span::Span;
  19
  20 declare_clippy_lint! {
  21     /// ### What it does
  22     /// Suggests using `strip_{prefix,suffix}` over `str::{starts,ends}_with` and slicing using
  23     /// the pattern's length.
  24     ///
  25     /// ### Why is this bad?
  26     /// Using `str:strip_{prefix,suffix}` is safer and may have better performance as there is no
  27     /// slicing which may panic and the compiler does not need to insert this panic code. It is
  28     /// also sometimes more readable as it removes the need for duplicating or storing the pattern
  29     /// used by `str::{starts,ends}_with` and in the slicing.
  30     ///
  31     /// ### Example
  32     /// ```rust
  33     /// let s = "hello, world!";
  34     /// if s.starts_with("hello, ") {
  35     ///     assert_eq!(s["hello, ".len()..].to_uppercase(), "WORLD!");
  36     /// }
  37     /// ```
  38     /// Use instead:
  39     /// ```rust
  40     /// let s = "hello, world!";
  41     /// if let Some(end) = s.strip_prefix("hello, ") {
  42     ///     assert_eq!(end.to_uppercase(), "WORLD!");
  43     /// }
  44     /// ```
  45     #[clippy::version = "1.48.0"]
  46     pub MANUAL_STRIP,
  47     complexity,
  48     "suggests using `strip_{prefix,suffix}` over `str::{starts,ends}_with` and slicing"
  49 }
  50
  51 pub struct ManualStrip {
  52     msrv: Option<RustcVersion>,
  53 }
  54
  55 impl ManualStrip {
  56     #[must_use]
  57     pub fn new(msrv: Option<RustcVersion>) -> Self {
  58         Self { msrv }
  59     }
  60 }
  61
  62 impl_lint_pass!(ManualStrip => [MANUAL_STRIP]);
  63
  64 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
  65 enum StripKind {
  66     Prefix,
  67     Suffix,
  68 }
  69
  70 impl<'tcx> LateLintPass<'tcx> for ManualStrip {
  71     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  72         if !meets_msrv(self.msrv.as_ref(), &msrvs::STR_STRIP_PREFIX) {
  73             return;
  74         }
  75
  76         if_chain! {
  77             if let Some(higher::If { cond, then, .. }) = higher::If::hir(expr);
  78             if let ExprKind::MethodCall(_, _, [target_arg, pattern], _) = cond.kind;
  79             if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(cond.hir_id);
  80             if let ExprKind::Path(target_path) = &target_arg.kind;
  81             then {
  82                 let strip_kind = if match_def_path(cx, method_def_id, &paths::STR_STARTS_WITH) {
  83                     StripKind::Prefix
  84                 } else if match_def_path(cx, method_def_id, &paths::STR_ENDS_WITH) {
  85                     StripKind::Suffix
  86                 } else {
  87                     return;
  88                 };
  89                 let target_res = cx.qpath_res(target_path, target_arg.hir_id);
  90                 if target_res == Res::Err {
  91                     return;
  92                 };
  93
  94                 if_chain! {
  95                     if let Res::Local(hir_id) = target_res;
  96                     if let Some(used_mutably) = mutated_variables(then, cx);
  97                     if used_mutably.contains(&hir_id);
  98                     then {
  99                         return;
 100                     }
 101                 }
 102
 103                 let strippings = find_stripping(cx, strip_kind, target_res, pattern, then);
 104                 if !strippings.is_empty() {
 105
 106                     let kind_word = match strip_kind {
 107                         StripKind::Prefix => "prefix",
 108                         StripKind::Suffix => "suffix",
 109                     };
 110
 111                     let test_span = expr.span.until(then.span);
 112                     span_lint_and_then(cx, MANUAL_STRIP, strippings[0], &format!("stripping a {} manually", kind_word), |diag| {
 113                         diag.span_note(test_span, &format!("the {} was tested here", kind_word));
 114                         multispan_sugg(
 115                             diag,
 116                             &format!("try using the `strip_{}` method", kind_word),
 117                             vec![(test_span,
 118                                   format!("if let Some(<stripped>) = {}.strip_{}({}) ",
 119                                           snippet(cx, target_arg.span, ".."),
 120                                           kind_word,
 121                                           snippet(cx, pattern.span, "..")))]
 122                             .into_iter().chain(strippings.into_iter().map(|span| (span, "<stripped>".into()))),
 123                         );
 124                     });
 125                 }
 126             }
 127         }
 128     }
 129
 130     extract_msrv_attr!(LateContext);
 131 }
 132
 133 // Returns `Some(arg)` if `expr` matches `arg.len()` and `None` otherwise.
 134 fn len_arg<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
 135     if_chain! {
 136         if let ExprKind::MethodCall(_, _, [arg], _) = expr.kind;
 137         if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
 138         if match_def_path(cx, method_def_id, &paths::STR_LEN);
 139         then {
 140             Some(arg)
 141         } else {
 142             None
 143         }
 144     }
 145 }
 146
 147 // Returns the length of the `expr` if it's a constant string or char.
 148 fn constant_length(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<u128> {
 149     let (value, _) = constant(cx, cx.typeck_results(), expr)?;
 150     match value {
 151         Constant::Str(value) => Some(value.len() as u128),
 152         Constant::Char(value) => Some(value.len_utf8() as u128),
 153         _ => None,
 154     }
 155 }
 156
 157 // Tests if `expr` equals the length of the pattern.
 158 fn eq_pattern_length<'tcx>(cx: &LateContext<'tcx>, pattern: &Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
 159     if let ExprKind::Lit(Spanned {
 160         node: LitKind::Int(n, _),
 161         ..
 162     }) = expr.kind
 163     {
 164         constant_length(cx, pattern).map_or(false, |length| length == n)
 165     } else {
 166         len_arg(cx, expr).map_or(false, |arg| eq_expr_value(cx, pattern, arg))
 167     }
 168 }
 169
 170 // Tests if `expr` is a `&str`.
 171 fn is_ref_str(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
 172     match cx.typeck_results().expr_ty_adjusted(expr).kind() {
 173         ty::Ref(_, ty, _) => ty.is_str(),
 174         _ => false,
 175     }
 176 }
 177
 178 // Removes the outer `AddrOf` expression if needed.
 179 fn peel_ref<'a>(expr: &'a Expr<'_>) -> &'a Expr<'a> {
 180     if let ExprKind::AddrOf(BorrowKind::Ref, _, unref) = &expr.kind {
 181         unref
 182     } else {
 183         expr
 184     }
 185 }
 186
 187 // Find expressions where `target` is stripped using the length of `pattern`.
 188 // We'll suggest replacing these expressions with the result of the `strip_{prefix,suffix}`
 189 // method.
 190 fn find_stripping<'tcx>(
 191     cx: &LateContext<'tcx>,
 192     strip_kind: StripKind,
 193     target: Res,
 194     pattern: &'tcx Expr<'_>,
 195     expr: &'tcx Expr<'_>,
 196 ) -> Vec<Span> {
 197     struct StrippingFinder<'a, 'tcx> {
 198         cx: &'a LateContext<'tcx>,
 199         strip_kind: StripKind,
 200         target: Res,
 201         pattern: &'tcx Expr<'tcx>,
 202         results: Vec<Span>,
 203     }
 204
 205     impl<'a, 'tcx> Visitor<'tcx> for StrippingFinder<'a, 'tcx> {
 206         type Map = Map<'tcx>;
 207         fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
 208             NestedVisitorMap::None
 209         }
 210
 211         fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
 212             if_chain! {
 213                 if is_ref_str(self.cx, ex);
 214                 let unref = peel_ref(ex);
 215                 if let ExprKind::Index(indexed, index) = &unref.kind;
 216                 if let Some(higher::Range { start, end, .. }) = higher::Range::hir(index);
 217                 if let ExprKind::Path(path) = &indexed.kind;
 218                 if self.cx.qpath_res(path, ex.hir_id) == self.target;
 219                 then {
 220                     match (self.strip_kind, start, end) {
 221                         (StripKind::Prefix, Some(start), None) => {
 222                             if eq_pattern_length(self.cx, self.pattern, start) {
 223                                 self.results.push(ex.span);
 224                                 return;
 225                             }
 226                         },
 227                         (StripKind::Suffix, None, Some(end)) => {
 228                             if_chain! {
 229                                 if let ExprKind::Binary(Spanned { node: BinOpKind::Sub, .. }, left, right) = end.kind;
 230                                 if let Some(left_arg) = len_arg(self.cx, left);
 231                                 if let ExprKind::Path(left_path) = &left_arg.kind;
 232                                 if self.cx.qpath_res(left_path, left_arg.hir_id) == self.target;
 233                                 if eq_pattern_length(self.cx, self.pattern, right);
 234                                 then {
 235                                     self.results.push(ex.span);
 236                                     return;
 237                                 }
 238                             }
 239                         },
 240                         _ => {}
 241                     }
 242                 }
 243             }
 244
 245             walk_expr(self, ex);
 246         }
 247     }
 248
 249     let mut finder = StrippingFinder {
 250         cx,
 251         strip_kind,
 252         target,
 253         pattern,
 254         results: vec![],
 255     };
 256     walk_expr(&mut finder, expr);
 257     finder.results
 258 }