clippy_lints/src/ranges.rs

   1 use if_chain::if_chain;
   2 use rustc::hir::*;
   3 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   4 use rustc::{declare_lint_pass, declare_tool_lint};
   5 use rustc_errors::Applicability;
   6 use syntax::ast::RangeLimits;
   7 use syntax::source_map::Spanned;
   8
   9 use crate::utils::sugg::Sugg;
  10 use crate::utils::{get_trait_def_id, higher, implements_trait, SpanlessEq};
  11 use crate::utils::{is_integer_literal, paths, snippet, snippet_opt, span_lint, span_lint_and_then};
  12
  13 declare_clippy_lint! {
  14     /// **What it does:** Checks for calling `.step_by(0)` on iterators,
  15     /// which never terminates.
  16     ///
  17     /// **Why is this bad?** This very much looks like an oversight, since with
  18     /// `loop { .. }` there is an obvious better way to endlessly loop.
  19     ///
  20     /// **Known problems:** None.
  21     ///
  22     /// **Example:**
  23     /// ```ignore
  24     /// for x in (5..5).step_by(0) {
  25     ///     ..
  26     /// }
  27     /// ```
  28     pub ITERATOR_STEP_BY_ZERO,
  29     correctness,
  30     "using `Iterator::step_by(0)`, which produces an infinite iterator"
  31 }
  32
  33 declare_clippy_lint! {
  34     /// **What it does:** Checks for zipping a collection with the range of
  35     /// `0.._.len()`.
  36     ///
  37     /// **Why is this bad?** The code is better expressed with `.enumerate()`.
  38     ///
  39     /// **Known problems:** None.
  40     ///
  41     /// **Example:**
  42     /// ```rust
  43     /// # let x = vec![1];
  44     /// x.iter().zip(0..x.len());
  45     /// ```
  46     pub RANGE_ZIP_WITH_LEN,
  47     complexity,
  48     "zipping iterator with a range when `enumerate()` would do"
  49 }
  50
  51 declare_clippy_lint! {
  52     /// **What it does:** Checks for exclusive ranges where 1 is added to the
  53     /// upper bound, e.g., `x..(y+1)`.
  54     ///
  55     /// **Why is this bad?** The code is more readable with an inclusive range
  56     /// like `x..=y`.
  57     ///
  58     /// **Known problems:** Will add unnecessary pair of parentheses when the
  59     /// expression is not wrapped in a pair but starts with a opening parenthesis
  60     /// and ends with a closing one.
  61     /// I.e., `let _ = (f()+1)..(f()+1)` results in `let _ = ((f()+1)..=f())`.
  62     ///
  63     /// **Example:**
  64     /// ```rust,ignore
  65     /// for x..(y+1) { .. }
  66     /// ```
  67     pub RANGE_PLUS_ONE,
  68     complexity,
  69     "`x..(y+1)` reads better as `x..=y`"
  70 }
  71
  72 declare_clippy_lint! {
  73     /// **What it does:** Checks for inclusive ranges where 1 is subtracted from
  74     /// the upper bound, e.g., `x..=(y-1)`.
  75     ///
  76     /// **Why is this bad?** The code is more readable with an exclusive range
  77     /// like `x..y`.
  78     ///
  79     /// **Known problems:** None.
  80     ///
  81     /// **Example:**
  82     /// ```rust,ignore
  83     /// for x..=(y-1) { .. }
  84     /// ```
  85     pub RANGE_MINUS_ONE,
  86     complexity,
  87     "`x..=(y-1)` reads better as `x..y`"
  88 }
  89
  90 declare_lint_pass!(Ranges => [
  91     ITERATOR_STEP_BY_ZERO,
  92     RANGE_ZIP_WITH_LEN,
  93     RANGE_PLUS_ONE,
  94     RANGE_MINUS_ONE
  95 ]);
  96
  97 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Ranges {
  98     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  99         if let ExprKind::MethodCall(ref path, _, ref args) = expr.node {
 100             let name = path.ident.as_str();
 101
 102             // Range with step_by(0).
 103             if name == "step_by" && args.len() == 2 && has_step_by(cx, &args[0]) {
 104                 use crate::consts::{constant, Constant};
 105                 if let Some((Constant::Int(0), _)) = constant(cx, cx.tables, &args[1]) {
 106                     span_lint(
 107                         cx,
 108                         ITERATOR_STEP_BY_ZERO,
 109                         expr.span,
 110                         "Iterator::step_by(0) will panic at runtime",
 111                     );
 112                 }
 113             } else if name == "zip" && args.len() == 2 {
 114                 let iter = &args[0].node;
 115                 let zip_arg = &args[1];
 116                 if_chain! {
 117                     // `.iter()` call
 118                     if let ExprKind::MethodCall(ref iter_path, _, ref iter_args ) = *iter;
 119                     if iter_path.ident.name == sym!(iter);
 120                     // range expression in `.zip()` call: `0..x.len()`
 121                     if let Some(higher::Range { start: Some(start), end: Some(end), .. }) = higher::range(cx, zip_arg);
 122                     if is_integer_literal(start, 0);
 123                     // `.len()` call
 124                     if let ExprKind::MethodCall(ref len_path, _, ref len_args) = end.node;
 125                     if len_path.ident.name == sym!(len) && len_args.len() == 1;
 126                     // `.iter()` and `.len()` called on same `Path`
 127                     if let ExprKind::Path(QPath::Resolved(_, ref iter_path)) = iter_args[0].node;
 128                     if let ExprKind::Path(QPath::Resolved(_, ref len_path)) = len_args[0].node;
 129                     if SpanlessEq::new(cx).eq_path_segments(&iter_path.segments, &len_path.segments);
 130                      then {
 131                          span_lint(cx,
 132                                    RANGE_ZIP_WITH_LEN,
 133                                    expr.span,
 134                                    &format!("It is more idiomatic to use {}.iter().enumerate()",
 135                                             snippet(cx, iter_args[0].span, "_")));
 136                     }
 137                 }
 138             }
 139         }
 140
 141         // exclusive range plus one: `x..(y+1)`
 142         if_chain! {
 143             if let Some(higher::Range {
 144                 start,
 145                 end: Some(end),
 146                 limits: RangeLimits::HalfOpen
 147             }) = higher::range(cx, expr);
 148             if let Some(y) = y_plus_one(end);
 149             then {
 150                 let span = if expr.span.from_expansion() {
 151                     expr.span
 152                         .ctxt()
 153                         .outer_expn_data()
 154                         .call_site
 155                 } else {
 156                     expr.span
 157                 };
 158                 span_lint_and_then(
 159                     cx,
 160                     RANGE_PLUS_ONE,
 161                     span,
 162                     "an inclusive range would be more readable",
 163                     |db| {
 164                         let start = start.map_or(String::new(), |x| Sugg::hir(cx, x, "x").to_string());
 165                         let end = Sugg::hir(cx, y, "y");
 166                         if let Some(is_wrapped) = &snippet_opt(cx, span) {
 167                             if is_wrapped.starts_with('(') && is_wrapped.ends_with(')') {
 168                                 db.span_suggestion(
 169                                     span,
 170                                     "use",
 171                                     format!("({}..={})", start, end),
 172                                     Applicability::MaybeIncorrect,
 173                                 );
 174                             } else {
 175                                 db.span_suggestion(
 176                                     span,
 177                                     "use",
 178                                     format!("{}..={}", start, end),
 179                                     Applicability::MachineApplicable, // snippet
 180                                 );
 181                             }
 182                         }
 183                     },
 184                 );
 185             }
 186         }
 187
 188         // inclusive range minus one: `x..=(y-1)`
 189         if_chain! {
 190             if let Some(higher::Range { start, end: Some(end), limits: RangeLimits::Closed }) = higher::range(cx, expr);
 191             if let Some(y) = y_minus_one(end);
 192             then {
 193                 span_lint_and_then(
 194                     cx,
 195                     RANGE_MINUS_ONE,
 196                     expr.span,
 197                     "an exclusive range would be more readable",
 198                     |db| {
 199                         let start = start.map_or(String::new(), |x| Sugg::hir(cx, x, "x").to_string());
 200                         let end = Sugg::hir(cx, y, "y");
 201                         db.span_suggestion(
 202                             expr.span,
 203                             "use",
 204                             format!("{}..{}", start, end),
 205                             Applicability::MachineApplicable, // snippet
 206                         );
 207                     },
 208                 );
 209             }
 210         }
 211     }
 212 }
 213
 214 fn has_step_by(cx: &LateContext<'_, '_>, expr: &Expr) -> bool {
 215     // No need for `walk_ptrs_ty` here because `step_by` moves `self`, so it
 216     // can't be called on a borrowed range.
 217     let ty = cx.tables.expr_ty_adjusted(expr);
 218
 219     get_trait_def_id(cx, &paths::ITERATOR).map_or(false, |iterator_trait| implements_trait(cx, ty, iterator_trait, &[]))
 220 }
 221
 222 fn y_plus_one(expr: &Expr) -> Option<&Expr> {
 223     match expr.node {
 224         ExprKind::Binary(
 225             Spanned {
 226                 node: BinOpKind::Add, ..
 227             },
 228             ref lhs,
 229             ref rhs,
 230         ) => {
 231             if is_integer_literal(lhs, 1) {
 232                 Some(rhs)
 233             } else if is_integer_literal(rhs, 1) {
 234                 Some(lhs)
 235             } else {
 236                 None
 237             }
 238         },
 239         _ => None,
 240     }
 241 }
 242
 243 fn y_minus_one(expr: &Expr) -> Option<&Expr> {
 244     match expr.node {
 245         ExprKind::Binary(
 246             Spanned {
 247                 node: BinOpKind::Sub, ..
 248             },
 249             ref lhs,
 250             ref rhs,
 251         ) if is_integer_literal(rhs, 1) => Some(lhs),
 252         _ => None,
 253     }
 254 }