clippy_lints/src/ranges.rs

   1 use crate::utils::sugg::Sugg;
   2 use crate::utils::{get_trait_def_id, higher, implements_trait, SpanlessEq};
   3 use crate::utils::{is_integer_literal, paths, snippet, snippet_opt, span_lint, span_lint_and_then};
   4 use if_chain::if_chain;
   5 use rustc::hir::*;
   6 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   7 use rustc::{declare_tool_lint, lint_array};
   8 use rustc_errors::Applicability;
   9 use syntax::ast::RangeLimits;
  10 use syntax::source_map::Spanned;
  11
  12 /// **What it does:** Checks for calling `.step_by(0)` on iterators,
  13 /// which never terminates.
  14 ///
  15 /// **Why is this bad?** This very much looks like an oversight, since with
  16 /// `loop { .. }` there is an obvious better way to endlessly loop.
  17 ///
  18 /// **Known problems:** None.
  19 ///
  20 /// **Example:**
  21 /// ```rust
  22 /// for x in (5..5).step_by(0) {
  23 ///     ..
  24 /// }
  25 /// ```
  26 declare_clippy_lint! {
  27     pub ITERATOR_STEP_BY_ZERO,
  28     correctness,
  29     "using `Iterator::step_by(0)`, which produces an infinite iterator"
  30 }
  31
  32 /// **What it does:** Checks for zipping a collection with the range of
  33 /// `0.._.len()`.
  34 ///
  35 /// **Why is this bad?** The code is better expressed with `.enumerate()`.
  36 ///
  37 /// **Known problems:** None.
  38 ///
  39 /// **Example:**
  40 /// ```rust
  41 /// x.iter().zip(0..x.len())
  42 /// ```
  43 declare_clippy_lint! {
  44     pub RANGE_ZIP_WITH_LEN,
  45     complexity,
  46     "zipping iterator with a range when `enumerate()` would do"
  47 }
  48
  49 /// **What it does:** Checks for exclusive ranges where 1 is added to the
  50 /// upper bound, e.g. `x..(y+1)`.
  51 ///
  52 /// **Why is this bad?** The code is more readable with an inclusive range
  53 /// like `x..=y`.
  54 ///
  55 /// **Known problems:** Will add unnecessary pair of parentheses when the
  56 /// expression is not wrapped in a pair but starts with a opening parenthesis
  57 /// and ends with a closing one.
  58 /// I.e: `let _ = (f()+1)..(f()+1)` results in `let _ = ((f()+1)..=f())`.
  59 ///
  60 /// **Example:**
  61 /// ```rust
  62 /// for x..(y+1) { .. }
  63 /// ```
  64 declare_clippy_lint! {
  65     pub RANGE_PLUS_ONE,
  66     complexity,
  67     "`x..(y+1)` reads better as `x..=y`"
  68 }
  69
  70 /// **What it does:** Checks for inclusive ranges where 1 is subtracted from
  71 /// the upper bound, e.g. `x..=(y-1)`.
  72 ///
  73 /// **Why is this bad?** The code is more readable with an exclusive range
  74 /// like `x..y`.
  75 ///
  76 /// **Known problems:** None.
  77 ///
  78 /// **Example:**
  79 /// ```rust
  80 /// for x..=(y-1) { .. }
  81 /// ```
  82 declare_clippy_lint! {
  83     pub RANGE_MINUS_ONE,
  84     complexity,
  85     "`x..=(y-1)` reads better as `x..y`"
  86 }
  87
  88 #[derive(Copy, Clone)]
  89 pub struct Pass;
  90
  91 impl LintPass for Pass {
  92     fn get_lints(&self) -> LintArray {
  93         lint_array!(
  94             ITERATOR_STEP_BY_ZERO,
  95             RANGE_ZIP_WITH_LEN,
  96             RANGE_PLUS_ONE,
  97             RANGE_MINUS_ONE
  98         )
  99     }
 100
 101     fn name(&self) -> &'static str {
 102         "Ranges"
 103     }
 104 }
 105
 106 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
 107     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
 108         if let ExprKind::MethodCall(ref path, _, ref args) = expr.node {
 109             let name = path.ident.as_str();
 110
 111             // Range with step_by(0).
 112             if name == "step_by" && args.len() == 2 && has_step_by(cx, &args[0]) {
 113                 use crate::consts::{constant, Constant};
 114                 if let Some((Constant::Int(0), _)) = constant(cx, cx.tables, &args[1]) {
 115                     span_lint(
 116                         cx,
 117                         ITERATOR_STEP_BY_ZERO,
 118                         expr.span,
 119                         "Iterator::step_by(0) will panic at runtime",
 120                     );
 121                 }
 122             } else if name == "zip" && args.len() == 2 {
 123                 let iter = &args[0].node;
 124                 let zip_arg = &args[1];
 125                 if_chain! {
 126                     // .iter() call
 127                     if let ExprKind::MethodCall(ref iter_path, _, ref iter_args ) = *iter;
 128                     if iter_path.ident.name == "iter";
 129                     // range expression in .zip() call: 0..x.len()
 130                     if let Some(higher::Range { start: Some(start), end: Some(end), .. }) = higher::range(cx, zip_arg);
 131                     if is_integer_literal(start, 0);
 132                     // .len() call
 133                     if let ExprKind::MethodCall(ref len_path, _, ref len_args) = end.node;
 134                     if len_path.ident.name == "len" && len_args.len() == 1;
 135                     // .iter() and .len() called on same Path
 136                     if let ExprKind::Path(QPath::Resolved(_, ref iter_path)) = iter_args[0].node;
 137                     if let ExprKind::Path(QPath::Resolved(_, ref len_path)) = len_args[0].node;
 138                     if SpanlessEq::new(cx).eq_path_segments(&iter_path.segments, &len_path.segments);
 139                      then {
 140                          span_lint(cx,
 141                                    RANGE_ZIP_WITH_LEN,
 142                                    expr.span,
 143                                    &format!("It is more idiomatic to use {}.iter().enumerate()",
 144                                             snippet(cx, iter_args[0].span, "_")));
 145                     }
 146                 }
 147             }
 148         }
 149
 150         // exclusive range plus one: x..(y+1)
 151         if_chain! {
 152             if let Some(higher::Range {
 153                 start,
 154                 end: Some(end),
 155                 limits: RangeLimits::HalfOpen
 156             }) = higher::range(cx, expr);
 157             if let Some(y) = y_plus_one(end);
 158             then {
 159                 span_lint_and_then(
 160                     cx,
 161                     RANGE_PLUS_ONE,
 162                     expr.span,
 163                     "an inclusive range would be more readable",
 164                     |db| {
 165                         let start = start.map_or(String::new(), |x| Sugg::hir(cx, x, "x").to_string());
 166                         let end = Sugg::hir(cx, y, "y");
 167                         if let Some(is_wrapped) = &snippet_opt(cx, expr.span) {
 168                             if is_wrapped.starts_with('(') && is_wrapped.ends_with(')') {
 169                                 db.span_suggestion(
 170                                     expr.span,
 171                                     "use",
 172                                     format!("({}..={})", start, end),
 173                                     Applicability::MaybeIncorrect,
 174                                 );
 175                             } else {
 176                                 db.span_suggestion(
 177                                     expr.span,
 178                                     "use",
 179                                     format!("{}..={}", start, end),
 180                                     Applicability::MachineApplicable, // snippet
 181                                 );
 182                             }
 183                         }
 184                     },
 185                 );
 186             }
 187         }
 188
 189         // inclusive range minus one: x..=(y-1)
 190         if_chain! {
 191             if let Some(higher::Range { start, end: Some(end), limits: RangeLimits::Closed }) = higher::range(cx, expr);
 192             if let Some(y) = y_minus_one(end);
 193             then {
 194                 span_lint_and_then(
 195                     cx,
 196                     RANGE_MINUS_ONE,
 197                     expr.span,
 198                     "an exclusive range would be more readable",
 199                     |db| {
 200                         let start = start.map_or(String::new(), |x| Sugg::hir(cx, x, "x").to_string());
 201                         let end = Sugg::hir(cx, y, "y");
 202                         db.span_suggestion(
 203                             expr.span,
 204                             "use",
 205                             format!("{}..{}", start, end),
 206                             Applicability::MachineApplicable, // snippet
 207                         );
 208                     },
 209                 );
 210             }
 211         }
 212     }
 213 }
 214
 215 fn has_step_by(cx: &LateContext<'_, '_>, expr: &Expr) -> bool {
 216     // No need for walk_ptrs_ty here because step_by moves self, so it
 217     // can't be called on a borrowed range.
 218     let ty = cx.tables.expr_ty_adjusted(expr);
 219
 220     get_trait_def_id(cx, &paths::ITERATOR).map_or(false, |iterator_trait| implements_trait(cx, ty, iterator_trait, &[]))
 221 }
 222
 223 fn y_plus_one(expr: &Expr) -> Option<&Expr> {
 224     match expr.node {
 225         ExprKind::Binary(
 226             Spanned {
 227                 node: BinOpKind::Add, ..
 228             },
 229             ref lhs,
 230             ref rhs,
 231         ) => {
 232             if is_integer_literal(lhs, 1) {
 233                 Some(rhs)
 234             } else if is_integer_literal(rhs, 1) {
 235                 Some(lhs)
 236             } else {
 237                 None
 238             }
 239         },
 240         _ => None,
 241     }
 242 }
 243
 244 fn y_minus_one(expr: &Expr) -> Option<&Expr> {
 245     match expr.node {
 246         ExprKind::Binary(
 247             Spanned {
 248                 node: BinOpKind::Sub, ..
 249             },
 250             ref lhs,
 251             ref rhs,
 252         ) if is_integer_literal(rhs, 1) => Some(lhs),
 253         _ => None,
 254     }
 255 }