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_tool_lint, lint_array};
   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     /// x.iter().zip(0..x.len())
  44     /// ```
  45     pub RANGE_ZIP_WITH_LEN,
  46     complexity,
  47     "zipping iterator with a range when `enumerate()` would do"
  48 }
  49
  50 declare_clippy_lint! {
  51     /// **What it does:** Checks for exclusive ranges where 1 is added to the
  52     /// upper bound, e.g., `x..(y+1)`.
  53     ///
  54     /// **Why is this bad?** The code is more readable with an inclusive range
  55     /// like `x..=y`.
  56     ///
  57     /// **Known problems:** Will add unnecessary pair of parentheses when the
  58     /// expression is not wrapped in a pair but starts with a opening parenthesis
  59     /// and ends with a closing one.
  60     /// I.e., `let _ = (f()+1)..(f()+1)` results in `let _ = ((f()+1)..=f())`.
  61     ///
  62     /// **Example:**
  63     /// ```rust
  64     /// for x..(y+1) { .. }
  65     /// ```
  66     pub RANGE_PLUS_ONE,
  67     complexity,
  68     "`x..(y+1)` reads better as `x..=y`"
  69 }
  70
  71 declare_clippy_lint! {
  72     /// **What it does:** Checks for inclusive ranges where 1 is subtracted from
  73     /// the upper bound, e.g., `x..=(y-1)`.
  74     ///
  75     /// **Why is this bad?** The code is more readable with an exclusive range
  76     /// like `x..y`.
  77     ///
  78     /// **Known problems:** None.
  79     ///
  80     /// **Example:**
  81     /// ```rust
  82     /// for x..=(y-1) { .. }
  83     /// ```
  84     pub RANGE_MINUS_ONE,
  85     complexity,
  86     "`x..=(y-1)` reads better as `x..y`"
  87 }
  88
  89 #[derive(Copy, Clone)]
  90 pub struct Pass;
  91
  92 impl LintPass for Pass {
  93     fn get_lints(&self) -> LintArray {
  94         lint_array!(
  95             ITERATOR_STEP_BY_ZERO,
  96             RANGE_ZIP_WITH_LEN,
  97             RANGE_PLUS_ONE,
  98             RANGE_MINUS_ONE
  99         )
 100     }
 101
 102     fn name(&self) -> &'static str {
 103         "Ranges"
 104     }
 105 }
 106
 107 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
 108     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
 109         if let ExprKind::MethodCall(ref path, _, ref args) = expr.node {
 110             let name = path.ident.as_str();
 111
 112             // Range with step_by(0).
 113             if name == "step_by" && args.len() == 2 && has_step_by(cx, &args[0]) {
 114                 use crate::consts::{constant, Constant};
 115                 if let Some((Constant::Int(0), _)) = constant(cx, cx.tables, &args[1]) {
 116                     span_lint(
 117                         cx,
 118                         ITERATOR_STEP_BY_ZERO,
 119                         expr.span,
 120                         "Iterator::step_by(0) will panic at runtime",
 121                     );
 122                 }
 123             } else if name == "zip" && args.len() == 2 {
 124                 let iter = &args[0].node;
 125                 let zip_arg = &args[1];
 126                 if_chain! {
 127                     // `.iter()` call
 128                     if let ExprKind::MethodCall(ref iter_path, _, ref iter_args ) = *iter;
 129                     if iter_path.ident.name == "iter";
 130                     // range expression in `.zip()` call: `0..x.len()`
 131                     if let Some(higher::Range { start: Some(start), end: Some(end), .. }) = higher::range(cx, zip_arg);
 132                     if is_integer_literal(start, 0);
 133                     // `.len()` call
 134                     if let ExprKind::MethodCall(ref len_path, _, ref len_args) = end.node;
 135                     if len_path.ident.name == "len" && len_args.len() == 1;
 136                     // `.iter()` and `.len()` called on same `Path`
 137                     if let ExprKind::Path(QPath::Resolved(_, ref iter_path)) = iter_args[0].node;
 138                     if let ExprKind::Path(QPath::Resolved(_, ref len_path)) = len_args[0].node;
 139                     if SpanlessEq::new(cx).eq_path_segments(&iter_path.segments, &len_path.segments);
 140                      then {
 141                          span_lint(cx,
 142                                    RANGE_ZIP_WITH_LEN,
 143                                    expr.span,
 144                                    &format!("It is more idiomatic to use {}.iter().enumerate()",
 145                                             snippet(cx, iter_args[0].span, "_")));
 146                     }
 147                 }
 148             }
 149         }
 150
 151         // exclusive range plus one: `x..(y+1)`
 152         if_chain! {
 153             if let Some(higher::Range {
 154                 start,
 155                 end: Some(end),
 156                 limits: RangeLimits::HalfOpen
 157             }) = higher::range(cx, expr);
 158             if let Some(y) = y_plus_one(end);
 159             then {
 160                 span_lint_and_then(
 161                     cx,
 162                     RANGE_PLUS_ONE,
 163                     expr.span,
 164                     "an inclusive range would be more readable",
 165                     |db| {
 166                         let start = start.map_or(String::new(), |x| Sugg::hir(cx, x, "x").to_string());
 167                         let end = Sugg::hir(cx, y, "y");
 168                         if let Some(is_wrapped) = &snippet_opt(cx, expr.span) {
 169                             if is_wrapped.starts_with('(') && is_wrapped.ends_with(')') {
 170                                 db.span_suggestion(
 171                                     expr.span,
 172                                     "use",
 173                                     format!("({}..={})", start, end),
 174                                     Applicability::MaybeIncorrect,
 175                                 );
 176                             } else {
 177                                 db.span_suggestion(
 178                                     expr.span,
 179                                     "use",
 180                                     format!("{}..={}", start, end),
 181                                     Applicability::MachineApplicable, // snippet
 182                                 );
 183                             }
 184                         }
 185                     },
 186                 );
 187             }
 188         }
 189
 190         // inclusive range minus one: `x..=(y-1)`
 191         if_chain! {
 192             if let Some(higher::Range { start, end: Some(end), limits: RangeLimits::Closed }) = higher::range(cx, expr);
 193             if let Some(y) = y_minus_one(end);
 194             then {
 195                 span_lint_and_then(
 196                     cx,
 197                     RANGE_MINUS_ONE,
 198                     expr.span,
 199                     "an exclusive range would be more readable",
 200                     |db| {
 201                         let start = start.map_or(String::new(), |x| Sugg::hir(cx, x, "x").to_string());
 202                         let end = Sugg::hir(cx, y, "y");
 203                         db.span_suggestion(
 204                             expr.span,
 205                             "use",
 206                             format!("{}..{}", start, end),
 207                             Applicability::MachineApplicable, // snippet
 208                         );
 209                     },
 210                 );
 211             }
 212         }
 213     }
 214 }
 215
 216 fn has_step_by(cx: &LateContext<'_, '_>, expr: &Expr) -> bool {
 217     // No need for `walk_ptrs_ty` here because `step_by` moves `self`, so it
 218     // can't be called on a borrowed range.
 219     let ty = cx.tables.expr_ty_adjusted(expr);
 220
 221     get_trait_def_id(cx, &paths::ITERATOR).map_or(false, |iterator_trait| implements_trait(cx, ty, iterator_trait, &[]))
 222 }
 223
 224 fn y_plus_one(expr: &Expr) -> Option<&Expr> {
 225     match expr.node {
 226         ExprKind::Binary(
 227             Spanned {
 228                 node: BinOpKind::Add, ..
 229             },
 230             ref lhs,
 231             ref rhs,
 232         ) => {
 233             if is_integer_literal(lhs, 1) {
 234                 Some(rhs)
 235             } else if is_integer_literal(rhs, 1) {
 236                 Some(lhs)
 237             } else {
 238                 None
 239             }
 240         },
 241         _ => None,
 242     }
 243 }
 244
 245 fn y_minus_one(expr: &Expr) -> Option<&Expr> {
 246     match expr.node {
 247         ExprKind::Binary(
 248             Spanned {
 249                 node: BinOpKind::Sub, ..
 250             },
 251             ref lhs,
 252             ref rhs,
 253         ) if is_integer_literal(rhs, 1) => Some(lhs),
 254         _ => None,
 255     }
 256 }