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     /// 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 declare_lint_pass!(Ranges => [
  90     ITERATOR_STEP_BY_ZERO,
  91     RANGE_ZIP_WITH_LEN,
  92     RANGE_PLUS_ONE,
  93     RANGE_MINUS_ONE
  94 ]);
  95
  96 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Ranges {
  97     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  98         if let ExprKind::MethodCall(ref path, _, ref args) = expr.node {
  99             let name = path.ident.as_str();
 100
 101             // Range with step_by(0).
 102             if name == "step_by" && args.len() == 2 && has_step_by(cx, &args[0]) {
 103                 use crate::consts::{constant, Constant};
 104                 if let Some((Constant::Int(0), _)) = constant(cx, cx.tables, &args[1]) {
 105                     span_lint(
 106                         cx,
 107                         ITERATOR_STEP_BY_ZERO,
 108                         expr.span,
 109                         "Iterator::step_by(0) will panic at runtime",
 110                     );
 111                 }
 112             } else if name == "zip" && args.len() == 2 {
 113                 let iter = &args[0].node;
 114                 let zip_arg = &args[1];
 115                 if_chain! {
 116                     // `.iter()` call
 117                     if let ExprKind::MethodCall(ref iter_path, _, ref iter_args ) = *iter;
 118                     if iter_path.ident.name == "iter";
 119                     // range expression in `.zip()` call: `0..x.len()`
 120                     if let Some(higher::Range { start: Some(start), end: Some(end), .. }) = higher::range(cx, zip_arg);
 121                     if is_integer_literal(start, 0);
 122                     // `.len()` call
 123                     if let ExprKind::MethodCall(ref len_path, _, ref len_args) = end.node;
 124                     if len_path.ident.name == "len" && len_args.len() == 1;
 125                     // `.iter()` and `.len()` called on same `Path`
 126                     if let ExprKind::Path(QPath::Resolved(_, ref iter_path)) = iter_args[0].node;
 127                     if let ExprKind::Path(QPath::Resolved(_, ref len_path)) = len_args[0].node;
 128                     if SpanlessEq::new(cx).eq_path_segments(&iter_path.segments, &len_path.segments);
 129                      then {
 130                          span_lint(cx,
 131                                    RANGE_ZIP_WITH_LEN,
 132                                    expr.span,
 133                                    &format!("It is more idiomatic to use {}.iter().enumerate()",
 134                                             snippet(cx, iter_args[0].span, "_")));
 135                     }
 136                 }
 137             }
 138         }
 139
 140         // exclusive range plus one: `x..(y+1)`
 141         if_chain! {
 142             if let Some(higher::Range {
 143                 start,
 144                 end: Some(end),
 145                 limits: RangeLimits::HalfOpen
 146             }) = higher::range(cx, expr);
 147             if let Some(y) = y_plus_one(end);
 148             then {
 149                 let span = expr.span
 150                     .ctxt()
 151                     .outer()
 152                     .expn_info()
 153                     .map_or(expr.span, |info| info.call_site);
 154                 span_lint_and_then(
 155                     cx,
 156                     RANGE_PLUS_ONE,
 157                     span,
 158                     "an inclusive range would be more readable",
 159                     |db| {
 160                         let start = start.map_or(String::new(), |x| Sugg::hir(cx, x, "x").to_string());
 161                         let end = Sugg::hir(cx, y, "y");
 162                         if let Some(is_wrapped) = &snippet_opt(cx, span) {
 163                             if is_wrapped.starts_with('(') && is_wrapped.ends_with(')') {
 164                                 db.span_suggestion(
 165                                     span,
 166                                     "use",
 167                                     format!("({}..={})", start, end),
 168                                     Applicability::MaybeIncorrect,
 169                                 );
 170                             } else {
 171                                 db.span_suggestion(
 172                                     span,
 173                                     "use",
 174                                     format!("{}..={}", start, end),
 175                                     Applicability::MachineApplicable, // snippet
 176                                 );
 177                             }
 178                         }
 179                     },
 180                 );
 181             }
 182         }
 183
 184         // inclusive range minus one: `x..=(y-1)`
 185         if_chain! {
 186             if let Some(higher::Range { start, end: Some(end), limits: RangeLimits::Closed }) = higher::range(cx, expr);
 187             if let Some(y) = y_minus_one(end);
 188             then {
 189                 span_lint_and_then(
 190                     cx,
 191                     RANGE_MINUS_ONE,
 192                     expr.span,
 193                     "an exclusive range would be more readable",
 194                     |db| {
 195                         let start = start.map_or(String::new(), |x| Sugg::hir(cx, x, "x").to_string());
 196                         let end = Sugg::hir(cx, y, "y");
 197                         db.span_suggestion(
 198                             expr.span,
 199                             "use",
 200                             format!("{}..{}", start, end),
 201                             Applicability::MachineApplicable, // snippet
 202                         );
 203                     },
 204                 );
 205             }
 206         }
 207     }
 208 }
 209
 210 fn has_step_by(cx: &LateContext<'_, '_>, expr: &Expr) -> bool {
 211     // No need for `walk_ptrs_ty` here because `step_by` moves `self`, so it
 212     // can't be called on a borrowed range.
 213     let ty = cx.tables.expr_ty_adjusted(expr);
 214
 215     get_trait_def_id(cx, &paths::ITERATOR).map_or(false, |iterator_trait| implements_trait(cx, ty, iterator_trait, &[]))
 216 }
 217
 218 fn y_plus_one(expr: &Expr) -> Option<&Expr> {
 219     match expr.node {
 220         ExprKind::Binary(
 221             Spanned {
 222                 node: BinOpKind::Add, ..
 223             },
 224             ref lhs,
 225             ref rhs,
 226         ) => {
 227             if is_integer_literal(lhs, 1) {
 228                 Some(rhs)
 229             } else if is_integer_literal(rhs, 1) {
 230                 Some(lhs)
 231             } else {
 232                 None
 233             }
 234         },
 235         _ => None,
 236     }
 237 }
 238
 239 fn y_minus_one(expr: &Expr) -> Option<&Expr> {
 240     match expr.node {
 241         ExprKind::Binary(
 242             Spanned {
 243                 node: BinOpKind::Sub, ..
 244             },
 245             ref lhs,
 246             ref rhs,
 247         ) if is_integer_literal(rhs, 1) => Some(lhs),
 248         _ => None,
 249     }
 250 }