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::sym;
  11 use crate::utils::{get_trait_def_id, higher, implements_trait, SpanlessEq};
  12 use crate::utils::{is_integer_literal, paths, snippet, snippet_opt, span_lint, span_lint_and_then};
  13
  14 declare_clippy_lint! {
  15     /// **What it does:** Checks for calling `.step_by(0)` on iterators,
  16     /// which never terminates.
  17     ///
  18     /// **Why is this bad?** This very much looks like an oversight, since with
  19     /// `loop { .. }` there is an obvious better way to endlessly loop.
  20     ///
  21     /// **Known problems:** None.
  22     ///
  23     /// **Example:**
  24     /// ```ignore
  25     /// for x in (5..5).step_by(0) {
  26     ///     ..
  27     /// }
  28     /// ```
  29     pub ITERATOR_STEP_BY_ZERO,
  30     correctness,
  31     "using `Iterator::step_by(0)`, which produces an infinite iterator"
  32 }
  33
  34 declare_clippy_lint! {
  35     /// **What it does:** Checks for zipping a collection with the range of
  36     /// `0.._.len()`.
  37     ///
  38     /// **Why is this bad?** The code is better expressed with `.enumerate()`.
  39     ///
  40     /// **Known problems:** None.
  41     ///
  42     /// **Example:**
  43     /// ```rust
  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
  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
  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 = expr.span
 151                     .ctxt()
 152                     .outer()
 153                     .expn_info()
 154                     .map_or(expr.span, |info| info.call_site);
 155                 span_lint_and_then(
 156                     cx,
 157                     RANGE_PLUS_ONE,
 158                     span,
 159                     "an inclusive range would be more readable",
 160                     |db| {
 161                         let start = start.map_or(String::new(), |x| Sugg::hir(cx, x, "x").to_string());
 162                         let end = Sugg::hir(cx, y, "y");
 163                         if let Some(is_wrapped) = &snippet_opt(cx, span) {
 164                             if is_wrapped.starts_with('(') && is_wrapped.ends_with(')') {
 165                                 db.span_suggestion(
 166                                     span,
 167                                     "use",
 168                                     format!("({}..={})", start, end),
 169                                     Applicability::MaybeIncorrect,
 170                                 );
 171                             } else {
 172                                 db.span_suggestion(
 173                                     span,
 174                                     "use",
 175                                     format!("{}..={}", start, end),
 176                                     Applicability::MachineApplicable, // snippet
 177                                 );
 178                             }
 179                         }
 180                     },
 181                 );
 182             }
 183         }
 184
 185         // inclusive range minus one: `x..=(y-1)`
 186         if_chain! {
 187             if let Some(higher::Range { start, end: Some(end), limits: RangeLimits::Closed }) = higher::range(cx, expr);
 188             if let Some(y) = y_minus_one(end);
 189             then {
 190                 span_lint_and_then(
 191                     cx,
 192                     RANGE_MINUS_ONE,
 193                     expr.span,
 194                     "an exclusive range would be more readable",
 195                     |db| {
 196                         let start = start.map_or(String::new(), |x| Sugg::hir(cx, x, "x").to_string());
 197                         let end = Sugg::hir(cx, y, "y");
 198                         db.span_suggestion(
 199                             expr.span,
 200                             "use",
 201                             format!("{}..{}", start, end),
 202                             Applicability::MachineApplicable, // snippet
 203                         );
 204                     },
 205                 );
 206             }
 207         }
 208     }
 209 }
 210
 211 fn has_step_by(cx: &LateContext<'_, '_>, expr: &Expr) -> bool {
 212     // No need for `walk_ptrs_ty` here because `step_by` moves `self`, so it
 213     // can't be called on a borrowed range.
 214     let ty = cx.tables.expr_ty_adjusted(expr);
 215
 216     get_trait_def_id(cx, &*paths::ITERATOR)
 217         .map_or(false, |iterator_trait| implements_trait(cx, ty, iterator_trait, &[]))
 218 }
 219
 220 fn y_plus_one(expr: &Expr) -> Option<&Expr> {
 221     match expr.node {
 222         ExprKind::Binary(
 223             Spanned {
 224                 node: BinOpKind::Add, ..
 225             },
 226             ref lhs,
 227             ref rhs,
 228         ) => {
 229             if is_integer_literal(lhs, 1) {
 230                 Some(rhs)
 231             } else if is_integer_literal(rhs, 1) {
 232                 Some(lhs)
 233             } else {
 234                 None
 235             }
 236         },
 237         _ => None,
 238     }
 239 }
 240
 241 fn y_minus_one(expr: &Expr) -> Option<&Expr> {
 242     match expr.node {
 243         ExprKind::Binary(
 244             Spanned {
 245                 node: BinOpKind::Sub, ..
 246             },
 247             ref lhs,
 248             ref rhs,
 249         ) if is_integer_literal(rhs, 1) => Some(lhs),
 250         _ => None,
 251     }
 252 }