clippy_lints/src/ranges.rs

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