clippy_lints/src/assign_ops.rs

   1 use rustc::hir;
   2 use rustc::lint::*;
   3 use syntax::ast;
   4 use utils::{span_lint_and_then, snippet_opt, SpanlessEq, get_trait_def_id, implements_trait};
   5 use utils::{higher, sugg};
   6
   7 /// **What it does:** Checks for compound assignment operations (`+=` and similar).
   8 ///
   9 /// **Why is this bad?** Projects with many developers from languages without
  10 /// those operations may find them unreadable and not worth their weight.
  11 ///
  12 /// **Known problems:** Types implementing `OpAssign` don't necessarily implement `Op`.
  13 ///
  14 /// **Example:**
  15 /// ```rust
  16 /// a += 1;
  17 /// ```
  18 declare_restriction_lint! {
  19     pub ASSIGN_OPS,
  20     "any compound assignment operation"
  21 }
  22
  23 /// **What it does:** Checks for `a = a op b` or `a = b commutative_op a` patterns.
  24 ///
  25 /// **Why is this bad?** These can be written as the shorter `a op= b`.
  26 ///
  27 /// **Known problems:** While forbidden by the spec, `OpAssign` traits may have
  28 /// implementations that differ from the regular `Op` impl.
  29 ///
  30 /// **Example:**
  31 /// ```rust
  32 /// let mut a = 5;
  33 /// ...
  34 /// a = a + b;
  35 /// ```
  36 declare_lint! {
  37     pub ASSIGN_OP_PATTERN,
  38     Warn,
  39     "assigning the result of an operation on a variable to that same variable"
  40 }
  41
  42 /// **What it does:** Checks for `a op= a op b` or `a op= b op a` patterns.
  43 ///
  44 /// **Why is this bad?** Most likely these are bugs where one meant to write `a op= b`.
  45 ///
  46 /// **Known problems:** Someone might actually mean `a op= a op b`, but that
  47 /// should rather be written as `a = (2 * a) op b` where applicable.
  48 ///
  49 /// **Example:**
  50 /// ```rust
  51 /// let mut a = 5;
  52 /// ...
  53 /// a += a + b;
  54 /// ```
  55 declare_lint! {
  56     pub MISREFACTORED_ASSIGN_OP,
  57     Warn,
  58     "having a variable on both sides of an assign op"
  59 }
  60
  61 #[derive(Copy, Clone, Default)]
  62 pub struct AssignOps;
  63
  64 impl LintPass for AssignOps {
  65     fn get_lints(&self) -> LintArray {
  66         lint_array!(ASSIGN_OPS, ASSIGN_OP_PATTERN, MISREFACTORED_ASSIGN_OP)
  67     }
  68 }
  69
  70 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for AssignOps {
  71     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr) {
  72         match expr.node {
  73             hir::ExprAssignOp(op, ref lhs, ref rhs) => {
  74                 span_lint_and_then(cx, ASSIGN_OPS, expr.span, "assign operation detected", |db| {
  75                     let lhs = &sugg::Sugg::hir(cx, lhs, "..");
  76                     let rhs = &sugg::Sugg::hir(cx, rhs, "..");
  77
  78                     db.span_suggestion(expr.span,
  79                                        "replace it with",
  80                                        format!("{} = {}", lhs, sugg::make_binop(higher::binop(op.node), lhs, rhs)));
  81                 });
  82                 if let hir::ExprBinary(binop, ref l, ref r) = rhs.node {
  83                     if op.node == binop.node {
  84                         let lint = |assignee: &hir::Expr, rhs: &hir::Expr| {
  85                             span_lint_and_then(cx,
  86                                                MISREFACTORED_ASSIGN_OP,
  87                                                expr.span,
  88                                                "variable appears on both sides of an assignment operation",
  89                                                |db| if let (Some(snip_a), Some(snip_r)) =
  90                                                    (snippet_opt(cx, assignee.span), snippet_opt(cx, rhs.span)) {
  91                                                    db.span_suggestion(expr.span,
  92                                                                       "replace it with",
  93                                                                       format!("{} {}= {}",
  94                                                                               snip_a,
  95                                                                               op.node.as_str(),
  96                                                                               snip_r));
  97                                                });
  98                         };
  99                         // lhs op= l op r
 100                         if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs, l) {
 101                             lint(lhs, r);
 102                         }
 103                         // lhs op= l commutative_op r
 104                         if is_commutative(op.node) && SpanlessEq::new(cx).ignore_fn().eq_expr(lhs, r) {
 105                             lint(lhs, l);
 106                         }
 107                     }
 108                 }
 109             },
 110             hir::ExprAssign(ref assignee, ref e) => {
 111                 if let hir::ExprBinary(op, ref l, ref r) = e.node {
 112                     #[allow(cyclomatic_complexity)]
 113                     let lint = |assignee: &hir::Expr, rhs: &hir::Expr| {
 114                         let ty = cx.tables.expr_ty(assignee);
 115                         let rty = cx.tables.expr_ty(rhs);
 116                         macro_rules! ops {
 117                             ($op:expr,
 118                              $cx:expr,
 119                              $ty:expr,
 120                              $rty:expr,
 121                              $($trait_name:ident:$full_trait_name:ident),+) => {
 122                                 match $op {
 123                                     $(hir::$full_trait_name => {
 124                                         let [krate, module] = ::utils::paths::OPS_MODULE;
 125                                         let path = [krate, module, concat!(stringify!($trait_name), "Assign")];
 126                                         let trait_id = if let Some(trait_id) = get_trait_def_id($cx, &path) {
 127                                             trait_id
 128                                         } else {
 129                                             return; // useless if the trait doesn't exist
 130                                         };
 131                                         // check that we are not inside an `impl AssignOp` of this exact operation
 132                                         let parent_fn = cx.tcx.hir.get_parent(e.id);
 133                                         let parent_impl = cx.tcx.hir.get_parent(parent_fn);
 134                                         // the crate node is the only one that is not in the map
 135                                         if_let_chain!{[
 136                                             parent_impl != ast::CRATE_NODE_ID,
 137                                             let hir::map::Node::NodeItem(item) = cx.tcx.hir.get(parent_impl),
 138                                             let hir::Item_::ItemImpl(_, _, _, _, Some(ref trait_ref), _, _) = item.node,
 139                                             trait_ref.path.def.def_id() == trait_id
 140                                         ], { return; }}
 141                                         implements_trait($cx, $ty, trait_id, &[$rty])
 142                                     },)*
 143                                     _ => false,
 144                                 }
 145                             }
 146                         }
 147                         if ops!(op.node,
 148                                 cx,
 149                                 ty,
 150                                 rty,
 151                                 Add: BiAdd,
 152                                 Sub: BiSub,
 153                                 Mul: BiMul,
 154                                 Div: BiDiv,
 155                                 Rem: BiRem,
 156                                 And: BiAnd,
 157                                 Or: BiOr,
 158                                 BitAnd: BiBitAnd,
 159                                 BitOr: BiBitOr,
 160                                 BitXor: BiBitXor,
 161                                 Shr: BiShr,
 162                                 Shl: BiShl) {
 163                             span_lint_and_then(cx,
 164                                                ASSIGN_OP_PATTERN,
 165                                                expr.span,
 166                                                "manual implementation of an assign operation",
 167                                                |db| if let (Some(snip_a), Some(snip_r)) =
 168                                                    (snippet_opt(cx, assignee.span), snippet_opt(cx, rhs.span)) {
 169                                                    db.span_suggestion(expr.span,
 170                                                                       "replace it with",
 171                                                                       format!("{} {}= {}",
 172                                                                               snip_a,
 173                                                                               op.node.as_str(),
 174                                                                               snip_r));
 175                                                });
 176                         }
 177                     };
 178                     // a = a op b
 179                     if SpanlessEq::new(cx).ignore_fn().eq_expr(assignee, l) {
 180                         lint(assignee, r);
 181                     }
 182                     // a = b commutative_op a
 183                     if SpanlessEq::new(cx).ignore_fn().eq_expr(assignee, r) {
 184                         match op.node {
 185                             hir::BiAdd | hir::BiMul | hir::BiAnd | hir::BiOr | hir::BiBitXor | hir::BiBitAnd |
 186                             hir::BiBitOr => {
 187                                 lint(assignee, l);
 188                             },
 189                             _ => {},
 190                         }
 191                     }
 192                 }
 193             },
 194             _ => {},
 195         }
 196     }
 197 }
 198
 199 fn is_commutative(op: hir::BinOp_) -> bool {
 200     use rustc::hir::BinOp_::*;
 201     match op {
 202         BiAdd | BiMul | BiAnd | BiOr | BiBitXor | BiBitAnd | BiBitOr | BiEq | BiNe => true,
 203         BiSub | BiDiv | BiRem | BiShl | BiShr | BiLt | BiLe | BiGe | BiGt => false,
 204     }
 205 }