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                             let ty = cx.tables.expr_ty(assignee);
  86                             if ty.walk_shallow().next().is_some() {
  87                                 return; // implements_trait does not work with generics
  88                             }
  89                             let rty = cx.tables.expr_ty(rhs);
  90                             if rty.walk_shallow().next().is_some() {
  91                                 return; // implements_trait does not work with generics
  92                             }
  93                             span_lint_and_then(cx,
  94                                                MISREFACTORED_ASSIGN_OP,
  95                                                expr.span,
  96                                                "variable appears on both sides of an assignment operation",
  97                                                |db| {
  98                                 if let (Some(snip_a), Some(snip_r)) =
  99                                     (snippet_opt(cx, assignee.span), snippet_opt(cx, rhs.span)) {
 100                                     db.span_suggestion(expr.span,
 101                                                        "replace it with",
 102                                                        format!("{} {}= {}", snip_a, op.node.as_str(), snip_r));
 103                                 }
 104                             });
 105                         };
 106                         // lhs op= l op r
 107                         if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs, l) {
 108                             lint(lhs, r);
 109                         }
 110                         // lhs op= l commutative_op r
 111                         if is_commutative(op.node) && SpanlessEq::new(cx).ignore_fn().eq_expr(lhs, r) {
 112                             lint(lhs, l);
 113                         }
 114                     }
 115                 }
 116             },
 117             hir::ExprAssign(ref assignee, ref e) => {
 118                 if let hir::ExprBinary(op, ref l, ref r) = e.node {
 119                     #[allow(cyclomatic_complexity)]
 120                     let lint = |assignee: &hir::Expr, rhs: &hir::Expr| {
 121                         let ty = cx.tables.expr_ty(assignee);
 122                         if ty.walk_shallow().next().is_some() {
 123                             return; // implements_trait does not work with generics
 124                         }
 125                         let rty = cx.tables.expr_ty(rhs);
 126                         if rty.walk_shallow().next().is_some() {
 127                             return; // implements_trait does not work with generics
 128                         }
 129                         macro_rules! ops {
 130                             ($op:expr,
 131                              $cx:expr,
 132                              $ty:expr,
 133                              $rty:expr,
 134                              $($trait_name:ident:$full_trait_name:ident),+) => {
 135                                 match $op {
 136                                     $(hir::$full_trait_name => {
 137                                         let [krate, module] = ::utils::paths::OPS_MODULE;
 138                                         let path = [krate, module, concat!(stringify!($trait_name), "Assign")];
 139                                         let trait_id = if let Some(trait_id) = get_trait_def_id($cx, &path) {
 140                                             trait_id
 141                                         } else {
 142                                             return; // useless if the trait doesn't exist
 143                                         };
 144                                         // check that we are not inside an `impl AssignOp` of this exact operation
 145                                         let parent_fn = cx.tcx.map.get_parent(e.id);
 146                                         let parent_impl = cx.tcx.map.get_parent(parent_fn);
 147                                         // the crate node is the only one that is not in the map
 148                                         if_let_chain!{[
 149                                             parent_impl != ast::CRATE_NODE_ID,
 150                                             let hir::map::Node::NodeItem(item) = cx.tcx.map.get(parent_impl),
 151                                             let hir::Item_::ItemImpl(_, _, _, Some(ref trait_ref), _, _) = item.node,
 152                                             trait_ref.path.def.def_id() == trait_id
 153                                         ], { return; }}
 154                                         implements_trait($cx, $ty, trait_id, vec![$rty])
 155                                     },)*
 156                                     _ => false,
 157                                 }
 158                             }
 159                         }
 160                         if ops!(op.node,
 161                                 cx,
 162                                 ty,
 163                                 rty,
 164                                 Add: BiAdd,
 165                                 Sub: BiSub,
 166                                 Mul: BiMul,
 167                                 Div: BiDiv,
 168                                 Rem: BiRem,
 169                                 And: BiAnd,
 170                                 Or: BiOr,
 171                                 BitAnd: BiBitAnd,
 172                                 BitOr: BiBitOr,
 173                                 BitXor: BiBitXor,
 174                                 Shr: BiShr,
 175                                 Shl: BiShl) {
 176                             span_lint_and_then(cx,
 177                                                ASSIGN_OP_PATTERN,
 178                                                expr.span,
 179                                                "manual implementation of an assign operation",
 180                                                |db| {
 181                                 if let (Some(snip_a), Some(snip_r)) =
 182                                     (snippet_opt(cx, assignee.span), snippet_opt(cx, rhs.span)) {
 183                                     db.span_suggestion(expr.span,
 184                                                        "replace it with",
 185                                                        format!("{} {}= {}", snip_a, op.node.as_str(), snip_r));
 186                                 }
 187                             });
 188                         }
 189                     };
 190                     // a = a op b
 191                     if SpanlessEq::new(cx).ignore_fn().eq_expr(assignee, l) {
 192                         lint(assignee, r);
 193                     }
 194                     // a = b commutative_op a
 195                     if SpanlessEq::new(cx).ignore_fn().eq_expr(assignee, r) {
 196                         match op.node {
 197                             hir::BiAdd | hir::BiMul | hir::BiAnd | hir::BiOr | hir::BiBitXor | hir::BiBitAnd |
 198                             hir::BiBitOr => {
 199                                 lint(assignee, l);
 200                             },
 201                             _ => {},
 202                         }
 203                     }
 204                 }
 205             },
 206             _ => {},
 207         }
 208     }
 209 }
 210
 211 fn is_commutative(op: hir::BinOp_) -> bool {
 212     use rustc::hir::BinOp_::*;
 213     match op {
 214         BiAdd | BiMul | BiAnd | BiOr | BiBitXor | BiBitAnd | BiBitOr | BiEq | BiNe => true,
 215         BiSub | BiDiv | BiRem | BiShl | BiShr | BiLt | BiLe | BiGe | BiGt => false,
 216     }
 217 }