// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution. // // Licensed under the Apache License, Version 2.0 or the MIT license // , at your // option. This file may not be copied, modified, or distributed // except according to those terms. use crate::utils::{get_trait_def_id, implements_trait, snippet_opt, span_lint_and_then, SpanlessEq}; use crate::utils::{higher, sugg}; use if_chain::if_chain; use rustc::hir; use rustc::hir::intravisit::{walk_expr, NestedVisitorMap, Visitor}; use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass}; use rustc::{declare_tool_lint, lint_array}; use rustc_errors::Applicability; use syntax::ast; /// **What it does:** Checks for `a = a op b` or `a = b commutative_op a` /// patterns. /// /// **Why is this bad?** These can be written as the shorter `a op= b`. /// /// **Known problems:** While forbidden by the spec, `OpAssign` traits may have /// implementations that differ from the regular `Op` impl. /// /// **Example:** /// ```rust /// let mut a = 5; /// ... /// a = a + b; /// ``` declare_clippy_lint! { pub ASSIGN_OP_PATTERN, style, "assigning the result of an operation on a variable to that same variable" } /// **What it does:** Checks for `a op= a op b` or `a op= b op a` patterns. /// /// **Why is this bad?** Most likely these are bugs where one meant to write `a /// op= b`. /// /// **Known problems:** Clippy cannot know for sure if `a op= a op b` should have /// been `a = a op a op b` or `a = a op b`/`a op= b`. Therefore it suggests both. /// If `a op= a op b` is really the correct behaviour it should be /// written as `a = a op a op b` as it's less confusing. /// /// **Example:** /// ```rust /// let mut a = 5; /// ... /// a += a + b; /// ``` declare_clippy_lint! { pub MISREFACTORED_ASSIGN_OP, complexity, "having a variable on both sides of an assign op" } #[derive(Copy, Clone, Default)] pub struct AssignOps; impl LintPass for AssignOps { fn get_lints(&self) -> LintArray { lint_array!(ASSIGN_OP_PATTERN, MISREFACTORED_ASSIGN_OP) } } impl<'a, 'tcx> LateLintPass<'a, 'tcx> for AssignOps { fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr) { match &expr.node { hir::ExprKind::AssignOp(op, lhs, rhs) => { if let hir::ExprKind::Binary(binop, l, r) = &rhs.node { if op.node == binop.node { let lint = |assignee: &hir::Expr, rhs_other: &hir::Expr| { span_lint_and_then( cx, MISREFACTORED_ASSIGN_OP, expr.span, "variable appears on both sides of an assignment operation", |db| { if let (Some(snip_a), Some(snip_r)) = (snippet_opt(cx, assignee.span), snippet_opt(cx, rhs_other.span)) { let a = &sugg::Sugg::hir(cx, assignee, ".."); let r = &sugg::Sugg::hir(cx, rhs, ".."); let long = format!("{} = {}", snip_a, sugg::make_binop(higher::binop(op.node), a, r)); db.span_suggestion_with_applicability( expr.span, &format!( "Did you mean {} = {} {} {} or {}? Consider replacing it with", snip_a, snip_a, op.node.as_str(), snip_r, long ), format!("{} {}= {}", snip_a, op.node.as_str(), snip_r), Applicability::MachineApplicable, ); db.span_suggestion_with_applicability( expr.span, "or", long, Applicability::MachineApplicable, // snippet ); } }, ); }; // lhs op= l op r if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs, l) { lint(lhs, r); } // lhs op= l commutative_op r if is_commutative(op.node) && SpanlessEq::new(cx).ignore_fn().eq_expr(lhs, r) { lint(lhs, l); } } } }, hir::ExprKind::Assign(assignee, e) => { if let hir::ExprKind::Binary(op, l, r) = &e.node { #[allow(clippy::cyclomatic_complexity)] let lint = |assignee: &hir::Expr, rhs: &hir::Expr| { let ty = cx.tables.expr_ty(assignee); let rty = cx.tables.expr_ty(rhs); macro_rules! ops { ($op:expr, $cx:expr, $ty:expr, $rty:expr, $($trait_name:ident),+) => { match $op { $(hir::BinOpKind::$trait_name => { let [krate, module] = crate::utils::paths::OPS_MODULE; let path = [krate, module, concat!(stringify!($trait_name), "Assign")]; let trait_id = if let Some(trait_id) = get_trait_def_id($cx, &path) { trait_id } else { return; // useless if the trait doesn't exist }; // check that we are not inside an `impl AssignOp` of this exact operation let parent_fn = cx.tcx.hir().get_parent(e.id); let parent_impl = cx.tcx.hir().get_parent(parent_fn); // the crate node is the only one that is not in the map if_chain! { if parent_impl != ast::CRATE_NODE_ID; if let hir::Node::Item(item) = cx.tcx.hir().get(parent_impl); if let hir::ItemKind::Impl(_, _, _, _, Some(trait_ref), _, _) = &item.node; if trait_ref.path.def.def_id() == trait_id; then { return; } } implements_trait($cx, $ty, trait_id, &[$rty]) },)* _ => false, } } } if ops!( op.node, cx, ty, rty.into(), Add, Sub, Mul, Div, Rem, And, Or, BitAnd, BitOr, BitXor, Shr, Shl ) { span_lint_and_then( cx, ASSIGN_OP_PATTERN, expr.span, "manual implementation of an assign operation", |db| { if let (Some(snip_a), Some(snip_r)) = (snippet_opt(cx, assignee.span), snippet_opt(cx, rhs.span)) { db.span_suggestion_with_applicability( expr.span, "replace it with", format!("{} {}= {}", snip_a, op.node.as_str(), snip_r), Applicability::MachineApplicable, ); } }, ); } }; let mut visitor = ExprVisitor { assignee, counter: 0, cx, }; walk_expr(&mut visitor, e); if visitor.counter == 1 { // a = a op b if SpanlessEq::new(cx).ignore_fn().eq_expr(assignee, l) { lint(assignee, r); } // a = b commutative_op a // Limited to primitive type as these ops are know to be commutative if SpanlessEq::new(cx).ignore_fn().eq_expr(assignee, r) && cx.tables.expr_ty(assignee).is_primitive_ty() { match op.node { hir::BinOpKind::Add | hir::BinOpKind::Mul | hir::BinOpKind::And | hir::BinOpKind::Or | hir::BinOpKind::BitXor | hir::BinOpKind::BitAnd | hir::BinOpKind::BitOr => { lint(assignee, l); }, _ => {}, } } } } }, _ => {}, } } } fn is_commutative(op: hir::BinOpKind) -> bool { use rustc::hir::BinOpKind::*; match op { Add | Mul | And | Or | BitXor | BitAnd | BitOr | Eq | Ne => true, Sub | Div | Rem | Shl | Shr | Lt | Le | Ge | Gt => false, } } struct ExprVisitor<'a, 'tcx: 'a> { assignee: &'a hir::Expr, counter: u8, cx: &'a LateContext<'a, 'tcx>, } impl<'a, 'tcx: 'a> Visitor<'tcx> for ExprVisitor<'a, 'tcx> { fn visit_expr(&mut self, expr: &'tcx hir::Expr) { if SpanlessEq::new(self.cx).ignore_fn().eq_expr(self.assignee, expr) { self.counter += 1; } walk_expr(self, expr); } fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> { NestedVisitorMap::None } }