rust-clippy/clippy_lints/src/assign_ops.rs

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// 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 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
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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;
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/// **What it does:** Checks for `a = a op b` or `a = b commutative_op a`
/// patterns.
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///
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/// **Why is this bad?** These can be written as the shorter `a op= b`.
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///
/// **Known problems:** While forbidden by the spec, `OpAssign` traits may have
/// implementations that differ from the regular `Op` impl.
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///
/// **Example:**
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/// ```rust
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/// let mut a = 5;
/// ...
/// a = a + b;
/// ```
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declare_clippy_lint! {
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pub ASSIGN_OP_PATTERN,
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style,
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"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.
///
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/// **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;
/// ```
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declare_clippy_lint! {
pub MISREFACTORED_ASSIGN_OP,
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complexity,
"having a variable on both sides of an assign op"
}
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#[derive(Copy, Clone, Default)]
pub struct AssignOps;
impl LintPass for AssignOps {
fn get_lints(&self) -> LintArray {
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lint_array!(ASSIGN_OP_PATTERN, MISREFACTORED_ASSIGN_OP)
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}
}
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| {
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span_lint_and_then(
cx,
MISREFACTORED_ASSIGN_OP,
expr.span,
"variable appears on both sides of an assignment operation",
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|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(
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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,
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);
db.span_suggestion_with_applicability(
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expr.span,
"or",
long,
Applicability::MachineApplicable, // snippet
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);
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}
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},
);
};
// 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);
}
}
}
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},
hir::ExprKind::Assign(assignee, e) => {
if let hir::ExprKind::Binary(op, l, r) = &e.node {
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#[allow(clippy::cyclomatic_complexity)]
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let lint = |assignee: &hir::Expr, rhs: &hir::Expr| {
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let ty = cx.tables.expr_ty(assignee);
let rty = cx.tables.expr_ty(rhs);
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macro_rules! ops {
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($op:expr,
$cx:expr,
$ty:expr,
$rty:expr,
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$($trait_name:ident),+) => {
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match $op {
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$(hir::BinOpKind::$trait_name => {
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let [krate, module] = crate::utils::paths::OPS_MODULE;
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let path = [krate, module, concat!(stringify!($trait_name), "Assign")];
let trait_id = if let Some(trait_id) = get_trait_def_id($cx, &path) {
trait_id
} else {
return; // useless if the trait doesn't exist
};
// check that we are not inside an `impl AssignOp` of this exact operation
let parent_fn = cx.tcx.hir().get_parent(e.id);
let parent_impl = cx.tcx.hir().get_parent(parent_fn);
// the crate node is the only one that is not in the map
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if_chain! {
if parent_impl != ast::CRATE_NODE_ID;
if let hir::Node::Item(item) = cx.tcx.hir().get(parent_impl);
if let hir::ItemKind::Impl(_, _, _, _, Some(trait_ref), _, _) =
&item.node;
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if trait_ref.path.def.def_id() == trait_id;
then { return; }
}
implements_trait($cx, $ty, trait_id, &[$rty])
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},)*
_ => false,
}
}
}
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if ops!(
op.node,
cx,
ty,
rty.into(),
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Add,
Sub,
Mul,
Div,
Rem,
And,
Or,
BitAnd,
BitOr,
BitXor,
Shr,
Shl
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) {
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span_lint_and_then(
cx,
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ASSIGN_OP_PATTERN,
expr.span,
"manual implementation of an assign operation",
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|db| {
if let (Some(snip_a), Some(snip_r)) =
(snippet_opt(cx, assignee.span), snippet_opt(cx, rhs.span))
{
db.span_suggestion_with_applicability(
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expr.span,
"replace it with",
format!("{} {}= {}", snip_a, op.node.as_str(), snip_r),
Applicability::MachineApplicable,
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);
}
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},
);
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}
};
let mut visitor = ExprVisitor {
assignee,
counter: 0,
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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)
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&& cx.tables.expr_ty(assignee).is_primitive_ty()
{
match op.node {
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hir::BinOpKind::Add
| hir::BinOpKind::Mul
| hir::BinOpKind::And
| hir::BinOpKind::Or
| hir::BinOpKind::BitXor
| hir::BinOpKind::BitAnd
| hir::BinOpKind::BitOr => {
lint(assignee, l);
},
_ => {},
}
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}
}
}
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},
_ => {},
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}
}
}
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fn is_commutative(op: hir::BinOpKind) -> bool {
use rustc::hir::BinOpKind::*;
match op {
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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
}
}