use rustc::hir;
use rustc::lint::*;
use syntax::ast;
use utils::{span_lint_and_then, snippet_opt, SpanlessEq, get_trait_def_id, implements_trait};
use utils::{higher, sugg};
/// **What it does:** Checks for compound assignment operations (`+=` and similar).
///
/// **Why is this bad?** Projects with many developers from languages without
/// those operations may find them unreadable and not worth their weight.
///
/// **Known problems:** Types implementing `OpAssign` don't necessarily implement `Op`.
///
/// **Example:**
/// ```rust
/// a += 1;
/// ```
declare_restriction_lint! {
pub ASSIGN_OPS,
"any compound assignment operation"
}
/// **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_lint! {
pub ASSIGN_OP_PATTERN,
Warn,
"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:** Someone might actually mean `a op= a op b`, but that
/// should rather be written as `a = (2 * a) op b` where applicable.
///
/// **Example:**
/// ```rust
/// let mut a = 5;
/// ...
/// a += a + b;
/// ```
declare_lint! {
pub MISREFACTORED_ASSIGN_OP,
Warn,
"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_OPS, 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::ExprAssignOp(op, ref lhs, ref rhs) => {
span_lint_and_then(cx, ASSIGN_OPS, expr.span, "assign operation detected", |db| {
let lhs = &sugg::Sugg::hir(cx, lhs, "..");
let rhs = &sugg::Sugg::hir(cx, rhs, "..");
db.span_suggestion(expr.span,
"replace it with",
format!("{} = {}", lhs, sugg::make_binop(higher::binop(op.node), lhs, rhs)));
});
if let hir::ExprBinary(binop, ref l, ref r) = rhs.node {
if op.node == binop.node {
let lint = |assignee: &hir::Expr, rhs: &hir::Expr| {
let ty = cx.tables.expr_ty(assignee);
if ty.walk_shallow().next().is_some() {
return; // implements_trait does not work with generics
}
let rty = cx.tables.expr_ty(rhs);
if rty.walk_shallow().next().is_some() {
return; // implements_trait does not work with generics
}
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.span)) {
db.span_suggestion(expr.span,
"replace it with",
format!("{} {}= {}",
snip_a,
op.node.as_str(),
snip_r));
});
};
// 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::ExprAssign(ref assignee, ref e) => {
if let hir::ExprBinary(op, ref l, ref r) = e.node {
#[allow(cyclomatic_complexity)]
let lint = |assignee: &hir::Expr, rhs: &hir::Expr| {
let ty = cx.tables.expr_ty(assignee);
if ty.walk_shallow().next().is_some() {
return; // implements_trait does not work with generics
}
let rty = cx.tables.expr_ty(rhs);
if rty.walk_shallow().next().is_some() {
return; // implements_trait does not work with generics
}
macro_rules! ops {
($op:expr,
$cx:expr,
$ty:expr,
$rty:expr,
$($trait_name:ident:$full_trait_name:ident),+) => {
match $op {
$(hir::$full_trait_name => {
let [krate, module] = ::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_let_chain!{[
parent_impl != ast::CRATE_NODE_ID,
let hir::map::Node::NodeItem(item) = cx.tcx.hir.get(parent_impl),
let hir::Item_::ItemImpl(_, _, _, _, Some(ref trait_ref), _, _) = item.node,
trait_ref.path.def.def_id() == trait_id
], { return; }}
implements_trait($cx, $ty, trait_id, &[$rty], None)
},)*
_ => false,
}
}
}
if ops!(op.node,
cx,
ty,
rty,
Add: BiAdd,
Sub: BiSub,
Mul: BiMul,
Div: BiDiv,
Rem: BiRem,
And: BiAnd,
Or: BiOr,
BitAnd: BiBitAnd,
BitOr: BiBitOr,
BitXor: BiBitXor,
Shr: BiShr,
Shl: BiShl) {
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(expr.span,
"replace it with",
format!("{} {}= {}",
snip_a,
op.node.as_str(),
snip_r));
});
}
};
// a = a op b
if SpanlessEq::new(cx).ignore_fn().eq_expr(assignee, l) {
lint(assignee, r);
}
// a = b commutative_op a
if SpanlessEq::new(cx).ignore_fn().eq_expr(assignee, r) {
match op.node {
hir::BiAdd | hir::BiMul | hir::BiAnd | hir::BiOr | hir::BiBitXor | hir::BiBitAnd |
hir::BiBitOr => {
lint(assignee, l);
},
_ => {},
}
}
}
},
_ => {},
}
}
}
fn is_commutative(op: hir::BinOp_) -> bool {
use rustc::hir::BinOp_::*;
match op {
BiAdd | BiMul | BiAnd | BiOr | BiBitXor | BiBitAnd | BiBitOr | BiEq | BiNe => true,
BiSub | BiDiv | BiRem | BiShl | BiShr | BiLt | BiLe | BiGe | BiGt => false,
}
}