220 lines
10 KiB
Rust
220 lines
10 KiB
Rust
use rustc::hir;
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use rustc::lint::*;
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use syntax::ast;
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use utils::{span_lint_and_then, snippet_opt, SpanlessEq, get_trait_def_id, implements_trait};
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use utils::{higher, sugg};
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/// **What it does:** Checks for compound assignment operations (`+=` and similar).
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///
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/// **Why is this bad?** Projects with many developers from languages without
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/// those operations may find them unreadable and not worth their weight.
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///
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/// **Known problems:** Types implementing `OpAssign` don't necessarily implement `Op`.
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///
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/// **Example:**
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/// ```rust
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/// a += 1;
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/// ```
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declare_restriction_lint! {
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pub ASSIGN_OPS,
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"any compound assignment operation"
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}
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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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///
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/// **Known problems:** While forbidden by the spec, `OpAssign` traits may have
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/// implementations that differ from the regular `Op` impl.
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///
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/// **Example:**
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/// ```rust
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/// let mut a = 5;
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/// ...
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/// a = a + b;
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/// ```
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declare_lint! {
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pub ASSIGN_OP_PATTERN,
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Warn,
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"assigning the result of an operation on a variable to that same variable"
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}
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/// **What it does:** Checks for `a op= a op b` or `a op= b op a` patterns.
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///
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/// **Why is this bad?** Most likely these are bugs where one meant to write `a op= b`.
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///
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/// **Known problems:** Someone might actually mean `a op= a op b`, but that
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/// should rather be written as `a = (2 * a) op b` where applicable.
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///
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/// **Example:**
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/// ```rust
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/// let mut a = 5;
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/// ...
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/// a += a + b;
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/// ```
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declare_lint! {
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pub MISREFACTORED_ASSIGN_OP,
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Warn,
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"having a variable on both sides of an assign op"
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}
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#[derive(Copy, Clone, Default)]
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pub struct AssignOps;
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impl LintPass for AssignOps {
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fn get_lints(&self) -> LintArray {
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lint_array!(ASSIGN_OPS, ASSIGN_OP_PATTERN, MISREFACTORED_ASSIGN_OP)
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for AssignOps {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr) {
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match expr.node {
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hir::ExprAssignOp(op, ref lhs, ref rhs) => {
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span_lint_and_then(cx, ASSIGN_OPS, expr.span, "assign operation detected", |db| {
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let lhs = &sugg::Sugg::hir(cx, lhs, "..");
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let rhs = &sugg::Sugg::hir(cx, rhs, "..");
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db.span_suggestion(expr.span,
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"replace it with",
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format!("{} = {}", lhs, sugg::make_binop(higher::binop(op.node), lhs, rhs)));
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});
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if let hir::ExprBinary(binop, ref l, ref r) = rhs.node {
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if op.node == binop.node {
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let lint = |assignee: &hir::Expr, rhs: &hir::Expr| {
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let ty = cx.tables.expr_ty(assignee);
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if ty.walk_shallow().next().is_some() {
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return; // implements_trait does not work with generics
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}
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let rty = cx.tables.expr_ty(rhs);
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if rty.walk_shallow().next().is_some() {
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return; // implements_trait does not work with generics
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}
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span_lint_and_then(cx,
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MISREFACTORED_ASSIGN_OP,
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expr.span,
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"variable appears on both sides of an assignment operation",
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|db| if let (Some(snip_a), Some(snip_r)) =
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(snippet_opt(cx, assignee.span), snippet_opt(cx, rhs.span)) {
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db.span_suggestion(expr.span,
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"replace it with",
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format!("{} {}= {}",
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snip_a,
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op.node.as_str(),
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snip_r));
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});
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};
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// lhs op= l op r
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if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs, l) {
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lint(lhs, r);
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}
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// lhs op= l commutative_op r
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if is_commutative(op.node) && SpanlessEq::new(cx).ignore_fn().eq_expr(lhs, r) {
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lint(lhs, l);
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}
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}
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}
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},
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hir::ExprAssign(ref assignee, ref e) => {
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if let hir::ExprBinary(op, ref l, ref r) = e.node {
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#[allow(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);
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if ty.walk_shallow().next().is_some() {
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return; // implements_trait does not work with generics
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}
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let rty = cx.tables.expr_ty(rhs);
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if rty.walk_shallow().next().is_some() {
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return; // implements_trait does not work with generics
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}
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macro_rules! ops {
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($op:expr,
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$cx:expr,
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$ty:expr,
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$rty:expr,
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$($trait_name:ident:$full_trait_name:ident),+) => {
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match $op {
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$(hir::$full_trait_name => {
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let [krate, module] = ::utils::paths::OPS_MODULE;
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let path = [krate, module, concat!(stringify!($trait_name), "Assign")];
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let trait_id = if let Some(trait_id) = get_trait_def_id($cx, &path) {
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trait_id
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} else {
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return; // useless if the trait doesn't exist
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};
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// check that we are not inside an `impl AssignOp` of this exact operation
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let parent_fn = cx.tcx.hir.get_parent(e.id);
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let parent_impl = cx.tcx.hir.get_parent(parent_fn);
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// the crate node is the only one that is not in the map
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if_let_chain!{[
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parent_impl != ast::CRATE_NODE_ID,
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let hir::map::Node::NodeItem(item) = cx.tcx.hir.get(parent_impl),
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let hir::Item_::ItemImpl(_, _, _, _, Some(ref trait_ref), _, _) = item.node,
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trait_ref.path.def.def_id() == trait_id
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], { return; }}
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implements_trait($cx, $ty, trait_id, &[$rty], None)
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},)*
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_ => false,
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}
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}
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}
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if ops!(op.node,
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cx,
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ty,
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rty,
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Add: BiAdd,
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Sub: BiSub,
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Mul: BiMul,
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Div: BiDiv,
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Rem: BiRem,
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And: BiAnd,
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Or: BiOr,
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BitAnd: BiBitAnd,
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BitOr: BiBitOr,
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BitXor: BiBitXor,
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Shr: BiShr,
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Shl: BiShl) {
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span_lint_and_then(cx,
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ASSIGN_OP_PATTERN,
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expr.span,
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"manual implementation of an assign operation",
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|db| if let (Some(snip_a), Some(snip_r)) =
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(snippet_opt(cx, assignee.span), snippet_opt(cx, rhs.span)) {
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db.span_suggestion(expr.span,
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"replace it with",
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format!("{} {}= {}",
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snip_a,
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op.node.as_str(),
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snip_r));
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});
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}
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};
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// a = a op b
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if SpanlessEq::new(cx).ignore_fn().eq_expr(assignee, l) {
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lint(assignee, r);
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}
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// a = b commutative_op a
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if SpanlessEq::new(cx).ignore_fn().eq_expr(assignee, r) {
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match op.node {
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hir::BiAdd | hir::BiMul | hir::BiAnd | hir::BiOr | hir::BiBitXor | hir::BiBitAnd |
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hir::BiBitOr => {
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lint(assignee, l);
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},
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_ => {},
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}
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}
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}
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},
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_ => {},
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}
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}
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}
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fn is_commutative(op: hir::BinOp_) -> bool {
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use rustc::hir::BinOp_::*;
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match op {
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BiAdd | BiMul | BiAnd | BiOr | BiBitXor | BiBitAnd | BiBitOr | BiEq | BiNe => true,
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BiSub | BiDiv | BiRem | BiShl | BiShr | BiLt | BiLe | BiGe | BiGt => false,
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}
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}
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