Move `AssignOps` into `Operators` lint pass

9 files changed, 261 insertions, 243 deletions

diff --git a/clippy_lints/src/assign_ops.rs b/clippy_lints/src/assign_ops.rs
deleted file mode 100644
index f81da2d4223..00000000000
--- a/clippy_lints/src/assign_ops.rs
+++ /dev/null
@@ -1,235 +0,0 @@
-use clippy_utils::diagnostics::span_lint_and_then;
-use clippy_utils::source::snippet_opt;
-use clippy_utils::ty::implements_trait;
-use clippy_utils::{binop_traits, sugg};
-use clippy_utils::{eq_expr_value, trait_ref_of_method};
-use if_chain::if_chain;
-use rustc_errors::Applicability;
-use rustc_hir as hir;
-use rustc_hir::intravisit::{walk_expr, Visitor};
-use rustc_lint::{LateContext, LateLintPass};
-use rustc_session::{declare_lint_pass, declare_tool_lint};
-
-declare_clippy_lint! {
-    /// ### 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;
-    /// let b = 0;
-    /// // ...
-    ///
-    /// a = a + b;
-    /// ```
-    ///
-    /// Use instead:
-    /// ```rust
-    /// let mut a = 5;
-    /// let b = 0;
-    /// // ...
-    ///
-    /// a += b;
-    /// ```
-    #[clippy::version = "pre 1.29.0"]
-    pub ASSIGN_OP_PATTERN,
-    style,
-    "assigning the result of an operation on a variable to that same variable"
-}
-
-declare_clippy_lint! {
-    /// ### 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 behavior it should be
-    /// written as `a = a op a op b` as it's less confusing.
-    ///
-    /// ### Example
-    /// ```rust
-    /// let mut a = 5;
-    /// let b = 2;
-    /// // ...
-    /// a += a + b;
-    /// ```
-    #[clippy::version = "pre 1.29.0"]
-    pub MISREFACTORED_ASSIGN_OP,
-    suspicious,
-    "having a variable on both sides of an assign op"
-}
-
-declare_lint_pass!(AssignOps => [ASSIGN_OP_PATTERN, MISREFACTORED_ASSIGN_OP]);
-
-impl<'tcx> LateLintPass<'tcx> for AssignOps {
-    #[allow(clippy::too_many_lines)]
-    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
-        match &expr.kind {
-            hir::ExprKind::AssignOp(op, lhs, rhs) => {
-                if let hir::ExprKind::Binary(binop, l, r) = &rhs.kind {
-                    if op.node != binop.node {
-                        return;
-                    }
-                    // lhs op= l op r
-                    if eq_expr_value(cx, lhs, l) {
-                        lint_misrefactored_assign_op(cx, expr, *op, rhs, lhs, r);
-                    }
-                    // lhs op= l commutative_op r
-                    if is_commutative(op.node) && eq_expr_value(cx, lhs, r) {
-                        lint_misrefactored_assign_op(cx, expr, *op, rhs, lhs, l);
-                    }
-                }
-            },
-            hir::ExprKind::Assign(assignee, e, _) => {
-                if let hir::ExprKind::Binary(op, l, r) = &e.kind {
-                    let lint = |assignee: &hir::Expr<'_>, rhs: &hir::Expr<'_>| {
-                        let ty = cx.typeck_results().expr_ty(assignee);
-                        let rty = cx.typeck_results().expr_ty(rhs);
-                        if_chain! {
-                            if let Some((_, lang_item)) = binop_traits(op.node);
-                            if let Ok(trait_id) = cx.tcx.lang_items().require(lang_item);
-                            let parent_fn = cx.tcx.hir().get_parent_item(e.hir_id);
-                            if trait_ref_of_method(cx, parent_fn)
-                                .map_or(true, |t| t.path.res.def_id() != trait_id);
-                            if implements_trait(cx, ty, trait_id, &[rty.into()]);
-                            then {
-                                span_lint_and_then(
-                                    cx,
-                                    ASSIGN_OP_PATTERN,
-                                    expr.span,
-                                    "manual implementation of an assign operation",
-                                    |diag| {
-                                        if let (Some(snip_a), Some(snip_r)) =
-                                            (snippet_opt(cx, assignee.span), snippet_opt(cx, rhs.span))
-                                        {
-                                            diag.span_suggestion(
-                                                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 eq_expr_value(cx, assignee, l) {
-                            lint(assignee, r);
-                        }
-                        // a = b commutative_op a
-                        // Limited to primitive type as these ops are know to be commutative
-                        if eq_expr_value(cx, assignee, r) && cx.typeck_results().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 lint_misrefactored_assign_op(
-    cx: &LateContext<'_>,
-    expr: &hir::Expr<'_>,
-    op: hir::BinOp,
-    rhs: &hir::Expr<'_>,
-    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",
-        |diag| {
-            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(op.node.into(), a, r));
-                diag.span_suggestion(
-                    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::MaybeIncorrect,
-                );
-                diag.span_suggestion(
-                    expr.span,
-                    "or",
-                    long,
-                    Applicability::MaybeIncorrect, // snippet
-                );
-            }
-        },
-    );
-}
-
-#[must_use]
-fn is_commutative(op: hir::BinOpKind) -> bool {
-    use rustc_hir::BinOpKind::{
-        Add, And, BitAnd, BitOr, BitXor, Div, Eq, Ge, Gt, Le, Lt, Mul, Ne, Or, Rem, Shl, Shr, Sub,
-    };
-    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> {
-    assignee: &'a hir::Expr<'a>,
-    counter: u8,
-    cx: &'a LateContext<'tcx>,
-}
-
-impl<'a, 'tcx> Visitor<'tcx> for ExprVisitor<'a, 'tcx> {
-    fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) {
-        if eq_expr_value(self.cx, self.assignee, expr) {
-            self.counter += 1;
-        }
-
-        walk_expr(self, expr);
-    }
-}
diff --git a/clippy_lints/src/lib.register_all.rs b/clippy_lints/src/lib.register_all.rs
index 7728157d228..b43c11330f0 100644
--- a/clippy_lints/src/lib.register_all.rs
+++ b/clippy_lints/src/lib.register_all.rs
@@ -6,8 +6,6 @@ store.register_group(true, "clippy::all", Some("clippy_all"), vec![
     LintId::of(almost_complete_letter_range::ALMOST_COMPLETE_LETTER_RANGE),
     LintId::of(approx_const::APPROX_CONSTANT),
     LintId::of(assertions_on_constants::ASSERTIONS_ON_CONSTANTS),
-    LintId::of(assign_ops::ASSIGN_OP_PATTERN),
-    LintId::of(assign_ops::MISREFACTORED_ASSIGN_OP),
     LintId::of(async_yields_async::ASYNC_YIELDS_ASYNC),
     LintId::of(attrs::BLANKET_CLIPPY_RESTRICTION_LINTS),
     LintId::of(attrs::DEPRECATED_CFG_ATTR),
@@ -260,6 +258,8 @@ store.register_group(true, "clippy::all", Some("clippy_all"), vec![
     LintId::of(octal_escapes::OCTAL_ESCAPES),
     LintId::of(open_options::NONSENSICAL_OPEN_OPTIONS),
     LintId::of(operators::ABSURD_EXTREME_COMPARISONS),
+    LintId::of(operators::ASSIGN_OP_PATTERN),
+    LintId::of(operators::MISREFACTORED_ASSIGN_OP),
     LintId::of(option_env_unwrap::OPTION_ENV_UNWRAP),
     LintId::of(overflow_check_conditional::OVERFLOW_CHECK_CONDITIONAL),
     LintId::of(partialeq_ne_impl::PARTIALEQ_NE_IMPL),
diff --git a/clippy_lints/src/lib.register_lints.rs b/clippy_lints/src/lib.register_lints.rs
index 787ae1e79ec..231511d46b7 100644
--- a/clippy_lints/src/lib.register_lints.rs
+++ b/clippy_lints/src/lib.register_lints.rs
@@ -42,8 +42,6 @@ store.register_lints(&[
     asm_syntax::INLINE_ASM_X86_ATT_SYNTAX,
     asm_syntax::INLINE_ASM_X86_INTEL_SYNTAX,
     assertions_on_constants::ASSERTIONS_ON_CONSTANTS,
-    assign_ops::ASSIGN_OP_PATTERN,
-    assign_ops::MISREFACTORED_ASSIGN_OP,
     async_yields_async::ASYNC_YIELDS_ASYNC,
     attrs::ALLOW_ATTRIBUTES_WITHOUT_REASON,
     attrs::BLANKET_CLIPPY_RESTRICTION_LINTS,
@@ -435,8 +433,10 @@ store.register_lints(&[
     only_used_in_recursion::ONLY_USED_IN_RECURSION,
     open_options::NONSENSICAL_OPEN_OPTIONS,
     operators::ABSURD_EXTREME_COMPARISONS,
+    operators::ASSIGN_OP_PATTERN,
     operators::FLOAT_ARITHMETIC,
     operators::INTEGER_ARITHMETIC,
+    operators::MISREFACTORED_ASSIGN_OP,
     option_env_unwrap::OPTION_ENV_UNWRAP,
     option_if_let_else::OPTION_IF_LET_ELSE,
     overflow_check_conditional::OVERFLOW_CHECK_CONDITIONAL,
diff --git a/clippy_lints/src/lib.register_style.rs b/clippy_lints/src/lib.register_style.rs
index d52ec50e542..78df54a4fff 100644
--- a/clippy_lints/src/lib.register_style.rs
+++ b/clippy_lints/src/lib.register_style.rs
@@ -4,7 +4,6 @@
 
 store.register_group(true, "clippy::style", Some("clippy_style"), vec![
     LintId::of(assertions_on_constants::ASSERTIONS_ON_CONSTANTS),
-    LintId::of(assign_ops::ASSIGN_OP_PATTERN),
     LintId::of(blacklisted_name::BLACKLISTED_NAME),
     LintId::of(blocks_in_if_conditions::BLOCKS_IN_IF_CONDITIONS),
     LintId::of(bool_assert_comparison::BOOL_ASSERT_COMPARISON),
@@ -98,6 +97,7 @@ store.register_group(true, "clippy::style", Some("clippy_style"), vec![
     LintId::of(non_copy_const::BORROW_INTERIOR_MUTABLE_CONST),
     LintId::of(non_copy_const::DECLARE_INTERIOR_MUTABLE_CONST),
     LintId::of(non_expressive_names::JUST_UNDERSCORES_AND_DIGITS),
+    LintId::of(operators::ASSIGN_OP_PATTERN),
     LintId::of(ptr::CMP_NULL),
     LintId::of(ptr::PTR_ARG),
     LintId::of(ptr_eq::PTR_EQ),
diff --git a/clippy_lints/src/lib.register_suspicious.rs b/clippy_lints/src/lib.register_suspicious.rs
index 7b13713c36e..4ee89b7bec5 100644
--- a/clippy_lints/src/lib.register_suspicious.rs
+++ b/clippy_lints/src/lib.register_suspicious.rs
@@ -4,7 +4,6 @@
 
 store.register_group(true, "clippy::suspicious", Some("clippy_suspicious"), vec![
     LintId::of(almost_complete_letter_range::ALMOST_COMPLETE_LETTER_RANGE),
-    LintId::of(assign_ops::MISREFACTORED_ASSIGN_OP),
     LintId::of(attrs::BLANKET_CLIPPY_RESTRICTION_LINTS),
     LintId::of(await_holding_invalid::AWAIT_HOLDING_INVALID_TYPE),
     LintId::of(await_holding_invalid::AWAIT_HOLDING_LOCK),
@@ -29,6 +28,7 @@ store.register_group(true, "clippy::suspicious", Some("clippy_suspicious"), vec!
     LintId::of(methods::SUSPICIOUS_MAP),
     LintId::of(mut_key::MUTABLE_KEY_TYPE),
     LintId::of(octal_escapes::OCTAL_ESCAPES),
+    LintId::of(operators::MISREFACTORED_ASSIGN_OP),
     LintId::of(rc_clone_in_vec_init::RC_CLONE_IN_VEC_INIT),
     LintId::of(suspicious_trait_impl::SUSPICIOUS_ARITHMETIC_IMPL),
     LintId::of(suspicious_trait_impl::SUSPICIOUS_OP_ASSIGN_IMPL),
diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs
index f1d28201309..0f9e3b06233 100644
--- a/clippy_lints/src/lib.rs
+++ b/clippy_lints/src/lib.rs
@@ -174,7 +174,6 @@ mod as_conversions;
 mod as_underscore;
 mod asm_syntax;
 mod assertions_on_constants;
-mod assign_ops;
 mod async_yields_async;
 mod attrs;
 mod await_holding_invalid;
@@ -704,7 +703,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(move || Box::new(doc::DocMarkdown::new(doc_valid_idents.clone())));
     store.register_late_pass(|| Box::new(neg_multiply::NegMultiply));
     store.register_late_pass(|| Box::new(mem_forget::MemForget));
-    store.register_late_pass(|| Box::new(assign_ops::AssignOps));
     store.register_late_pass(|| Box::new(let_if_seq::LetIfSeq));
     store.register_late_pass(|| Box::new(mixed_read_write_in_expression::EvalOrderDependence));
     store.register_late_pass(|| Box::new(missing_doc::MissingDoc::new()));
diff --git a/clippy_lints/src/operators/assign_op_pattern.rs b/clippy_lints/src/operators/assign_op_pattern.rs
new file mode 100644
index 00000000000..979e0a66707
--- /dev/null
+++ b/clippy_lints/src/operators/assign_op_pattern.rs
@@ -0,0 +1,101 @@
+use clippy_utils::binop_traits;
+use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::source::snippet_opt;
+use clippy_utils::ty::implements_trait;
+use clippy_utils::{eq_expr_value, trait_ref_of_method};
+use if_chain::if_chain;
+use rustc_errors::Applicability;
+use rustc_hir as hir;
+use rustc_hir::intravisit::{walk_expr, Visitor};
+use rustc_lint::LateContext;
+
+use super::ASSIGN_OP_PATTERN;
+
+pub(super) fn check<'tcx>(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx hir::Expr<'_>,
+    assignee: &'tcx hir::Expr<'_>,
+    e: &'tcx hir::Expr<'_>,
+) {
+    if let hir::ExprKind::Binary(op, l, r) = &e.kind {
+        let lint = |assignee: &hir::Expr<'_>, rhs: &hir::Expr<'_>| {
+            let ty = cx.typeck_results().expr_ty(assignee);
+            let rty = cx.typeck_results().expr_ty(rhs);
+            if_chain! {
+                if let Some((_, lang_item)) = binop_traits(op.node);
+                if let Ok(trait_id) = cx.tcx.lang_items().require(lang_item);
+                let parent_fn = cx.tcx.hir().get_parent_item(e.hir_id);
+                if trait_ref_of_method(cx, parent_fn)
+                    .map_or(true, |t| t.path.res.def_id() != trait_id);
+                if implements_trait(cx, ty, trait_id, &[rty.into()]);
+                then {
+                    span_lint_and_then(
+                        cx,
+                        ASSIGN_OP_PATTERN,
+                        expr.span,
+                        "manual implementation of an assign operation",
+                        |diag| {
+                            if let (Some(snip_a), Some(snip_r)) =
+                                (snippet_opt(cx, assignee.span), snippet_opt(cx, rhs.span))
+                            {
+                                diag.span_suggestion(
+                                    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 eq_expr_value(cx, assignee, l) {
+                lint(assignee, r);
+            }
+            // a = b commutative_op a
+            // Limited to primitive type as these ops are know to be commutative
+            if eq_expr_value(cx, assignee, r) && cx.typeck_results().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);
+                    },
+                    _ => {},
+                }
+            }
+        }
+    }
+}
+
+struct ExprVisitor<'a, 'tcx> {
+    assignee: &'a hir::Expr<'a>,
+    counter: u8,
+    cx: &'a LateContext<'tcx>,
+}
+
+impl<'a, 'tcx> Visitor<'tcx> for ExprVisitor<'a, 'tcx> {
+    fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) {
+        if eq_expr_value(self.cx, self.assignee, expr) {
+            self.counter += 1;
+        }
+
+        walk_expr(self, expr);
+    }
+}
diff --git a/clippy_lints/src/operators/misrefactored_assign_op.rs b/clippy_lints/src/operators/misrefactored_assign_op.rs
new file mode 100644
index 00000000000..0024384d927
--- /dev/null
+++ b/clippy_lints/src/operators/misrefactored_assign_op.rs
@@ -0,0 +1,84 @@
+use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::eq_expr_value;
+use clippy_utils::source::snippet_opt;
+use clippy_utils::sugg;
+use rustc_errors::Applicability;
+use rustc_hir as hir;
+use rustc_lint::LateContext;
+
+use super::MISREFACTORED_ASSIGN_OP;
+
+pub(super) fn check<'tcx>(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx hir::Expr<'_>,
+    op: hir::BinOpKind,
+    lhs: &'tcx hir::Expr<'_>,
+    rhs: &'tcx hir::Expr<'_>,
+) {
+    if let hir::ExprKind::Binary(binop, l, r) = &rhs.kind {
+        if op != binop.node {
+            return;
+        }
+        // lhs op= l op r
+        if eq_expr_value(cx, lhs, l) {
+            lint_misrefactored_assign_op(cx, expr, op, rhs, lhs, r);
+        }
+        // lhs op= l commutative_op r
+        if is_commutative(op) && eq_expr_value(cx, lhs, r) {
+            lint_misrefactored_assign_op(cx, expr, op, rhs, lhs, l);
+        }
+    }
+}
+
+fn lint_misrefactored_assign_op(
+    cx: &LateContext<'_>,
+    expr: &hir::Expr<'_>,
+    op: hir::BinOpKind,
+    rhs: &hir::Expr<'_>,
+    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",
+        |diag| {
+            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(op.into(), a, r));
+                diag.span_suggestion(
+                    expr.span,
+                    &format!(
+                        "did you mean `{} = {} {} {}` or `{}`? Consider replacing it with",
+                        snip_a,
+                        snip_a,
+                        op.as_str(),
+                        snip_r,
+                        long
+                    ),
+                    format!("{} {}= {}", snip_a, op.as_str(), snip_r),
+                    Applicability::MaybeIncorrect,
+                );
+                diag.span_suggestion(
+                    expr.span,
+                    "or",
+                    long,
+                    Applicability::MaybeIncorrect, // snippet
+                );
+            }
+        },
+    );
+}
+
+#[must_use]
+fn is_commutative(op: hir::BinOpKind) -> bool {
+    use rustc_hir::BinOpKind::{
+        Add, And, BitAnd, BitOr, BitXor, Div, Eq, Ge, Gt, Le, Lt, Mul, Ne, Or, Rem, Shl, Shr, Sub,
+    };
+    match op {
+        Add | Mul | And | Or | BitXor | BitAnd | BitOr | Eq | Ne => true,
+        Sub | Div | Rem | Shl | Shr | Lt | Le | Ge | Gt => false,
+    }
+}
diff --git a/clippy_lints/src/operators/mod.rs b/clippy_lints/src/operators/mod.rs
index a7495f042da..c1d038aa2b1 100644
--- a/clippy_lints/src/operators/mod.rs
+++ b/clippy_lints/src/operators/mod.rs
@@ -3,6 +3,8 @@ use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::{declare_tool_lint, impl_lint_pass};
 
 mod absurd_extreme_comparisons;
+mod assign_op_pattern;
+mod misrefactored_assign_op;
 mod numeric_arithmetic;
 
 declare_clippy_lint! {
@@ -82,6 +84,68 @@ declare_clippy_lint! {
     "any floating-point arithmetic statement"
 }
 
+declare_clippy_lint! {
+    /// ### 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;
+    /// let b = 0;
+    /// // ...
+    ///
+    /// a = a + b;
+    /// ```
+    ///
+    /// Use instead:
+    /// ```rust
+    /// let mut a = 5;
+    /// let b = 0;
+    /// // ...
+    ///
+    /// a += b;
+    /// ```
+    #[clippy::version = "pre 1.29.0"]
+    pub ASSIGN_OP_PATTERN,
+    style,
+    "assigning the result of an operation on a variable to that same variable"
+}
+
+declare_clippy_lint! {
+    /// ### 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 behavior it should be
+    /// written as `a = a op a op b` as it's less confusing.
+    ///
+    /// ### Example
+    /// ```rust
+    /// let mut a = 5;
+    /// let b = 2;
+    /// // ...
+    /// a += a + b;
+    /// ```
+    #[clippy::version = "pre 1.29.0"]
+    pub MISREFACTORED_ASSIGN_OP,
+    suspicious,
+    "having a variable on both sides of an assign op"
+}
+
 #[derive(Default)]
 pub struct Operators {
     arithmetic_context: numeric_arithmetic::Context,
@@ -90,6 +154,8 @@ impl_lint_pass!(Operators => [
     ABSURD_EXTREME_COMPARISONS,
     INTEGER_ARITHMETIC,
     FLOAT_ARITHMETIC,
+    ASSIGN_OP_PATTERN,
+    MISREFACTORED_ASSIGN_OP,
 ]);
 impl<'tcx> LateLintPass<'tcx> for Operators {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
@@ -102,6 +168,10 @@ impl<'tcx> LateLintPass<'tcx> for Operators {
             },
             ExprKind::AssignOp(op, lhs, rhs) => {
                 self.arithmetic_context.check_binary(cx, e, op.node, lhs, rhs);
+                misrefactored_assign_op::check(cx, e, op.node, lhs, rhs);
+            },
+            ExprKind::Assign(lhs, rhs, _) => {
+                assign_op_pattern::check(cx, e, lhs, rhs);
             },
             ExprKind::Unary(op, arg) => {
                 if op == UnOp::Neg {