Tighten up assignment operator representations.

In the AST, currently we use `BinOpKind` within `ExprKind::AssignOp` and
`AssocOp::AssignOp`, even though this allows some nonsensical
combinations. E.g. there is no `&&=` operator. Likewise for HIR and
THIR.

This commit introduces `AssignOpKind` which only includes the ten
assignable operators, and uses it in `ExprKind::AssignOp` and
`AssocOp::AssignOp`. (And does similar things for `hir::ExprKind` and
`thir::ExprKind`.) This avoids the possibility of nonsensical
combinations, as seen by the removal of the `bug!` case in
`lang_item_for_binop`.

The commit is mostly plumbing, including:
- Adds an `impl From<AssignOpKind> for BinOpKind` (AST) and `impl
  From<AssignOp> for BinOp` (MIR/THIR).
- `BinOpCategory` can now be created from both `BinOpKind` and
  `AssignOpKind`.
- Replaces the `IsAssign` type with `Op`, which has more information and
  a few methods.
- `suggest_swapping_lhs_and_rhs`: moves the condition to the call site,
  it's easier that way.
- `check_expr_inner`: had to factor out some code into a separate
  method.

I'm on the fence about whether avoiding the nonsensical combinations is
worth the extra code.

Author: nnethercote

clippy_lints/src/format_push_string.rs

@@ -1,7 +1,7 @@
 use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::higher;
 use clippy_utils::ty::is_type_lang_item;
-use rustc_hir::{BinOpKind, Expr, ExprKind, LangItem, MatchSource};
+use rustc_hir::{AssignOpKind, Expr, ExprKind, LangItem, MatchSource};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::declare_lint_pass;
 use rustc_span::sym;
@@ -77,7 +77,7 @@ impl<'tcx> LateLintPass<'tcx> for FormatPushString {
                     return;
                 }
             },
-            ExprKind::AssignOp(op, left, arg) if op.node == BinOpKind::Add && is_string(cx, left) => arg,
+            ExprKind::AssignOp(op, left, arg) if op.node == AssignOpKind::AddAssign && is_string(cx, left) => arg,
             _ => return,
         };
         if is_format(cx, arg) {

clippy_lints/src/implicit_saturating_add.rs

@@ -5,7 +5,7 @@ use clippy_utils::source::snippet_with_context;
 use rustc_ast::ast::{LitIntType, LitKind};
 use rustc_data_structures::packed::Pu128;
 use rustc_errors::Applicability;
-use rustc_hir::{BinOpKind, Block, Expr, ExprKind, Stmt, StmtKind};
+use rustc_hir::{AssignOpKind, BinOpKind, Block, Expr, ExprKind, Stmt, StmtKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty::{IntTy, Ty, UintTy};
 use rustc_session::declare_lint_pass;
@@ -68,7 +68,7 @@ impl<'tcx> LateLintPass<'tcx> for ImplicitSaturatingAdd {
             && ex.span.ctxt() == ctxt
             && expr1.span.ctxt() == ctxt
             && clippy_utils::SpanlessEq::new(cx).eq_expr(l, target)
-            && BinOpKind::Add == op1.node
+            && AssignOpKind::AddAssign == op1.node
             && let ExprKind::Lit(lit) = value.kind
             && let LitKind::Int(Pu128(1), LitIntType::Unsuffixed) = lit.node
             && block.expr.is_none()

clippy_lints/src/implicit_saturating_sub.rs

@@ -8,7 +8,7 @@ use clippy_utils::{
 use rustc_ast::ast::LitKind;
 use rustc_data_structures::packed::Pu128;
 use rustc_errors::Applicability;
-use rustc_hir::{BinOp, BinOpKind, Expr, ExprKind, QPath};
+use rustc_hir::{AssignOpKind, BinOp, BinOpKind, Expr, ExprKind, QPath};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::impl_lint_pass;
 use rustc_span::Span;
@@ -366,7 +366,7 @@ fn subtracts_one<'a>(cx: &LateContext<'_>, expr: &'a Expr<'a>) -> Option<&'a Exp
     match peel_blocks_with_stmt(expr).kind {
         ExprKind::AssignOp(ref op1, target, value) => {
             // Check if literal being subtracted is one
-            (BinOpKind::Sub == op1.node && is_integer_literal(value, 1)).then_some(target)
+            (AssignOpKind::SubAssign == op1.node && is_integer_literal(value, 1)).then_some(target)
         },
         ExprKind::Assign(target, value, _) => {
             if let ExprKind::Binary(ref op1, left1, right1) = value.kind

clippy_lints/src/loops/utils.rs

@@ -3,7 +3,9 @@ use clippy_utils::{get_parent_expr, is_integer_const, path_to_local, path_to_loc
 use rustc_ast::ast::{LitIntType, LitKind};
 use rustc_errors::Applicability;
 use rustc_hir::intravisit::{Visitor, walk_expr, walk_local};
-use rustc_hir::{BinOpKind, BorrowKind, Expr, ExprKind, HirId, HirIdMap, LetStmt, Mutability, PatKind};
+use rustc_hir::{
+    AssignOpKind, BorrowKind, Expr, ExprKind, HirId, HirIdMap, LetStmt, Mutability, PatKind
+};
 use rustc_lint::LateContext;
 use rustc_middle::hir::nested_filter;
 use rustc_middle::ty::{self, Ty};
@@ -58,7 +60,7 @@ impl<'tcx> Visitor<'tcx> for IncrementVisitor<'_, 'tcx> {
                 match parent.kind {
                     ExprKind::AssignOp(op, lhs, rhs) => {
                         if lhs.hir_id == expr.hir_id {
-                            *state = if op.node == BinOpKind::Add
+                            *state = if op.node == AssignOpKind::AddAssign
                                 && is_integer_const(self.cx, rhs, 1)
                                 && *state == IncrementVisitorVarState::Initial
                                 && self.depth == 0

clippy_lints/src/mixed_read_write_in_expression.rs

@@ -261,10 +261,11 @@ fn check_expr<'tcx>(vis: &mut ReadVisitor<'_, 'tcx>, expr: &'tcx Expr<'_>) -> St
         | ExprKind::Assign(..)
         | ExprKind::Index(..)
         | ExprKind::Repeat(_, _)
-        | ExprKind::Struct(_, _, _) => {
+        | ExprKind::Struct(_, _, _)
+        | ExprKind::AssignOp(_, _, _) => {
             walk_expr(vis, expr);
         },
-        ExprKind::Binary(op, _, _) | ExprKind::AssignOp(op, _, _) => {
+        ExprKind::Binary(op, _, _) => {
             if op.node == BinOpKind::And || op.node == BinOpKind::Or {
                 // x && y and x || y always evaluate x first, so these are
                 // strictly sequenced.

clippy_lints/src/operators/arithmetic_side_effects.rs

@@ -335,9 +335,12 @@ impl<'tcx> LateLintPass<'tcx> for ArithmeticSideEffects {
             return;
         }
         match &expr.kind {
-            hir::ExprKind::AssignOp(op, lhs, rhs) | hir::ExprKind::Binary(op, lhs, rhs) => {
+            hir::ExprKind::Binary(op, lhs, rhs) => {
                 self.manage_bin_ops(cx, expr, op.node, lhs, rhs);
             },
+            hir::ExprKind::AssignOp(op, lhs, rhs) => {
+                self.manage_bin_ops(cx, expr, op.node.into(), lhs, rhs);
+            },
             hir::ExprKind::MethodCall(ps, receiver, args, _) => {
                 self.manage_method_call(args, cx, expr, ps, receiver);
             },

clippy_lints/src/operators/mod.rs

@@ -913,9 +913,10 @@ 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);
-                modulo_arithmetic::check(cx, e, op.node, lhs, rhs, false);
+                let bin_op = op.node.into();
+                self.arithmetic_context.check_binary(cx, e, bin_op, lhs, rhs);
+                misrefactored_assign_op::check(cx, e, bin_op, lhs, rhs);
+                modulo_arithmetic::check(cx, e, bin_op, lhs, rhs, false);
             },
             ExprKind::Assign(lhs, rhs, _) => {
                 assign_op_pattern::check(cx, e, lhs, rhs);

clippy_lints/src/suspicious_trait_impl.rs

@@ -5,6 +5,7 @@ use core::ops::ControlFlow;
 use rustc_hir as hir;
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::declare_lint_pass;
+use rustc_span::Span;
 
 declare_clippy_lint! {
     /// ### What it does
@@ -56,8 +57,27 @@ declare_lint_pass!(SuspiciousImpl => [SUSPICIOUS_ARITHMETIC_IMPL, SUSPICIOUS_OP_
 
 impl<'tcx> LateLintPass<'tcx> for SuspiciousImpl {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
-        if let hir::ExprKind::Binary(binop, _, _) | hir::ExprKind::AssignOp(binop, ..) = expr.kind
-            && let Some((binop_trait_lang, op_assign_trait_lang)) = binop_traits(binop.node)
+        match expr.kind {
+            hir::ExprKind::Binary(op, _, _) => {
+                self.check_expr_inner(cx, expr, op.node, op.span);
+            }
+            hir::ExprKind::AssignOp(op, _, _) => {
+                self.check_expr_inner(cx, expr, op.node.into(), op.span);
+            }
+            _ => {}
+        }
+    }
+}
+
+impl<'tcx> SuspiciousImpl {
+    fn check_expr_inner(
+        &mut self,
+        cx: &LateContext<'tcx>,
+        expr: &'tcx hir::Expr<'_>,
+        binop: hir::BinOpKind,
+        span: Span,
+    ) {
+        if let Some((binop_trait_lang, op_assign_trait_lang)) = binop_traits(binop)
             && let Some(binop_trait_id) = cx.tcx.lang_items().get(binop_trait_lang)
             && let Some(op_assign_trait_id) = cx.tcx.lang_items().get(op_assign_trait_lang)
 
@@ -82,10 +102,10 @@ impl<'tcx> LateLintPass<'tcx> for SuspiciousImpl {
             span_lint(
                 cx,
                 lint,
-                binop.span,
+                span,
                 format!(
                     "suspicious use of `{}` in `{}` impl",
-                    binop.node.as_str(),
+                    binop.as_str(),
                     cx.tcx.item_name(trait_id)
                 ),
             );

clippy_lints/src/swap.rs

@@ -10,7 +10,7 @@ use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir::intravisit::{Visitor, walk_expr};
 
 use rustc_errors::Applicability;
-use rustc_hir::{BinOpKind, Block, Expr, ExprKind, LetStmt, PatKind, QPath, Stmt, StmtKind};
+use rustc_hir::{AssignOpKind, Block, Expr, ExprKind, LetStmt, PatKind, QPath, Stmt, StmtKind};
 use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_middle::ty;
 use rustc_session::declare_lint_pass;
@@ -307,7 +307,7 @@ fn extract_sides_of_xor_assign<'a, 'hir>(
     if let StmtKind::Semi(expr) = stmt.kind
         && let ExprKind::AssignOp(
             Spanned {
-                node: BinOpKind::BitXor,
+                node: AssignOpKind::BitXorAssign,
                 ..
             },
             lhs,

clippy_utils/src/sugg.rs

@@ -357,7 +357,7 @@ fn binop_to_string(op: AssocOp, lhs: &str, rhs: &str) -> String {
     match op {
         AssocOp::Binary(op) => format!("{lhs} {} {rhs}", op.as_str()),
         AssocOp::Assign => format!("{lhs} = {rhs}"),
-        AssocOp::AssignOp(op) => format!("{lhs} {}= {rhs}", op.as_str()),
+        AssocOp::AssignOp(op) => format!("{lhs} {} {rhs}", op.as_str()),
         AssocOp::Cast => format!("{lhs} as {rhs}"),
         AssocOp::Range(limits) => format!("{lhs}{}{rhs}", limits.as_str()),
     }