Move expression logic to subtracts_one

Author: pmk21

clippy_lints/src/implicit_saturating_sub.rs

@@ -63,11 +63,10 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImplicitSaturatingSub {
 
             // Check if assign operation is done
             if let StmtKind::Semi(ref e) = block.stmts[0].kind;
-            if subtracts_one(e);
-            if let ExprKind::AssignOp(_, ref target, _) = e.kind;
-            if let ExprKind::Path(ref assign_path) = target.kind;
+            if let (true, Some(target)) = subtracts_one(cx, e);
 
             // Extracting out the variable name
+            if let ExprKind::Path(ref assign_path) = target.kind;
             if let QPath::Resolved(_, ref ares_path) = assign_path;
 
             then {
@@ -126,19 +125,39 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImplicitSaturatingSub {
     }
 }
 
-fn subtracts_one(expr: &Expr<'_>) -> bool {
-    if_chain! {
-        if let ExprKind::AssignOp(ref op1, _, ref value) = expr.kind;
-        if BinOpKind::Sub == op1.node;
+fn subtracts_one<'a>(cx: &LateContext<'_, '_>, expr: &Expr<'a>) -> (bool, Option<&'a Expr<'a>>) {
+    match expr.kind {
+        ExprKind::AssignOp(ref op1, ref target, ref value) => {
+            if_chain! {
+                if BinOpKind::Sub == op1.node;
+                // Check if literal being subtracted is one
+                if let ExprKind::Lit(ref lit1) = value.kind;
+                if let LitKind::Int(1, _) = lit1.node;
+                then {
+                    (true, Option::Some(target))
+                } else {
+                    (false, None)
+                }
+            }
+        },
+        ExprKind::Assign(ref target, ref value, _) => {
+            if_chain! {
+                if let ExprKind::Binary(ref op1, ref left1, ref right1) = value.kind;
+                if BinOpKind::Sub == op1.node;
+
+                if SpanlessEq::new(cx).eq_expr(left1, target);
 
-        // Check if literal being subtracted is one
-        if let ExprKind::Lit(ref lit1) = value.kind;
-        if let LitKind::Int(1, _) = lit1.node;
-        then {
-            return true;
-        }
+                if let ExprKind::Lit(ref lit1) = right1.kind;
+                if let LitKind::Int(1, _) = lit1.node;
+                then {
+                    (true, Some(target))
+                } else {
+                    (false, None)
+                }
+            }
+        },
+        _ => (false, None),
     }
-    false
 }
 
 fn print_lint_and_sugg(cx: &LateContext<'_, '_>, var_name: &str, expr: &Expr<'_>) {