1 files changed, 65 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/multi_assignments.rs b/src/tools/clippy/clippy_lints/src/multi_assignments.rs
new file mode 100644
index 000000000..81eb1a085
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/multi_assignments.rs
@@ -0,0 +1,65 @@
+use clippy_utils::diagnostics::span_lint;
+use rustc_ast::ast::{Expr, ExprKind, Stmt, StmtKind};
+use rustc_lint::{EarlyContext, EarlyLintPass};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for nested assignments.
+    ///
+    /// ### Why is this bad?
+    /// While this is in most cases already a type mismatch,
+    /// the result of an assignment being `()` can throw off people coming from languages like python or C,
+    /// where such assignments return a copy of the assigned value.
+    ///
+    /// ### Example
+    /// ```rust
+    ///# let (a, b);
+    /// a = b = 42;
+    /// ```
+    /// Use instead:
+    /// ```rust
+    ///# let (a, b);
+    /// b = 42;
+    /// a = b;
+    /// ```
+    #[clippy::version = "1.65.0"]
+    pub MULTI_ASSIGNMENTS,
+    suspicious,
+    "instead of using `a = b = c;` use `a = c; b = c;`"
+}
+
+declare_lint_pass!(MultiAssignments => [MULTI_ASSIGNMENTS]);
+
+fn strip_paren_blocks(expr: &Expr) -> &Expr {
+    match &expr.kind {
+        ExprKind::Paren(e) => strip_paren_blocks(e),
+        ExprKind::Block(b, _) => {
+            if let [
+                Stmt {
+                    kind: StmtKind::Expr(e),
+                    ..
+                },
+            ] = &b.stmts[..]
+            {
+                strip_paren_blocks(e)
+            } else {
+                expr
+            }
+        },
+        _ => expr,
+    }
+}
+
+impl EarlyLintPass for MultiAssignments {
+    fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
+        if let ExprKind::Assign(target, source, _) = &expr.kind {
+            if let ExprKind::Assign(_target, _source, _) = &strip_paren_blocks(target).kind {
+                span_lint(cx, MULTI_ASSIGNMENTS, expr.span, "assignments don't nest intuitively");
+            };
+            if let ExprKind::Assign(_target, _source, _) = &strip_paren_blocks(source).kind {
+                span_lint(cx, MULTI_ASSIGNMENTS, expr.span, "assignments don't nest intuitively");
+            }
+        };
+    }
+}