From 79485ec5da29a2ad89cd55ed244b49fe547e51d4 Mon Sep 17 00:00:00 2001
From: Anders Schack-Mulligen <aschackmull@users.noreply.github.com>
Date: Wed, 13 Oct 2021 09:01:54 +0000
Subject: [PATCH] New query: Singleton set literal.

---
 ql/src/codeql_ql/ast/Ast.qll                |  2 +-
 ql/src/queries/style/SingletonSetLiteral.ql | 15 +++++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)
 create mode 100644 ql/src/queries/style/SingletonSetLiteral.ql

diff --git a/ql/src/codeql_ql/ast/Ast.qll b/ql/src/codeql_ql/ast/Ast.qll
index 4d8da8d8ee5..367355e2e5d 100644
--- a/ql/src/codeql_ql/ast/Ast.qll
+++ b/ql/src/codeql_ql/ast/Ast.qll
@@ -1926,7 +1926,7 @@ class Set extends TSet, Expr {
   Set() { this = TSet(set) }
 
   /**
-   * Gets the ith element in the set literal expression.
+   * Gets the `i`th element in this set literal expression.
    */
   Expr getElement(int i) { toGenerated(result) = set.getChild(i) }
 
diff --git a/ql/src/queries/style/SingletonSetLiteral.ql b/ql/src/queries/style/SingletonSetLiteral.ql
new file mode 100644
index 00000000000..c05b3dca71d
--- /dev/null
+++ b/ql/src/queries/style/SingletonSetLiteral.ql
@@ -0,0 +1,15 @@
+/**
+ * @name Singleton set literal
+ * @description A singleton set literal can be replaced by its member.
+ * @kind problem
+ * @problem.severity warning
+ * @id ql/singleton-set-literal
+ * @tags maintainability
+ * @precision very-high
+ */
+
+import ql
+
+from Set setlit
+where exists(unique(Expr e | e = setlit.getElement(_)))
+select setlit, "Singleton set literal can be replaced by its member."