From 0c5c2a3509b0f06678674d5ae94db42a5e8f8b94 Mon Sep 17 00:00:00 2001
From: Michael Nebel <michaelnebel@github.com>
Date: Tue, 14 Jan 2025 15:50:04 +0100
Subject: [PATCH] C#: Add implicit to string test.

---
 .../implicittostring/implicitToString.cs      | 44 +++++++++++++++++++
 .../implicitToString.expected                 |  4 ++
 .../implicittostring/implicitToString.ql      |  5 +++
 3 files changed, 53 insertions(+)
 create mode 100644 csharp/ql/test/library-tests/implicittostring/implicitToString.cs
 create mode 100644 csharp/ql/test/library-tests/implicittostring/implicitToString.expected
 create mode 100644 csharp/ql/test/library-tests/implicittostring/implicitToString.ql

diff --git a/csharp/ql/test/library-tests/implicittostring/implicitToString.cs b/csharp/ql/test/library-tests/implicittostring/implicitToString.cs
new file mode 100644
index 000000000000..d75044246f8e
--- /dev/null
+++ b/csharp/ql/test/library-tests/implicittostring/implicitToString.cs
@@ -0,0 +1,44 @@
+using System;
+
+public class TestImplicitToString
+{
+    public class Container
+    {
+        public override string ToString()
+        {
+            return "Container";
+        }
+    }
+
+    public class FormattableContainer : IFormattable
+    {
+        public string ToString(string format, IFormatProvider formatProvider)
+        {
+            return "Formatted container";
+        }
+
+
+        public override string ToString()
+        {
+            return "Container";
+        }
+    }
+
+    public void M()
+    {
+        var container = new Container();
+
+        var y = "Hello" + container; // Implicit ToString call
+        y = "Hello" + container.ToString();
+        y = $"Hello {container}"; // Implicit ToString() call
+        y = $"Hello {container.ToString()}";
+        y = $"Hello {container:D}"; // Implicit ToString() call.
+
+        var z = "Hello" + y; // No implicit ToString call as `y` is already a string.
+
+        var formattableContainer = new FormattableContainer();
+        y = "Hello" + formattableContainer; // Implicit call to ToString().
+        y = $"Hello {formattableContainer}"; // Implicit call to ToString(string, IFormatProvider). We don't handle this.
+        y = $"Hello {formattableContainer:D}"; // Implicit call to ToString(string, IFormatProvider). We don't handle this.
+    }
+}
diff --git a/csharp/ql/test/library-tests/implicittostring/implicitToString.expected b/csharp/ql/test/library-tests/implicittostring/implicitToString.expected
new file mode 100644
index 000000000000..4878b12a4fdb
--- /dev/null
+++ b/csharp/ql/test/library-tests/implicittostring/implicitToString.expected
@@ -0,0 +1,4 @@
+| implicitToString.cs:31:27:31:35 | call to method ToString |
+| implicitToString.cs:33:22:33:30 | call to method ToString |
+| implicitToString.cs:35:22:35:30 | call to method ToString |
+| implicitToString.cs:40:23:40:42 | call to method ToString |
diff --git a/csharp/ql/test/library-tests/implicittostring/implicitToString.ql b/csharp/ql/test/library-tests/implicittostring/implicitToString.ql
new file mode 100644
index 000000000000..4eb518d84c39
--- /dev/null
+++ b/csharp/ql/test/library-tests/implicittostring/implicitToString.ql
@@ -0,0 +1,5 @@
+import csharp
+
+from MethodCall c
+where c.isImplicit()
+select c