C#: Add extractor support for list- and slice patterns.

Author: michaelnebel

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Patterns/ListPattern.cs

@@ -0,0 +1,15 @@
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Semmle.Extraction.Kinds;
+using Semmle.Util;
+
+namespace Semmle.Extraction.CSharp.Entities.Expressions
+{
+    internal class ListPattern : Expression
+    {
+        internal ListPattern(Context cx, ListPatternSyntax syntax, IExpressionParentEntity parent, int child) :
+            base(new ExpressionInfo(cx, null, cx.CreateLocation(syntax.GetLocation()), ExprKind.LIST_PATTERN, parent, child, false, null))
+        {
+            syntax.Patterns.ForEach((p, i) => Pattern.Create(cx, p, this, i));
+        }
+    }
+}

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Patterns/Pattern.cs

@@ -74,6 +74,12 @@ internal static Expression Create(Context cx, PatternSyntax syntax, IExpressionP
                 case DiscardPatternSyntax dp:
                     return new Discard(cx, dp, parent, child);
 
+                case ListPatternSyntax listPattern:
+                    return new ListPattern(cx, listPattern, parent, child);
+
+                case SlicePatternSyntax slicePattern:
+                    return new SlicePattern(cx, slicePattern, parent, child);
+
                 default:
                     throw new InternalError(syntax, "Pattern not handled");
             }

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Patterns/SlicePattern.cs

@@ -0,0 +1,17 @@
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Semmle.Extraction.Kinds;
+
+namespace Semmle.Extraction.CSharp.Entities.Expressions
+{
+    internal class SlicePattern : Expression
+    {
+        public SlicePattern(Context cx, SlicePatternSyntax syntax, IExpressionParentEntity parent, int child) :
+            base(new ExpressionInfo(cx, null, cx.CreateLocation(syntax.GetLocation()), ExprKind.SLICE_PATTERN, parent, child, false, null))
+        {
+            if (syntax.Pattern is not null)
+            {
+                Pattern.Create(cx, syntax.Pattern, this, 0);
+            }
+        }
+    }
+}

csharp/extractor/Semmle.Util/IEnumerableExtensions.cs

@@ -79,6 +79,19 @@ public static void ForEach<T>(this IEnumerable<T> items, Action<T> a)
                 a(item);
         }
 
+        /// <summary>
+        /// Applies the action <paramref name="a"/> to each item and its index in this collection.
+        /// </summary>
+        public static void ForEach<T>(this IEnumerable<T> items, Action<T, int> a)
+        {
+            var i = 0;
+            foreach (var item in items)
+            {
+                a(item, i);
+                i++;
+            }
+        }
+
         /// <summary>
         /// Forces enumeration of this collection and discards the result.
         /// </summary>