Merge pull request #11594 from michaelnebel/csharp/listpattern

C#: Support List and Slice patterns.

csharp/downgrades/83aca6b3e4fa38dd2b97b9b51dfc199a2ba9c7f2/expressions.ql

@@ -0,0 +1,13 @@
+class Expression extends @expr {
+  string toString() { none() }
+}
+
+class TypeOrRef extends @type_or_ref {
+  string toString() { none() }
+}
+
+from Expression e, int k, int kind, TypeOrRef t
+where
+  expressions(e, k, t) and
+  if k = [131, 132] then kind = 106 else kind = k
+select e, kind, t

csharp/downgrades/83aca6b3e4fa38dd2b97b9b51dfc199a2ba9c7f2/upgrade.properties

@@ -0,0 +1,3 @@
+description: Remove list- and slice pattern expression kinds.
+compatibility: backwards
+expressions.rel: run expressions.qlo

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 @@ namespace Semmle.Extraction.CSharp.Entities.Expressions
                 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.Extraction.CSharp/Kinds/ExprKind.cs

@@ -125,6 +125,8 @@ namespace Semmle.Extraction.Kinds
         OR_PATTERN = 128,
         FUNCTION_POINTER_INVOCATION = 129,
         WITH = 130,
-        DEFINE_SYMBOL = 999
+        LIST_PATTERN = 131,
+        SLICE_PATTERN = 132,
+        DEFINE_SYMBOL = 999,
     }
 }

csharp/extractor/Semmle.Util/IEnumerableExtensions.cs

@@ -79,6 +79,19 @@ namespace Semmle.Util
                 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>

csharp/ql/lib/change-notes/2022-12-08-listpatterns.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* C# 11: Added support for list- and slice patterns in the extractor.

csharp/ql/lib/semmle/code/csharp/exprs/Expr.qll

@@ -321,6 +321,18 @@ private predicate hasChildPattern(ControlFlowElement pm, Expr child) {
     mid instanceof @tuple_expr and
     child = mid.getAChildExpr()
   )
+  or
+  exists(Expr mid |
+    hasChildPattern(pm, mid) and
+    mid instanceof @list_pattern_expr and
+    child = mid.getAChildExpr()
+  )
+  or
+  exists(Expr mid |
+    hasChildPattern(pm, mid) and
+    mid instanceof @slice_pattern_expr and
+    child = mid.getAChildExpr()
+  )
 }
 
 /**
@@ -506,6 +518,26 @@ class PositionalPatternExpr extends PatternExpr, @positional_pattern_expr {
   override string getAPrimaryQlClass() { result = "PositionalPatternExpr" }
 }
 
+/** A list pattern. For example `[1, 2, int y]` in `x is [1, 2, int y]`. */
+class ListPatternExpr extends PatternExpr, @list_pattern_expr {
+  override string toString() { result = "[ ... ]" }
+
+  /** Gets the `n`th pattern. */
+  PatternExpr getPattern(int n) { result = this.getChild(n) }
+
+  override string getAPrimaryQlClass() { result = "ListPatternExpr" }
+}
+
+/** A slice pattern. For example `..` in `x is [1, .., 2]. */
+class SlicePatternExpr extends PatternExpr, @slice_pattern_expr {
+  override string toString() { result = ".." }
+
+  /** Gets the subpattern, if any. */
+  PatternExpr getPattern() { result = this.getChild(0) }
+
+  override string getAPrimaryQlClass() { result = "SlicePatternExpr" }
+}
+
 /** A unary pattern. For example, `not 1`. */
 class UnaryPatternExpr extends PatternExpr, @unary_pattern_expr {
   /** Gets the underlying pattern. */

csharp/ql/lib/semmlecode.csharp.dbscheme

@@ -1134,6 +1134,9 @@ case @expr.kind of
 | 128 = @or_pattern_expr
 | 129 = @function_pointer_invocation_expr
 | 130 = @with_expr
+/* C# 11.0 */
+| 131 = @list_pattern_expr
+| 132 = @slice_pattern_expr
 /* Preprocessor */
 | 999 = @define_symbol_expr
 ;

csharp/ql/lib/upgrades/4ac7d8bcac6f664b1e83c858aa71f8dc761cc603/upgrade.properties

@@ -0,0 +1,2 @@
+description: Add list- and slice pattern expressions kinds.
+compatibility: backwards

csharp/ql/test/library-tests/csharp11/ListPattern.cs

@@ -0,0 +1,38 @@
+using System.Collections.Generic;
+
+class ListPattern
+{
+    public void M1(int[] x)
+    {
+        if (x is []) { }
+        if (x is [1]) { }
+        if (x is [_, 2]) { }
+        if (x is [var y, 3, 4]) { }
+        if (x is [5 or 6, _, 7]) { }
+        if (x is [var a, .., 2]) { }
+        if (x is [var b, .. { Length: 2 or 5 }, 2]) { }
+    }
+
+    public void M2(string[] x)
+    {
+        switch (x)
+        {
+            case []:
+                break;
+            case ["A"]:
+                break;
+            case [_, "B"]:
+                break;
+            case [var y, "C", "D"]:
+                break;
+            case ["E" or "F", _, "G"]:
+                break;
+            case [var a, .., "H"]:
+                break;
+            case [var b, .. var c, "I"]:
+                break;
+            default:
+                break;
+        }
+    }
+}

csharp/ql/test/library-tests/csharp11/listPattern.expected

@@ -0,0 +1,20 @@
+listPattern
+| ListPattern.cs:7:18:7:19 | [ ... ] |  |
+| ListPattern.cs:8:18:8:20 | [ ... ] | 1 |
+| ListPattern.cs:9:18:9:23 | [ ... ] | _, 2 |
+| ListPattern.cs:10:18:10:30 | [ ... ] | Int32 y, 3, 4 |
+| ListPattern.cs:11:18:11:31 | [ ... ] | ... or ..., _, 7 |
+| ListPattern.cs:12:18:12:31 | [ ... ] | Int32 a, .., 2 |
+| ListPattern.cs:13:18:13:50 | [ ... ] | Int32 b, .., 2 |
+| ListPattern.cs:20:18:20:19 | [ ... ] |  |
+| ListPattern.cs:22:18:22:22 | [ ... ] | "A" |
+| ListPattern.cs:24:18:24:25 | [ ... ] | _, "B" |
+| ListPattern.cs:26:18:26:34 | [ ... ] | String y, "C", "D" |
+| ListPattern.cs:28:18:28:37 | [ ... ] | ... or ..., _, "G" |
+| ListPattern.cs:30:18:30:33 | [ ... ] | String a, .., "H" |
+| ListPattern.cs:32:18:32:39 | [ ... ] | String b, .., "I" |
+slicePattern
+| ListPattern.cs:12:26:12:27 | .. | ..: |
+| ListPattern.cs:13:26:13:46 | .. | ..:{ ... } |
+| ListPattern.cs:30:26:30:27 | .. | ..: |
+| ListPattern.cs:32:26:32:33 | .. | ..:String[] c |

csharp/ql/test/library-tests/csharp11/listPattern.ql

@@ -0,0 +1,19 @@
+import csharp
+
+private string childPatterns(ListPatternExpr e) {
+  result = concat(string child, int n | child = e.getPattern(n).toString() | child, ", " order by n)
+}
+
+query predicate listPattern(ListPatternExpr pattern, string children) {
+  pattern.getFile().getStem() = "ListPattern" and
+  children = childPatterns(pattern)
+}
+
+query predicate slicePattern(SlicePatternExpr pattern, string s) {
+  pattern.getFile().getStem() = "ListPattern" and
+  exists(string child |
+    if exists(pattern.getPattern()) then child = pattern.getPattern().toString() else child = ""
+  |
+    s = pattern.toString() + ":" + child
+  )
+}