C#: Extract unary patterns

Author: tamasvajk

csharp/change-notes/2020-11-19-Unary-pattern.md

@@ -0,0 +1,3 @@
+lgtm,codescanning
+* The `UnaryPatternExpr` and `NotPatternExpr` classes have been added to support
+C# 9 unary `not` pattern.

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

@@ -20,6 +20,9 @@ internal static Expression Create(Context cx, PatternSyntax syntax, IExpressionP
                 case TypePatternSyntax typePattern:
                     return Expressions.TypeAccess.Create(cx, typePattern.Type, parent, child);
 
+                case UnaryPatternSyntax unaryPattern:
+                    return new UnaryPattern(cx, unaryPattern, parent, child);
+
                 case DeclarationPatternSyntax declPattern:
                     // Creates a single local variable declaration.
                     {

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

@@ -0,0 +1,15 @@
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Semmle.Extraction.Entities;
+using Semmle.Extraction.Kinds;
+
+namespace Semmle.Extraction.CSharp.Entities.Expressions
+{
+    internal class UnaryPattern : Expression
+    {
+        public UnaryPattern(Context cx, UnaryPatternSyntax syntax, IExpressionParentEntity parent, int child) :
+            base(new ExpressionInfo(cx, NullType.Create(cx), cx.Create(syntax.GetLocation()), ExprKind.NOT_PATTERN, parent, child, false, null))
+        {
+            Pattern.Create(cx, syntax.Pattern, this, 0);
+        }
+    }
+}

csharp/extractor/Semmle.Extraction.CSharp/Kinds/ExprKind.cs

@@ -115,6 +115,7 @@ public enum ExprKind
         SWITCH_CASE = 118,
         ASSIGN_COALESCE = 119,
         SUPPRESS_NULLABLE_WARNING = 120,
-        NAMESPACE_ACCESS = 121
+        NAMESPACE_ACCESS = 121,
+        NOT_PATTERN = 126
     }
 }

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

@@ -295,6 +295,12 @@ private predicate hasChildPattern(ControlFlowElement pm, Expr child) {
     child = mid.getChild(2).getAChildExpr() or
     child = mid.getChild(3).getAChildExpr()
   )
+  or
+  exists(Expr mid |
+    hasChildPattern(pm, mid) and
+    mid instanceof @unary_pattern_expr and
+    child = mid.getChild(0)
+  )
 }
 
 /**
@@ -444,6 +450,19 @@ class PositionalPatternExpr extends Expr, @positional_pattern_expr {
   override string getAPrimaryQlClass() { result = "PositionalPatternExpr" }
 }
 
+/** A unary pattern. For example, `not 1`. */
+class UnaryPatternExpr extends PatternExpr, @unary_pattern_expr {
+  /** Gets the underlying pattern. */
+  PatternExpr getPattern() { result = this.getChild(0) }
+}
+
+/** A not pattern. For example, `not 1`. */
+class NotPatternExpr extends UnaryPatternExpr, @not_pattern_expr {
+  override string toString() { result = "not ..." }
+
+  override string getAPrimaryQlClass() { result = "NotPatternExpr" }
+}
+
 /**
  * An expression or statement that matches the value of an expression against
  * a pattern. Either an `is` expression or a `case` expression/statement.

csharp/ql/src/semmlecode.csharp.dbscheme

@@ -1009,11 +1009,14 @@ case @expr.kind of
 | 119 = @assign_coalesce_expr
 | 120 = @suppress_nullable_warning_expr
 | 121 = @namespace_access_expr
+/* C# 9.0 */
+| 126 = @not_pattern_expr
 ;
 
 @switch = @switch_stmt | @switch_expr;
 @case = @case_stmt | @switch_case_expr;
 @pattern_match = @case | @is_expr;
+@unary_pattern_expr = @not_pattern_expr;
 
 @integer_literal_expr = @int_literal_expr | @long_literal_expr | @uint_literal_expr | @ulong_literal_expr;
 @real_literal_expr = @float_literal_expr | @double_literal_expr | @decimal_literal_expr;

csharp/ql/test/library-tests/csharp9/PrintAst.expected

@@ -764,3 +764,59 @@ TypePattern.cs:
 #   14|             0: [VariablePatternExpr] Object o
 #   14|               0: [TypeMention] object
 #   14|             2: [LocalVariableAccess] access to local variable o
+UnaryPattern.cs:
+#    3| [Class] UnaryPattern
+#    5|   5: [Property] P1
+#    5|     -1: [TypeMention] int
+#    5|     3: [Getter] get_P1
+#    5|     4: [Setter] set_P1
+#-----|       2: (Parameters)
+#    5|         0: [Parameter] value
+#    7|   6: [Method] M1
+#    7|     -1: [TypeMention] bool
+#-----|     2: (Parameters)
+#    7|       0: [Parameter] c
+#    7|         -1: [TypeMention] char
+#    8|     4: [IsExpr] ... is ...
+#    8|       0: [ParameterAccess] access to parameter c
+#    8|       1: [NotPatternExpr] not ...
+#    8|         0: [CharLiteral,ConstantPatternExpr] a
+#    9|   7: [Method] M2
+#    9|     -1: [TypeMention] bool
+#-----|     2: (Parameters)
+#    9|       0: [Parameter] c
+#    9|         -1: [TypeMention] object
+#   10|     4: [IsExpr] ... is ...
+#   10|       0: [ParameterAccess] access to parameter c
+#   10|       1: [NotPatternExpr] not ...
+#   10|         0: [ConstantPatternExpr,NullLiteral] null
+#   11|   8: [Method] M3
+#   11|     -1: [TypeMention] bool
+#-----|     2: (Parameters)
+#   11|       0: [Parameter] c
+#   11|         -1: [TypeMention] object
+#   12|     4: [IsExpr] ... is ...
+#   12|       0: [ParameterAccess] access to parameter c
+#   12|       1: [NotPatternExpr] not ...
+#   12|         0: [RecursivePatternExpr] { ... }
+#   12|           0: [LocalVariableDeclExpr] UnaryPattern u
+#   12|           1: [TypeAccess] access to type UnaryPattern
+#   12|             0: [TypeMention] UnaryPattern
+#   12|           3: [PropertyPatternExpr] { ... }
+#   12|             0: [ConstantPatternExpr,IntLiteral,LabeledPatternExpr] 1
+#   14|   9: [Method] M4
+#   14|     -1: [TypeMention] string
+#-----|     2: (Parameters)
+#   14|       0: [Parameter] i
+#   14|         -1: [TypeMention] int
+#   15|     4: [BlockStmt] {...}
+#   16|       0: [ReturnStmt] return ...;
+#   16|         0: [SwitchExpr] ... switch { ... }
+#   16|           -1: [ParameterAccess] access to parameter i
+#   18|           0: [SwitchCaseExpr] ... => ...
+#   18|             0: [NotPatternExpr] not ...
+#   18|               0: [ConstantPatternExpr,IntLiteral] 1
+#   18|             2: [StringLiteral] "not 1"
+#   19|           1: [SwitchCaseExpr] ... => ...
+#   19|             0: [DiscardPatternExpr] _
+#   19|             2: [StringLiteral] "other"

csharp/ql/test/library-tests/csharp9/UnaryPattern.cs

@@ -0,0 +1,22 @@
+using System;
+
+public class UnaryPattern
+{
+    public int P1 { get; set; }
+
+    public static bool M1(char c) =>
+        c is not 'a';
+    public static bool M2(object c) =>
+        c is not null;
+    public static bool M3(object c) =>
+        c is not UnaryPattern { P1: 1 } u;
+
+    public static string M4(int i)
+    {
+        return i switch
+        {
+            not 1 => "not 1",
+            _ => "other"
+        };
+    }
+}

csharp/ql/test/library-tests/csharp9/unaryPattern.expected

@@ -0,0 +1,4 @@
+| UnaryPattern.cs:8:14:8:20 | not ... | UnaryPattern.cs:8:18:8:20 | a |
+| UnaryPattern.cs:10:14:10:21 | not ... | UnaryPattern.cs:10:18:10:21 | null |
+| UnaryPattern.cs:12:14:12:41 | not ... | UnaryPattern.cs:12:18:12:41 | { ... } |
+| UnaryPattern.cs:18:13:18:17 | not ... | UnaryPattern.cs:18:17:18:17 | 1 |

csharp/ql/test/library-tests/csharp9/unaryPattern.ql

@@ -0,0 +1,4 @@
+import csharp
+
+from UnaryPatternExpr pattern
+select pattern, pattern.getAChild()