Merge pull request #4656 from tamasvajk/feature/csharp9-not-pattern

C#: Extract unary patterns

Author: tamasvajk

csharp/change-notes/2021-01-14-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;