C# Add relational patterns extraction

Author: tamasvajk

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

@@ -0,0 +1,3 @@
+lgtm,codescanning
+* The `RelationalPatternExpr` and its 4 sub class have been added to support C# 9
+relational `<`, `>`, `<=`, and `>=` patterns.

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

@@ -45,6 +45,9 @@ internal static Expression Create(Context cx, PatternSyntax syntax, IExpressionP
                 case RecursivePatternSyntax recPattern:
                     return new RecursivePattern(cx, recPattern, parent, child);
 
+                case RelationalPatternSyntax relPattern:
+                    return new RelationalPattern(cx, relPattern, parent, child);
+
                 case VarPatternSyntax varPattern:
                     switch (varPattern.Designation)
                     {

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

@@ -15,7 +15,6 @@ internal class RecursivePattern : Expression
         /// <param name="syntax">The syntax node of the recursive pattern.</param>
         /// <param name="parent">The parent pattern/expression.</param>
         /// <param name="child">The child index of this pattern.</param>
-        /// <param name="isTopLevel">If this pattern is in the top level of a case/is. In that case, the variable and type access are populated elsewhere.</param>
         public RecursivePattern(Context cx, RecursivePatternSyntax syntax, IExpressionParentEntity parent, int child) :
             base(new ExpressionInfo(cx, Entities.NullType.Create(cx), cx.Create(syntax.GetLocation()), ExprKind.RECURSIVE_PATTERN, parent, child, false, null))
         {

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

@@ -0,0 +1,29 @@
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.CSharp;
+using Semmle.Extraction.Kinds;
+using Semmle.Extraction.Entities;
+
+namespace Semmle.Extraction.CSharp.Entities.Expressions
+{
+    internal class RelationalPattern : Expression
+    {
+        public RelationalPattern(Context cx, RelationalPatternSyntax syntax, IExpressionParentEntity parent, int child) :
+             base(new ExpressionInfo(cx, NullType.Create(cx), cx.Create(syntax.GetLocation()), GetKind(syntax.OperatorToken), parent, child, false, null))
+        {
+            Expression.Create(cx, syntax.Expression, this, 0);
+        }
+
+        private static ExprKind GetKind(SyntaxToken operatorToken)
+        {
+            return operatorToken.Kind() switch
+            {
+                SyntaxKind.LessThanEqualsToken => ExprKind.LE_PATTERN,
+                SyntaxKind.GreaterThanEqualsToken => ExprKind.GE_PATTERN,
+                SyntaxKind.LessThanToken => ExprKind.LT_PATTERN,
+                SyntaxKind.GreaterThanToken => ExprKind.GT_PATTERN,
+                _ => throw new InternalError(operatorToken.Parent, $"Relation pattern with operator token '{operatorToken.Kind()}' is not supported."),
+            };
+        }
+    }
+}

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

@@ -116,6 +116,10 @@ public enum ExprKind
         ASSIGN_COALESCE = 119,
         SUPPRESS_NULLABLE_WARNING = 120,
         NAMESPACE_ACCESS = 121,
+        LT_PATTERN = 122,
+        GT_PATTERN = 123,
+        LE_PATTERN = 124,
+        GE_PATTERN = 125,
         NOT_PATTERN = 126
     }
 }

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

@@ -345,6 +345,45 @@ class ConstantPatternExpr extends PatternExpr {
   override string getAPrimaryQlClass() { result = "ConstantPatternExpr" }
 }
 
+/** A relational pattern, for example `>1` in `x is >1`. */
+class RelationalPatternExpr extends PatternExpr, @relational_pattern_expr {
+  /** Gets the name of the operator in this pattern. */
+  string getOperator() { none() }
+
+  /** Gets the expression of this relational pattern. */
+  Expr getExpr() { result = this.getChild(0) }
+
+  override string toString() { result = getOperator() + " ..." }
+}
+
+/** A less-than pattern, for example `< 10` in `x is < 10`. */
+class LTPattern extends RelationalPatternExpr, @lt_pattern_expr {
+  override string getOperator() { result = "<" }
+
+  override string getAPrimaryQlClass() { result = "LTPattern" }
+}
+
+/** A greater-than pattern, for example `> 10` in `x is > 10`. */
+class GTPattern extends RelationalPatternExpr, @gt_pattern_expr {
+  override string getOperator() { result = ">" }
+
+  override string getAPrimaryQlClass() { result = "GTPattern" }
+}
+
+/** A less-than or equals pattern, for example `<= 10` in `x is <= 10`. */
+class LEPattern extends RelationalPatternExpr, @le_pattern_expr {
+  override string getOperator() { result = "<=" }
+
+  override string getAPrimaryQlClass() { result = "LEPattern" }
+}
+
+/** A greater-than or equals pattern, for example `>= 10` in `x is >= 10` */
+class GEPattern extends RelationalPatternExpr, @ge_pattern_expr {
+  override string getOperator() { result = ">=" }
+
+  override string getAPrimaryQlClass() { result = "GEPattern" }
+}
+
 /**
  * A type pattern, for example `string` in `x is string`, `string s` in
  * `x is string s`, or `string _` in `x is string _`.

csharp/ql/src/semmlecode.csharp.dbscheme

@@ -1010,13 +1010,18 @@ case @expr.kind of
 | 120 = @suppress_nullable_warning_expr
 | 121 = @namespace_access_expr
 /* C# 9.0 */
+| 122 = @lt_pattern_expr
+| 123 = @gt_pattern_expr
+| 124 = @le_pattern_expr
+| 125 = @ge_pattern_expr
 | 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;
+@relational_pattern_expr = @gt_pattern_expr | @lt_pattern_expr | @ge_pattern_expr | @le_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

@@ -473,6 +473,63 @@ ParenthesizedPattern.cs:
 #   27|               0: [TypeAccessPatternExpr] access to type String
 #   27|                 0: [TypeMention] string
 #   27|               2: [IntLiteral] 5
+RelationalPattern.cs:
+#    3| [Class] RelationalPattern
+#    5|   5: [Method] M1
+#    5|     -1: [TypeMention] bool
+#-----|     2: (Parameters)
+#    5|       0: [Parameter] c
+#    5|         -1: [TypeMention] char
+#    6|     4: [IsExpr] ... is ...
+#    6|       0: [ParameterAccess] access to parameter c
+#    6|       1: [GEPattern] >= ...
+#    6|         0: [CharLiteral] a
+#    7|   6: [Method] M2
+#    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: [GTPattern] > ...
+#    8|         0: [CharLiteral] a
+#    9|   7: [Method] M3
+#    9|     -1: [TypeMention] bool
+#-----|     2: (Parameters)
+#    9|       0: [Parameter] c
+#    9|         -1: [TypeMention] char
+#   10|     4: [IsExpr] ... is ...
+#   10|       0: [ParameterAccess] access to parameter c
+#   10|       1: [LEPattern] <= ...
+#   10|         0: [CharLiteral] a
+#   11|   8: [Method] M4
+#   11|     -1: [TypeMention] bool
+#-----|     2: (Parameters)
+#   11|       0: [Parameter] c
+#   11|         -1: [TypeMention] char
+#   12|     4: [IsExpr] ... is ...
+#   12|       0: [ParameterAccess] access to parameter c
+#   12|       1: [LTPattern] < ...
+#   12|         0: [CharLiteral] a
+#   14|   9: [Method] M5
+#   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: [ConstantPatternExpr,IntLiteral] 1
+#   18|             2: [StringLiteral] "1"
+#   19|           1: [SwitchCaseExpr] ... => ...
+#   19|             0: [GTPattern] > ...
+#   19|               0: [IntLiteral] 1
+#   19|             2: [StringLiteral] ">1"
+#   20|           2: [SwitchCaseExpr] ... => ...
+#   20|             0: [DiscardPatternExpr] _
+#   20|             2: [StringLiteral] "other"
 TargetType.cs:
 #    5| [Class] TargetType
 #    7|   5: [Method] M2

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

@@ -0,0 +1,23 @@
+using System;
+
+public class RelationalPattern
+{
+    public static bool M1(char c) =>
+        c is >= 'a';
+    public static bool M2(char c) =>
+        c is > 'a';
+    public static bool M3(char c) =>
+        c is <= 'a';
+    public static bool M4(char c) =>
+        c is < 'a';
+
+    public static string M5(int i)
+    {
+        return i switch
+        {
+            1 => "1",
+            >1 => ">1",
+            _ => "other"
+        };
+    }
+}

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

@@ -0,0 +1,5 @@
+| RelationalPattern.cs:6:14:6:19 | >= ... | >= |
+| RelationalPattern.cs:8:14:8:18 | > ... | > |
+| RelationalPattern.cs:10:14:10:19 | <= ... | <= |
+| RelationalPattern.cs:12:14:12:18 | < ... | < |
+| RelationalPattern.cs:19:13:19:14 | > ... | > |