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C#: Extract relational patterns
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‎csharp/change-notes/2020-11-19-Relational-pattern.md‎

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lgtm,codescanning
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* The `RelationalPatternExpr` and its 4 subclass have been added to support C# 9
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relational `<`, `>`, `<=`, and `>=` patterns.

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

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@@ -42,6 +42,9 @@ internal static Expression Create(Context cx, PatternSyntax syntax, IExpressionP
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case RecursivePatternSyntax recPattern:
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return new RecursivePattern(cx, recPattern, parent, child);
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case RelationalPatternSyntax relPattern:
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return new RelationalPattern(cx, relPattern, parent, child);
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case VarPatternSyntax varPattern:
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switch (varPattern.Designation)
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{

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

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@@ -6,7 +6,7 @@
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namespace Semmle.Extraction.CSharp.Entities.Expressions
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{
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internal class RecursivePattern : Expression
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internal partial class RecursivePattern : Expression
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{
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/// <summary>
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/// Creates and populates a recursive pattern.

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

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

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

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@@ -115,6 +115,10 @@ public enum ExprKind
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SWITCH_CASE = 118,
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ASSIGN_COALESCE = 119,
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SUPPRESS_NULLABLE_WARNING = 120,
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NAMESPACE_ACCESS = 121
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NAMESPACE_ACCESS = 121,
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LT_PATTERN = 122,
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GT_PATTERN = 123,
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LE_PATTERN = 124,
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GE_PATTERN = 125,
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}
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}

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

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@@ -342,6 +342,45 @@ class ConstantPatternExpr extends PatternExpr {
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override string getAPrimaryQlClass() { result = "ConstantPatternExpr" }
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}
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/** A relational pattern, for example `>1` in `x is >1`. */
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abstract class RelationalPatternExpr extends PatternExpr, @relational_pattern_expr {
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/** Get the operator of this relational pattern. */
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string getOperator() { none() }
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/** Gets the expression of this relational pattern. */
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Expr getExpr() { result = this.getChild(0) }
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override string toString() { result = getOperator() + " ..." }
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}
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/** A 'less than' pattern */
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class LTPattern extends RelationalPatternExpr, @lt_pattern_expr {
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override string getOperator() { result = "<" }
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override string getAPrimaryQlClass() { result = "LTPattern" }
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}
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/** A 'greater than' pattern */
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class GTPattern extends RelationalPatternExpr, @gt_pattern_expr {
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override string getOperator() { result = ">" }
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override string getAPrimaryQlClass() { result = "GTPattern" }
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}
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/** A 'less than equal' pattern */
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class LEPattern extends RelationalPatternExpr, @le_pattern_expr {
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override string getOperator() { result = "<=" }
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override string getAPrimaryQlClass() { result = "LEPattern" }
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}
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/** A 'greater than equal' pattern */
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class GEPattern extends RelationalPatternExpr, @ge_pattern_expr {
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override string getOperator() { result = ">=" }
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override string getAPrimaryQlClass() { result = "GEPattern" }
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}
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/**
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* A type pattern, for example `string` in `x is string`, `string s` in
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* `x is string s`, or `string _` in `x is string _`.

‎csharp/ql/src/semmlecode.csharp.dbscheme‎

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@@ -998,11 +998,17 @@ case @expr.kind of
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| 119 = @assign_coalesce_expr
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| 120 = @suppress_nullable_warning_expr
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| 121 = @namespace_access_expr
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/* C# 9.0 */
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| 122 = @lt_pattern_expr
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| 123 = @gt_pattern_expr
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| 124 = @le_pattern_expr
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| 125 = @ge_pattern_expr
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;
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@switch = @switch_stmt | @switch_expr;
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@case = @case_stmt | @switch_case_expr;
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@pattern_match = @case | @is_expr;
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@relational_pattern_expr = @gt_pattern_expr | @lt_pattern_expr | @ge_pattern_expr | @le_pattern_expr;
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@integer_literal_expr = @int_literal_expr | @long_literal_expr | @uint_literal_expr | @ulong_literal_expr;
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@real_literal_expr = @float_literal_expr | @double_literal_expr | @decimal_literal_expr;

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

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@@ -335,6 +335,63 @@ ParenthesizedPattern.cs:
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# 27| 0: [TypeAccessPatternExpr] access to type String
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# 27| 0: [TypeMention] string
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# 27| 2: [IntLiteral] 5
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RelationalPattern.cs:
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# 3| [Class] RelationalPattern
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# 5| 5: [Method] M1
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# 5| -1: [TypeMention] bool
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#-----| 2: (Parameters)
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# 5| 0: [Parameter] c
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# 5| -1: [TypeMention] char
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# 6| 4: [IsExpr] ... is ...
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# 6| 0: [ParameterAccess] access to parameter c
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# 6| 1: [GEPattern] >= ...
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# 6| 0: [CharLiteral] a
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# 7| 6: [Method] M2
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# 7| -1: [TypeMention] bool
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#-----| 2: (Parameters)
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# 7| 0: [Parameter] c
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# 7| -1: [TypeMention] char
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# 8| 4: [IsExpr] ... is ...
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# 8| 0: [ParameterAccess] access to parameter c
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# 8| 1: [GTPattern] > ...
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# 8| 0: [CharLiteral] a
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# 9| 7: [Method] M3
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# 9| -1: [TypeMention] bool
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#-----| 2: (Parameters)
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# 9| 0: [Parameter] c
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# 9| -1: [TypeMention] char
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# 10| 4: [IsExpr] ... is ...
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# 10| 0: [ParameterAccess] access to parameter c
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# 10| 1: [LEPattern] <= ...
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# 10| 0: [CharLiteral] a
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# 11| 8: [Method] M4
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# 11| -1: [TypeMention] bool
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#-----| 2: (Parameters)
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# 11| 0: [Parameter] c
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# 11| -1: [TypeMention] char
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# 12| 4: [IsExpr] ... is ...
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# 12| 0: [ParameterAccess] access to parameter c
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# 12| 1: [LTPattern] < ...
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# 12| 0: [CharLiteral] a
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# 14| 9: [Method] M5
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# 14| -1: [TypeMention] string
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#-----| 2: (Parameters)
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# 14| 0: [Parameter] i
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# 14| -1: [TypeMention] int
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# 15| 4: [BlockStmt] {...}
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# 16| 0: [ReturnStmt] return ...;
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# 16| 0: [SwitchExpr] ... switch { ... }
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# 16| -1: [ParameterAccess] access to parameter i
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# 18| 0: [SwitchCaseExpr] ... => ...
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# 18| 0: [ConstantPatternExpr,IntLiteral] 1
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# 18| 2: [StringLiteral] "1"
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# 19| 1: [SwitchCaseExpr] ... => ...
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# 19| 0: [GTPattern] > ...
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# 19| 0: [IntLiteral] 1
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# 19| 2: [StringLiteral] ">1"
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# 20| 2: [SwitchCaseExpr] ... => ...
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# 20| 0: [DiscardPatternExpr] _
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# 20| 2: [StringLiteral] "other"
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TargetType.cs:
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# 5| [Class] TargetType
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# 7| 5: [Method] M2

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

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

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

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| RelationalPattern.cs:6:14:6:19 | >= ... | >= |
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| RelationalPattern.cs:8:14:8:18 | > ... | > |
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| RelationalPattern.cs:10:14:10:19 | <= ... | <= |
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| RelationalPattern.cs:12:14:12:18 | < ... | < |
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| RelationalPattern.cs:19:13:19:14 | > ... | > |

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