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C# 14: Support for partial event declarations. #21325

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2b78a7b
C#: Add PartialEvent test case.
michaelnebel Feb 16, 2026
eec4739
C#: Add viable callable test for partial event.
michaelnebel Feb 16, 2026
9289ac2
C#: Support for partial event declarations.
michaelnebel Feb 13, 2026
43c6e7d
C#: Update test expected output.
michaelnebel Feb 16, 2026
c29bac2
C#: Add change-note.
michaelnebel Feb 16, 2026
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12 changes: 8 additions & 4 deletions csharp/extractor/Semmle.Extraction.CSharp/Entities/Event.cs
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Expand Up @@ -11,6 +11,10 @@ internal class Event : CachedSymbol<IEventSymbol>
private Event(Context cx, IEventSymbol init)
: base(cx, init) { }

protected override IEventSymbol BodyDeclaringSymbol => Symbol.PartialImplementationPart ?? Symbol;

public override Microsoft.CodeAnalysis.Location? ReportingLocation => BodyDeclaringSymbol.Locations.BestOrDefault();

public override void WriteId(EscapingTextWriter trapFile)
{
trapFile.WriteSubId(ContainingType!);
Expand All @@ -27,13 +31,13 @@ public override void Populate(TextWriter trapFile)
var type = Type.Create(Context, Symbol.Type);
trapFile.events(this, Symbol.GetName(), ContainingType!, type.TypeRef, Create(Context, Symbol.OriginalDefinition));

var adder = Symbol.AddMethod;
var remover = Symbol.RemoveMethod;
var adder = BodyDeclaringSymbol.AddMethod;
var remover = BodyDeclaringSymbol.RemoveMethod;

if (!(adder is null))
if (adder is not null)
Method.Create(Context, adder);

if (!(remover is null))
if (remover is not null)
Method.Create(Context, remover);

PopulateModifiers(trapFile);
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4 changes: 4 additions & 0 deletions csharp/extractor/Semmle.Extraction.CSharp/Entities/EventAccessor.cs
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Expand Up @@ -13,6 +13,10 @@ private EventAccessor(Context cx, IMethodSymbol init, IEventSymbol @event)
this.@event = @event;
}

public override bool NeedsPopulation =>
base.NeedsPopulation &&
!Symbol.IsPartialDefinition; // Accessors always have an implementing declaration as well.

/// <summary>
/// Gets the event symbol associated with accessor `symbol`, or `null`
/// if there is no associated symbol.
Expand Down
4 changes: 4 additions & 0 deletions csharp/ql/lib/change-notes/2026-02-16-partial-events.md
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@@ -0,0 +1,4 @@
---
category: minorAnalysis
---
* C# 14: Added support for partial events.
10 changes: 6 additions & 4 deletions csharp/ql/test/library-tests/dispatch/CallGraph.expected
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Expand Up @@ -270,7 +270,9 @@
| ViableCallable.cs:679:17:679:20 | Run3 | ViableCallable.cs:637:21:637:21 | M |
| ViableCallable.cs:679:17:679:20 | Run3 | ViableCallable.cs:646:21:646:21 | M |
| ViableCallable.cs:679:17:679:20 | Run3 | ViableCallable.cs:648:21:648:21 | M |
| ViableCallable.cs:707:17:707:20 | Run1 | ViableCallable.cs:702:42:702:44 | get_Property |
| ViableCallable.cs:707:17:707:20 | Run1 | ViableCallable.cs:702:63:702:65 | set_Property |
| ViableCallable.cs:707:17:707:20 | Run1 | ViableCallable.cs:704:49:704:51 | get_Item |
| ViableCallable.cs:707:17:707:20 | Run1 | ViableCallable.cs:704:70:704:72 | set_Item |
| ViableCallable.cs:709:17:709:20 | Run1 | ViableCallable.cs:703:42:703:44 | get_Property |
| ViableCallable.cs:709:17:709:20 | Run1 | ViableCallable.cs:703:63:703:65 | set_Property |
| ViableCallable.cs:709:17:709:20 | Run1 | ViableCallable.cs:705:49:705:51 | get_Item |
| ViableCallable.cs:709:17:709:20 | Run1 | ViableCallable.cs:705:70:705:72 | set_Item |
| ViableCallable.cs:709:17:709:20 | Run1 | ViableCallable.cs:706:51:706:53 | add_Event |
| ViableCallable.cs:709:17:709:20 | Run1 | ViableCallable.cs:706:59:706:64 | remove_Event |
10 changes: 6 additions & 4 deletions csharp/ql/test/library-tests/dispatch/GetADynamicTarget.expected
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Expand Up @@ -518,7 +518,9 @@
| ViableCallable.cs:683:9:683:16 | call to method M | C22+TestOverloadResolution2<System.Int32>.M(Int32[]) |
| ViableCallable.cs:687:9:687:16 | call to method M | C22+TestOverloadResolution1<System.Int32>.M(List<int>) |
| ViableCallable.cs:687:9:687:16 | call to method M | C22+TestOverloadResolution2<System.Int32>.M(List<int>) |
| ViableCallable.cs:712:9:712:18 | access to property Property | C23+Partial1.set_Property(object) |
| ViableCallable.cs:715:13:715:22 | access to property Property | C23+Partial1.get_Property() |
| ViableCallable.cs:718:9:718:12 | access to indexer | C23+Partial1.set_Item(int, object) |
| ViableCallable.cs:721:13:721:16 | access to indexer | C23+Partial1.get_Item(int) |
| ViableCallable.cs:714:9:714:18 | access to property Property | C23+Partial1.set_Property(object) |
| ViableCallable.cs:717:13:717:22 | access to property Property | C23+Partial1.get_Property() |
| ViableCallable.cs:720:9:720:12 | access to indexer | C23+Partial1.set_Item(int, object) |
| ViableCallable.cs:723:13:723:16 | access to indexer | C23+Partial1.get_Item(int) |
| ViableCallable.cs:726:9:726:15 | access to event Event | C23+Partial1.add_Event(EventHandler) |
| ViableCallable.cs:729:9:729:15 | access to event Event | C23+Partial1.remove_Event(EventHandler) |
8 changes: 8 additions & 0 deletions csharp/ql/test/library-tests/dispatch/ViableCallable.cs
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Expand Up @@ -695,13 +695,15 @@ public partial class Partial1
public partial object Property { get; set; }

public partial object this[int index] { get; set; }
public partial event EventHandler Event;
}

public partial class Partial1
{
public partial object Property { get { return null; } set { } }

public partial object this[int index] { get { return null; } set { } }
public partial event EventHandler Event { add { } remove { } }
}

public void Run1(Partial1 p)
Expand All @@ -719,5 +721,11 @@ public void Run1(Partial1 p)

// Viable callable: Partial1.get_Item(int)
o = p[0];

// Viable callable: Partial1.add_Event
p.Event += (sender, e) => { };

// Viable callable: Partial1.remove_Event
p.Event -= (sender, e) => { };
}
}
14 changes: 7 additions & 7 deletions csharp/ql/test/library-tests/partial/MethodIsPartial.expected
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@@ -1,7 +1,7 @@
| Partial.cs:4:18:4:42 | PartialMethodWithoutBody1 | true |
| Partial.cs:5:17:5:23 | Method2 | false |
| Partial.cs:14:18:14:39 | PartialMethodWithBody1 | true |
| Partial.cs:15:17:15:23 | Method3 | false |
| Partial.cs:34:18:34:42 | PartialMethodWithoutBody2 | true |
| Partial.cs:35:17:35:23 | Method4 | false |
| Partial.cs:40:17:40:23 | Method5 | false |
| Partial.cs:6:18:6:42 | PartialMethodWithoutBody1 | true |
| Partial.cs:7:17:7:23 | Method2 | false |
| Partial.cs:18:18:18:39 | PartialMethodWithBody1 | true |
| Partial.cs:19:17:19:23 | Method3 | false |
| Partial.cs:41:18:41:42 | PartialMethodWithoutBody2 | true |
| Partial.cs:42:17:42:23 | Method4 | false |
| Partial.cs:47:17:47:23 | Method5 | false |
8 changes: 8 additions & 0 deletions csharp/ql/test/library-tests/partial/Partial.cs
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@@ -1,3 +1,5 @@
using System;

partial class TwoPartClass
{
partial void PartialMethodWithBody1();
Expand All @@ -7,6 +9,8 @@ public void Method2() { }
public partial object PartialProperty1 { get; set; }
// Declaring declaration.
public partial object this[int index] { get; set; }
// Declaring declaration.
public partial event EventHandler PartialEvent1;
}

partial class TwoPartClass
Expand All @@ -27,6 +31,9 @@ public partial object this[int index]
get { return _backingArray[index]; }
set { _backingArray[index] = value; }
}

// Implementation declaration.
public partial event EventHandler PartialEvent1 { add { } remove { } }
}

partial class OnePartPartialClass
Expand All @@ -44,4 +51,5 @@ public object this[int index]
get { return null; }
set { }
}
public event EventHandler Event;
}
27 changes: 15 additions & 12 deletions csharp/ql/test/library-tests/partial/Partial1.expected
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@@ -1,14 +1,17 @@
| Partial.cs:1:15:1:26 | TwoPartClass |
| Partial.cs:4:18:4:42 | PartialMethodWithoutBody1 |
| Partial.cs:12:15:12:26 | TwoPartClass |
| Partial.cs:14:18:14:39 | PartialMethodWithBody1 |
| Partial.cs:18:27:18:42 | PartialProperty1 |
| Partial.cs:20:9:20:11 | get_PartialProperty1 |
| Partial.cs:21:9:21:11 | set_PartialProperty1 |
| Partial.cs:25:27:25:30 | Item |
| Partial.cs:27:9:27:11 | get_Item |
| Partial.cs:28:9:28:11 | set_Item |
| Partial.cs:32:15:32:33 | OnePartPartialClass |
| Partial.cs:34:18:34:42 | PartialMethodWithoutBody2 |
| Partial.cs:3:15:3:26 | TwoPartClass |
| Partial.cs:6:18:6:42 | PartialMethodWithoutBody1 |
| Partial.cs:16:15:16:26 | TwoPartClass |
| Partial.cs:18:18:18:39 | PartialMethodWithBody1 |
| Partial.cs:22:27:22:42 | PartialProperty1 |
| Partial.cs:24:9:24:11 | get_PartialProperty1 |
| Partial.cs:25:9:25:11 | set_PartialProperty1 |
| Partial.cs:29:27:29:30 | Item |
| Partial.cs:31:9:31:11 | get_Item |
| Partial.cs:32:9:32:11 | set_Item |
| Partial.cs:36:39:36:51 | PartialEvent1 |
| Partial.cs:36:55:36:57 | add_PartialEvent1 |
| Partial.cs:36:63:36:68 | remove_PartialEvent1 |
| Partial.cs:39:15:39:33 | OnePartPartialClass |
| Partial.cs:41:18:41:42 | PartialMethodWithoutBody2 |
| PartialMultipleFiles1.cs:1:22:1:41 | PartialMultipleFiles |
| PartialMultipleFiles2.cs:1:22:1:41 | PartialMultipleFiles |
26 changes: 13 additions & 13 deletions csharp/ql/test/library-tests/partial/Partial2.expected
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@@ -1,15 +1,15 @@
| Partial.cs:1:15:1:26 | TwoPartClass | Partial.cs:1:15:1:26 | <object initializer> |
| Partial.cs:1:15:1:26 | TwoPartClass | Partial.cs:4:18:4:42 | PartialMethodWithoutBody1 |
| Partial.cs:1:15:1:26 | TwoPartClass | Partial.cs:5:17:5:23 | Method2 |
| Partial.cs:1:15:1:26 | TwoPartClass | Partial.cs:14:18:14:39 | PartialMethodWithBody1 |
| Partial.cs:1:15:1:26 | TwoPartClass | Partial.cs:15:17:15:23 | Method3 |
| Partial.cs:12:15:12:26 | TwoPartClass | Partial.cs:1:15:1:26 | <object initializer> |
| Partial.cs:12:15:12:26 | TwoPartClass | Partial.cs:4:18:4:42 | PartialMethodWithoutBody1 |
| Partial.cs:12:15:12:26 | TwoPartClass | Partial.cs:5:17:5:23 | Method2 |
| Partial.cs:12:15:12:26 | TwoPartClass | Partial.cs:14:18:14:39 | PartialMethodWithBody1 |
| Partial.cs:12:15:12:26 | TwoPartClass | Partial.cs:15:17:15:23 | Method3 |
| Partial.cs:32:15:32:33 | OnePartPartialClass | Partial.cs:32:15:32:33 | <object initializer> |
| Partial.cs:32:15:32:33 | OnePartPartialClass | Partial.cs:34:18:34:42 | PartialMethodWithoutBody2 |
| Partial.cs:32:15:32:33 | OnePartPartialClass | Partial.cs:35:17:35:23 | Method4 |
| Partial.cs:3:15:3:26 | TwoPartClass | Partial.cs:3:15:3:26 | <object initializer> |
| Partial.cs:3:15:3:26 | TwoPartClass | Partial.cs:6:18:6:42 | PartialMethodWithoutBody1 |
| Partial.cs:3:15:3:26 | TwoPartClass | Partial.cs:7:17:7:23 | Method2 |
| Partial.cs:3:15:3:26 | TwoPartClass | Partial.cs:18:18:18:39 | PartialMethodWithBody1 |
| Partial.cs:3:15:3:26 | TwoPartClass | Partial.cs:19:17:19:23 | Method3 |
| Partial.cs:16:15:16:26 | TwoPartClass | Partial.cs:3:15:3:26 | <object initializer> |
| Partial.cs:16:15:16:26 | TwoPartClass | Partial.cs:6:18:6:42 | PartialMethodWithoutBody1 |
| Partial.cs:16:15:16:26 | TwoPartClass | Partial.cs:7:17:7:23 | Method2 |
| Partial.cs:16:15:16:26 | TwoPartClass | Partial.cs:18:18:18:39 | PartialMethodWithBody1 |
| Partial.cs:16:15:16:26 | TwoPartClass | Partial.cs:19:17:19:23 | Method3 |
| Partial.cs:39:15:39:33 | OnePartPartialClass | Partial.cs:39:15:39:33 | <object initializer> |
| Partial.cs:39:15:39:33 | OnePartPartialClass | Partial.cs:41:18:41:42 | PartialMethodWithoutBody2 |
| Partial.cs:39:15:39:33 | OnePartPartialClass | Partial.cs:42:17:42:23 | Method4 |
| PartialMultipleFiles1.cs:1:22:1:41 | PartialMultipleFiles | PartialMultipleFiles1.cs:1:22:1:41 | <object initializer> |
| PartialMultipleFiles2.cs:1:22:1:41 | PartialMultipleFiles | PartialMultipleFiles1.cs:1:22:1:41 | <object initializer> |
20 changes: 12 additions & 8 deletions csharp/ql/test/library-tests/partial/PartialAccessors.expected
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@@ -1,8 +1,12 @@
| Partial.cs:20:9:20:11 | get_PartialProperty1 | true |
| Partial.cs:21:9:21:11 | set_PartialProperty1 | true |
| Partial.cs:27:9:27:11 | get_Item | true |
| Partial.cs:28:9:28:11 | set_Item | true |
| Partial.cs:41:30:41:32 | get_Property | false |
| Partial.cs:41:35:41:37 | set_Property | false |
| Partial.cs:44:9:44:11 | get_Item | false |
| Partial.cs:45:9:45:11 | set_Item | false |
| Partial.cs:24:9:24:11 | get_PartialProperty1 | true |
| Partial.cs:25:9:25:11 | set_PartialProperty1 | true |
| Partial.cs:31:9:31:11 | get_Item | true |
| Partial.cs:32:9:32:11 | set_Item | true |
| Partial.cs:36:55:36:57 | add_PartialEvent1 | true |
| Partial.cs:36:63:36:68 | remove_PartialEvent1 | true |
| Partial.cs:48:30:48:32 | get_Property | false |
| Partial.cs:48:35:48:37 | set_Property | false |
| Partial.cs:51:9:51:11 | get_Item | false |
| Partial.cs:52:9:52:11 | set_Item | false |
| Partial.cs:54:31:54:35 | add_Event | false |
| Partial.cs:54:31:54:35 | remove_Event | false |
6 changes: 3 additions & 3 deletions csharp/ql/test/library-tests/partial/PartialConstructors.expected
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@@ -1,4 +1,4 @@
| Partial.cs:1:15:1:26 | TwoPartClass | Partial.cs:1:15:1:26 | {...} |
| Partial.cs:32:15:32:33 | OnePartPartialClass | Partial.cs:32:15:32:33 | {...} |
| Partial.cs:38:7:38:21 | NonPartialClass | Partial.cs:38:7:38:21 | {...} |
| Partial.cs:3:15:3:26 | TwoPartClass | Partial.cs:3:15:3:26 | {...} |
| Partial.cs:39:15:39:33 | OnePartPartialClass | Partial.cs:39:15:39:33 | {...} |
| Partial.cs:45:7:45:21 | NonPartialClass | Partial.cs:45:7:45:21 | {...} |
| PartialMultipleFiles1.cs:1:22:1:41 | PartialMultipleFiles | PartialMultipleFiles1.cs:1:22:1:41 | {...} |
2 changes: 2 additions & 0 deletions csharp/ql/test/library-tests/partial/PartialEvents.expected
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@@ -0,0 +1,2 @@
| Partial.cs:36:39:36:51 | PartialEvent1 | true |
| Partial.cs:54:31:54:35 | Event | false |
7 changes: 7 additions & 0 deletions csharp/ql/test/library-tests/partial/PartialEvents.ql
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@@ -0,0 +1,7 @@
import csharp

private boolean isPartial(Event e) { if e.isPartial() then result = true else result = false }

from Event e
where e.fromSource()
select e, isPartial(e)
4 changes: 2 additions & 2 deletions csharp/ql/test/library-tests/partial/PartialIndexers.expected
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@@ -1,2 +1,2 @@
| Partial.cs:25:27:25:30 | Item | true |
| Partial.cs:42:19:42:22 | Item | false |
| Partial.cs:29:27:29:30 | Item | true |
| Partial.cs:49:19:49:22 | Item | false |
6 changes: 3 additions & 3 deletions csharp/ql/test/library-tests/partial/PartialMethodBody.expected
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@@ -1,3 +1,3 @@
| Partial.cs:4:18:4:42 | PartialMethodWithoutBody1 | false |
| Partial.cs:14:18:14:39 | PartialMethodWithBody1 | true |
| Partial.cs:34:18:34:42 | PartialMethodWithoutBody2 | false |
| Partial.cs:6:18:6:42 | PartialMethodWithoutBody1 | false |
| Partial.cs:18:18:18:39 | PartialMethodWithBody1 | true |
| Partial.cs:41:18:41:42 | PartialMethodWithoutBody2 | false |
4 changes: 2 additions & 2 deletions csharp/ql/test/library-tests/partial/PartialProperties.expected
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@@ -1,2 +1,2 @@
| Partial.cs:18:27:18:42 | PartialProperty1 | true |
| Partial.cs:41:19:41:26 | Property | false |
| Partial.cs:22:27:22:42 | PartialProperty1 | true |
| Partial.cs:48:19:48:26 | Property | false |
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