feat: Use source generator for event dispatch extensions #1758

linkdotnet · 2025-09-19T21:39:39Z

What we talked about today.

Moved a lot of the code to source code generators, with some changes to the current version:

Dropped the overloads with all the optional parameters
Added the this Task<IElement> overload for the async versions
Aligned (hopefully all) convenient functions to work with sync and async (for example KeyPress('c') and KeyPressAsync('c')).

egil · 2025-09-28T15:55:13Z

Cool. Think this is heading in a good direction.

Would it make sense to read EventHandlers.cs from the generator and get all the html event names (e.g., onclick) from there, as well as getting code doc parts from codedocs on properties on the event types themselves, e.g., MouseEventArgs.cs, such that it is not hardcoded in the generator.

Obviously, there needs to be the special-cases explicitly in the generator, or just in a partial handcoded type.

Looking at the Blazor sources, they actually have "reader" types that explicitly show what types of parameters can be passed in, e.g., we can see that ChangeEventArgsReader.cs supports, null, string, true, false, and string[]. It would be neat to have explicit overloads for Change() that takes these types explicitly, instead of using object?.

egil · 2025-09-29T19:18:53Z

Also, want to add, that if this works as is correctly, we can always add my suggestions as an issue for future improvements, and get this merged in.

Copilot

Pull Request Overview

This PR implements a source generator to replace manually written event dispatch extension methods. The changes move from hand-coded event dispatch extensions to source-generated ones, which improves maintainability and consistency across the codebase.

Introduces a new source generator for event dispatch extensions
Removes manually written event dispatch extension files
Updates existing extensions to use partial classes to work with the generated code
Fixes style inconsistencies and adds Task overloads for async operations

Reviewed Changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/bunit.tests/EventDispatchExtensions/WheelEventDispatchExtensionsTest.cs	Fixed type reference from MouseEventDispatchExtensions to WheelEventDispatchExtensions
src/bunit/EventDispatchExtensions/TouchEventDispatchExtensions.cs	Removed entire file - functionality moved to source generator
src/bunit/EventDispatchExtensions/ProgressEventDispatchExtensions.cs	Removed entire file - functionality moved to source generator
src/bunit/EventDispatchExtensions/PointerEventDispatchExtensions.cs	Removed entire file - functionality moved to source generator
src/bunit/EventDispatchExtensions/MouseEventDispatchExtensions.cs	Removed entire file - functionality moved to source generator
src/bunit/EventDispatchExtensions/MediaEventDispatchExtensions.cs	Updated to fix style and add Task overloads
src/bunit/EventDispatchExtensions/KeyboardEventDispatchExtensions.cs	Changed to partial class and simplified methods to work with generator
src/bunit/EventDispatchExtensions/InputEventDispatchExtensions.cs	Changed to partial class and added Task overloads
src/bunit/EventDispatchExtensions/FocusEventDispatchExtensions.cs	Removed entire file - functionality moved to source generator
src/bunit/EventDispatchExtensions/DragEventDispatchExtensions.cs	Removed entire file - functionality moved to source generator
src/bunit/EventDispatchExtensions/DialogEventDispatchExtensions.cs	Removed entire file - functionality moved to source generator
src/bunit/EventDispatchExtensions/ClipboardEventDispatchExtensions.cs	Removed entire file - functionality moved to source generator
src/bunit.generators.internal/bunit.generators.internal.csproj	Added packaging configuration for the analyzer
src/bunit.generators.internal/Blazor/EventDispatcherExtensionGenerator.cs	New source generator that creates event dispatch extension methods

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Copilot · 2025-09-29T19:23:15Z

src/bunit.generators.internal/Blazor/EventDispatcherExtensionGenerator.cs

+		var methodName = eventArgsType.Replace("EventArgs", "");
+		var eventName = $"on{methodName.ToLowerInvariant()}";


The event name generation using ToLowerInvariant() may not work correctly for all event types. For example, ClipboardEventArgs would generate onclipboard instead of the correct event names like oncopy, oncut, onpaste. This could lead to incorrect event binding.

Copilot · 2025-09-29T19:23:16Z

src/bunit.generators.internal/Blazor/EventDispatcherExtensionGenerator.cs

+	private static void GenerateGenericEventExtension(StringBuilder sourceBuilder, string eventArgsType)
+	{
+		var methodName = eventArgsType.Replace("EventArgs", "");
+		var eventName = $"on{methodName.ToLowerInvariant()}";
+		GenerateAsyncEventMethod(sourceBuilder, methodName, eventName, eventArgsType);
+	}


The generic event extension generation is overly simplistic and doesn't handle complex event types properly. EventArgs types like ClipboardEventArgs, DragEventArgs, and FocusEventArgs have multiple specific events (copy/cut/paste, drag/dragend/drop, focus/blur) that can't be mapped with this simple string replacement approach.

Copilot

Pull Request Overview

Copilot reviewed 28 out of 28 changed files in this pull request and generated 1 comment.

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Copilot · 2025-10-04T10:37:38Z

tests/bunit.tests/EventDispatchExtensions/EventDispatchExtensionsTest.cs


 		return helperClassType.GetMethods()
 			.Where(x => x.GetParameters().FirstOrDefault()?.ParameterType == typeof(IElement))
+			.Where(x => x.GetParameters().Skip(1).FirstOrDefault()?.ParameterType == typeof(TEventArgs))


[nitpick] Consider extracting the magic number 1 into a named constant to improve readability and make the intent clearer (e.g., SKIP_FIRST_PARAMETER = 1).

egil · 2025-10-04T16:19:57Z

@linkdotnet I trust you let me know when I should do a proper review.

linkdotnet · 2025-10-05T07:14:12Z

@linkdotnet I trust you let me know when I should do a proper review.

Yeah will notify you. Have some more local stuff and the in-laws over ;) have to balance that out a bit :)

linkdotnet · 2025-10-05T09:29:16Z

@egil I do feel that thing is in a good state.

linkdotnet · 2025-10-05T09:29:39Z

<3 <3

Copilot

Pull Request Overview

Copilot reviewed 28 out of 28 changed files in this pull request and generated 3 comments.

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src/bunit.generators.internal/bunit.generators.internal.csproj

src/bunit.generators.internal/Blazor/EventDispatcherExtensionGenerator.cs

Copilot · 2025-10-05T09:31:29Z

src/bunit.generators.internal/Blazor/EventDispatcherExtensionGenerator.cs

+			var qualifiedEventArgsType = eventArgsType == "ErrorEventArgs"
+				? "Microsoft.AspNetCore.Components.Web.ErrorEventArgs"
+				: eventArgsType;


Hard-coding the special case for ErrorEventArgs makes the code brittle. Consider creating a mapping dictionary or using reflection to determine the fully qualified type name for better maintainability.

egil · 2025-10-05T12:41:02Z

src/bunit.generators.internal/Blazor/EventDispatcherExtensionGenerator.cs

+			foreach (var word in WordBoundaries.OrderByDescending(w => w.Length))
+			{
+				if (i + word.Length <= eventName.Length &&
+				    eventName.AsSpan(i, word.Length).Equals(word.AsSpan(), StringComparison.OrdinalIgnoreCase))


I know CoPilot recommended this, but it seems super redundant. string comparison will do this for you if it makes any sense at all in terms of performance.

Will revert htat, and maybe move this into a variable. Have anyway some doc changes coming up

Well before we had a SubString which for sure does incur a new object.

That said, the change itself does make sense but it is convoluted and i will refactor it

egil

Assuming all tests pass, this looks great.

linkdotnet · 2025-10-05T13:21:17Z

@egil Updated the docs and made a small refactoring. I would merge that bad boy in

linkdotnet requested a review from egil September 19, 2025 21:39

linkdotnet force-pushed the dispatch-extensions-as-scg branch from b9ffb2c to dc2a16a Compare September 19, 2025 21:51

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linkdotnet force-pushed the dispatch-extensions-as-scg branch 2 times, most recently from b6462f4 to 9762345 Compare October 5, 2025 09:24

linkdotnet force-pushed the dispatch-extensions-as-scg branch from 9762345 to 7aa3753 Compare October 5, 2025 09:29

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linkdotnet force-pushed the dispatch-extensions-as-scg branch 4 times, most recently from b1667f2 to a5e5934 Compare October 5, 2025 12:35

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egil previously approved these changes Oct 5, 2025

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linkdotnet dismissed egil’s stale review via c139607 October 5, 2025 12:52

linkdotnet force-pushed the dispatch-extensions-as-scg branch 3 times, most recently from 809e357 to 5ca8821 Compare October 5, 2025 13:10

feat: Use source generator for event dispatch extensions

894f15a

linkdotnet force-pushed the dispatch-extensions-as-scg branch from 5ca8821 to 894f15a Compare October 5, 2025 13:15

linkdotnet merged commit 5bda93c into main Oct 5, 2025
9 of 10 checks passed

linkdotnet deleted the dispatch-extensions-as-scg branch October 5, 2025 15:25

		var methodName = eventArgsType.Replace("EventArgs", "");
		var eventName = $"on{methodName.ToLowerInvariant()}";

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