Is this a bug that lambda discards aren't highlighted as keyword?

[KyouyamaKazusa0805]

Version Used:
VS 16.9 Preview 5

Steps to Reproduce:

var model = ViewModel.PanelViewModel;

model.GridChanged += (SudokuPanelViewModel _, in SudokuGrid _) => ViewModel.Image = ViewModel.Generator.Paint();

Expected Behavior:

Both two underscore _ in SudokuPanelViewModel _ and in SudokuGrid _ should be highlighted as keyword (I mean, in blue as same color as keyword highlights).

Actual Behavior:

The color doesn't change no matter how I change the code (Lambdas, anonymous functions...)

Screenshots:

For the last picture, I don't know whether the syntax is valid. I just test the cases that makes the discards to be highlighted as keywords.

---

Update (2022/8/15):

It seems that the discard highlights behave differently between light and dark themes.

In dark theme, discards are not highlighted correctly:

But in light theme, discards are displayed successfully:

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Update (2023/12/1):

I think it has been fixed.

[hez2010]

I think discard _ is not a keyword, it's a valid identifier.

[jmarolf]

upvote dotnet/csharplang#4460

[KyouyamaKazusa0805]

@jmarolf @hez2010

Hmmmm... In fact I mean the discards will be highlighted as blue.

Only lambda parameters (_) is in white, while other discards are in blue.

[jnm2]

I noticed this as well. It would be nice for the visual cue to work based on semantics with parameter discards like with other discards.

[KyouyamaKazusa0805]

I noticed this as well. It would be nice for the visual cue to work based on semantics with parameter discards like with other discards.

Yeah, that's it!

[CyrusNajmabadi]

It should be. Sounds like a bug. PRs welcome.

[KyouyamaKazusa0805]

It should be. Sounds like a bug. PRs welcome.

@CyrusNajmabadi XD

I've been learning the Roslyn source code, but I don't think I have any ability to create a PR at present.

If I have the ability, I will. :)

[Youssef1313]

This is weird. It is already tested 😱

roslyn/src/EditorFeatures/CSharpTest/Classification/SemanticClassifierTests.cs

Lines 4277 to 4294 in 6da1274

	[Theory]
	[CombinatorialData]
	public async Task DiscardsInLambda(TestHost testHost)
	{
	await TestAsync(@"
	class X
	{
	void N()
	{
	System.Func<int, int, int> a = (int _, int _) => 0;
	}
	}",
	testHost,
	Namespace("System"),
	Delegate("Func"),
	Keyword("_"),
	Keyword("_"));
	}

For reference: this was added in #40396. But for some weird reason it doesn't work despite the test is passing.

The following code may be related (not sure) - but still, the test should have failed:

roslyn/src/Workspaces/CSharp/Portable/Classification/ClassificationHelpers.cs

Lines 264 to 267 in 6da1274

	else if (token.Parent is ParameterSyntax parameterSyntax && parameterSyntax.Identifier == token)
	{
	return ClassificationTypeNames.ParameterName;
	}

[Youssef1313]

The semantic classifier works correctly, but the syntactic one doesn't (at least this is what the tests say). This causes SemanticClassifierTests to pass, while things doesn't actually work. @CyrusNajmabadi Is there a way to order the semantic classifier to be run after the syntactic classifier?

[CyrusNajmabadi]

I believe we have 'total classifier' tests

[KyouyamaKazusa0805]

Close this issue. This issue is solved.