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Classify parameter discards earlier, syntactically instead of semantically, resolving classification conflict #85225

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Merged
akhera99 merged 2 commits into from
Sep 9, 2026
Merged

Classify parameter discards earlier, syntactically instead of semantically, resolving classification conflict #85225

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b22edaa
Classify parameter discards earlier, syntactically instead of semanti…
jnm2 Sep 9, 2026
26222f8
These scenarios are fully covered by the new total classifier tests
jnm2 Sep 9, 2026
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65 changes: 0 additions & 65 deletions src/EditorFeatures/CSharpTest/Classification/SemanticClassifierTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -3286,71 +3286,6 @@ bool N(object x)
Parameter("x"),
Keyword("_"));

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

[Theory, CombinatorialData]
public Task UsedUnderscoreParameterInLambda(TestHost testHost)
=> TestAsync("""
class X
{
void N()
{
System.Func<int, int> a = (int _) => _;
}
}
""",
testHost,
Namespace("System"),
Delegate("Func"),
Parameter("_"));

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

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

[Theory, CombinatorialData]
public Task NativeInteger(TestHost testHost)
=> TestInMethodAsync(
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2 changes: 1 addition & 1 deletion src/EditorFeatures/CSharpTest/Classification/SyntacticClassifierTests_Preprocessor.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1102,7 +1102,7 @@ public Task DiscardInLambda(TestHost testHost)
=> TestInMethodAsync(
code: @"x = (_, _) => 1;",
testHost: testHost,
expected: Classifications(Identifier("x"), Operators.Equals, Punctuation.OpenParen, Parameter("_"), Punctuation.Comma, Parameter("_"), Punctuation.CloseParen,
expected: Classifications(Identifier("x"), Operators.Equals, Punctuation.OpenParen, Keyword("_"), Punctuation.Comma, Keyword("_"), Punctuation.CloseParen,
Operators.EqualsGreaterThan, Number("1"), Punctuation.Semicolon));

[Theory, CombinatorialData]
Expand Down
39 changes: 39 additions & 0 deletions src/EditorFeatures/CSharpTest/Classification/TotalClassifierTests.cs
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Expand Up @@ -2942,6 +2942,45 @@ void M()
], actualFormatted);
}

[WpfTheory]
[InlineData("System.Action<int, int> lambda = (_, p) => { };", false)]
[InlineData("System.Action<int, int> lambda = (int _, int p) => { };", false)]
[InlineData("System.Action<int, int, int> lambda = (_, _, p) => { };", true)]
[InlineData("System.Action<int, int, int> lambda = (int _, int _, int p) => { };", true)]
public async Task TestTotalClassifier_LambdaDiscards(string declaration, bool isDiscard)
{
using var workspace = EditorTestWorkspace.CreateCSharp($$"""
class C
{
void M()
{
{{declaration}}
}
}
""");
var document = workspace.Documents.First();
var provider = new TotalClassificationTaggerProvider(
workspace.GetService<TaggerHost>(),
workspace.GetService<ClassificationTypeMap>());

var buffer = document.GetTextBuffer();
using var tagger = provider.CreateTagger(document.GetTextView(), buffer);

var listenerProvider = workspace.ExportProvider.GetExportedValue<IAsynchronousOperationListenerProvider>();
await listenerProvider.GetWaiter(FeatureAttribute.Classification).ExpeditedWaitAsync();

var tags = tagger!.GetTags(new NormalizedSnapshotSpanCollection(buffer.CurrentSnapshot.GetFullSpan()));
var actual = tags.OrderBy(tag => tag.Span.Start.Position)
.Where(tag => tag.Span.GetText() is "_" or "p")
.Select(tag => new FormattedClassification(tag.Span.GetText(), tag.Tag.ClassificationType.Classification));

AssertEx.Equal<FormattedClassification>(
isDiscard
? [Keyword("_"), Keyword("_"), Parameter("p")]
: [Parameter("_"), Parameter("p")],
actual);
}

[WpfFact]
public void TestCopyPasteClassifier()
{
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11 changes: 11 additions & 0 deletions src/Workspaces/CSharp/Portable/Classification/ClassificationHelpers.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -256,6 +256,17 @@ private static bool IsVerbatimStringToken(SyntaxToken token)
}
else if (token.Parent is ParameterSyntax parameterSyntax && parameterSyntax.Identifier == token)
{
if (token.Text == "_" && parameterSyntax.Parent is ParameterListSyntax { Parent: AnonymousFunctionExpressionSyntax } parameterList)
{
foreach (var otherParameter in parameterList.Parameters)
{
if (otherParameter != parameterSyntax && otherParameter.Identifier.Text == "_")
{
return ClassificationTypeNames.Keyword;
}
}
}

return ClassificationTypeNames.ParameterName;
}
else if (token.Parent is ForEachStatementSyntax forEachStatementSyntax && forEachStatementSyntax.Identifier == token)
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12 changes: 1 addition & 11 deletions ...Workspaces/CSharp/Portable/Classification/SyntaxClassification/DiscardSyntaxClassifier.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@ namespace Microsoft.CodeAnalysis.CSharp.Classification.Classifiers;

internal sealed class DiscardSyntaxClassifier : AbstractSyntaxClassifier
{
public override ImmutableArray<Type> SyntaxNodeTypes { get; } = [typeof(DiscardDesignationSyntax), typeof(DiscardPatternSyntax), typeof(ParameterSyntax), typeof(IdentifierNameSyntax)];
public override ImmutableArray<Type> SyntaxNodeTypes { get; } = [typeof(DiscardDesignationSyntax), typeof(DiscardPatternSyntax), typeof(IdentifierNameSyntax)];

public override void AddClassifications(
SyntaxNode syntax,
Expand All @@ -33,16 +33,6 @@ public override void AddClassifications(

switch (syntax)
{
case ParameterSyntax parameter when parameter.Identifier.Text == "_":
var symbol = semanticModel.GetDeclaredSymbol(parameter, cancellationToken);

if (symbol?.IsDiscard == true)
{
result.Add(new ClassifiedSpan(parameter.Identifier.Span, ClassificationTypeNames.Keyword));
}

break;

case IdentifierNameSyntax identifierName when identifierName.Identifier.Text == "_":
var symbolInfo = semanticModel.GetSymbolInfo(identifierName, cancellationToken);

Expand Down