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Fix WTG3014/WTG3013 code-fix to emit explicit type argument when needed #239

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Fix WTG3014/WTG3013 code-fix to emit explicit type argument when needed #239

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5229d46
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Copilot May 26, 2026
7821ce8
Fix WTG3014/WTG3013 code-fix to add explicit type argument when eleme…
Copilot May 26, 2026
ba72978
Replace SemanticModel usage with syntactic TypeSyntax extraction and …
Copilot May 26, 2026
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19 changes: 19 additions & 0 deletions src/WTG.Analyzers.Test/TestData/LinqEnumerableAnalyzer/PrependTypeMismatch/Diagnostics.xml
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Original file line number Diff line number Diff line change
@@ -0,0 +1,19 @@
<?xml version="1.0" encoding="utf-8" ?>
<diagnostics severity="Info">
<group id="WTG3014" message="Don't use Concat when prepending a single element to an enumerable.">
<diagnostic>
<location>Test0.cs: (10, 3-36)</location>
</diagnostic>
<diagnostic>
<location>Test0.cs: (11, 3-20)</location>
</diagnostic>
</group>
<group id="WTG3013" message="Don't use Concat when appending a single element to an enumerable.">
<diagnostic>
<location>Test0.cs: (12, 3-25)</location>
</diagnostic>
<diagnostic>
<location>Test0.cs: (13, 3-20)</location>
</diagnostic>
</group>
</diagnostics>
20 changes: 20 additions & 0 deletions src/WTG.Analyzers.Test/TestData/LinqEnumerableAnalyzer/PrependTypeMismatch/Result.cs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,20 @@
using System.Collections.Generic;
using System.Linq;

public class Bob
{
public void Method()
{
var viewModel = new ViewModel();

viewModel.Items.Prepend<object>(viewModel);
Enumerable.Prepend<object>(viewModel.Items, viewModel);
viewModel.Items.Append<object>(viewModel);
Enumerable.Append<object>(viewModel.Items, viewModel);
}
}

public class ViewModel
{
public IEnumerable<ViewModel> Items { get; set; }
}
20 changes: 20 additions & 0 deletions src/WTG.Analyzers.Test/TestData/LinqEnumerableAnalyzer/PrependTypeMismatch/Source.cs
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@@ -0,0 +1,20 @@
using System.Collections.Generic;
using System.Linq;

public class Bob
{
public void Method()
{
var viewModel = new ViewModel();

new object[] { viewModel }.Concat(viewModel.Items);
Enumerable.Concat(new object[] { viewModel }, viewModel.Items);
viewModel.Items.Concat(new object[] { viewModel });
Enumerable.Concat(viewModel.Items, new object[] { viewModel });
}
}

public class ViewModel
{
public IEnumerable<ViewModel> Items { get; set; }
}
56 changes: 50 additions & 6 deletions src/WTG.Analyzers/Analyzers/LinqEnumerable/LinqEnumerableCodeFixProvider.cs
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Expand Up @@ -104,15 +104,19 @@ public static SyntaxNode FixConcatWithAppendMethod(MemberAccessExpressionSyntax

var listOfArgumentsAndSeparators = new List<SyntaxNodeOrToken>();

ExpressionSyntax singleElementCollection;

switch (invocation.ArgumentList.Arguments.Count)
{
case 1:
listOfArgumentsAndSeparators.Add(Argument(LinqEnumerableUtils.GetFirstValue(invocation.ArgumentList.Arguments[0].Expression)!));
singleElementCollection = invocation.ArgumentList.Arguments[0].Expression;
listOfArgumentsAndSeparators.Add(Argument(LinqEnumerableUtils.GetFirstValue(singleElementCollection)!));
break;
case 2:
singleElementCollection = invocation.ArgumentList.Arguments[1].Expression;
listOfArgumentsAndSeparators.Add(invocation.ArgumentList.Arguments[0]);
listOfArgumentsAndSeparators.Add(Token(SyntaxKind.CommaToken));
listOfArgumentsAndSeparators.Add(Argument(LinqEnumerableUtils.GetFirstValue(invocation.ArgumentList.Arguments[1].Expression)!));
listOfArgumentsAndSeparators.Add(Argument(LinqEnumerableUtils.GetFirstValue(singleElementCollection)!));
break;
default:
throw new InvalidOperationException("Unreachable - Code fix should never trigger for >2 arguments.");
Expand All @@ -125,7 +129,7 @@ public static SyntaxNode FixConcatWithAppendMethod(MemberAccessExpressionSyntax
.WithTriviaFrom(m.Expression)
.WithAdditionalAnnotations(Simplifier.Annotation),
m.OperatorToken,
IdentifierName(nameof(Enumerable.Append))
GetMethodName(nameof(Enumerable.Append), singleElementCollection)
.WithTriviaFrom(m.Name)))
.WithArgumentList(
ArgumentList(
Expand All @@ -141,19 +145,22 @@ public static SyntaxNode FixConcatWithAppendMethod(MemberAccessExpressionSyntax
var listOfArgumentsAndSeparators = new List<SyntaxNodeOrToken>();

ExpressionSyntax member;
ExpressionSyntax singleElementCollection;

switch (invocation.ArgumentList.Arguments.Count)
{
case 1:
listOfArgumentsAndSeparators.Add(Argument(LinqEnumerableUtils.GetFirstValue(m.Expression.TryGetExpressionFromParenthesizedExpression())!));
singleElementCollection = m.Expression.TryGetExpressionFromParenthesizedExpression();
listOfArgumentsAndSeparators.Add(Argument(LinqEnumerableUtils.GetFirstValue(singleElementCollection)!));
member = ParenthesizedExpression(invocation.ArgumentList.Arguments[0].Expression.WithoutTrivia())
.WithTriviaFrom(m.Expression)
.WithAdditionalAnnotations(Simplifier.Annotation);
break;
case 2:
singleElementCollection = invocation.ArgumentList.Arguments[0].Expression;
listOfArgumentsAndSeparators.Add(invocation.ArgumentList.Arguments[1]);
listOfArgumentsAndSeparators.Add(Token(SyntaxKind.CommaToken));
listOfArgumentsAndSeparators.Add(Argument(LinqEnumerableUtils.GetFirstValue(invocation.ArgumentList.Arguments[0].Expression)!));
listOfArgumentsAndSeparators.Add(Argument(LinqEnumerableUtils.GetFirstValue(singleElementCollection)!));
member = m.Expression;
break;

Expand All @@ -166,7 +173,7 @@ public static SyntaxNode FixConcatWithAppendMethod(MemberAccessExpressionSyntax
SyntaxKind.SimpleMemberAccessExpression,
member,
m.OperatorToken,
IdentifierName(nameof(Enumerable.Prepend))
GetMethodName(nameof(Enumerable.Prepend), singleElementCollection)
.WithTriviaFrom(m.Name)))
.WithArgumentList(
ArgumentList(
Expand Down Expand Up @@ -213,5 +220,42 @@ public static SyntaxNode FixConcatWithNewCollection(MemberAccessExpressionSyntax
.WithTriviaFrom(invocation)
.WithAdditionalAnnotations(Simplifier.Annotation);
}

static SimpleNameSyntax GetMethodName(string methodName, ExpressionSyntax singleElementCollection)
{
var elementType = GetCollectionElementType(singleElementCollection.TryGetExpressionFromParenthesizedExpression());

if (elementType != null)
{
return GenericName(Identifier(methodName))
.WithTypeArgumentList(
TypeArgumentList(
SingletonSeparatedList<TypeSyntax>(
elementType.WithoutTrivia())))
.WithAdditionalAnnotations(Simplifier.Annotation);
}

return IdentifierName(methodName);
}

static TypeSyntax? GetCollectionElementType(ExpressionSyntax expression)
{
switch (expression.Kind())
{
case SyntaxKind.ArrayCreationExpression:
return ((ArrayCreationExpressionSyntax)expression).Type.ElementType;

case SyntaxKind.ObjectCreationExpression:
var objectCreationType = ((ObjectCreationExpressionSyntax)expression).Type;
if (objectCreationType is GenericNameSyntax genericName && genericName.TypeArgumentList.Arguments.Count == 1)
{
return genericName.TypeArgumentList.Arguments[0];
}

break;
}

return null;
}
}
}