Fix Y0002 codefix crash for foreach deconstruction patterns

[Copilot]

Applying the Y0002 code fix to foreach (var (a, b) in x) crashes with NullReferenceException because model.GetTypeInfo(var).ConvertedType is null in a deconstruction context — var doesn't map to a single type.

Changes

• UseImplicitOrExplicitTypeCodeFix.cs

  • In RegisterCodeFixesAsync, detect DeclarationExpressionSyntax with ParenthesizedVariableDesignationSyntax and route to a dedicated handler instead of falling through to the GetTypeInfo path
  • Add UseExplicitDeconstructionTypeAsync: iterates each variable in the designation, resolves its type via GetDeclaredSymbol, and constructs a TupleExpressionSyntax replacement

• UseImplicitOrExplicitTypeAnalyzerTests.cs

  • Remove [Ignore] from TestDeconstruction

Example

// Before (crashes):
foreach (var (a, b) in x) { }

// After applying Y0002 fix:
foreach ((int a, string b) in x) { }

Nested deconstruction patterns (e.g. var ((a, b), c)) are intentionally left without a fix registration until fully supported.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Y0002 codefix crash for 'foreach (var (a, b) in x)'</issue_title>
<issue_description>StackTrace:

System.NullReferenceException : Object reference not set to an instance of an object.
   at Microsoft.CodeAnalysis.CSharp.Extensions.ITypeSymbolExtensions.GenerateTypeSyntax(INamespaceOrTypeSymbol symbol,Boolean nameSyntax,Boolean allowVar)
   at Microsoft.CodeAnalysis.CSharp.CodeGeneration.CSharpSyntaxGenerator.TypeExpression(ITypeSymbol typeSymbol)
   at async YAnalyzers.CSharp.UseImplicitOrExplicitTypeCodeFix.UseExplicitTypeAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.CodeActions.CodeAction.GetChangedSolutionAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.CodeActions.CodeAction.ComputeOperationsAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.CodeActions.CodeAction.GetPreviewOperationsAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.Editor.Implementation.Suggestions.SuggestedAction.GetPreviewResultAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.Editor.Implementation.Suggestions.SuggestedActionWithNestedFlavors.<>c__DisplayClass11_0.<GetPreviewAsync>b__0(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.Extensions.IExtensionManagerExtensions.PerformFunctionAsync[T](<Unknown Parameters>)

The form foreach (var (a, b) in x) should be converted into foreach ((TypeA a, TypeB b) in x)</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Y0002 codefix crash for 'foreach (var (a, b) in x)' #33

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