Add implementation for DisposeWith on variable declarations

Author: Mafii

IDisposableAnalyzers/Helpers/Disposable.ShouldDispose.cs

@@ -22,6 +22,11 @@ internal static bool ShouldDispose(LocalOrParameter localOrParameter, SemanticMo
             return false;
         }
 
+        if (Scope() is BlockSyntax localBlock && IsVariableDeclarationWithDisposeAsExtensionCall(localBlock))
+        {
+            return false;
+        }
+
         using var recursion = Recursion.Borrow(localOrParameter.Symbol.ContainingType, semanticModel, cancellationToken);
         using var walker = UsagesWalker.Borrow(localOrParameter, semanticModel, cancellationToken);
         foreach (var usage in walker.Usages)
@@ -112,4 +117,51 @@ static bool ShouldNotDispose(IdentifierNameSyntax usage, Recursion recursion)
             return false;
         }
     }
+
+    private static bool IsVariableDeclarationWithDisposeAsExtensionCall(BlockSyntax localBlock)
+    {
+        if (localBlock is not { Statements: { Count: 1 } statements })
+        {
+            return false;
+        }
+
+        if (statements[0] is not LocalDeclarationStatementSyntax { Declaration: { } variableDeclaration })
+        {
+            return false;
+        }
+
+        if (variableDeclaration.Variables is not { Count: 1 } vars)
+        {
+            return false;
+        }
+
+        if (vars[0].Initializer is not { } rhs)
+        {
+            return false;
+        }
+
+        // For simplicity reasons, we do not validate the variable type, or what is to the left of the call.
+        // Instead, we simply check if the last invocation of the rhs is `.DisposeWith(<one argument>);`
+        if (rhs.Value is not InvocationExpressionSyntax lastInvocationInChain)
+        {
+            return false;
+        }
+
+        if (lastInvocationInChain.Expression is not MemberAccessExpressionSyntax memberAccess)
+        {
+            return false;
+        }
+
+        if (memberAccess.Name.Identifier.Value is not "DisposeWith")
+        {
+            return false;
+        }
+
+        if (lastInvocationInChain.ArgumentList.Arguments is not { Count: 1 } arguments)
+        {
+            return false;
+        }
+
+        return true;
+    }
 }