ProxyAll for interface part 1...

src/ProxyInterfaceSourceGenerator/FileGenerators/BaseGenerator.cs

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+using System;
+using System.Collections.Generic;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using ProxyInterfaceSourceGenerator.SyntaxReceiver;
+
+namespace ProxyInterfaceSourceGenerator.FileGenerators
+{
+    internal abstract class BaseGenerator
+    {
+        protected readonly Context _context;
+        protected readonly IDictionary<InterfaceDeclarationSyntax, ProxyData> _candidateInterfaces;
+
+        public BaseGenerator(Context context, IDictionary<InterfaceDeclarationSyntax, ProxyData> candidateInterfaces)
+        {
+            _context = context;
+            _candidateInterfaces = candidateInterfaces;
+        }
+
+        protected INamedTypeSymbol GetType(string name)
+        {
+            var symbol = _context.GeneratorExecutionContext.Compilation.GetTypeByMetadataName(name);
+            if (symbol is null)
+            {
+                throw new Exception($"The type '{name}' is not found.");
+            }
+
+            return symbol;
+        }
+    }
+}