Convert assignments to fields within constructors into field initializers.

Currently this works only if you click on the whole type, not an individual constructor.

ICSharpCode.Decompiler/Ast/Transforms/ConvertConstructorCallIntoInitializer.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Linq;
 using ICSharpCode.NRefactory.CSharp;
+using ICSharpCode.NRefactory.CSharp.PatternMatching;
 using Mono.Cecil;
 
 namespace ICSharpCode.Decompiler.Ast.Transforms
@@ -32,26 +33,91 @@ namespace ICSharpCode.Decompiler.Ast.Transforms
 					return null;
 				// Move arguments from invocation to initializer:
 				invocation.Arguments.MoveTo(ci.Arguments);
-				// Add the initializer:
-				constructorDeclaration.Initializer = ci.WithAnnotation(invocation.Annotation<MethodReference>());
+				// Add the initializer: (unless it is the default 'base()')
+				if (!(ci.ConstructorInitializerType == ConstructorInitializerType.Base && ci.Arguments.Count == 0))
+					constructorDeclaration.Initializer = ci.WithAnnotation(invocation.Annotation<MethodReference>());
 				// Remove the statement:
 				stmt.Remove();
 			}
 			return null;
 		}
 		
+		static readonly ExpressionStatement fieldInitializerPattern = new ExpressionStatement {
+			Expression = new AssignmentExpression {
+				Left = new NamedNode("fieldAccess", new MemberReferenceExpression { Target = new ThisReferenceExpression() }),
+				Operator = AssignmentOperatorType.Assign,
+				Right = new AnyNode("initializer")
+			}
+		};
+		
 		public override object VisitTypeDeclaration(TypeDeclaration typeDeclaration, object data)
 		{
+			var instanceCtors = typeDeclaration.Members.OfType<ConstructorDeclaration>().Where(c => (c.Modifiers & Modifiers.Static) == 0).ToArray();
+			if (instanceCtors.Length > 0 && typeDeclaration.ClassType == NRefactory.TypeSystem.ClassType.Class) {
+				// Recognize field initializers:
+				// Convert first statement in all ctors (if all ctors have the same statement) into a field initializer.
+				bool allSame;
+				do {
+					Match m = fieldInitializerPattern.Match(instanceCtors[0].Body.FirstOrDefault());
+					if (m == null)
+						break;
+					
+					FieldDefinition fieldDef = m.Get("fieldAccess").Single().Annotation<FieldDefinition>();
+					if (fieldDef == null)
+						break;
+					FieldDeclaration fieldDecl = typeDeclaration.Members.OfType<FieldDeclaration>().FirstOrDefault(f => f.Annotation<FieldDefinition>() == fieldDef);
+					if (fieldDecl == null)
+						break;
+					
+					allSame = true;
+					for (int i = 1; i < instanceCtors.Length; i++) {
+						if (instanceCtors[0].Body.First().Match(instanceCtors[i].Body.FirstOrDefault()) == null)
+							allSame = false;
+					}
+					if (allSame) {
+						foreach (var ctor in instanceCtors)
+							ctor.Body.First().Remove();
+						fieldDecl.Variables.Single().Initializer = m.Get<Expression>("initializer").Single().Detach();
+					}
+				} while (allSame);
+			}
+			
+			// Now convert base constructor calls to initializers:
 			base.VisitTypeDeclaration(typeDeclaration, data);
+			
 			// Remove single empty constructor:
-			var ctors = typeDeclaration.Members.OfType<ConstructorDeclaration>().Where(c => (c.Modifiers & Modifiers.Static) == 0).ToArray();
-			if (ctors.Length == 1 && ctors[0].Body.Children.Count() == 0
-			    && ctors[0].Initializer.ConstructorInitializerType == ConstructorInitializerType.Base
-			    && ctors[0].Initializer.Arguments.Count() == 0
-				&& ctors[0].Parameters.Count == 0
-			    && ctors[0].Modifiers == ((typeDeclaration.Modifiers & Modifiers.Abstract) == Modifiers.Abstract ? Modifiers.Protected : Modifiers.Public))
-			{
-				ctors[0].Remove();
+			if (instanceCtors.Length == 1) {
+				ConstructorDeclaration emptyCtor = new ConstructorDeclaration();
+				emptyCtor.Modifiers = ((typeDeclaration.Modifiers & Modifiers.Abstract) == Modifiers.Abstract ? Modifiers.Protected : Modifiers.Public);
+				emptyCtor.Body = new BlockStatement();
+				if (emptyCtor.Match(instanceCtors[0]) != null)
+					instanceCtors[0].Remove();
+			}
+			
+			// Convert static constructor into field initializers if the class is BeforeFieldInit
+			var staticCtor = typeDeclaration.Members.OfType<ConstructorDeclaration>().FirstOrDefault(c => (c.Modifiers & Modifiers.Static) == Modifiers.Static);
+			if (staticCtor != null) {
+				TypeDefinition typeDef = typeDeclaration.Annotation<TypeDefinition>();
+				if (typeDef != null && typeDef.IsBeforeFieldInit) {
+					while (true) {
+						ExpressionStatement es = staticCtor.Body.Statements.FirstOrDefault() as ExpressionStatement;
+						if (es == null)
+							break;
+						AssignmentExpression assignment = es.Expression as AssignmentExpression;
+						if (assignment == null || assignment.Operator != AssignmentOperatorType.Assign)
+							break;
+						FieldDefinition fieldDef = assignment.Left.Annotation<FieldDefinition>();
+						if (fieldDef == null || !fieldDef.IsStatic)
+							break;
+						FieldDeclaration fieldDecl = typeDeclaration.Members.OfType<FieldDeclaration>().FirstOrDefault(f => f.Annotation<FieldDefinition>() == fieldDef);
+						if (fieldDecl == null)
+							break;
+						fieldDecl.Variables.Single().Initializer = assignment.Right.Detach();
+						es.Remove();
+					}
+					if (staticCtor.Body.Statements.Count == 0)
+						staticCtor.Remove();
+				}
 			}
 			return null;
 		}