Add basic defer implementation

compiler/NubLang/Generation/Generator.cs

@@ -1,3 +1,4 @@
+using System.Diagnostics;
 using NubLang.Ast;
 
 namespace NubLang.Generation;
@@ -7,6 +8,8 @@ public class Generator
     private readonly List<DefinitionNode> _definitions;
     private readonly HashSet<NubStructType> _structTypes;
     private readonly IndentedTextWriter _writer;
+    private readonly Stack<List<DeferNode>> _deferStack = [];
+    private int _tmpIndex;
 
     public Generator(List<DefinitionNode> definitions, HashSet<NubStructType> structTypes)
     {
@@ -15,6 +18,12 @@ public class Generator
         _writer = new IndentedTextWriter();
     }
 
+    // todo(nub31): Handle name collissions
+    private string NewTmp()
+    {
+        return $"_t{++_tmpIndex}";
+    }
+
     private static string MapType(NubType nubType)
     {
         return nubType switch
@@ -246,7 +255,7 @@ public class Generator
 
     private void EmitDefer(DeferNode deferNode)
     {
-        throw new NotImplementedException();
+        _deferStack.Peek().Add(deferNode);
     }
 
     private void EmitIf(IfNode ifNode)
@@ -273,12 +282,27 @@ public class Generator
     {
         if (returnNode.Value == null)
         {
+            var blockDefers = _deferStack.Peek();
+            for (var i = blockDefers.Count - 1; i >= 0; i--)
+            {
+                EmitStatement(blockDefers[i].Statement);
+            }
+
             _writer.WriteLine("return;");
         }
         else
         {
             var returnValue = EmitExpression(returnNode.Value);
-            _writer.WriteLine($"return {returnValue};");
+            var tmp = NewTmp();
+            _writer.WriteLine($"{MapType(returnNode.Value.Type)} {tmp} = {returnValue};");
+
+            var blockDefers = _deferStack.Peek();
+            for (var i = blockDefers.Count - 1; i >= 0; i--)
+            {
+                EmitStatement(blockDefers[i].Statement);
+            }
+
+            _writer.WriteLine($"return {tmp};");
         }
     }
 
@@ -559,10 +583,18 @@ public class Generator
         _writer.WriteLine("{");
         using (_writer.Indent())
         {
+            _deferStack.Push([]);
+
             foreach (var statementNode in blockNode.Statements)
             {
                 EmitStatement(statementNode);
             }
+
+            var blockDefers = _deferStack.Pop();
+            for (var i = blockDefers.Count - 1; i >= 0; i--)
+            {
+                EmitStatement(blockDefers[i].Statement);
+            }
         }
 
         _writer.WriteLine("}");