Improve Typemaker return type inference

DMCompiler/DM/DMValueType.cs

@@ -1,4 +1,4 @@
-namespace DMCompiler.DM;
+namespace DMCompiler.DM;
 
 // If you are modifying this, you must also modify OpenDreamShared.Dream.DreamValueType !!
 // Unfortunately the client needs this and it can't reference DMCompiler due to the sandbox
@@ -181,6 +181,15 @@ public class DMListValueTypes(DMComplexValueType nestedListKeyType, DMComplexVal
     public static DMListValueTypes MergeListValueTypes(DMCompiler compiler, DMListValueTypes type1, DMListValueTypes type2) {
         return new(DMComplexValueType.MergeComplexValueTypes(compiler, type1.NestedListKeyType, type2.NestedListKeyType), (type1.NestedListValType.HasValue && type2.NestedListValType.HasValue) ? DMComplexValueType.MergeComplexValueTypes(compiler, type1.NestedListValType.Value, type2.NestedListValType.Value) : (type1.NestedListValType ?? type2.NestedListValType));
     }
+    public static DMComplexValueType GetKeyValType(DMListValueTypes? listValueTypes) {
+        if (listValueTypes is null) return DMValueType.Anything;
+        return listValueTypes.NestedListKeyType | DMValueType.Null;
+    }
+    public static DMComplexValueType GetValueValType(DMListValueTypes? listValueTypes) {
+        if (listValueTypes is null) return DMValueType.Anything;
+        if (listValueTypes.NestedListValType is null) return listValueTypes.NestedListKeyType; // non-assoc list, keys are also values
+        return (DMComplexValueType)(listValueTypes.NestedListValType | DMValueType.Null);
+    }
     public override string ToString() {
         if (NestedListValType is not null)
             return $"{NestedListKeyType} = {NestedListValType}";

DMCompiler/DM/Expressions/Builtins.cs

@@ -561,6 +561,14 @@ public override void EmitPushValue(ExpressionContext ctx) {
 
 // initial(x)
 internal class Initial(Location location, DMExpression expr) : DMExpression(location) {
+    public override DMComplexValueType ValType {
+        get {
+            if (Expression is LValue lValue) {
+                return lValue.ValType;
+            }
+            return DMValueType.Anything;
+        }
+    }
     protected DMExpression Expression { get; } = expr;
 
     public override void EmitPushValue(ExpressionContext ctx) {

DMCompiler/DM/Expressions/Dereference.cs

@@ -60,27 +60,35 @@ public sealed class CallOperation : NamedOperation {
     public override DreamPath? Path { get; }
     public override DreamPath? NestedPath { get; }
     public override bool PathIsFuzzy => Path == null;
-    public override DMComplexValueType ValType { get; }
+    public override DMComplexValueType ValType {
+        get {
+            if (_valType is null) _valType = DetermineValType(_objectTree);
+            return _valType.Value;
+        }
+    }
+    private DMComplexValueType? _valType;
 
     private readonly DMExpression _expression;
     private readonly Operation[] _operations;
+    private readonly DMObjectTree _objectTree;
 
     public Dereference(DMObjectTree objectTree, Location location, DreamPath? path, DMExpression expression, Operation[] operations)
         : base(location, null) {
         _expression = expression;
         Path = path;
         _operations = operations;
+        _objectTree = objectTree;
 
         if (_operations.Length == 0) {
             throw new InvalidOperationException("deref expression has no operations");
         }
 
         NestedPath = _operations[^1].Path;
-        ValType = DetermineValType(objectTree);
     }
 
     private DMComplexValueType DetermineValType(DMObjectTree objectTree) {
         var type = _expression.ValType;
+        if (type.IsAnything && _expression.Path is not null) type = new DMComplexValueType(DMValueType.Instance, _expression.Path);
         var i = 0;
         while (!type.IsAnything && i < _operations.Length) {
             var operation = _operations[i++];
@@ -94,7 +102,7 @@ private DMComplexValueType DetermineValType(DMObjectTree objectTree) {
 
             type = operation switch {
                 FieldOperation fieldOperation => dmObject.GetVariable(fieldOperation.Identifier)?.ValType ?? DMValueType.Anything,
-                IndexOperation indexOperation => indexOperation.UnnestValType(type.ListValueTypes), // TODO: Keys of assoc lists
+                IndexOperation indexOperation => indexOperation.UnnestValType(type.ListValueTypes),
                 CallOperation callOperation => dmObject.GetProcReturnTypes(callOperation.Identifier, callOperation.Parameters) ?? DMValueType.Anything,
                 _ => throw new InvalidOperationException("Unimplemented dereference operation")
             };

DMCompiler/DM/Expressions/LValue.cs

@@ -77,6 +77,7 @@ public override DMReference EmitReference(ExpressionContext ctx, string endLabel
 
 // world
 internal sealed class World(Location location) : LValue(location, DreamPath.World) {
+    public override DMComplexValueType ValType => new DMComplexValueType(DMValueType.Instance, DreamPath.World);
     public override DMReference EmitReference(ExpressionContext ctx, string endLabel,
         ShortCircuitMode shortCircuitMode = ShortCircuitMode.KeepNull) {
         return DMReference.World;
@@ -93,7 +94,7 @@ public override DMComplexValueType ValType {
             //todo: allow local variables to be param-typed again
             // WITHOUT having to pass procParameters through the whole parser chain
             //if (valType is not null) return proc.GetBaseProc().GetParameterValueTypes(valType.Value, null);
-            if (valType is not null) return valType.Value;
+            if (valType is not null && !valType.Value.IsAnything) return valType.Value;
             return LocalVar.Type is not null ? new DMComplexValueType(DMValueType.Instance | DMValueType.Path | DMValueType.Null, LocalVar.Type) : DMValueType.Anything;
         }
     }