Overhaul `RefPtr` and `String`

- `RefPtr` no longer tries to have distinct cases for interal-vs-external reference counts. Instead we always require an internal reference count.

  - Types the used `RefPtr` but weren't `RefObject` were made to inherit `RefObject`

  - The `ReferenceCounted` base class was removed, so that only `RefObject` remains

  - Implicit conversion from `RefPtr<T>` to `T*` added
    - This created some complicates for other types that relied on implicit conversions, so this isn't a net cleanup right now

- The main type that got messed up by the above was `String`, which previously held a `RefPtr<char, ...>`. This change thus *also* includes a major overhaul of `String`:

  - `String` now holds all its data via indirection, using a `StringRepresentation` that is a `RefObject`. This object holds a length, capacity, and directly stores the character data in its allocation. This means that `sizeof(String)==sizeof(void*)`

  - It is now possible to directly mutate a `String` by appending to its representation (we just need to ensure it has a reference count of `1`, possibly by cloning it). This means that `StringBuilder` is now basically just an idomatic use of `String`

  - A couple operations that just return sub-ranges of a `String` now return `StringSlice` to avoid allocation when it isn't needed. This required more work.

  - Indices into strings changed from `int` to `UInt` (which is pointer-sized). This had a bunch of follow-on changes because the value `-1` sometimes needs to be special-cased in code that uses indices. Further cleanups are probably needed here.

1 files changed, 7 insertions, 22 deletions

diff --git a/source/slang/syntax.h b/source/slang/syntax.h
index 05d3b6a79..b4d7e146e 100644
--- a/source/slang/syntax.h
+++ b/source/slang/syntax.h
@@ -664,26 +664,11 @@ namespace Slang
             : IsLeftValue(false)
         {}
 
-        QualType(RefPtr<ExpressionType> type)
-            : type(type)
-            , IsLeftValue(false)
-        {}
-
         QualType(ExpressionType* type)
             : type(type)
             , IsLeftValue(false)
         {}
 
-        void operator=(RefPtr<ExpressionType> t)
-        {
-            *this = QualType(t);
-        }
-
-        void operator=(ExpressionType* t)
-        {
-            *this = QualType(t);
-        }
-
         ExpressionType* Ptr() { return type.Ptr(); }
 
         operator RefPtr<ExpressionType>() { return type; }
@@ -1444,7 +1429,7 @@ namespace Slang
             return type->Equals(other.Ptr());
         }
         ExpressionType* Ptr() { return type.Ptr(); }
-        operator RefPtr<ExpressionType>()
+        operator ExpressionType*()
         {
             return type;
         }
@@ -1473,7 +1458,7 @@ namespace Slang
 
     inline RefPtr<ExpressionType> GetType(DeclRef<VarDeclBase> const& declRef)
     {
-        return declRef.Substitute(declRef.getDecl()->Type);
+        return declRef.Substitute(declRef.getDecl()->Type.Ptr());
     }
 
     inline RefPtr<ExpressionSyntaxNode> getInitExpr(DeclRef<VarDeclBase> const& declRef)
@@ -1519,7 +1504,7 @@ namespace Slang
 
     inline RefPtr<ExpressionType> GetTargetType(DeclRef<ExtensionDecl> const& declRef)
     {
-        return declRef.Substitute(declRef.getDecl()->targetType);
+        return declRef.Substitute(declRef.getDecl()->targetType.Ptr());
     }
 
     // Declaration of a type that represents some sort of aggregate
@@ -1620,7 +1605,7 @@ namespace Slang
 
     inline RefPtr<ExpressionType> GetType(DeclRef<TypeDefDecl> const& declRef)
     {
-        return declRef.Substitute(declRef.getDecl()->Type);
+        return declRef.Substitute(declRef.getDecl()->Type.Ptr());
     }
 
     // A type alias of some kind (e.g., via `typedef`)
@@ -2423,12 +2408,12 @@ namespace Slang
 
     inline RefPtr<ExpressionType> GetSub(DeclRef<GenericTypeConstraintDecl> const& declRef)
     {
-        return declRef.Substitute(declRef.getDecl()->sub);
+        return declRef.Substitute(declRef.getDecl()->sub.Ptr());
     }
 
     inline RefPtr<ExpressionType> GetSup(DeclRef<GenericTypeConstraintDecl> const& declRef)
     {
-        return declRef.Substitute(declRef.getDecl()->sup);
+        return declRef.Substitute(declRef.getDecl()->sup.Ptr());
     }
 
     class GenericValueParamDecl : public VarDeclBase
@@ -2482,7 +2467,7 @@ namespace Slang
 
     //
 
-    class SyntaxVisitor
+    class SyntaxVisitor : public RefObject
     {
     protected:
         DiagnosticSink * sink = nullptr;