Yet more refactoring around Artifact (#2352)

* #include an absolute path didn't work - because paths were taken to always be relative.

* WIP with hierarchical enums.

* Some small fixes and improvements around artifact desc related types.

* Improvements around hierarchical enum.

* Fixes to get Artifact types refactor to be able to execute tests.

* Attempt to better categorize PTX.

* Work around for potentially unused function warning.

* Typo fix.

* Simplify Artifact header.

* Small improvements around Artifact kind/payload/style.

* Added IDestroyable/ICastable

* Add IArtifactList.

* First impl of IArtifactUtil.

* Use the ICastable interface for IArtifactRepresentation.

* Added IArtifactRepresentation & IArtifactAssociated.

* Add SLANG_OVERRIDE to avoid gcc/clang warning.

* Fix calling convention issue on win32.

* Fix missing SLANG_OVERRIDE.

* First attempt at file abstraction around Artifact.

* Added creation of lock file.

* Move functionality for determining file paths to the IArtifactUtil.
Add casting to ICastable.

* Added some casting/finding mechanisms.

* Simplify IArtifact interface, and use Items for file reps.

* Fix problem with libraries on DXIL.

* Split out ArtifactRepresentation.

* Move ArtifactDesc functionality to ArtifactDescUtil. ArtifactInfoUtil becomes ArtifactDescUtil.

* Split implementations from the interfaces for Artifact.

* Use TypeTextUtil for target name outputting.

* Add artifact impls.

* Add ICastableList

* Added UnknownCastableAdapter

* Make ISlangSharedLibrary derive from ICastable, and remain backwards compatible with slang-llvm.

* Refactor Representation on Artifact.

* Make our ISlangBlobs also derive from ICastable.
Make ISlangBlob atomic ref counted.

* Split out CastableList and related types, and placed in core.

* Small fixes around IArtifact.
Improve IArtifact docs.
First impl of getChildren for IArtifact.

* Documentation improvements for Artifact related types.

* Fix typo.

* Special case adding a ICastableList to a LazyCastableList.

* Small simplification of LazyCastableList, by adding State member.

* Removed the ILockFile interface because IFileArtifactRepresentation can be used.

19 files changed, 712 insertions, 644 deletions

diff --git a/build/visual-studio/core/core.vcxproj b/build/visual-studio/core/core.vcxproj
index c4a28f94b..13e933326 100644
--- a/build/visual-studio/core/core.vcxproj
+++ b/build/visual-studio/core/core.vcxproj
@@ -281,6 +281,8 @@
     <ClInclude Include="..\..\..\source\core\slang-basic.h" />
     <ClInclude Include="..\..\..\source\core\slang-blob.h" />
     <ClInclude Include="..\..\..\source\core\slang-byte-encode-util.h" />
+    <ClInclude Include="..\..\..\source\core\slang-castable-list-impl.h" />
+    <ClInclude Include="..\..\..\source\core\slang-castable-list.h" />
     <ClInclude Include="..\..\..\source\core\slang-char-encode.h" />
     <ClInclude Include="..\..\..\source\core\slang-char-util.h" />
     <ClInclude Include="..\..\..\source\core\slang-chunked-list.h" />
@@ -299,6 +301,7 @@
     <ClInclude Include="..\..\..\source\core\slang-hex-dump-util.h" />
     <ClInclude Include="..\..\..\source\core\slang-http.h" />
     <ClInclude Include="..\..\..\source\core\slang-io.h" />
+    <ClInclude Include="..\..\..\source\core\slang-lazy-castable-list.h" />
     <ClInclude Include="..\..\..\source\core\slang-linked-list.h" />
     <ClInclude Include="..\..\..\source\core\slang-list.h" />
     <ClInclude Include="..\..\..\source\core\slang-lz4-compression-system.h" />
@@ -342,6 +345,7 @@
     <ClCompile Include="..\..\..\source\core\slang-archive-file-system.cpp" />
     <ClCompile Include="..\..\..\source\core\slang-blob.cpp" />
     <ClCompile Include="..\..\..\source\core\slang-byte-encode-util.cpp" />
+    <ClCompile Include="..\..\..\source\core\slang-castable-list-impl.cpp" />
     <ClCompile Include="..\..\..\source\core\slang-char-encode.cpp" />
     <ClCompile Include="..\..\..\source\core\slang-char-util.cpp" />
     <ClCompile Include="..\..\..\source\core\slang-command-line.cpp" />
@@ -351,6 +355,7 @@
     <ClCompile Include="..\..\..\source\core\slang-hex-dump-util.cpp" />
     <ClCompile Include="..\..\..\source\core\slang-http.cpp" />
     <ClCompile Include="..\..\..\source\core\slang-io.cpp" />
+    <ClCompile Include="..\..\..\source\core\slang-lazy-castable-list.cpp" />
     <ClCompile Include="..\..\..\source\core\slang-lz4-compression-system.cpp" />
     <ClCompile Include="..\..\..\source\core\slang-memory-arena.cpp" />
     <ClCompile Include="..\..\..\source\core\slang-offset-container.cpp" />
diff --git a/build/visual-studio/core/core.vcxproj.filters b/build/visual-studio/core/core.vcxproj.filters
index 91a852b8e..3d394caa8 100644
--- a/build/visual-studio/core/core.vcxproj.filters
+++ b/build/visual-studio/core/core.vcxproj.filters
@@ -30,6 +30,12 @@
     <ClInclude Include="..\..\..\source\core\slang-byte-encode-util.h">
       <Filter>Header Files</Filter>
     </ClInclude>
+    <ClInclude Include="..\..\..\source\core\slang-castable-list-impl.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
+    <ClInclude Include="..\..\..\source\core\slang-castable-list.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
     <ClInclude Include="..\..\..\source\core\slang-char-encode.h">
       <Filter>Header Files</Filter>
     </ClInclude>
@@ -84,6 +90,9 @@
     <ClInclude Include="..\..\..\source\core\slang-io.h">
       <Filter>Header Files</Filter>
     </ClInclude>
+    <ClInclude Include="..\..\..\source\core\slang-lazy-castable-list.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
     <ClInclude Include="..\..\..\source\core\slang-linked-list.h">
       <Filter>Header Files</Filter>
     </ClInclude>
@@ -209,6 +218,9 @@
     <ClCompile Include="..\..\..\source\core\slang-byte-encode-util.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="..\..\..\source\core\slang-castable-list-impl.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
     <ClCompile Include="..\..\..\source\core\slang-char-encode.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
@@ -236,6 +248,9 @@
     <ClCompile Include="..\..\..\source\core\slang-io.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="..\..\..\source\core\slang-lazy-castable-list.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
     <ClCompile Include="..\..\..\source\core\slang-lz4-compression-system.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
diff --git a/build/visual-studio/slang-rt/slang-rt.vcxproj b/build/visual-studio/slang-rt/slang-rt.vcxproj
index 723f5360e..1c1190be2 100644
--- a/build/visual-studio/slang-rt/slang-rt.vcxproj
+++ b/build/visual-studio/slang-rt/slang-rt.vcxproj
@@ -281,6 +281,8 @@
     <ClInclude Include="..\..\..\source\core\slang-basic.h" />
     <ClInclude Include="..\..\..\source\core\slang-blob.h" />
     <ClInclude Include="..\..\..\source\core\slang-byte-encode-util.h" />
+    <ClInclude Include="..\..\..\source\core\slang-castable-list-impl.h" />
+    <ClInclude Include="..\..\..\source\core\slang-castable-list.h" />
     <ClInclude Include="..\..\..\source\core\slang-char-encode.h" />
     <ClInclude Include="..\..\..\source\core\slang-char-util.h" />
     <ClInclude Include="..\..\..\source\core\slang-chunked-list.h" />
@@ -299,6 +301,7 @@
     <ClInclude Include="..\..\..\source\core\slang-hex-dump-util.h" />
     <ClInclude Include="..\..\..\source\core\slang-http.h" />
     <ClInclude Include="..\..\..\source\core\slang-io.h" />
+    <ClInclude Include="..\..\..\source\core\slang-lazy-castable-list.h" />
     <ClInclude Include="..\..\..\source\core\slang-linked-list.h" />
     <ClInclude Include="..\..\..\source\core\slang-list.h" />
     <ClInclude Include="..\..\..\source\core\slang-lz4-compression-system.h" />
@@ -343,6 +346,7 @@
     <ClCompile Include="..\..\..\source\core\slang-archive-file-system.cpp" />
     <ClCompile Include="..\..\..\source\core\slang-blob.cpp" />
     <ClCompile Include="..\..\..\source\core\slang-byte-encode-util.cpp" />
+    <ClCompile Include="..\..\..\source\core\slang-castable-list-impl.cpp" />
     <ClCompile Include="..\..\..\source\core\slang-char-encode.cpp" />
     <ClCompile Include="..\..\..\source\core\slang-char-util.cpp" />
     <ClCompile Include="..\..\..\source\core\slang-command-line.cpp" />
@@ -352,6 +356,7 @@
     <ClCompile Include="..\..\..\source\core\slang-hex-dump-util.cpp" />
     <ClCompile Include="..\..\..\source\core\slang-http.cpp" />
     <ClCompile Include="..\..\..\source\core\slang-io.cpp" />
+    <ClCompile Include="..\..\..\source\core\slang-lazy-castable-list.cpp" />
     <ClCompile Include="..\..\..\source\core\slang-lz4-compression-system.cpp" />
     <ClCompile Include="..\..\..\source\core\slang-memory-arena.cpp" />
     <ClCompile Include="..\..\..\source\core\slang-offset-container.cpp" />
diff --git a/build/visual-studio/slang-rt/slang-rt.vcxproj.filters b/build/visual-studio/slang-rt/slang-rt.vcxproj.filters
index 68fc24316..65952c3e7 100644
--- a/build/visual-studio/slang-rt/slang-rt.vcxproj.filters
+++ b/build/visual-studio/slang-rt/slang-rt.vcxproj.filters
@@ -30,6 +30,12 @@
     <ClInclude Include="..\..\..\source\core\slang-byte-encode-util.h">
       <Filter>Header Files</Filter>
     </ClInclude>
+    <ClInclude Include="..\..\..\source\core\slang-castable-list-impl.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
+    <ClInclude Include="..\..\..\source\core\slang-castable-list.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
     <ClInclude Include="..\..\..\source\core\slang-char-encode.h">
       <Filter>Header Files</Filter>
     </ClInclude>
@@ -84,6 +90,9 @@
     <ClInclude Include="..\..\..\source\core\slang-io.h">
       <Filter>Header Files</Filter>
     </ClInclude>
+    <ClInclude Include="..\..\..\source\core\slang-lazy-castable-list.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
     <ClInclude Include="..\..\..\source\core\slang-linked-list.h">
       <Filter>Header Files</Filter>
     </ClInclude>
@@ -212,6 +221,9 @@
     <ClCompile Include="..\..\..\source\core\slang-byte-encode-util.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="..\..\..\source\core\slang-castable-list-impl.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
     <ClCompile Include="..\..\..\source\core\slang-char-encode.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
@@ -239,6 +251,9 @@
     <ClCompile Include="..\..\..\source\core\slang-io.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="..\..\..\source\core\slang-lazy-castable-list.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
     <ClCompile Include="..\..\..\source\core\slang-lz4-compression-system.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
diff --git a/source/compiler-core/slang-artifact-desc-util.cpp b/source/compiler-core/slang-artifact-desc-util.cpp
index 413858c32..69a9b66f1 100644
--- a/source/compiler-core/slang-artifact-desc-util.cpp
+++ b/source/compiler-core/slang-artifact-desc-util.cpp
@@ -651,9 +651,9 @@ UnownedStringSlice ArtifactDescUtil::getDefaultExtension(const ArtifactDesc& des
     Index pos = Path::findLastSeparatorIndex(basePath);
     if (pos >= 0)
     {
-        outPath.append(basePath.head(pos));
-        outPath.append(Path::kPathDelimiter);
-
+        // Keep the stem including the delimiter
+        outPath.append(basePath.head(pos + 1));
+        // Get the baseName
         baseName = basePath.tail(pos + 1);
     }
 
diff --git a/source/compiler-core/slang-artifact-impl.cpp b/source/compiler-core/slang-artifact-impl.cpp
index d57edd2c8..73927db96 100644
--- a/source/compiler-core/slang-artifact-impl.cpp
+++ b/source/compiler-core/slang-artifact-impl.cpp
@@ -5,368 +5,9 @@
 
 #include "slang-artifact-util.h"
 
-namespace Slang {
-
-/*
-If we use LazyCastableList for Items, it means we'll have to use the
-UnknownCastableAdapter for ISharedLibrary, IBlob etc. 
-
-That means when we look for an item in the list, we will always do a query interface on those types, 
-although it will always fail (so no atomic ref count). 
-
-That doesn't seem wholey unreasonable. 
-
-Note that we *can* derive from ICastable for *our* implementations of ISlangBlob, ISharedLibrary. So the 
-kludge is only needed for types that really do require adaption. For Blob we'll require multiple interface inheritance.
-*/
-
-/* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! LazyCastableList !!!!!!!!!!!!!!!!!!!!!!!!!!! */
-
-void LazyCastableList::removeAt(Index index)
-{
-    SLANG_ASSERT(index >= 0 && index < getCount());
-
-    if (auto list = as<ICastableList>(m_castable))
-    {
-        list->removeAt(index);
-    }
-    else
-    {
-        SLANG_ASSERT(index == 0);
-        m_castable.setNull();
-    }
-}
-
-void LazyCastableList::clear()
-{
-    if (m_castable)
-    {
-        if (auto list = as<ICastableList>(m_castable))
-        {
-            list->clear();
-        }
-        else
-        {
-            m_castable.setNull();
-        }
-    }
-}
-
-void LazyCastableList::clearAndDeallocate()
-{
-    m_castable.setNull();
-}
+#include "../core/slang-castable-list-impl.h"
 
-Count LazyCastableList::getCount() const
-{
-    if (m_castable)
-    {
-        if (auto list = as<ICastableList>(m_castable))
-        {
-            return list->getCount();
-        }
-        return 1;
-    }
-    return 0;
-}
-
-void LazyCastableList::add(ICastable* castable)
-{
-    SLANG_ASSERT(castable);
-    SLANG_ASSERT(castable != m_castable);
-
-    if (m_castable)
-    {
-        if (auto list = as<ICastableList>(m_castable))
-        {
-            // Shouldn't be in the list
-            SLANG_ASSERT(list->indexOf(castable) < 0);
-            list->add(castable);
-        }
-        else
-        {
-            list = new CastableList;
-            list->add(m_castable);
-            m_castable = list;
-            list->add(castable);
-        }
-    }
-    else
-    {
-        m_castable = castable;
-    }
-}
-
-ICastableList* LazyCastableList::requireList()
-{
-    if (m_castable)
-    {
-        if (auto list = as<ICastableList>(m_castable))
-        {
-            return list;
-        }
-        else
-        {
-            // Promote to a list with the element in it
-            list = new CastableList;
-            list->add(m_castable);
-            m_castable = list;
-            return list;
-        }
-    }
-    else
-    {
-        // Create an empty list
-        ICastableList* list = new CastableList;
-        m_castable = list;
-        return list;
-    }
-}
-
-ICastableList* LazyCastableList::getList()
-{
-    return (m_castable == nullptr) ? nullptr : requireList();
-}
-
-void* LazyCastableList::find(const Guid& guid)
-{
-    if (!m_castable)
-    {
-        return nullptr;
-    }
-    if (auto list = as<ICastableList>(m_castable))
-    {
-        return list->find(guid);
-    }
-    else
-    {
-        return m_castable->castAs(guid);
-    }
-}
-
-ConstArrayView<ICastable*> LazyCastableList::getView() const
-{
-    if (!m_castable)
-    {
-        // Empty
-        return ConstArrayView<ICastable*>();
-    }
-
-    if (auto list = as<ICastableList>(m_castable))
-    {
-        const auto count = list->getCount();
-        const auto buffer = list->getBuffer();
-
-        return ConstArrayView<ICastable*>(buffer, count);
-    }
-    else
-    {
-        return ConstArrayView<ICastable*>((ICastable*const*)&m_castable, 1);
-    }
-}
-
-Index LazyCastableList::indexOf(ICastable* castable) const
-{
-    return getView().indexOf(castable);
-}
-
-Index LazyCastableList::indexOfUnknown(ISlangUnknown* unk) const
-{
-    {
-        ComPtr<ICastable> castable;
-        if (SLANG_SUCCEEDED(unk->queryInterface(ICastable::getTypeGuid(), (void**)castable.writeRef())) && castable)
-        {
-            return indexOf(castable);
-        }
-    }
-
-    // It's not derived from ICastable, so can only be in list via an adapter
-    const auto view = getView();
-
-    const Count count = view.getCount();
-    for (Index i = 0; i < count; ++i)
-    {
-        auto adapter = as<IUnknownCastableAdapter>(view[i]);
-        if (adapter && adapter->getContained() == unk)
-        {
-            return i;
-        }
-    }
-
-    return -1;
-}
-
-/* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! UnknownCastableAdapter !!!!!!!!!!!!!!!!!!!!!!!!!!! */
-
-void* UnknownCastableAdapter::castAs(const Guid& guid)
-{
-    if (auto intf = getInterface(guid))
-    {
-        return intf;
-    }
-    if (auto obj = getObject(guid))
-    {
-        return obj;
-    }
-
-    if (m_found && guid == m_foundGuid)
-    {
-        return m_found;
-    }
-
-    ComPtr<ISlangUnknown> cast;
-    if (SLANG_SUCCEEDED(m_contained->queryInterface(guid, (void**)cast.writeRef())) && cast)
-    {
-        // Save the interface in the cache
-        m_found = cast;
-        m_foundGuid = guid;
-
-        return cast;
-    }
-    return nullptr;
-}
-
-void* UnknownCastableAdapter::getInterface(const Guid& guid)
-{
-    if (guid == ISlangUnknown::getTypeGuid() ||
-        guid == ICastable::getTypeGuid())
-    {
-        return static_cast<ICastable*>(this);
-    }
-    return nullptr;
-}
-
-void* UnknownCastableAdapter::getObject(const Guid& guid)
-{
-    SLANG_UNUSED(guid);
-    return nullptr;
-}
-
-/* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! CastableList !!!!!!!!!!!!!!!!!!!!!!!!!!! */
-
-CastableList::~CastableList()
-{
-    for (auto castable : m_list)
-    {
-        castable->release();
-    }
-}
-
-void* CastableList::castAs(const Guid& guid)
-{
-    if (auto intf = getInterface(guid))
-    {
-        return intf;
-    }
-    return getObject(guid);
-}
-
-void* CastableList::getInterface(const Guid& guid)
-{
-    if (guid == ISlangUnknown::getTypeGuid() ||
-        guid == ICastable::getTypeGuid() ||
-        guid == ICastableList::getTypeGuid())
-    {
-        return static_cast<ICastableList*>(this);
-    }
-    return nullptr;
-}
-
-void* CastableList::getObject(const Guid& guid)
-{
-    SLANG_UNUSED(guid);
-    return nullptr;
-}
-
-void* CastableList::find(const Guid& guid)
-{
-    for (ICastable* castable : m_list)
-    {
-        if (auto ptr = castable->castAs(guid))
-        {
-            return ptr;
-        }
-    }
-    return nullptr;
-}
-
-Index CastableList::indexOf(ICastable* castable)
-{
-    const Count count = m_list.getCount();
-    for (Index i = 0; i < count; ++i)
-    {
-        ICastable* cur = m_list[i];
-        if (cur == castable)
-        {
-            return i;
-        }
-    }
-    return -1;
-}
-
-void CastableList::add(ICastable* castable) 
-{ 
-    SLANG_ASSERT(castable);
-    castable->addRef();
-    m_list.add(castable);
-}
-
-void CastableList::removeAt(Index i) 
-{ 
-    auto castable = m_list[i];
-    m_list.removeAt(i);
-    castable->release();
-}
-
-void CastableList::clear() 
-{ 
-    for (auto castable : m_list)
-    {
-        castable->release();
-    }
-    m_list.clear(); 
-}
-
-void CastableList::addUnknown(ISlangUnknown* unk)
-{
-    // If it has ICastable interface we can just add as that
-    {
-        ComPtr<ICastable> castable;
-        if (SLANG_SUCCEEDED(unk->queryInterface(ICastable::getTypeGuid(), (void**)castable.writeRef())) && castable)
-        {
-            return add(castable);
-        }
-    }
-
-    // Wrap it in an adapter
-    IUnknownCastableAdapter* adapter = new UnknownCastableAdapter(unk);
-    add(adapter);
-}
-
-Index CastableList::indexOfUnknown(ISlangUnknown* unk)
-{
-    SLANG_ASSERT(unk);
-    // If it has a castable interface we can just look for that
-    {
-        ComPtr<ICastable> castable;
-        if (SLANG_SUCCEEDED(unk->queryInterface(ICastable::getTypeGuid(), (void**)castable.writeRef())) && castable)
-        {
-            return indexOf(castable);
-        }
-    }
-
-    // It's not derived from ICastable, so can only be in list via an adapter
-    const Count count = m_list.getCount();
-    for (Index i = 0; i < count; ++i)
-    {
-        auto adapter = as<IUnknownCastableAdapter>(m_list[i]);
-        if (adapter && adapter->getContained() == unk)
-        {
-            return i;
-        }
-    }
-    return -1;
-}
+namespace Slang {
 
 /* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ArtifactList !!!!!!!!!!!!!!!!!!!!!!!!!!! */
 
@@ -535,15 +176,15 @@ ICastableList* Artifact::getAssociated()
     return m_associated.requireList();
 }
 
-void Artifact::addRepresentation(IArtifactRepresentation* rep)
+void Artifact::addRepresentation(ICastable* castable)
 {
-    SLANG_ASSERT(rep);
-    if (m_representations.indexOf(rep) >= 0)
+    SLANG_ASSERT(castable);
+    if (m_representations.indexOf(castable) >= 0)
     {
         SLANG_ASSERT_FAILURE("Already have this representation");
         return;
     }
-    m_representations.add(rep);
+    m_representations.add(castable);
 }
 
 void Artifact::addRepresentationUnknown(ISlangUnknown* unk)
@@ -582,4 +223,19 @@ ICastableList* Artifact::getRepresentations()
     return m_representations.requireList();
 }
 
+IArtifactList* Artifact::getChildren()
+{
+    // If it has already evaluated, return it.
+    if (m_children)
+    {
+        return m_children;
+    }
+
+    auto util = ArtifactUtilImpl::getSingleton();
+    util->getChildrenDefaultImpl(this, m_children.writeRef());
+
+    return m_children;
+}
+
+
 } // namespace Slang
diff --git a/source/compiler-core/slang-artifact-impl.h b/source/compiler-core/slang-artifact-impl.h
index 79aad3b64..e4db46222 100644
--- a/source/compiler-core/slang-artifact-impl.h
+++ b/source/compiler-core/slang-artifact-impl.h
@@ -4,6 +4,8 @@
 
 #include "slang-artifact.h"
 
+#include "../core/slang-lazy-castable-list.h"
+
 #include "../../slang-com-helper.h"
 #include "../../slang-com-ptr.h"
 
@@ -12,89 +14,6 @@
 namespace Slang
 {
 
-/* An adapter such that types which aren't derived from ICastable, can be used as such. 
-
-With the following caveats.
-* the interfaces/objects of the adapter are checked *first*, so IUnknown will always be for the adapter
-* assumes when doing a queryInterface on the contained item 
-*/
-class UnknownCastableAdapter : public ComBaseObject, public IUnknownCastableAdapter
-{
-public:
-    SLANG_COM_BASE_IUNKNOWN_ALL
-
-    // ICastable
-    SLANG_NO_THROW void* SLANG_MCALL castAs(const Guid& guid) SLANG_OVERRIDE;
-
-    // IUnknownCastableAdapter
-    virtual SLANG_NO_THROW ISlangUnknown* SLANG_MCALL getContained() SLANG_OVERRIDE { return m_contained; }
-
-    UnknownCastableAdapter(ISlangUnknown* unk):
-        m_contained(unk)
-    {
-        SLANG_ASSERT(unk);
-    }
-
-protected:
-    void* getInterface(const Guid& guid);
-    void* getObject(const Guid& guid);
-
-    ComPtr<ISlangUnknown> m_contained;
-
-    // We hold a cache for a single lookup to make things a little faster
-    void* m_found = nullptr;
-    Guid m_foundGuid;
-};
-
-class CastableList : public ComBaseObject, public ICastableList
-{
-public:
-    SLANG_COM_BASE_IUNKNOWN_ALL
-
-    // ICastable
-    SLANG_NO_THROW void* SLANG_MCALL castAs(const Guid& guid) SLANG_OVERRIDE;
-
-    // ICastableList
-    virtual Count SLANG_MCALL getCount() SLANG_OVERRIDE { return m_list.getCount(); }
-    virtual ICastable* SLANG_MCALL getAt(Index i) SLANG_OVERRIDE { return m_list[i]; }
-    virtual void SLANG_MCALL add(ICastable* castable) SLANG_OVERRIDE;
-    virtual void SLANG_MCALL addUnknown(ISlangUnknown* unk) SLANG_OVERRIDE;
-    virtual void SLANG_MCALL removeAt(Index i) SLANG_OVERRIDE;
-    virtual void SLANG_MCALL clear() SLANG_OVERRIDE;
-    virtual Index SLANG_MCALL indexOf(ICastable* castable) SLANG_OVERRIDE;
-    virtual Index SLANG_MCALL indexOfUnknown(ISlangUnknown* unk) SLANG_OVERRIDE;
-    virtual void* SLANG_MCALL find(const Guid& guid) SLANG_OVERRIDE;
-    virtual ICastable* const* SLANG_MCALL getBuffer() SLANG_OVERRIDE { return m_list.getBuffer(); }
-
-    virtual ~CastableList();
-
-protected:
-    void* getInterface(const Guid& guid);
-    void* getObject(const Guid& guid);
-
-    List<ICastable*> m_list;
-};
-
-class LazyCastableList
-{
-public:
-    void add(ICastable* castable);
-    Count getCount() const;
-    void removeAt(Index index);
-    void clear();
-    void clearAndDeallocate();
-    void* find(const Guid& guid);
-    ConstArrayView<ICastable*> getView() const;
-    Index indexOf(ICastable* castable) const;
-    Index indexOfUnknown(ISlangUnknown* unk) const;
-
-    ICastableList* requireList();
-    ICastableList* getList();
-
-protected:
-    ComPtr<ICastable> m_castable;
-};
-
 class ArtifactList : public ComBaseObject, public IArtifactList
 {
 public:
@@ -134,15 +53,6 @@ protected:
 /*
 Discussion:
 
-It could make sense to remove the explicit variables of a ISlangBlob, and the file backing from this interface, as they could 
-all be implemented as element types presumably deriving from IArtifactInstance. Doing so would mean how a 'file' is turned into
-a blob is abstracted. 
-
-It may be helpful to be able to add temporary files to the artifact (such that they will be deleted when the artifact goes out of 
-scope). Using an implementation of the File backed IArtifactInstance, with a suitable desc would sort of work, but it breaks the idea 
-that any IArtifactInstance *represents* the contents of Artifact that contains it. Of course there could be types *not* deriving 
-from IArtifactInstance that handle temporary file existance. This is probably the simplest answer to the problem.
-
 Another issue occurs around wanting to hold multiple kernels within a container. The problem here is that although through the desc
 we can identify what target a kernel is for, there is no way of telling what stage it is for.
 
@@ -174,11 +84,13 @@ public:
     virtual void* SLANG_MCALL SLANG_MCALL findAssociated(const Guid& unk) SLANG_OVERRIDE;
     virtual ICastableList* SLANG_MCALL getAssociated() SLANG_OVERRIDE;
 
-    virtual SLANG_NO_THROW void SLANG_MCALL addRepresentation(IArtifactRepresentation* rep) SLANG_OVERRIDE;
+    virtual SLANG_NO_THROW void SLANG_MCALL addRepresentation(ICastable* castable) SLANG_OVERRIDE;
     virtual SLANG_NO_THROW void SLANG_MCALL addRepresentationUnknown(ISlangUnknown* rep) SLANG_OVERRIDE;
     virtual void* SLANG_MCALL SLANG_MCALL findRepresentation(const Guid& guid) SLANG_OVERRIDE;
     virtual ICastableList* SLANG_MCALL getRepresentations() SLANG_OVERRIDE;
 
+    virtual IArtifactList* SLANG_MCALL getChildren() SLANG_OVERRIDE;
+
     /// Ctor
     Artifact(const Desc& desc, const String& name) :
         m_desc(desc),
diff --git a/source/compiler-core/slang-artifact-representation-impl.cpp b/source/compiler-core/slang-artifact-representation-impl.cpp
index 20480ae07..d1de75c79 100644
--- a/source/compiler-core/slang-artifact-representation-impl.cpp
+++ b/source/compiler-core/slang-artifact-representation-impl.cpp
@@ -77,71 +77,21 @@ bool FileArtifactRepresentation::exists()
     return SLANG_SUCCEEDED(res) && pathType == SLANG_PATH_TYPE_FILE;
 }
 
-FileArtifactRepresentation::~FileArtifactRepresentation()
-{
-    if (m_kind == Kind::Owned)
-    {
-        auto fileSystem = _getFileSystem();
-        fileSystem->remove(m_path.getBuffer());
-    }
-}
-
-/* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!! LockFile !!!!!!!!!!!!!!!!!!!!!!!!!!! */
-
-void* LockFile::getInterface(const Guid& guid)
+void FileArtifactRepresentation::disown()
 {
-    if (guid == ISlangUnknown::getTypeGuid() ||
-        guid == ICastable::getTypeGuid() ||
-        guid == ILockFile::getTypeGuid())
+    if (_isOwned())
     {
-        return static_cast<ILockFile*>(this);
+        m_kind = Kind::Reference;
     }
-    return nullptr;
-}
-
-void* LockFile::getObject(const Guid& guid)
-{
-    SLANG_UNUSED(guid);
-    return nullptr;
 }
 
-ISlangMutableFileSystem* LockFile::_getFileSystem()
-{
-    return m_fileSystem ? m_fileSystem : OSFileSystem::getMutableSingleton();
-}
-
-void* LockFile::castAs(const Guid& guid)
-{
-    if (auto intf = getInterface(guid))
-    {
-        return intf;
-    }
-    return getObject(guid);
-}
-
-const char* LockFile::getPath()
-{
-    return (m_path.getLength() > 0) ? m_path.getBuffer() : nullptr;
-}
-
-ISlangMutableFileSystem* LockFile::getFileSystem()
-{
-    return m_fileSystem;
-}
-
-LockFile::~LockFile()
+FileArtifactRepresentation::~FileArtifactRepresentation()
 {
-    if (m_path.getLength() > 0)
+    if (_isOwned())
     {
         auto fileSystem = _getFileSystem();
         fileSystem->remove(m_path.getBuffer());
     }
 }
 
-void LockFile::disown()
-{
-    m_path = String();
-    m_fileSystem.setNull();
-}
-
 } // namespace Slang
diff --git a/source/compiler-core/slang-artifact-representation-impl.h b/source/compiler-core/slang-artifact-representation-impl.h
index 9c2066e55..a40adf0e9 100644
--- a/source/compiler-core/slang-artifact-representation-impl.h
+++ b/source/compiler-core/slang-artifact-representation-impl.h
@@ -12,41 +12,7 @@
 namespace Slang
 {
 
-/* An implementation of ILockFile */
-class LockFile : public ComBaseObject, public ILockFile
-{
-public:
-    SLANG_COM_BASE_IUNKNOWN_ALL
-
-        // ICastable
-        SLANG_NO_THROW void* SLANG_MCALL castAs(const Guid& guid) SLANG_OVERRIDE;
-
-    // ILockFile
-    SLANG_NO_THROW const char* SLANG_MCALL getPath() SLANG_OVERRIDE;
-    SLANG_NO_THROW ISlangMutableFileSystem* SLANG_MCALL getFileSystem() SLANG_OVERRIDE;
-    SLANG_NO_THROW void SLANG_MCALL disown() SLANG_OVERRIDE;
-
-    /// Ctor
-    LockFile(String path, ISlangMutableFileSystem* fileSystem) :
-        m_path(path),
-        m_fileSystem(fileSystem)
-    {
-    }
-
-    ~LockFile();
-
-protected:
-    void* getInterface(const Guid& uuid);
-    void* getObject(const Guid& uuid);
-
-    ISlangMutableFileSystem* _getFileSystem();
-
-    String m_path;
-    ComPtr<ISlangMutableFileSystem> m_fileSystem;
-};
-
-/*
-A representation of an artifact that is held in a file */
+/* A representation of an artifact that is held in a file */
 class FileArtifactRepresentation : public ComBaseObject, public IFileArtifactRepresentation
 {
 public:
@@ -64,10 +30,11 @@ public:
     // IFileArtifactRepresentation
     virtual SLANG_NO_THROW Kind SLANG_MCALL getKind() SLANG_OVERRIDE { return m_kind; }
     virtual SLANG_NO_THROW const char* SLANG_MCALL getPath() SLANG_OVERRIDE { return m_path.getBuffer(); }
-    virtual SLANG_NO_THROW ILockFile* SLANG_MCALL getLockFile() SLANG_OVERRIDE { return m_lockFile; }
     virtual SLANG_NO_THROW ISlangMutableFileSystem* SLANG_MCALL getFileSystem() SLANG_OVERRIDE { return m_fileSystem; }
+    virtual SLANG_NO_THROW void SLANG_MCALL disown() SLANG_OVERRIDE;
+    virtual SLANG_NO_THROW IFileArtifactRepresentation* SLANG_MCALL getLockFile() SLANG_OVERRIDE { return m_lockFile; }
 
-    FileArtifactRepresentation(Kind kind, String path, ILockFile* lockFile, ISlangMutableFileSystem* fileSystem):
+    FileArtifactRepresentation(Kind kind, String path, IFileArtifactRepresentation* lockFile, ISlangMutableFileSystem* fileSystem):
         m_kind(kind),
         m_path(path),
         m_lockFile(lockFile),
@@ -81,11 +48,14 @@ protected:
     void* getInterface(const Guid& uuid);
     void* getObject(const Guid& uuid);
 
+        /// True if the file is owned
+    bool _isOwned() const { return Index(m_kind) >= Index(Kind::Owned); }
+
     ISlangMutableFileSystem* _getFileSystem();
 
     Kind m_kind;
     String m_path;
-    ComPtr<ILockFile> m_lockFile;
+    ComPtr<IFileArtifactRepresentation> m_lockFile;
     ComPtr<ISlangMutableFileSystem> m_fileSystem;
 };
 
diff --git a/source/compiler-core/slang-artifact-representation.h b/source/compiler-core/slang-artifact-representation.h
index 00a5c9e5b..230283ce4 100644
--- a/source/compiler-core/slang-artifact-representation.h
+++ b/source/compiler-core/slang-artifact-representation.h
@@ -7,20 +7,6 @@
 namespace Slang
 {
 
-/* A lock file */
-class ILockFile : public ICastable
-{
-    SLANG_COM_INTERFACE(0x9177ea36, 0xa608, 0x4490, { 0x87, 0xf0, 0xf3, 0x93, 0x9, 0x7d, 0x36, 0xce })
-
-        /// The path to a lock file. 
-    virtual SLANG_NO_THROW const char* SLANG_MCALL getPath() = 0;
-        /// Optional, the file system it's on. If nullptr its on 'regular' OS file system.
-    virtual SLANG_NO_THROW ISlangMutableFileSystem* SLANG_MCALL getFileSystem() = 0;
-
-        /// Makes the lock file no longer owned. Doing so will make the path nullptr, and getFileSystem nullptr. 
-    virtual SLANG_NO_THROW void SLANG_MCALL disown() = 0;
-};
-
 /* 
 A representation as a file. If it is a temporary file, it will likely disappear.
 A file representation does not have to be a representation of a file on the file system.
@@ -30,21 +16,26 @@ to be usable. */
 class IFileArtifactRepresentation : public IArtifactRepresentation
 {
 public:
+        // NOTE! 
     enum class Kind
     {
         Reference,          ///< References a file on the file system
-        Owned,              ///< File is *owned* by this instance and will be deleted when goes out of scope
         NameOnly,           ///< Typically used for items that can be found by the 'system'. The path is just a name, and cannot typically be loaded as a blob.
+        Owned,              ///< File is *owned* by this instance and will be deleted when goes out of scope
+        Lock,               ///< An owned type, indicates potentially in part may only exist to 'lock' a path for a temporary file
+        CountOf,
     };
-
+    
         /// The the kind of file. 
     virtual SLANG_NO_THROW Kind SLANG_MCALL getKind() = 0;                     
         /// The path (on the file system)
     virtual SLANG_NO_THROW const char* SLANG_MCALL getPath() = 0;              
-        /// Get the lock file. Return nullptr if there is no lock file.
-    virtual SLANG_NO_THROW ILockFile* SLANG_MCALL getLockFile() = 0;
         /// Optional, the file system it's on. If nullptr its on 'regular' OS file system.
     virtual SLANG_NO_THROW ISlangMutableFileSystem* SLANG_MCALL getFileSystem() = 0;       
+        /// Makes the file no longer owned. Only applicable for Owned/Lock and they will become 'Reference'
+    virtual SLANG_NO_THROW void SLANG_MCALL disown() = 0;
+        /// Gets the 'lock file' if any associated with this file. Returns nullptr if there isn't one.
+    virtual SLANG_NO_THROW IFileArtifactRepresentation* SLANG_MCALL getLockFile() = 0;
 };
 
 } // namespace Slang
diff --git a/source/compiler-core/slang-artifact-util.cpp b/source/compiler-core/slang-artifact-util.cpp
index 7f69a0464..909c9b3d2 100644
--- a/source/compiler-core/slang-artifact-util.cpp
+++ b/source/compiler-core/slang-artifact-util.cpp
@@ -67,7 +67,7 @@ ArtifactStyle ArtifactUtilImpl::getStyleParent(ArtifactStyle style) { return get
 UnownedStringSlice ArtifactUtilImpl::getStyleName(ArtifactStyle style) { return getName(style); }
 bool ArtifactUtilImpl::isStyleDerivedFrom(ArtifactStyle style, ArtifactStyle base) { return isDerivedFrom(style, base); }
 
-SlangResult ArtifactUtilImpl::createLockFile(const char* inNameBase, ISlangMutableFileSystem* fileSystem, ILockFile** outLockFile)
+SlangResult ArtifactUtilImpl::createLockFile(const char* inNameBase, ISlangMutableFileSystem* fileSystem, IFileArtifactRepresentation** outLockFile)
 {
 	if (fileSystem)
 	{
@@ -84,7 +84,7 @@ SlangResult ArtifactUtilImpl::createLockFile(const char* inNameBase, ISlangMutab
 	String lockPath;
 	SLANG_RETURN_ON_FAIL(File::generateTemporary(nameBase, lockPath));
 
-	ComPtr<ILockFile> lockFile(new LockFile(lockPath, fileSystem));
+	ComPtr<IFileArtifactRepresentation> lockFile(new FileArtifactRepresentation(IFileArtifactRepresentation::Kind::Lock, lockPath, nullptr, fileSystem));
 
 	*outLockFile = lockFile.detach();
 	return SLANG_OK;
@@ -114,7 +114,7 @@ SlangResult ArtifactUtilImpl::requireFileDefaultImpl(IArtifact* artifact, Artifa
 	SLANG_RETURN_ON_FAIL(artifact->loadBlob(keep, blob.writeRef()));
 
 	// Okay we need to store as a temporary. Get a lock file.
-	ComPtr<ILockFile> lockFile;
+	ComPtr<IFileArtifactRepresentation> lockFile;
 	SLANG_RETURN_ON_FAIL(createLockFile(artifact->getName(), nullptr, lockFile.writeRef()));
 
 	// Now we need the appropriate name for this item
@@ -126,25 +126,32 @@ SlangResult ArtifactUtilImpl::requireFileDefaultImpl(IArtifact* artifact, Artifa
 	// Write the contents
 	SLANG_RETURN_ON_FAIL(File::writeAllBytes(path, blob->getBufferPointer(), blob->getBufferSize()));
 
-	// If the paths are identical we don't need a lock file
+	ComPtr<IFileArtifactRepresentation> fileRep;
+
+	// TODO(JS): This path comparison is perhaps not perfect, in that it assumes the path is not changed
+	// in any way. For example an impl of calcArtifactPath that changed slashes or used a canonical path
+	// might mean the lock file and the rep have the same path. 
+	// As it stands calcArtifactPath impl doesn't do that, but that is perhaps somewhatfragile
+
+	// If the paths are identical, we can just use the lock file for the rep
 	if (UnownedStringSlice(lockFile->getPath()) == path.getUnownedSlice())
 	{
-		// Make the lockFile no longer own the file 
-		lockFile->disown();
-		// We no longer need the lock file
-		lockFile.setNull();
+		fileRep.swap(lockFile);
+	}
+	else
+	{
+		// Create a new rep that references the lock file
+		fileRep = new FileArtifactRepresentation(IFileArtifactRepresentation::Kind::Owned, path, lockFile, nullptr);
 	}
-	
+
 	// Create the rep
-	IFileArtifactRepresentation* fileRep = new FileArtifactRepresentation(IFileArtifactRepresentation::Kind::Owned, path, lockFile, nullptr);
 	if (canKeep(keep))
 	{
 		artifact->addRepresentation(fileRep);
 	}
 
-	// Return it
-	fileRep->addRef();
-	*outFile = fileRep;
+	// Return the file
+	*outFile = fileRep.detach();
 	return SLANG_OK;
 }
 
@@ -153,4 +160,19 @@ ArtifactDesc ArtifactUtilImpl::makeDescFromCompileTarget(SlangCompileTarget targ
 	return ArtifactDescUtil::makeDescFromCompileTarget(target);
 }
 
+SlangResult ArtifactUtilImpl::getChildrenDefaultImpl(IArtifact* artifact, IArtifactList** outList)
+{
+	auto desc = artifact->getDesc();
+
+	// If it's a container type for now, just create empty list of children
+	if (isDerivedFrom(desc.kind, ArtifactKind::Container))
+	{
+		*outList = ComPtr<IArtifactList>(new ArtifactList(artifact)).detach();
+		return SLANG_OK;
+	}
+
+	return SLANG_E_NOT_AVAILABLE;
+}
+
+
 } // namespace Slang
diff --git a/source/compiler-core/slang-artifact-util.h b/source/compiler-core/slang-artifact-util.h
index f9070a76e..c391a5056 100644
--- a/source/compiler-core/slang-artifact-util.h
+++ b/source/compiler-core/slang-artifact-util.h
@@ -28,7 +28,7 @@ class IArtifactUtil : public ISlangUnknown
 	virtual SLANG_NO_THROW UnownedStringSlice SLANG_MCALL getStyleName(ArtifactStyle style) = 0;
 	virtual SLANG_NO_THROW bool SLANG_MCALL isStyleDerivedFrom(ArtifactStyle style, ArtifactStyle base) = 0;
 
-	virtual SLANG_NO_THROW SlangResult SLANG_MCALL createLockFile(const char* nameBase, ISlangMutableFileSystem* fileSystem, ILockFile** outLockFile) = 0;
+	virtual SLANG_NO_THROW SlangResult SLANG_MCALL createLockFile(const char* nameBase, ISlangMutableFileSystem* fileSystem, IFileArtifactRepresentation** outLockFile) = 0;
 
 		/// Given a desc and a basePath returns a suitable name
 	virtual SLANG_NO_THROW SlangResult SLANG_MCALL calcArtifactPath(const ArtifactDesc& desc, const char* basePath, ISlangBlob** outPath) = 0;
@@ -37,6 +37,8 @@ class IArtifactUtil : public ISlangUnknown
 	virtual SLANG_NO_THROW SlangResult SLANG_MCALL requireFileDefaultImpl(IArtifact* artifact, ArtifactKeep keep, IFileArtifactRepresentation** outFileRep) = 0;
 
 	virtual SLANG_NO_THROW ArtifactDesc SLANG_MCALL makeDescFromCompileTarget(SlangCompileTarget target) = 0;
+
+	virtual SLANG_NO_THROW SlangResult SLANG_MCALL getChildrenDefaultImpl(IArtifact* artifact, IArtifactList** outList) = 0;
 };
 
 class ArtifactUtilImpl : public IArtifactUtil
@@ -64,7 +66,7 @@ public:
 	virtual SLANG_NO_THROW UnownedStringSlice SLANG_MCALL getStyleName(ArtifactStyle style) SLANG_OVERRIDE;
 	virtual SLANG_NO_THROW bool SLANG_MCALL isStyleDerivedFrom(ArtifactStyle style, ArtifactStyle base) SLANG_OVERRIDE;
 
-	virtual SLANG_NO_THROW SlangResult SLANG_MCALL createLockFile(const char* nameBase, ISlangMutableFileSystem* fileSystem, ILockFile** outLockFile) SLANG_OVERRIDE;
+	virtual SLANG_NO_THROW SlangResult SLANG_MCALL createLockFile(const char* nameBase, ISlangMutableFileSystem* fileSystem, IFileArtifactRepresentation** outLockFile) SLANG_OVERRIDE;
 
 	virtual SLANG_NO_THROW SlangResult SLANG_MCALL calcArtifactPath(const ArtifactDesc& desc, const char* basePath, ISlangBlob** outPath) SLANG_OVERRIDE;
 
@@ -72,6 +74,8 @@ public:
 
 	virtual SLANG_NO_THROW ArtifactDesc SLANG_MCALL makeDescFromCompileTarget(SlangCompileTarget target) SLANG_OVERRIDE;
 
+	virtual SLANG_NO_THROW SlangResult SLANG_MCALL getChildrenDefaultImpl(IArtifact* artifact, IArtifactList** outList) SLANG_OVERRIDE;
+
 	static IArtifactUtil* getSingleton() { return &g_singleton; }
 
 protected:
diff --git a/source/compiler-core/slang-artifact.h b/source/compiler-core/slang-artifact.h
index 3c991b7b6..55b3ff89f 100644
--- a/source/compiler-core/slang-artifact.h
+++ b/source/compiler-core/slang-artifact.h
@@ -4,9 +4,10 @@
 
 #include "../core/slang-basic.h"
 
-#include "../../slang-com-helper.h"
+//#include "../../slang-com-helper.h"
+//#include "../core/slang-destroyable.h"
 
-#include "../core/slang-destroyable.h"
+#include "../core/slang-castable-list.h"
 
 namespace Slang
 {
@@ -202,6 +203,7 @@ inline /* static */ArtifactDesc ArtifactDesc::make(Packed inPacked)
 // Forward declare
 class IFileArtifactRepresentation;
 class IArtifactRepresentation;
+class IArtifactList;
 
 // Controls what items can be kept. 
 enum class ArtifactKeep
@@ -218,40 +220,6 @@ SLANG_INLINE bool canKeep(ArtifactKeep keep) { return Index(keep) >= Index(Artif
 /// Returns the keep type for an intermediate
 SLANG_INLINE ArtifactKeep getIntermediateKeep(ArtifactKeep keep) { return (keep == ArtifactKeep::All) ? ArtifactKeep::All : ArtifactKeep::No; }
 
-/* A useful interface for handling lists of castable interfaces. Cannot hold nullptr */
-class ICastableList : public ICastable
-{
-    SLANG_COM_INTERFACE(0x335f3d40, 0x934c, 0x40dc, { 0xb5, 0xe1, 0xf7, 0x6e, 0x40, 0x3, 0x62, 0x5 })
-            
-        /// Get the count of all interfaces held in the list
-    virtual Count SLANG_MCALL getCount() = 0;
-        /// Get the interface at the specified index
-    virtual ICastable* SLANG_MCALL getAt(Index i) = 0;
-        /// Add an item to the list
-    virtual void SLANG_MCALL add(ICastable* unk) = 0;
-        /// Add IUnknown, will cast to ICastable and if that's not possible will wrap
-    virtual void SLANG_MCALL addUnknown(ISlangUnknown* unk) = 0;
-        /// Remove item at index, remaining items stay in the same order
-    virtual void SLANG_MCALL removeAt(Index i) = 0;
-        /// Clear the list
-    virtual void SLANG_MCALL clear() = 0;
-        /// Find the first index of castable, or -1 if not found
-    virtual Index SLANG_MCALL indexOf(ICastable* castable) = 0;
-        /// Find the index interface (handling wrapping if necessary)
-    virtual Index SLANG_MCALL indexOfUnknown(ISlangUnknown* unk) = 0;
-        /// Find the first item that casts to non null
-    virtual void* SLANG_MCALL find(const Guid& guid) = 0;
-        /// Access the internal buffer (any mutation can invalidate this value)
-    virtual ICastable*const* SLANG_MCALL getBuffer() = 0;
-};
-
-// Simply finding things in a ICastableList
-template <typename T>
-SLANG_FORCE_INLINE T* find(ICastableList* list)
-{
-    return reinterpret_cast<T*>(list->find(T::getTypeGuid())); 
-}
-
 /* The IArtifact interface is designed to represent some Artifact of compilation. It could be input to or output from a compilation.
 
 An abstraction is desirable here, because depending on the compiler the artifact/s could be
@@ -277,12 +245,23 @@ files could be a Container containing artifacts for
 * Files that contain known types
 * Callable interface (an ISlangSharedLibrary)
 
-Each one of these additions is an 'Element'. An Element is an interface pointer and a Desc that describes what the 
-inteface represents. Having the associated desc provides more detail about what the interface pointer actually is
-without having to make the interface know what it is being used for. This allows an interface to be used in multiple 
-ways - for example the ISlangBlob interface could be used to represent some text, or a compiled kernel. 
+There are several types of ways to associate data with an artifact:
+
+* A representation
+* Associated data
+* A child artifact
+
+A `representation` has to wholly represent the artifact. That representation could be a blob, a file on the file system,
+an in memory representation. There are two classes of `Representation` - ones that can be turned into blobs (and therefore 
+derive from IArtifactRepresentation) and ones that are in of themselves a representation (such as a blob or or ISlangSharedLibrary).
+
+`Associated data` is information that is associated with the artifact, but isn't a (whole) representation. It could be part 
+of the representation, or useful for the implementation of a representation. Could also be considered as a kind of side channel
+to associate arbitrary temporary data with an artifact.
+
+A `child artifact` belongs to the artifact, within the hierarchy of artifacts. Child artifacts are held in an IArtifactList.
 
-A more long term goals would be to
+More long term goals would be to
 
 * Make Diagnostics into an interface (such it can be added to a Artifact result)
 * Use Artifact and related types for downstream compiler
@@ -329,16 +308,27 @@ public:
         /// Get the list of associated items
     virtual ICastableList* SLANG_MCALL getAssociated() = 0;
 
-        /// Add a representation that derives from IArtifactRepresentation
-    virtual SLANG_NO_THROW void SLANG_MCALL addRepresentation(IArtifactRepresentation* rep) = 0;
+        /// Add a representation 
+    virtual SLANG_NO_THROW void SLANG_MCALL addRepresentation(ICastable* castable) = 0;
         /// Add a representation that doesn't derive from IArtifactRepresentation
     virtual SLANG_NO_THROW void SLANG_MCALL addRepresentationUnknown(ISlangUnknown* rep) = 0;
         /// Find representation
     virtual void* SLANG_MCALL SLANG_MCALL findRepresentation(const Guid& guid) = 0;
         /// Get the list of all representations
     virtual ICastableList* SLANG_MCALL getRepresentations() = 0;
+
+        /// Get the children. This may be evaluated lazily. 
+        /// Only artifacts with a ArtifactKind that derives from Container generally produce childen.
+        /// If an artifact doesn't support children, it can return nullptr.
+    virtual IArtifactList* SLANG_MCALL getChildren() = 0;
 };
 
+template <typename T>
+SLANG_FORCE_INLINE T* findRepresentation(IArtifact* artifact)
+{
+    return reinterpret_cast<T*>(artifact->findRepresentation(T::getTypeGuid()));
+}
+
 /* A list of artifacts. */
 class IArtifactList : public ICastable
 {
@@ -380,11 +370,6 @@ class IArtifactRepresentation : public ICastable
     virtual SLANG_NO_THROW bool SLANG_MCALL exists() = 0;
 };
 
-template <typename T>
-SLANG_FORCE_INLINE T* findRepresentation(IArtifact* artifact)
-{
-    return reinterpret_cast<T*>(artifact->findRepresentation(T::getTypeGuid()));
-}
 
 } // namespace Slang
 
diff --git a/source/core/slang-castable-list-impl.cpp b/source/core/slang-castable-list-impl.cpp
new file mode 100644
index 000000000..ee10ea995
--- /dev/null
+++ b/source/core/slang-castable-list-impl.cpp
@@ -0,0 +1,178 @@
+// slang-castable-list-impl.cpp
+#include "slang-castable-list-impl.h"
+
+namespace Slang {
+
+    /* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! UnknownCastableAdapter !!!!!!!!!!!!!!!!!!!!!!!!!!! */
+
+void* UnknownCastableAdapter::castAs(const Guid& guid)
+{
+    if (auto intf = getInterface(guid))
+    {
+        return intf;
+    }
+    if (auto obj = getObject(guid))
+    {
+        return obj;
+    }
+
+    if (m_found && guid == m_foundGuid)
+    {
+        return m_found;
+    }
+
+    ComPtr<ISlangUnknown> cast;
+    if (SLANG_SUCCEEDED(m_contained->queryInterface(guid, (void**)cast.writeRef())) && cast)
+    {
+        // Save the interface in the cache
+        m_found = cast;
+        m_foundGuid = guid;
+
+        return cast;
+    }
+    return nullptr;
+}
+
+void* UnknownCastableAdapter::getInterface(const Guid& guid)
+{
+    if (guid == ISlangUnknown::getTypeGuid() ||
+        guid == ICastable::getTypeGuid())
+    {
+        return static_cast<ICastable*>(this);
+    }
+    return nullptr;
+}
+
+void* UnknownCastableAdapter::getObject(const Guid& guid)
+{
+    SLANG_UNUSED(guid);
+    return nullptr;
+}
+
+/* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! CastableList !!!!!!!!!!!!!!!!!!!!!!!!!!! */
+
+CastableList::~CastableList()
+{
+    for (auto castable : m_list)
+    {
+        castable->release();
+    }
+}
+
+void* CastableList::castAs(const Guid& guid)
+{
+    if (auto intf = getInterface(guid))
+    {
+        return intf;
+    }
+    return getObject(guid);
+}
+
+void* CastableList::getInterface(const Guid& guid)
+{
+    if (guid == ISlangUnknown::getTypeGuid() ||
+        guid == ICastable::getTypeGuid() ||
+        guid == ICastableList::getTypeGuid())
+    {
+        return static_cast<ICastableList*>(this);
+    }
+    return nullptr;
+}
+
+void* CastableList::getObject(const Guid& guid)
+{
+    SLANG_UNUSED(guid);
+    return nullptr;
+}
+
+void* CastableList::find(const Guid& guid)
+{
+    for (ICastable* castable : m_list)
+    {
+        if (auto ptr = castable->castAs(guid))
+        {
+            return ptr;
+        }
+    }
+    return nullptr;
+}
+
+Index CastableList::indexOf(ICastable* castable)
+{
+    const Count count = m_list.getCount();
+    for (Index i = 0; i < count; ++i)
+    {
+        ICastable* cur = m_list[i];
+        if (cur == castable)
+        {
+            return i;
+        }
+    }
+    return -1;
+}
+
+void CastableList::add(ICastable* castable) 
+{ 
+    SLANG_ASSERT(castable);
+    castable->addRef();
+    m_list.add(castable);
+}
+
+void CastableList::removeAt(Index i) 
+{ 
+    auto castable = m_list[i];
+    m_list.removeAt(i);
+    castable->release();
+}
+
+void CastableList::clear() 
+{ 
+    for (auto castable : m_list)
+    {
+        castable->release();
+    }
+    m_list.clear(); 
+}
+
+void CastableList::addUnknown(ISlangUnknown* unk)
+{
+    // If it has ICastable interface we can just add as that
+    {
+        ComPtr<ICastable> castable;
+        if (SLANG_SUCCEEDED(unk->queryInterface(ICastable::getTypeGuid(), (void**)castable.writeRef())) && castable)
+        {
+            return add(castable);
+        }
+    }
+
+    // Wrap it in an adapter
+    IUnknownCastableAdapter* adapter = new UnknownCastableAdapter(unk);
+    add(adapter);
+}
+
+Index CastableList::indexOfUnknown(ISlangUnknown* unk)
+{
+    SLANG_ASSERT(unk);
+    // If it has a castable interface we can just look for that
+    {
+        ComPtr<ICastable> castable;
+        if (SLANG_SUCCEEDED(unk->queryInterface(ICastable::getTypeGuid(), (void**)castable.writeRef())) && castable)
+        {
+            return indexOf(castable);
+        }
+    }
+
+    // It's not derived from ICastable, so can only be in list via an adapter
+    const Count count = m_list.getCount();
+    for (Index i = 0; i < count; ++i)
+    {
+        auto adapter = as<IUnknownCastableAdapter>(m_list[i]);
+        if (adapter && adapter->getContained() == unk)
+        {
+            return i;
+        }
+    }
+    return -1;
+}
+
+} // namespace Slang
diff --git a/source/core/slang-castable-list-impl.h b/source/core/slang-castable-list-impl.h
new file mode 100644
index 000000000..6c03855f2
--- /dev/null
+++ b/source/core/slang-castable-list-impl.h
@@ -0,0 +1,83 @@
+// slang-castable-list.h
+#ifndef SLANG_CASTABLE_LIST_IMPL_H
+#define SLANG_CASTABLE_LIST_IMPL_H
+
+#include "slang-castable-list.h"
+
+#include "../../slang-com-helper.h"
+#include "../../slang-com-ptr.h"
+
+#include "../core/slang-com-object.h"
+
+namespace Slang
+{
+
+/* An adapter such that types which aren't derived from ICastable, can be used as such. 
+
+With the following caveats.
+* the interfaces/objects of the adapter are checked *first*, so IUnknown will always be for the adapter
+* assumes when doing a queryInterface on the contained item, it will remain in scope when released (this is *not* strict COM)
+*/
+class UnknownCastableAdapter : public ComBaseObject, public IUnknownCastableAdapter
+{
+public:
+    SLANG_COM_BASE_IUNKNOWN_ALL
+
+    // ICastable
+    SLANG_NO_THROW void* SLANG_MCALL castAs(const Guid& guid) SLANG_OVERRIDE;
+
+    // IUnknownCastableAdapter
+    virtual SLANG_NO_THROW ISlangUnknown* SLANG_MCALL getContained() SLANG_OVERRIDE { return m_contained; }
+
+    UnknownCastableAdapter(ISlangUnknown* unk):
+        m_contained(unk)
+    {
+        SLANG_ASSERT(unk);
+    }
+
+protected:
+    void* getInterface(const Guid& guid);
+    void* getObject(const Guid& guid);
+
+    ComPtr<ISlangUnknown> m_contained;
+
+    // We hold a cache for a single lookup to make things a little faster
+    void* m_found = nullptr;
+    Guid m_foundGuid;
+};
+
+/* Implementation of the ICastableList interface. 
+Is atomic reference counted*/
+class CastableList : public ComBaseObject, public ICastableList
+{
+public:
+    SLANG_COM_BASE_IUNKNOWN_ALL
+
+    // ICastable
+    SLANG_NO_THROW void* SLANG_MCALL castAs(const Guid& guid) SLANG_OVERRIDE;
+
+    // ICastableList
+    virtual Count SLANG_MCALL getCount() SLANG_OVERRIDE { return m_list.getCount(); }
+    virtual ICastable* SLANG_MCALL getAt(Index i) SLANG_OVERRIDE { return m_list[i]; }
+    virtual void SLANG_MCALL add(ICastable* castable) SLANG_OVERRIDE;
+    virtual void SLANG_MCALL addUnknown(ISlangUnknown* unk) SLANG_OVERRIDE;
+    virtual void SLANG_MCALL removeAt(Index i) SLANG_OVERRIDE;
+    virtual void SLANG_MCALL clear() SLANG_OVERRIDE;
+    virtual Index SLANG_MCALL indexOf(ICastable* castable) SLANG_OVERRIDE;
+    virtual Index SLANG_MCALL indexOfUnknown(ISlangUnknown* unk) SLANG_OVERRIDE;
+    virtual void* SLANG_MCALL find(const Guid& guid) SLANG_OVERRIDE;
+    virtual ICastable*const* SLANG_MCALL getBuffer() SLANG_OVERRIDE { return m_list.getBuffer(); }
+
+        /// Dtor
+    virtual ~CastableList();
+
+protected:
+    void* getInterface(const Guid& guid);
+    void* getObject(const Guid& guid);
+
+    List<ICastable*> m_list;
+};
+
+} // namespace Slang
+
+#endif
diff --git a/source/core/slang-castable-list.h b/source/core/slang-castable-list.h
new file mode 100644
index 000000000..942f53376
--- /dev/null
+++ b/source/core/slang-castable-list.h
@@ -0,0 +1,57 @@
+// slang-castable-list.h
+#ifndef SLANG_CASTABLE_LIST_H
+#define SLANG_CASTABLE_LIST_H
+
+#include "../core/slang-basic.h"
+
+#include "../core/slang-destroyable.h"
+
+namespace Slang
+{
+
+/* A useful interface for handling lists of castable interfaces. Cannot hold nullptr */
+class ICastableList : public ICastable
+{
+    SLANG_COM_INTERFACE(0x335f3d40, 0x934c, 0x40dc, { 0xb5, 0xe1, 0xf7, 0x6e, 0x40, 0x3, 0x62, 0x5 })
+            
+        /// Get the count of all interfaces held in the list
+    virtual Count SLANG_MCALL getCount() = 0;
+        /// Get the interface at the specified index
+    virtual ICastable* SLANG_MCALL getAt(Index i) = 0;
+        /// Add an item to the list
+    virtual void SLANG_MCALL add(ICastable* unk) = 0;
+        /// Add IUnknown, will cast to ICastable and if that's not possible will wrap
+    virtual void SLANG_MCALL addUnknown(ISlangUnknown* unk) = 0;
+        /// Remove item at index, remaining items stay in the same order
+    virtual void SLANG_MCALL removeAt(Index i) = 0;
+        /// Clear the list
+    virtual void SLANG_MCALL clear() = 0;
+        /// Find the first index of castable, or -1 if not found
+    virtual Index SLANG_MCALL indexOf(ICastable* castable) = 0;
+        /// Find the index interface (handling wrapping if necessary)
+    virtual Index SLANG_MCALL indexOfUnknown(ISlangUnknown* unk) = 0;
+        /// Find the first item that casts to non null
+    virtual void* SLANG_MCALL find(const Guid& guid) = 0;
+        /// Access the internal buffer (any mutation can invalidate this value)
+    virtual ICastable*const* SLANG_MCALL getBuffer() = 0;
+};
+
+// Simply finding things in a ICastableList
+template <typename T>
+SLANG_FORCE_INLINE T* find(ICastableList* list)
+{
+    return reinterpret_cast<T*>(list->find(T::getTypeGuid())); 
+}
+
+/* Adapter interface to make a non castable types work as ICastable */
+class IUnknownCastableAdapter : public ICastable
+{
+    SLANG_COM_INTERFACE(0x8b4aad81, 0x4934, 0x4a67, { 0xb2, 0xe2, 0xe9, 0x17, 0xfc, 0x29, 0x12, 0x54 });
+
+    /// When using the adapter, this provides a way to directly get the internal no ICastable type
+    virtual SLANG_NO_THROW ISlangUnknown* SLANG_MCALL getContained() = 0;
+};
+
+} // namespace Slang
+
+#endif
diff --git a/source/core/slang-destroyable.h b/source/core/slang-destroyable.h
index bf373ba33..390b16e7c 100644
--- a/source/core/slang-destroyable.h
+++ b/source/core/slang-destroyable.h
@@ -9,15 +9,6 @@
 namespace Slang
 {
 
-/* Adapter interface to make a non castable type work as ICastable */
-class IUnknownCastableAdapter : public ICastable
-{
-    SLANG_COM_INTERFACE(0x8b4aad81, 0x4934, 0x4a67, { 0xb2, 0xe2, 0xe9, 0x17, 0xfc, 0x29, 0x12, 0x54 } );
-
-        /// When using the adapter, this provides a way to directly get the internal no ICastable type
-    virtual SLANG_NO_THROW ISlangUnknown* SLANG_MCALL getContained() = 0;
-};
-
 /* An interface that allows for an object to implement 'destruction'. A destroyed 
 interface/object should release any other contained references. 
 Behavior of an interface that is IDestroyed should be defined on the interface. Typically 
diff --git a/source/core/slang-lazy-castable-list.cpp b/source/core/slang-lazy-castable-list.cpp
new file mode 100644
index 000000000..d9f0090d5
--- /dev/null
+++ b/source/core/slang-lazy-castable-list.cpp
@@ -0,0 +1,163 @@
+// slang-lazy-castable-list.cpp
+#include "slang-lazy-castable-list.h"
+
+#include "slang-castable-list-impl.h"
+
+namespace Slang {
+
+void LazyCastableList::removeAt(Index index)
+{
+    SLANG_ASSERT(index >= 0 && index < getCount());
+
+    switch (m_state)
+    {
+        case State::None:   break;
+        case State::One:    
+        {
+            m_state = State::None;
+            m_castable.setNull();
+            break;
+        }
+        case State::List:   
+        {
+            static_cast<ICastableList*>(m_castable.get())->removeAt(index);
+            break;
+        }
+    }
+}
+
+void LazyCastableList::clear()
+{
+    if (m_state == State::List)
+    {
+        auto list = static_cast<ICastableList*>(m_castable.get());
+        list->clear();
+    }
+    else
+    {
+        m_state = State::None;
+        m_castable.setNull();
+    }
+}
+
+void LazyCastableList::clearAndDeallocate()
+{
+    m_state = State::None;
+    m_castable.setNull();
+}
+
+Count LazyCastableList::getCount() const
+{
+    switch (m_state)
+    {
+        case State::None:   return 0;
+        case State::One:    return 1;
+        default:
+        case State::List:   return static_cast<ICastableList*>(m_castable.get())->getCount();
+    }
+}
+
+void LazyCastableList::add(ICastable* castable)
+{
+    SLANG_ASSERT(castable);
+    if (m_state == State::None)
+    {
+        m_castable = castable;
+        m_state = State::One;
+    }
+    else
+    {
+        requireList()->add(castable);
+    }
+}
+
+ICastableList* LazyCastableList::requireList()
+{
+    switch (m_state)
+    {
+        case State::None:
+        {
+            m_castable = new CastableList;
+            m_state = State::List;
+            break;
+        }
+        case State::One:
+        {
+            // Turn into a list
+            auto list = new CastableList;
+            list->add(m_castable);
+            m_castable = list;
+            m_state = State::List;
+            break;
+        }
+        default: break;
+    }
+    SLANG_ASSERT(m_state == State::List);
+    return static_cast<ICastableList*>(m_castable.get());
+}
+
+ICastableList* LazyCastableList::getList()
+{
+    return (m_state == State::None) ? nullptr : requireList();
+}
+
+void* LazyCastableList::find(const Guid& guid)
+{
+    for (auto castable : getView())
+    {
+        if (auto ptr = castable->castAs(guid))
+        {
+            return ptr;
+        }
+    }
+    return nullptr;
+}
+ 
+ConstArrayView<ICastable*> LazyCastableList::getView() const
+{
+    switch (m_state)
+    {
+        case State::None: return ConstArrayView<ICastable*>();
+        case State::One:  return ConstArrayView<ICastable*>((ICastable*const*)&m_castable, 1);
+        default:
+        case State::List:
+        {
+            auto list = static_cast<ICastableList*>(m_castable.get());
+            return ConstArrayView<ICastable*>(list->getBuffer(), list->getCount());
+        }
+    }
+}
+
+Index LazyCastableList::indexOf(ICastable* castable) const
+{
+    return getView().indexOf(castable);
+}
+
+Index LazyCastableList::indexOfUnknown(ISlangUnknown* unk) const
+{
+    // Try as a ICastable first
+    {
+        ComPtr<ICastable> castable;
+        if (SLANG_SUCCEEDED(unk->queryInterface(ICastable::getTypeGuid(), (void**)castable.writeRef())) && castable)
+        {
+            return indexOf(castable);
+        }
+    }
+
+    // It's not derived from ICastable, so can only be in list via an adapter
+    const auto view = getView();
+
+    const Count count = view.getCount();
+    for (Index i = 0; i < count; ++i)
+    {
+        auto adapter = as<IUnknownCastableAdapter>(view[i]);
+        if (adapter && adapter->getContained() == unk)
+        {
+            return i;
+        }
+    }
+
+    return -1;
+}
+
+} // namespace Slang
diff --git a/source/core/slang-lazy-castable-list.h b/source/core/slang-lazy-castable-list.h
new file mode 100644
index 000000000..4f73ce9ca
--- /dev/null
+++ b/source/core/slang-lazy-castable-list.h
@@ -0,0 +1,66 @@
+// slang-lazy-castable-list.h
+#ifndef SLANG_LAZY_CASTABLE_LIST_H
+#define SLANG_LAZY_CASTABLE_LIST_H
+
+#include "slang-castable-list.h"
+
+#include "../../slang-com-ptr.h"
+
+namespace Slang
+{
+
+/* Sometimes the overhead around having a potential list of items that might often be 
+empty or only contain a single element is considerable. 
+
+The `LazyCastableList` provides functionality around ICastableList to minimize allocation, or the 
+need to allocate an ICastableList. It does this by tracking state in m_state, and varying the 
+meaning of m_castable. 
+
+* State::None - there is no list 
+* State::One - there is a single entry, that is held in m_castable
+* State::List - m_castable is actually ICastableList, and holds the contents
+*/
+class LazyCastableList
+{
+public:
+        /// Add a castable to the lsit
+    void add(ICastable* castable);
+        /// Return the amount of items in the list
+    Count getCount() const;
+        /// Remove the item at the specified index
+    void removeAt(Index index);
+        /// Clear the list
+    void clear();
+        /// Clear and deallocate the list
+    void clearAndDeallocate();
+        /// Find the first item that castAs(guid) produces a result
+    void* find(const Guid& guid);
+        /// Get the contents of the list as a view
+    ConstArrayView<ICastable*> getView() const;
+        /// Get the index of castable in the list. Returns -1 if not found
+    Index indexOf(ICastable* castable) const;
+        /// Get the index of unk. Handles if the wrapping has been used.
+    Index indexOfUnknown(ISlangUnknown* unk) const;
+
+        /// Will always return a valid ICastableList
+    ICastableList* requireList();
+        /// Will return nullptr if the list is empty, else it returns a ICastableList holding the elements
+    ICastableList* getList();
+
+protected:
+    enum class State
+    {
+        None,
+        One,
+        List,
+    };
+    // A state is not *strictly* necessary, because we can always determine what m_castable is
+    // with a castAs. But doing so is not exactly fast, and using the state makes some code simpler
+    // additionally.
+    State m_state = State::None;
+    ComPtr<ICastable> m_castable;
+};
+
+} // namespace Slang
+
+#endif