Add basic support for namespaces (#1304)

This change adds logic for parsing `namespace` declarations, referencing them, and looking up their members.

* The parser changes are a bit subtle, because that is where we deal with the issue of "re-opening" a namespace. We kludge things a bit by re-using an existing `NamespaceDecl` in the same parent if one is available, and thereby ensure that all the members in the same namespace can see on another.

* In order to allow namespaces to be referenced by name they need to have a type so that a `DeclRefExpr` to them can be formed. For this purpose we introduce `NamespaceType` which is the (singleton) type of a reference to a given namespace.

* The new `NamespaceType` case is detected in the `MemberExpr` checking logic and routed to the same logic that `StaticMemberExpr` uses, and the static lookup logic was extended with support for looking up in a namespace (a thin wrapper around one of the existing worker routines in `slang-lookup.cpp`.

* I made `NamespaceDecl` have a shared base class with `ModuleDecl` in the hopes that this would allow us to allow references to modules by name in the future. That hasn't been tested as part of this change.

* I cleaned up a bunch of logic around `ModuleDecl` holding a `Scope` pointer that was being used for some of the more ad hoc lookup routines in the public API. Those have been switched over to something that is a bit more sensible given the language rules and that doesn't rely on keeping state sititng around on the `ModuleDecl`.

* I added a test case to make sure the new funcitonality works, which includes re-opening a namespace, and it also tests both `.` and `::` operations for lookup in a namespace.

* The main missing feature here is the ability to do something like C++ `using`. It would probably be cleanest if we used `import` for this, since we already have that syntax (and having both `import` and `using` seems like a recipe for confusion). Most of the infrastructure is present to support `import`ing one namespace into another (in a way that wouldn't automatically pollute the namespace for clients), but some careful thought needs to be put into how import of namespaces vs. modules should work.

1 files changed, 8 insertions, 2 deletions

diff --git a/source/slang/slang-check-decl.cpp b/source/slang/slang-check-decl.cpp
index ad3f506a6..5054b00bc 100644
--- a/source/slang/slang-check-decl.cpp
+++ b/source/slang/slang-check-decl.cpp
@@ -234,9 +234,10 @@ namespace Slang
         /// Is `decl` a global shader parameter declaration?
     bool isGlobalShaderParameter(VarDeclBase* decl)
     {
-        // A global shader parameter must be declared at global (module) scope.
+        // A global shader parameter must be declared at global or namespace
+        // scope, so that it has a single definition across the module.
         //
-        if(!as<ModuleDecl>(decl->ParentDecl)) return false;
+        if(!as<NamespaceDeclBase>(decl->ParentDecl)) return false;
 
         // A global variable marked `static` indicates a traditional
         // global variable (albeit one that is implicitly local to
@@ -408,6 +409,11 @@ namespace Slang
             auto type = GetSup(constraintDeclRef);
             return QualType(type);
         }
+        else if( auto namespaceDeclRef = declRef.as<NamespaceDeclBase>())
+        {
+            auto type = getNamespaceType(session, namespaceDeclRef);
+            return QualType(type);
+        }
         if( sink )
         {
             // The compiler is trying to form a reference to a declaration