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, 40 insertions, 1 deletions

diff --git a/source/slang/slang-check-expr.cpp b/source/slang/slang-check-expr.cpp
index fbe38bac7..a8114c8d6 100644
--- a/source/slang/slang-check-expr.cpp
+++ b/source/slang/slang-check-expr.cpp
@@ -1423,7 +1423,37 @@ namespace Slang
     {
         auto& baseType = baseExpression->type;
 
-        if (auto typeType = as<TypeType>(baseType))
+        // TODO: Need to handle overloaded case (in case we
+        // have multiple visible types and/or namespaces
+        // with the same name).
+
+        if (auto namespaceType = as<NamespaceType>(baseType))
+        {
+            // We are looking up a namespace member.
+            //
+            auto namespaceDeclRef = namespaceType->getDeclRef();
+
+            // This ought to be the easy case, because
+            // there are no restrictions on whether
+            // we can reference the declaration here.
+            //
+            LookupResult lookupResult = lookUpDirectAndTransparentMembers(
+                getSession(),
+                this,
+                expr->name,
+                namespaceDeclRef);
+            if (!lookupResult.isValid())
+            {
+                return lookupMemberResultFailure(expr, baseType);
+            }
+
+            return createLookupResultExpr(
+                expr->name,
+                lookupResult,
+                nullptr,
+                expr->loc);
+        }
+        else if (auto typeType = as<TypeType>(baseType))
         {
             // We are looking up a member inside a type.
             // We want to be careful here because we should only find members
@@ -1594,6 +1624,11 @@ namespace Slang
         //
         expr->BaseExpression = maybeOpenExistential(expr->BaseExpression);
 
+        // TODO: Handle the case of an overloaded base expression
+        // here, in case we can use the name of the member to
+        // disambiguate which of the candidates is meant, or if
+        // we can return an overloaded result.
+
         auto & baseType = expr->BaseExpression->type;
 
         // Note: Checking for vector types before declaration-reference types,
@@ -1619,6 +1654,10 @@ namespace Slang
                 baseScalarType,
                 1);
         }
+        else if( as<NamespaceType>(baseType) )
+        {
+            return _lookupStaticMember(expr, expr->BaseExpression);
+        }
         else if(auto typeType = as<TypeType>(baseType))
         {
             return _lookupStaticMember(expr, expr->BaseExpression);