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, 5 insertions, 19 deletions

diff --git a/source/slang/slang.cpp b/source/slang/slang.cpp
index 6c1a59ea4..aefe70a4a 100644
--- a/source/slang/slang.cpp
+++ b/source/slang/slang.cpp
@@ -890,24 +890,13 @@ Type* ComponentType::getTypeFromString(
     // the modules that were directly or
     // indirectly referenced.
     //
-    // TODO: This `scopesToTry` idiom appears
-    // all over the code, and isn't really
-    // how we should be handling this kind of
-    // lookup at all.
-    //
-    List<RefPtr<Scope>> scopesToTry;
-    for(auto module : getModuleDependencies())
-        scopesToTry.add(module->getModuleDecl()->scope);
+    RefPtr<Scope> scope = _createScopeForLegacyLookup();
 
     auto linkage = getLinkage();
-    for(auto& s : scopesToTry)
-    {
-        RefPtr<Expr> typeExpr = linkage->parseTermString(
-            typeStr, s);
-        type = checkProperType(linkage, TypeExp(typeExpr), sink);
-        if (type && !type.as<ErrorType>())
-            break;
-    }
+    RefPtr<Expr> typeExpr = linkage->parseTermString(
+        typeStr, scope);
+    type = checkProperType(linkage, TypeExp(typeExpr), sink);
+
     if( type )
     {
         m_types[typeStr] = type;
@@ -915,9 +904,6 @@ Type* ComponentType::getTypeFromString(
     return type;
 }
 
-
-
-
 CompileRequestBase::CompileRequestBase(
     Linkage*        linkage,
     DiagnosticSink* sink)