Initial support for a using construct (#1506)

The basic idea is that if you have a namespace:

    namespace MyCoolNamespace { void f() { ... } ... }

then you can bring the declarations from that namespace into scope with:

    using MyCoolNamespace;
    f();

The `using` construct is allowed in any scope where declarations are allowed. As an additional feature, the construct allows and then ignores the keyword `namespace` if it occurs right after `using`:

    using namespace MyCoolNamespace;

Note that unlike in C++, `using` a namespace inside another namespace doesn't implicitly make the symbols available to clients of that namespace:

    namespace hidden { void secret() {...} ... }
    namespace api { using hidden; ... }

    api.secret(); // ERROR: `secret()` isn't a member of `api`

The implementation of this feature was relatively simple, although it does leave out more advanced features that might be desirable in the future:

* No support for `using MCN = MyCoolNamespace` sorts of tricks to define a short name

* No support for `using` anything that isn't a namespace (e.g., to make the members of a type available without qualification)

* No support for cases where multiple visible modules have a namespace of the same name (or dealing with overloaded namespaces in general)

1 files changed, 1 insertions, 0 deletions

diff --git a/source/slang/slang-lower-to-ir.cpp b/source/slang/slang-lower-to-ir.cpp
index 864491f7e..f87b6bd69 100644
--- a/source/slang/slang-lower-to-ir.cpp
+++ b/source/slang/slang-lower-to-ir.cpp
@@ -5032,6 +5032,7 @@ struct DeclLoweringVisitor : DeclVisitor<DeclLoweringVisitor, LoweredValInfo>
     LoweredValInfo visit##NAME(NAME*) { return LoweredValInfo(); }
 
     IGNORED_CASE(ImportDecl)
+    IGNORED_CASE(UsingDecl)
     IGNORED_CASE(EmptyDecl)
     IGNORED_CASE(SyntaxDecl)
     IGNORED_CASE(AttributeDecl)