This rearranges the way dynamic loads work a bit. Previously, they¬
required an object, and did a dynamic lookup in the object's property¬
map. For real dynamic loads -- of the kind Python uses, obviously,¬
but also ECMAScript -- we need to search the "environment".
This change searches the environment by looking first in the lexical¬
scope in the current function. If a variable exists, we will use it.¬
If that misses, we then look in the module scope. If a variable exists¬
there, we will use it. Otherwise, if the variable is used in a non-lval
position, an dynamic error will be raised ("name not declared"). If
an lval, however, we will lazily allocate a slot for it.
Note that Python doesn't use block scoping in the same way that most
languages do. This behavior is simply achieved by Python not emitting
any lexically scoped blocks other than at the function level.
This doesn't perfectly achieve the scoping behavior, because we don't
yet bind every name in a way that they can be dynamically discovered.
The two obvious cases are class names and import names. Those will be
covered in a subsequent commit.
Also note that we are getting lucky here that class static/instance
variables aren't accessible in Python or ECMAScript "ambiently" like
they are in some languages (e.g., C#, Java); as a result, we don't need
to introduce a class scope in the dynamic lookup. Some day, when we
want to support such languages, we'll need to think about how to let
languages control the environment probe order; for instance, perhaps
the LoadDynamicExpression node can have an "environment" property.
f773000ef9