binder: expando declarations don't show up on symbol

[sandersn]

• expando on export default missing: declarationEmitDefaultExportWithStaticAssignment
• expando on interface/const merge missing: declarationEmitExpandoWithGenericConstraint
• expando on overloaded function missing: declarationEmitFunctionDuplicateNamespace
• expando with keyword names: declarationEmitFunctionKeywordProp
• expando with element access expressions: declarationEmitLateBoundAssignments2
• starting to think expandos just don't work: declarationEmitLateBoundAssignments

[sandersn]

This is correct, although it differs from Strada and we probably don't want it to differ in the long-term. In the following example, Point only has one declaration in Corsa and two in Strada, because Strada has assignment declarations and therefore treats Point as a namespace declaration containing zero.

function Point() { }
Point.zero = () => 0

The missing feature is transforming Point.zero into a synthetic--JS-only--namespace declaration:

function Point() { }
jsnamespace {
  jsexport var zero
}
Point.zero = () => 0

where the binder will need to allow jsnamespace to merge with other values, and the checker will need to follow the synthetic jsexport var to an original initialiser () => 0 to type check it. Oh, and the language service will need to report the synthetic jsnamespace's original location.