ParsedSource (especially module name source span) not available from Source Plugin
As discovered in https://github.com/google/haskell-indexer/pull/89\#discussion_r248081268, the
TcGblEnv received by a Source Plugin doesn't seem to have a way of accessing the SrcSpan of the module name.
When having access to the ParsedModule, it contains ParsedSource, which is
Located (HsModule GhcPs), whose inner datatype contains
Maybe (Located ModuleName), with the location's span pointing to the module name span.
TcGblEnv one can access the
ModSummary, which has a
Maybe HsParsedModule, but seems to be
I know this is a minor nit, but all other declarations are accessible by the source plugin so far, just this bit seems missing. Without this, haskell-indexer has to resort to source-code heuristics to get the module name span.