Description
From a discussion with @pjweinb and @adonovan:
The existence of line directives causes gopls all sorts of problems, because it means that there are two potentially valid source positions for a token.Pos, and it's not always clear which is correct in context. It also means that we need to access multiple files from operations that would otherwise be local to a single file. This has been a source of historical (and in all likelihood ongoing) bugs.
This issue records an outcome from that discussion: we should ignore line directives internally to gopls (in particular, being careful to call token.File.PositionFor instead of token.File.Position). If this causes usability issues in e.g. CGo programs, we should address those issues individually. For example, we could perform a post-processing pass on diagnostics that duplicates them to their mapped positions.
CC @golang/tools-team