This issue is about tracking the progress on that (since all previous issues related to this were closed).
I've looked into this a bit and it's not clear to me if the fix belongs in golang.org/x/tools/godoc itself, or if perhaps it can be implemented in a lower level component: one of go/doc, go/parser, go/scanner, go/ast, etc. (The workaround would need to stay until it's possible to fully rely on the lower level fix in stdlib.)
I'm also not sure if it's expected behavior for //line comments to show up in ast.CommentGroup or not.
Issue #5247, reported in 2013, was about godoc then not handling the following input properly:
//line file:2// G doc.funcG()
It was showing "line file:2 G doc." as the documentation of function G, rather than just "G doc." as it should've been. (If you were to change the line number in the comment to //line file:10, it wouldn't show up anymore.)
At that time, there was no API to obtain the raw source positions from a token.Pos, which was the main blocker and a long-standing TODO.