Duplicate anchors when type variables exist in type signatures about haskell-indexer

[jinwoo]

It looks like one of the anchors is for the declaration and the other is for the xref. @robinp , is there a reason to have a xref here?

[jinwoo]

To make it clearer, the xref points to itself.

[jinwoo]

Noting what I found so far. The decl in this case is an "implicit" decl because type vars don't have explicit definition sites. So it's correct to have both the decl node and the xref node. The problem is that currently both have the same span.

I saw this comment: https://github.com/google/haskell-indexer/blob/master/haskell-indexer-backend-ghc/src/Language/Haskell/Indexer/Backend/Ghc.hs#L254

As noted there, we can make those implicit decls have no spans. When I do that, this problem goes away.

[jinwoo]

Hm. Then we have problems in unit tests. They use declAt to find decl nodes at the given location and then verify that there are xrefs to that decl. I'll have to find a different way to test those.

[jinwoo]

Maybe this is not worth fixing. Kythe verifier has a flag --ignore_dups, which can bypass this failing check. We can probably enable it in our test script and be done with this.