use correct repo for xlang xrefs for mirrored repos

Summary:
Reminder: fbsource/www and www/ paths both map to the same dbs. In Glass, we consider that "fbsource/www" is a mirror of www, and we're careful to translate the returned paths so they match the repo query. See this [post](https://fb.workplace.com/groups/csi.eng/permalink/1990139908151741/).

There's a corner case that wasn't handled correctly: When processing DocumentSymbols() query, we need to resolve the location of cross-dbs entities. We pick the db based on
- the query repo
- the cross-db target entity language

The rules are currently
- (fbsource, thrift) -> fbsource.fbthrift
- (www, thrift) -> www.fbthrift

There's an issue in the case of fbsource/www hack documents. The source repo is fbsource, which means we use the wrong thrift db.

Proposed fix is to again use the MirrorConfig mapping and make sure we use the "origin" repo to determine the target entity db (e.g. www instead of fbsource).

Reviewed By: iamirzhan

Differential Revision: D66679488

fbshipit-source-id: a640830d21c5ee9eafc6dd3cc6eb32ad55e038db

glean/glass/Glean/Glass/Handler/Documents.hs

@@ -175,16 +175,19 @@ toFileReference :: RepoName -> Path -> FileReference
 toFileReference repo path =
   FileReference repo (toGleanPath $ SymbolRepoPath repo path)
 
+repoPathToMirror :: RepoName -> Path -> Maybe Mirror
+repoPathToMirror repository (Path filepath) =
+  let isReqInMirror (Mirror mirrorRepo prefix _) =
+        repository == mirrorRepo && isPrefixOf prefix filepath in
+  find isReqInMirror mirrorConfig
+
 translateMirroredRepoListXResult
   :: DocumentSymbolsRequest
   -> DocumentSymbolListXResult
   -> DocumentSymbolListXResult
 translateMirroredRepoListXResult
-  (DocumentSymbolsRequest repository (Path filepath) _ _) res =
-  let isReqInMirror (Mirror mirrorRepo prefix _) =
-        repository == mirrorRepo && isPrefixOf prefix filepath in
-  let maybeMirror = find isReqInMirror mirrorConfig in
-  case maybeMirror of
+  (DocumentSymbolsRequest repository path _ _) res =
+  case repoPathToMirror repository path of
     Just (Mirror mirror prefix origin) ->
       Utils.translateDocumentSymbolListXResult origin mirror prefix Nothing res
     _ -> res
@@ -217,7 +220,7 @@ fetchSymbolsAndAttributesGlean
       file mlimit be res1
 
   let be = fromMaybe (gleanBackend, dbInfo) mOtherBackend
-  res3 <- resolveXlangXrefs env res2 repo be
+  res3 <- resolveXlangXrefs env path res2 repo be
 
   let res4 = toDocumentSymbolResult res3
   let res5 = translateMirroredRepoListXResult req res4
@@ -548,26 +551,34 @@ fetchDocumentSymbols [email protected]{..} (FileReference scsrepo path)
 resolveXlangXrefs
   :: Glean.Backend b
   => Glass.Env
+  -> Path
   -> DocumentSymbols
   -> RepoName
   -> (b, GleanDBInfo)
   -> IO DocumentSymbols
 resolveXlangXrefs
   env@Glass.Env{tracer, sourceControl, repoMapping}
+  path
   docSyms@DocumentSymbols{..}
   scsrepo
   (gleanBackend, dbInfo) = do
   case (unresolvedXrefsXlang, srcFile) of
     ((ent, _) : _, Just srcFile) -> do
        -- we assume all xlang xrefs belong to the same db
+       -- we pick the xlang dbs based on target lang and
+       -- repo. Corner case: the document is in a mirror repo,
+       -- use to origin repo to determine xlang db
       let lang = entityLanguage ent
+          targetRepo = case repoPathToMirror scsrepo path of
+              Just (Mirror _mirror _prefix origin) -> origin
+              Nothing -> scsrepo
       gleanDBs <- getGleanRepos tracer sourceControl repoMapping dbInfo
-        scsrepo (Just lang) ChooseLatest Nothing
+        targetRepo (Just lang) ChooseLatest Nothing
       let gleanBe = GleanBackend {gleanDBs, tracer, gleanBackend}
       xlangRefs <- backendRunHaxl gleanBe env $ do
         xrefsXlang <- withRepo (snd (NonEmpty.head gleanDBs)) $ do
-          xrefs <- resolveEntitiesRange scsrepo fst unresolvedXrefsXlang
-          mapM (toReferenceSymbolXlang scsrepo srcFile offsets lang) xrefs
+          xrefs <- resolveEntitiesRange targetRepo fst unresolvedXrefsXlang
+          mapM (toReferenceSymbolXlang targetRepo srcFile offsets lang) xrefs
         return $ xRefDataToRefEntitySymbol <$> xrefsXlang
       return $ docSyms  { refs = refs ++ xlangRefs, unresolvedXrefsXlang = [] }
     _ -> return docSyms