Use relative file paths for HIE files and Stan's config maps

Stan expects relative paths. Without this change, file names won't map
correctly to their associated language extension data, which means no
enabled extensions will be detected. This causes annoying false
positives with, e.g., the `StrictData` extension. (See issue haskell#3174.)

plugins/hls-stan-plugin/src/Ide/Plugin/Stan.hs

@@ -164,24 +164,25 @@ rules recorder plId = do
               logWith recorder Debug (LogDebugStanEnvVars env)
               seTomlFiles <- liftIO $ usedTomlFiles useDefConfig (stanArgsConfigFile stanArgs)
 
+              -- Note that Stan works in terms of relative paths, but the HIE come in as absolute. Without
+              -- making its path relative, the file name(s) won't line up with the associated Map keys.
+              relativeHsFilePath <- liftIO $ makeRelativeToCurrentDirectory $ fromNormalizedFilePath file
+              let hieRelative = hie{hie_hs_file=relativeHsFilePath}
+
               (cabalExtensionsMap, checksMap, confIgnored) <- case configTrial of
                   FiascoL es -> do
                       logWith recorder Development.IDE.Warning (LogWarnConf es)
                       pure (Map.empty,
                             HM.fromList [(LSP.fromNormalizedFilePath file, inspectionsIds)],
                             [])
                   ResultL warnings stanConfig -> do
-                      let currentHSAbs = fromNormalizedFilePath file -- hie_hs_file hie
-                      currentHSRel <- liftIO $ makeRelativeToCurrentDirectory currentHSAbs
-                      cabalExtensionsMap <- liftIO $ createCabalExtensionsMap isLoud (stanArgsCabalFilePath stanArgs) [hie]
-
-                      -- Files (keys) in checksMap need to have an absolute path for the analysis, but applyConfig needs to receive relative
-                      -- filepaths to apply the config, because the toml config has relative paths. Stan itself seems to work only in terms of relative paths.
-                      let checksMap = HM.mapKeys (const currentHSAbs) $ applyConfig [currentHSRel] stanConfig
-
-                      let analysis = runAnalysis cabalExtensionsMap checksMap (configIgnored stanConfig) [hie]
+                      -- A Map from *relative* file paths (just one, in this case) to language extension info.
+                      cabalExtensionsMap <- liftIO $ createCabalExtensionsMap isLoud (stanArgsCabalFilePath stanArgs) [hieRelative]
+                      -- HashMap of *relative* file paths to info about enabled checks for those file paths.
+                      let checksMap = applyConfig [relativeHsFilePath] stanConfig
                       pure (cabalExtensionsMap, checksMap, configIgnored stanConfig)
-              let analysis = runAnalysis cabalExtensionsMap checksMap confIgnored [hie]
+
+              let analysis = runAnalysis cabalExtensionsMap checksMap confIgnored [hieRelative]
               return (analysisToDiagnostics file analysis, Just ())
       else return ([], Nothing)