From 17a9330df308d094f222e13966d63363859048dc Mon Sep 17 00:00:00 2001
From: Zubin Duggal <zubin.duggal@gmail.com>
Date: Wed, 26 Jul 2023 12:02:31 +0530
Subject: [PATCH] Allow pathToId to fail

---
 ghcide/src/Development/IDE/Core/Rules.hs      | 25 +++++++++++--------
 .../IDE/Import/DependencyInformation.hs       |  6 ++---
 2 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/ghcide/src/Development/IDE/Core/Rules.hs b/ghcide/src/Development/IDE/Core/Rules.hs
index 0cbec68a766..13ad47900a3 100644
--- a/ghcide/src/Development/IDE/Core/Rules.hs
+++ b/ghcide/src/Development/IDE/Core/Rules.hs
@@ -526,17 +526,20 @@ reportImportCyclesRule :: Recorder (WithPriority Log) -> Rules ()
 reportImportCyclesRule recorder =
     defineEarlyCutoff (cmapWithPrio LogShake recorder) $ Rule $ \ReportImportCycles file -> fmap (\errs -> if null errs then (Just "1",([], Just ())) else (Nothing, (errs, Nothing))) $ do
         DependencyInformation{..} <- useNoFile_ GetModuleGraph
-        let fileId = pathToId depPathIdMap file
-        case IntMap.lookup (getFilePathId fileId) depErrorNodes of
-            Nothing -> pure []
-            Just errs -> do
-                let cycles = mapMaybe (cycleErrorInFile fileId) (toList errs)
-                -- Convert cycles of files into cycles of module names
-                forM cycles $ \(imp, files) -> do
-                    modNames <- forM files $ \fileId -> do
-                        let file = idToPath depPathIdMap fileId
-                        getModuleName file
-                    pure $ toDiag imp $ sort modNames
+        case pathToId depPathIdMap file of
+          -- The header of the file does not parse, so it can't be part of any import cycles.
+          Nothing -> pure []
+          Just fileId ->
+            case IntMap.lookup (getFilePathId fileId) depErrorNodes of
+              Nothing -> pure []
+              Just errs -> do
+                  let cycles = mapMaybe (cycleErrorInFile fileId) (toList errs)
+                  -- Convert cycles of files into cycles of module names
+                  forM cycles $ \(imp, files) -> do
+                      modNames <- forM files $ \fileId -> do
+                          let file = idToPath depPathIdMap fileId
+                          getModuleName file
+                      pure $ toDiag imp $ sort modNames
     where cycleErrorInFile f (PartOfCycle imp fs)
             | f `elem` fs = Just (imp, fs)
           cycleErrorInFile _ _ = Nothing
diff --git a/ghcide/src/Development/IDE/Import/DependencyInformation.hs b/ghcide/src/Development/IDE/Import/DependencyInformation.hs
index b4c0f0a367a..d255c3ac1e8 100644
--- a/ghcide/src/Development/IDE/Import/DependencyInformation.hs
+++ b/ghcide/src/Development/IDE/Import/DependencyInformation.hs
@@ -105,8 +105,8 @@ getPathId path m@PathIdMap{..} =
 insertImport :: FilePathId -> Either ModuleParseError ModuleImports -> RawDependencyInformation -> RawDependencyInformation
 insertImport (FilePathId k) v rawDepInfo = rawDepInfo { rawImports = IntMap.insert k v (rawImports rawDepInfo) }
 
-pathToId :: PathIdMap -> NormalizedFilePath -> FilePathId
-pathToId PathIdMap{pathToIdMap} path = pathToIdMap HMS.! path
+pathToId :: PathIdMap -> NormalizedFilePath -> Maybe FilePathId
+pathToId PathIdMap{pathToIdMap} path = pathToIdMap HMS.!? path
 
 lookupPathToId :: PathIdMap -> NormalizedFilePath -> Maybe FilePathId
 lookupPathToId PathIdMap{pathToIdMap} path = HMS.lookup path pathToIdMap
@@ -343,7 +343,7 @@ immediateReverseDependencies file DependencyInformation{..} = do
 -- | returns all transitive dependencies in topological order.
 transitiveDeps :: DependencyInformation -> NormalizedFilePath -> Maybe TransitiveDependencies
 transitiveDeps DependencyInformation{..} file = do
-  let !fileId = pathToId depPathIdMap file
+  !fileId <- pathToId depPathIdMap file
   reachableVs <-
       -- Delete the starting node
       IntSet.delete (getFilePathId fileId) .