Fix mutual information not being set properly by the positivity check…

…er (agda#7149)

fix agda#7133: mutual information not being set properly by the positivity
checker

_Note to future git-bisecters_

The missing mutual information caused some functions to not be considered for projection-likeness, so if you end up blaming this commit, there might be a bug with projection-likeness.

src/full/Agda/TypeChecking/Positivity.hs

@@ -103,26 +103,34 @@ checkStrictlyPositive mi qset = do
         ]
   reportSLn "tc.pos.graph.sccs" 15 $
     "  sccs = " ++ prettyShow [ scc | CyclicSCC scc <- sccs ]
-  forM_ sccs $ \case
-    -- If the mutuality information has never been set, we set it to []
-    AcyclicSCC (DefNode q) -> whenM (isNothing <$> getMutual q) $ do
-      reportSLn "tc.pos.mutual" 10 $ "setting " ++ prettyShow q ++ " to non-recursive"
-      -- Andreas, 2017-04-26, issue #2555
-      -- We should not have @DefNode@s pointing outside our formal mutual block.
-      unless (Set.member q qset) __IMPOSSIBLE__
-      setMutual q []
-    AcyclicSCC (ArgNode{}) -> return ()
-    CyclicSCC scc          -> setMut [ q | DefNode q <- scc ]
+
+  -- #7133: Note that the graph doesn't necessarily contain all of qs in the case where there are no
+  -- occurrences of a name, but we still need to setMutual for them.
+  let sccMap = Map.unions [ case scc of
+                              AcyclicSCC (DefNode q) -> Map.singleton q []
+                              AcyclicSCC ArgNode{}   -> mempty
+                              CyclicSCC scc          -> Map.fromList [ (q, qs) | q <- qs ]
+                                where qs = [ q | DefNode q <- scc ]
+                          | scc <- sccs ]
+  inAbstractMode $ forM_ qs $ \ q ->
+    whenM (isNothing <$> getMutual q) $ do
+      let qs = fromMaybe [] $ Map.lookup q sccMap
+      reportSLn "tc.pos.mutual" 10 $ "setting " ++ prettyShow q ++ " to " ++
+                                     if | null qs        -> "non-recursive"
+                                        | length qs == 1 -> "recursive"
+                                        | otherwise      -> "mutually recursive"
+      setMutual q qs
+
   mapM_ (checkPos g gstar) qs
   reportSDoc "tc.pos.tick" 100 $ "checked positivity"
 
   where
     checkPos :: Graph Node (Edge OccursWhere) ->
                 Graph Node Occurrence ->
                 QName -> TCM ()
-    checkPos g gstar q = inConcreteOrAbstractMode q $ \ _def -> do
+    checkPos g gstar q = inConcreteOrAbstractMode q $ \ def -> do
       -- we check positivity only for data or record definitions
-      whenJustM (isDatatype q) $ \ dr -> do
+      whenJust (isDatatype def) $ \ dr -> do
         reportSDoc "tc.pos.check" 10 $ "Checking positivity of" <+> prettyTCM q
 
         let loop :: Maybe Occurrence
@@ -199,26 +207,13 @@ checkStrictlyPositive mi qset = do
 
     occ (Edge o _) = o
 
-    isDatatype :: QName -> TCM (Maybe DataOrRecord)
-    isDatatype q = do
-      def <- theDef <$> getConstInfo q
-      return $ case def of
+    isDatatype :: Definition -> Maybe DataOrRecord
+    isDatatype def = do
+      case theDef def of
         Datatype{dataClause = Nothing} -> Just IsData
         Record  {recClause  = Nothing, recPatternMatching } -> Just $ IsRecord recPatternMatching
         _ -> Nothing
 
-    -- Set the mutually recursive identifiers for a SCC.
-    setMut :: [QName] -> TCM ()
-    setMut [] = return ()  -- nothing to do
-    setMut qs = forM_ qs $ \ q -> do
-      reportSLn "tc.pos.mutual" 10 $ "setting " ++ prettyShow q ++ " to (mutually) recursive"
-      setMutual q qs
-      -- TODO: The previous line produces data of quadratic size
-      -- (which has to be processed upon serialization).  Presumably qs is
-      -- usually short, but in some cases (for instance for generated
-      -- code) it may be long. Wouldn't it be better to assign a
-      -- unique identifier to each SCC, and avoid storing lists?
-
     -- Set the polarity of the arguments to a couple of definitions
     setArgOccs :: Set QName -> [QName] -> Graph Node Occurrence -> TCM ()
     setArgOccs qset qs g = do

test/Succeed/Test4687.agda

@@ -1,3 +1,4 @@
+{-# OPTIONS --overlapping-instances #-}
 
 open import Agda.Primitive
 open import Agda.Builtin.List

test/interaction/Issue7133.agda

@@ -0,0 +1,18 @@
+
+module _ where
+
+open import Agda.Primitive
+
+record Point (A : Set) : Set where
+  field
+    pt : A
+
+record PointedSet : Set₁ where
+  field
+    Carrier : Set
+    point   : Point Carrier
+
+module _ (sto : PointedSet) where
+
+  foo : Set
+  foo = {!!}

test/interaction/Issue7133.in

@@ -0,0 +1,2 @@
+top_command (cmd_load currentFile [])
+goal_command 0 cmd_autoOne ""

test/interaction/Issue7133.out

@@ -0,0 +1,8 @@
+(agda2-status-action "")
+(agda2-info-action "*Type-checking*" "" nil)
+(agda2-highlight-clear)
+(agda2-status-action "")
+(agda2-info-action "*All Goals*" "?0 : Set " nil)
+((last . 1) . (agda2-goals-action '(0)))
+(agda2-give-action 0 "PointedSet.Carrier sto")
+((last . 1) . (agda2-goals-action '()))