containsTypeFamilies: Don't crash if reification fails

Instead of crashing when `reify` fails, we recover and conservatively assume
that the type does not contain any type families.

Fixes #1032.

CHANGELOG.markdown

@@ -1,3 +1,9 @@
+next [????.??.??]
+-----------------
+* Fix a bug in which the `declare*` Template Haskell functions would fail if a
+  data type's field has a type that is defined in the same Template Haskell
+  quotation.
+
 5.2.2 [2023.03.18]
 ------------------
 * Fix a bug in which calling `ix i` (where `i` is a negative number) on `Text`

src/Control/Lens/Internal/FieldTH.hs

@@ -433,7 +433,16 @@ makeFieldInstance defType className decs =
 
   containsTypeFamilies = go <=< D.resolveTypeSynonyms
     where
-    go (ConT nm) = has (_FamilyI . _1 . _TypeFamilyD) <$> reify nm
+    go :: Type -> Q Bool
+    go (ConT nm) =
+      -- Note that the call to `reify` can fail if `nm` is not yet defined.
+      -- (This can actually happen if `nm` is declared in a Template Haskell
+      -- quote.) If this fails, there is no way to tell if the type contains
+      -- type families, so we recover and conservatively assume that is does not
+      -- contain any.
+      recover
+        (pure False)
+        (has (_FamilyI . _1 . _TypeFamilyD) <$> reify nm)
     go ty = or <$> traverse go (ty ^.. plate)
 
     -- We want to catch type families, but not *data* families. See #799.

tests/templates.hs

@@ -468,5 +468,12 @@ $(declareWrapped [d|
   newtype instance T997FamB b = MkT997FamB b
   |])
 
+-- Ensure that a data type defined in a TH quote can have a field whose type
+-- references another data type defined in the same quote (#1032)
+declareFields [d|
+    data T1032A = T1032A { t1032ASubB :: T1032B }
+    data T1032B = T1032B { t1032BB :: Int }
+  |]
+
 main :: IO ()
 main = putStrLn "test/templates.hs: ok"