dhall-to-{json,yaml,yaml-ng}: Handle empty maps correctly (#1561)

Fixes #1559.

This requires aeson-yaml >= 1.0.5.0 since older versions
incorrectly encode empty objects.

The raised bound also fixes #1560. A regression test is included.

dhall-json/dhall-json.cabal

@@ -37,7 +37,7 @@ Library
         base                      >= 4.8.0.0  && < 5   ,
         aeson                     >= 1.0.0.0  && < 1.5 ,
         aeson-pretty                             < 0.9 ,
-        aeson-yaml                >= 1.0.4    && < 1.1 ,
+        aeson-yaml                >= 1.0.5    && < 1.1 ,
         bytestring                               < 0.11,
         containers                                     ,
         dhall                     >= 1.27.0   && < 1.28,

dhall-json/src/Dhall/JSON.hs

@@ -858,7 +858,7 @@ convertToHomogeneousMaps (Conversion {..}) e0 = loop (Core.normalize e0)
                 case elements of
                     [] ->
                         case a of
-                            Just (Core.Record m) -> do
+                            Just (Core.App Core.List (Core.Record m)) -> do
                                 guard (Foldable.length m == 2)
                                 guard (Dhall.Map.member mapKey   m)
                                 guard (Dhall.Map.member mapValue m)

dhall-json/tasty/Main.hs

@@ -31,6 +31,7 @@ testTree :: TestTree
 testTree =
     Test.Tasty.testGroup "dhall-json"
         [ testDhallToJSON "./tasty/data/issue48"
+        , testDhallToJSON "./tasty/data/emptyObjectStrongType"
         , testJSONToDhall "./tasty/data/emptyAlternative"
         , testJSONToDhall "./tasty/data/emptyObject"
         , testJSONToDhall "./tasty/data/emptyList"

dhall-yaml/tasty/Main.hs

@@ -10,6 +10,7 @@ import Test.Tasty (TestTree)
 
 import qualified Data.ByteString
 import qualified Data.Text.IO
+import qualified Dhall.JSON
 import qualified Dhall.JSON.Yaml
 import qualified Dhall.Yaml
 import qualified GHC.IO.Encoding
@@ -32,6 +33,13 @@ testTree =
         , testDhallToYaml
             Dhall.JSON.Yaml.defaultOptions
             "./tasty/data/special"
+        , testDhallToYaml
+            Dhall.JSON.Yaml.defaultOptions
+            "./tasty/data/emptyList"
+        , testDhallToYaml
+            Dhall.JSON.Yaml.defaultOptions
+                { conversion = Dhall.JSON.Conversion "mapKey" "mapValue" }
+            "./tasty/data/emptyMap"
         , Test.Tasty.ExpectedFailure.ignoreTestBecause "#1516" $
           testDhallToYaml
             (Dhall.JSON.Yaml.defaultOptions { quoted = True })

dhall-yaml/tasty/data/emptyList.dhall

@@ -0,0 +1 @@
+[] : List Bool

dhall-yaml/tasty/data/emptyList.yaml

@@ -0,0 +1 @@
+[]

dhall-yaml/tasty/data/emptyMap.dhall

@@ -0,0 +1 @@
+[] : List { mapKey : Text, mapValue : Natural }

dhall-yaml/tasty/data/emptyMap.yaml

@@ -0,0 +1 @@
+{}

nix/aeson-yaml.nix

@@ -4,8 +4,8 @@
 }:
 mkDerivation {
   pname = "aeson-yaml";
-  version = "1.0.4.0";
-  sha256 = "7a6ddaad23f50dc7b419707e49904ad3b5ea9fcd29d2cae0e4adaf300fbb8264";
+  version = "1.0.5.0";
+  sha256 = "e3c49b52b7000dcfe0a227af2e3a70aa7fd97f5c577156ad659470b17127a533";
   isLibrary = true;
   isExecutable = true;
   libraryHaskellDepends = [

stack.yaml

@@ -22,7 +22,7 @@ extra-deps:
   - HsYAML-aeson-0.2.0.0@sha256:04796abfc01cffded83f37a10e6edba4f0c0a15d45bef44fc5bb4313d9c87757,1791
   - ordered-containers-0.2.2@sha256:ebf2be3f592d9cf148ea6b8375f8af97148d44f82d8d04476899285e965afdbf,810
   - lsp-test-0.6.1.0@sha256:df0fc403c03b6d036be13de3ff23d9951ae2506080135cd6862eded2c969a6da,3483
-  - aeson-yaml-1.0.4.0@sha256:72d91a4a2ade87b8a4bdf73937d2c62bd2c60053df1841f8bf1e6204387959b8,1975
+  - aeson-yaml-1.0.5.0@sha256:5786f021c1e088d6a5aa259120ec5b1f22bb1757f4427c1a87e0513d00f17f31,1975
   - prettyprinter-1.5.1@sha256:fca87c3e2611d3499a0341a59857e9b424a23f31646e4737d535a18582284f96,5375
   - atomic-write-0.2.0.7@sha256:3b626dfbc288cd070f1ac31b1c15ddd49822a923778ffe21f92b2116ffc72dc3,4584
 nix: