α-normalize after β-normalization for integrity check (#554)

The reason you want to α-normalize last is because β-normalization can
introduce new bound variables when normalizing a `constructors` expression

Author: Gabriella439

src/Dhall/Import.hs

@@ -488,9 +488,11 @@ exprFromImport import_@(Import {..}) = do
 
                         Right _ -> do
                             let normalizedExpression =
-                                    Dhall.Core.normalizeWith
-                                        (getReifiedNormalizer _normalizer)
-                                            (Dhall.Core.alphaNormalize resolvedExpression)
+                                    Dhall.Core.alphaNormalize
+                                        (Dhall.Core.normalizeWith
+                                            (getReifiedNormalizer _normalizer)
+                                            resolvedExpression
+                                        )
 
                             let bytes =
                                     encodeExpression _protocolVersion normalizedExpression

tests/Import.hs

@@ -51,6 +51,10 @@ importTests =
                 "a semantic integrity check if fields are reordered"
                 "./tests/import/"
                 "./tests/import/fieldOrderC.dhall"
+            , shouldNotFailRelative
+                "a semantic integrity check when importing an expression using `constructors`"
+                "./tests/import/"
+                "./tests/import/issue553B.dhall"
             ]
         ]
 

tests/import/issue553A.dhall

@@ -0,0 +1,5 @@
+    let T = < A : {} | B : {} >
+
+in  let t = constructors T
+
+in  t

tests/import/issue553B.dhall

@@ -0,0 +1 @@
+./issue553A.dhall sha256:2324a5352105b6835db60b127c7096c5d5b81027969ccd368d163edc5d9692e0