Fix unindented type abbreviation with line comment. Fixes #567 (#603)

src/Fantomas.Tests/UnionTests.fs

@@ -168,7 +168,7 @@ type CustomerId = private | CustomerId of int
 """
 
 [<Test>]
-let ``Single case DU with member should be on a newline`` () =
+let ``single case DU with member should be on a newline`` () =
     formatSourceString false """
 type CustomerId =
     | CustomerId of int
@@ -217,4 +217,17 @@ type internal Foo = private | Bar
     |> should equal """namespace meh
 
 type internal Foo = private | Bar
+"""
+
+[<Test>]
+let ``single case DU with comment above clause, 567`` () =
+    formatSourceString false """type 'a MyGenericType =
+  ///
+  Foo
+"""  config
+    |> prepend newline
+    |> should equal """
+type 'a MyGenericType =
+    ///
+    Foo
 """

src/Fantomas/CodePrinter.fs

@@ -1553,13 +1553,18 @@ and genTypeDefn astContext (TypeDef(ats, px, ao, tds, tcs, tdr, ms, s, preferPos
 
     | Simple TDSRNone -> 
         typeName
-    | Simple(TDSRTypeAbbrev t) -> 
-        typeName +> sepEq +> sepSpace
-        +> genTrivia tdr.Range
-            (genType astContext false t
-            +> ifElse (List.isEmpty ms) (!- "") 
+    | Simple(TDSRTypeAbbrev t) ->
+        let genTypeAbbrev = genType astContext false t
+
+        let genMembers =
+            ifElse (List.isEmpty ms)
+                (!- "")
                 (indent ++ "with" +> indent +> genMemberDefnList { astContext with InterfaceRange = None } ms
-            +> unindent +> unindent))
+            +> unindent +> unindent)
+
+        let genTypeBody =  autoIndentNlnByFuture (genTrivia tdr.Range genTypeAbbrev) +> genMembers
+
+        typeName +> sepEq +> sepSpace +> genTypeBody
     | Simple(TDSRException(ExceptionDefRepr(ats, px, ao, uc))) ->
         genExceptionBody astContext ats px ao uc
         |> genTrivia tdr.Range