Fix newline idempotency issue with multiline abstract members

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### Fixed
 * SRTP or condition disappear when non-generic type is used. [#2168](https://github.com/fsprojects/fantomas/issues/2168)
+* Multiline AbstractSlot without constraints introduces newline [#2175](https://github.com/fsprojects/fantomas/issues/2175)
 
 ## [4.7.5] - 2022-03-27
 

src/Fantomas.Tests/NewlineBetweenTypeDefinitionAndMembersTests.fs

@@ -405,3 +405,26 @@ type A =
         | B x -> x
         | _ -> failwith "shouldn't happen"
 """
+
+[<Test>]
+let ``multiline abstract member without constraints, 2175`` () =
+    formatSourceString
+        false
+        """
+    type FuseSortFunctionItem =
+        abstract Item: key: string -> U2<{| ``$``: string |}, ResizeArray<{| ``$``: string; idx: float |}>> with get, set
+        abstract X : int
+"""
+        { config with MaxLineLength = 60 }
+    |> prepend newline
+    |> should
+        equal
+        """
+type FuseSortFunctionItem =
+    abstract Item:
+        key: string ->
+            U2<{| ``$``: string |}, ResizeArray<{| ``$``: string
+                                                   idx: float |}>> with get, set
+
+    abstract X: int
+"""

src/Fantomas/CodePrinter.fs

@@ -4835,7 +4835,12 @@ and genMemberDefn astContext node =
         +> ifElse hasGenerics sepColonWithSpacesFixed sepColon
         +> autoIndentAndNlnIfExpressionExceedsPageWidth (genTypeList astContext namedArgs)
         -- genPropertyKind (not isFunctionProperty) mf.MemberKind
-        +> autoIndentAndNlnIfExpressionExceedsPageWidth (genConstraints astContext t vi)
+        +> onlyIf
+            (match t with
+             | TWithGlobalConstraints _ -> true
+             | _ -> false)
+            autoIndentAndNlnIfExpressionExceedsPageWidth
+            (genConstraints astContext t vi)
 
     | md -> failwithf "Unexpected member definition: %O" md
     |> genTriviaFor (synMemberDefnToFsAstType node) node.Range