Fix 944

src/Fantomas.Tests/SignatureTests.fs

@@ -663,3 +663,23 @@ namespace B
 type Foo =
     member Item : 't -> unit when 't : comparison with set
 """
+
+[<Test>]
+let ``preserve abstract member in type, 944`` () =
+    formatSourceString true """
+namespace Baz
+
+type Foo =
+    abstract member Bar : Type
+    abstract Bar2 : Type
+    member Bar3 : Type
+"""  { config with SpaceBeforeColon = true }
+    |> prepend newline
+    |> should equal """
+namespace Baz
+
+type Foo =
+    abstract Bar : Type
+    abstract Bar2 : Type
+    member Bar3 : Type
+"""

src/Fantomas/Trivia.fs

@@ -282,7 +282,17 @@ let private addTriviaToTriviaNode
 
     | { Item = Keyword({ Content = keyword} as kw); Range = range } when (keyword = "override" || keyword = "default" || keyword = "member" || keyword = "abstract") ->
         findMemberDefnMemberNodeOnLine triviaNodes range.StartLine
-        |> updateTriviaNode (fun tn -> tn.ContentItself <- Some (Keyword(kw))) triviaNodes
+        |> updateTriviaNode (fun tn ->
+            match tn.Type, tn.ContentItself with
+            | MainNode("SynMemberSig.Member"), Some( Keyword ({ Content = existingKeyword })) when (existingKeyword = "abstract" && keyword = "member") ->
+                // edge case when for a signature file with:
+                // type Foo =
+                //    abstract member Bar : Type
+                //
+                // here we don't want to override the abstract keyword
+                ()
+            | _ -> tn.ContentItself <- Some (Keyword(kw))
+        ) triviaNodes
 
     | { Item = Keyword({ TokenInfo = {TokenName = tn}} as kw); Range = range } when (tn = "QMARK") ->
         findConstNodeAfter triviaNodes range