WIP preserve in keyword.

src/Fantomas.Tests/LetBindingTests.fs

@@ -967,3 +967,18 @@ let x =
 
     ()
 """
+
+[<Test>]
+let ``preserve in keyword via trivia, 340`` () =
+    formatSourceString false """
+let x = List.singleton <|
+        let item = "text"
+        item
+"""  config
+    |> prepend newline
+    |> should equal """
+let x =
+    List.singleton
+    <| let item = "text" in
+       item
+"""

src/Fantomas/CodePrinter.fs

@@ -715,6 +715,7 @@ and genLetBinding astContext pref b =
         +> leadingExpressionIsMultiline
             (afterLetKeyword
              +> genPat
+             +> dumpAndContinue
              +> enterNodeTokenByName rangeBetweenBindingPatternAndExpression EQUALS)
                (genExprSepEqPrependType astContext p e (Some(valInfo)))
 

src/Fantomas/TokenParser.fs

@@ -317,7 +317,8 @@ let private keywordTrivia =
       "DEFAULT"
       "ABSTRACT"
       "KEYWORD_STRING"
-      "QMARK" ]
+      "QMARK"
+      "IN" ]
 
 let private numberTrivia =
     [ "UINT8"

src/Fantomas/Trivia.fs

@@ -387,6 +387,11 @@ let private addTriviaToTriviaNode triviaBetweenAttributeAndParentBinding
         findConstNodeAfter triviaNodes range
         |> updateTriviaNode (fun tn -> tn.ContentBefore.Add(Keyword(kw))) triviaNodes
 
+    | { Item = Keyword ({ Content = keyword }); Range = range } when (keyword = "in") ->
+        // find largest SynExpr right before in range
+        findNodeBeforeLineAndColumn triviaNodes range.StartLine range.StartColumn
+        |> updateTriviaNode (fun tn -> tn.ContentAfter.Add trivia.Item) triviaNodes
+
     | { Item = Keyword ({ Content = keyword }); Range = range } when (keyword = "if"
                                                                       || keyword = "then"
                                                                       || keyword = "else"