From b4ccb7b876b418b62e5392cd821fb750b6919d77 Mon Sep 17 00:00:00 2001
From: Florian Verdonck <florian.verdonck@outlook.com>
Date: Tue, 25 May 2021 12:30:08 +0200
Subject: [PATCH] Keep track of newline inside trivia via special event
 WriteLineInsideTrivia. Fixes #1538. (#1752)

---
 src/Fantomas.Tests/ColMultilineItemTests.fs | 25 +++++++++++++++++++++
 src/Fantomas/Context.fs                     | 11 +++++++--
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/src/Fantomas.Tests/ColMultilineItemTests.fs b/src/Fantomas.Tests/ColMultilineItemTests.fs
index d823825ddb..2817c19382 100644
--- a/src/Fantomas.Tests/ColMultilineItemTests.fs
+++ b/src/Fantomas.Tests/ColMultilineItemTests.fs
@@ -527,3 +527,28 @@ let a = p
 let i = 0
 let y = p
 """
+
+[<Test>]
+let ``two short application followed by trailing block comment, 1538`` () =
+    formatSourceString
+        false
+        """
+printfn "%s" @"c:\def\ghi\jkl"
+printfn "%s" "c:\\def\\ghi\\jkl"
+
+(*
+xyz
+*)
+"""
+        config
+    |> prepend newline
+    |> should
+        equal
+        """
+printfn "%s" @"c:\def\ghi\jkl"
+printfn "%s" "c:\\def\\ghi\\jkl"
+
+(*
+xyz
+*)
+"""
diff --git a/src/Fantomas/Context.fs b/src/Fantomas/Context.fs
index 741805f33b..25b6a4fd70 100644
--- a/src/Fantomas/Context.fs
+++ b/src/Fantomas/Context.fs
@@ -15,6 +15,7 @@ type WriterEvent =
     | WriteLineInsideStringConst
     | WriteBeforeNewline of string
     | WriteLineBecauseOfTrivia
+    | WriteLineInsideTrivia
     | IndentBy of int
     | UnIndentBy of int
     | SetIndent of int
@@ -94,7 +95,8 @@ module WriterModel =
             match cmd with
             | WriteLine
             | WriteLineBecauseOfTrivia -> doNewline m
-            | WriteLineInsideStringConst ->
+            | WriteLineInsideStringConst
+            | WriteLineInsideTrivia ->
                 { m with
                       Lines = "" :: m.Lines
                       Column = 0 }
@@ -150,9 +152,14 @@ module WriterEvents =
     let normalize ev =
         match ev with
         | Write s when s.Contains("\n") ->
+            let writeLine =
+                match ev with
+                | CommentOrDefineEvent _ -> WriteLineInsideTrivia
+                | _ -> WriteLineInsideStringConst
+
             s.Split('\n')
             |> Seq.map (fun x -> [ Write x ])
-            |> Seq.reduce (fun x y -> x @ [ WriteLineInsideStringConst ] @ y)
+            |> Seq.reduce (fun x y -> x @ [ writeLine ] @ y)
             |> Seq.toList
         | _ -> [ ev ]