Don't collect triple slash comment in LineComments active pattern. Fixes

 fsprojects#2152.

CHANGELOG.md

@@ -1,11 +1,12 @@
 # Changelog
 
-## [Unreleased]
+## [4.7.3] - 2022-03-12
 
 ### Fixed
 * Option parameter name is lost in tuple. [#2144](https://github.com/fsprojects/fantomas/issues/2144)
 * Trivia between XmlDoc and member is not printed. [#2147](https://github.com/fsprojects/fantomas/issues/2147)
 * Emit correct keyword for properties with both getter and setter specified [#2129](https://github.com/fsprojects/fantomas/issues/2129)
+* Duplicate ///-comments when immediately preceded by a //-comment. [#2152](https://github.com/fsprojects/fantomas/issues/2152)
 
 ## [4.7.2] - 2022-03-11
 

src/Fantomas.Tests/CommentTests.fs

@@ -1843,3 +1843,26 @@ module Example =
     let dict2 =
         ConcurrentDictionary< (* some comment 2 *) int64, ConcurrentDictionary< (* some comment 3 *) int32, unit>>()
 """
+
+[<Test>]
+let ``correctly collect a double slash comment before a xml doc comment, 2152`` () =
+    formatSourceString
+        false
+        """
+// Maybe computation expression builder, copied from ExtCore library
+/// https://github.com/jack-pappas/ExtCore/blob/master/ExtCore/Control.fs
+[<Sealed>]
+type MaybeBuilder() = class end
+"""
+        config
+    |> prepend newline
+    |> should
+        equal
+        """
+// Maybe computation expression builder, copied from ExtCore library
+/// https://github.com/jack-pappas/ExtCore/blob/master/ExtCore/Control.fs
+[<Sealed>]
+type MaybeBuilder() =
+    class
+    end
+"""

src/Fantomas/TokenParser.fs

@@ -692,6 +692,11 @@ let private (|LineComments|_|) (tokens: Token list) =
         (finalContinuation: Token list -> Token list)
         : Token list * Token list =
         match tokens with
+        // When collecting a line comment, stop if we move from a double slash to a triple slash comment.
+        | LineCommentToken { Content = "///"
+                             LineNumber = tripleLn } :: _ when tripleLn = lastLineNumber + 1 ->
+            finalContinuation [], tokens
+        // Collect comment tokens when the current line is underneath the previous one.
         | LineCommentToken lc :: rest when (lc.LineNumber <= lastLineNumber + 1) ->
             collect rest lc.LineNumber (fun commentTokens -> lc :: commentTokens |> finalContinuation)
         | _ -> finalContinuation [], tokens
@@ -812,11 +817,7 @@ let rec private getTriviaFromTokensThemSelves
     =
     match tokens with
     // Skip triple slash comments
-    | TripleSlashLineComment (rest) ->
-        getTriviaFromTokensThemSelves mkRange lastButOneNonWhiteSpaceToken lastNonWhiteSpaceToken rest foundTrivia
-
-    // Skip triple slash comments
-    | LineComments ({ Content = "///" } :: _, rest) ->
+    | TripleSlashLineComment rest ->
         getTriviaFromTokensThemSelves mkRange lastButOneNonWhiteSpaceToken lastNonWhiteSpaceToken rest foundTrivia
 
     | LineComments ({ LineNumber = headLineNumber } :: _ as commentTokens, rest) ->