Limit range for arrow token trivia in desugared lambda

src/Fantomas.Tests/PatternMatchingTests.fs

@@ -711,3 +711,32 @@ let (|AndExpr|_|) =
     | ListSplitPick "&&" chooser (e1, e2) -> Some(BoolExpr.And(e1, e2))
     | _ -> None
 """
+
+[<Test>]
+let ``comment after arrow should not be duplicated, 1082`` () =
+    formatSourceString false """
+List.tryFind(fun { Type = t; Range = r }  ->
+                    match t with
+                    | MainNode SynMemberDefn_Member
+                    | MainNode SynMemberSig_Member -> // trying to get AST trivia
+                        RangeHelpers.``range contains`` r rangeOfBindingAndRhs
+
+                    | Token(MEMBER, _) -> // trying to get token trivia
+                        r.StartLine = rangeOfBindingAndRhs.StartLine
+
+                    | _ -> false
+                )
+"""  config
+    |> prepend newline
+    |> should equal """
+List.tryFind (fun { Type = t; Range = r } ->
+    match t with
+    | MainNode SynMemberDefn_Member
+    | MainNode SynMemberSig_Member -> // trying to get AST trivia
+        RangeHelpers.``range contains`` r rangeOfBindingAndRhs
+
+    | Token (MEMBER, _) -> // trying to get token trivia
+        r.StartLine = rangeOfBindingAndRhs.StartLine
+
+    | _ -> false)
+"""

src/Fantomas/CodePrinter.fs

@@ -1312,15 +1312,22 @@ and genExpr astContext synExpr =
     | Paren(DesugaredLambda(cps, e)) ->
         fun (ctx: Context) ->
             let lastLineOnlyContainsParenthesis = lastLineOnlyContains [| ' ';'('|] ctx
+
+            let arrowRange =
+                List.last cps
+                |> snd
+                |> fun lastPatRange ->
+                    mkRange "arrow range" lastPatRange.End e.Range.Start
+
             let hasLineCommentAfterArrow =
-                findTriviaTokenFromName RARROW synExpr.Range ctx
+                findTriviaTokenFromName RARROW arrowRange ctx
                 |> Option.isSome
 
             let expr =
                 sepOpenT
                 -- "fun "
-                +> col sepSpace cps (genComplexPats astContext)
-                +> triviaAfterArrow synExpr.Range
+                +> col sepSpace cps (fst >> genComplexPats astContext)
+                +> triviaAfterArrow arrowRange
                 +> ifElse hasLineCommentAfterArrow (genExpr astContext e)
                        (ifElse lastLineOnlyContainsParenthesis (autoIndentAndNlnIfExpressionExceedsPageWidth (genExpr astContext e))
                             (autoNlnIfExpressionExceedsPageWidth (genExpr astContext e)))
@@ -1329,7 +1336,7 @@ and genExpr astContext synExpr =
             expr ctx
 
     | DesugaredLambda(cps, e) ->
-        !- "fun " +>  col sepSpace cps (genComplexPats astContext) +> sepArrow
+        !- "fun " +>  col sepSpace cps (fst >> genComplexPats astContext) +> sepArrow
         +> autoIndentAndNlnIfExpressionExceedsPageWidth (genExpr astContext e)
     | Paren(Lambda(e, sps)) ->
         fun (ctx: Context) ->

src/Fantomas/SourceParser.fs

@@ -1098,10 +1098,15 @@ let rec transformPatterns ss = function
         List.map loop sps |> ComplexPats
     | SPSTyped(sp, t) -> ComplexTyped(transformPatterns ss sp, t)
 
+let getSynSimplePatsRange =
+    function
+    | SynSimplePats.SimplePats(_,r)
+    | SynSimplePats.Typed(_, _,r) -> r
+
 /// Process compiler-generated matches in an appropriate way
 let (|DesugaredLambda|_|) = function
     | Lambda(DesugaredMatch(ss, e), spss) ->
-        Some(List.map (transformPatterns ss) spss, e)
+        Some(List.map (fun sp -> transformPatterns ss sp, getSynSimplePatsRange sp) spss, e)
     | _ -> None
 
 // Type definitions