Correct Elif expression range when there is only a single elif. (#1659)

* Correct Elif expression range when there is only a single elif.

* Use end of previous elif body expression as start of correct elif range.

* Remove atCurrentColumnIndent for non special long condition expressions.

* Don't add extra space before long if expression.

* Use specific range for keywords in elif.

src/Fantomas.Tests/IfThenElseTests.fs

@@ -928,7 +928,7 @@ if // c1
 else // c5
 if // c6
     c // c7
-    then // c8
+then // c8
     d // c9
 else // c10
     e // c11
@@ -2223,3 +2223,197 @@ type internal Foo2 private () =
         else
             failwith ""
 """
+
+[<Test>]
+let ``multiline else if expression with nested if/then/else in body`` () =
+    formatSourceString
+        false
+        """
+if result.LaunchSuccess && result.ExitCode = 0 then
+    Ok r
+else if result.ExitCode = 1 then
+    let stdout, stderr =
+        output
+        |> List.map
+            (function
+            | StdErr e -> Error e
+            | StdOut l -> Ok l)
+        |> Result.partition
+
+    if not stderr.IsEmpty then
+        failwithf "Got stderr bad bad bad"
+
+    match stdout with
+    | [] -> failwithf "Got no stdout :("
+    | xs when
+        xs
+        |> List.exists (fun i -> i.Contains "magic string goes here!")
+        ->
+        Error(Ok r)
+    | _ -> Error(Error r)
+else
+    failwith ""
+"""
+        config
+    |> prepend newline
+    |> should
+        equal
+        """
+if result.LaunchSuccess && result.ExitCode = 0 then
+    Ok r
+else if result.ExitCode = 1 then
+    let stdout, stderr =
+        output
+        |> List.map
+            (function
+            | StdErr e -> Error e
+            | StdOut l -> Ok l)
+        |> Result.partition
+
+    if not stderr.IsEmpty then
+        failwithf "Got stderr bad bad bad"
+
+    match stdout with
+    | [] -> failwithf "Got no stdout :("
+    | xs when
+        xs
+        |> List.exists (fun i -> i.Contains "magic string goes here!")
+        ->
+        Error(Ok r)
+    | _ -> Error(Error r)
+else
+    failwith ""
+"""
+
+[<Test>]
+let ``multiline elif expression with nested if/then/else in body`` () =
+    formatSourceString
+        false
+        """
+if result.LaunchSuccess && result.ExitCode = 0 then
+    Ok r
+elif result.ExitCode = 1 then
+    let stdout, stderr =
+        output
+        |> List.map
+            (function
+            | StdErr e -> Error e
+            | StdOut l -> Ok l)
+        |> Result.partition
+
+    if not stderr.IsEmpty then
+        failwithf "Got stderr bad bad bad"
+
+    match stdout with
+    | [] -> failwithf "Got no stdout :("
+    | xs when
+        xs
+        |> List.exists (fun i -> i.Contains "magic string goes here!")
+        ->
+        Error(Ok r)
+    | _ -> Error(Error r)
+else
+    failwith ""
+"""
+        config
+    |> prepend newline
+    |> should
+        equal
+        """
+if result.LaunchSuccess && result.ExitCode = 0 then
+    Ok r
+elif result.ExitCode = 1 then
+    let stdout, stderr =
+        output
+        |> List.map
+            (function
+            | StdErr e -> Error e
+            | StdOut l -> Ok l)
+        |> Result.partition
+
+    if not stderr.IsEmpty then
+        failwithf "Got stderr bad bad bad"
+
+    match stdout with
+    | [] -> failwithf "Got no stdout :("
+    | xs when
+        xs
+        |> List.exists (fun i -> i.Contains "magic string goes here!")
+        ->
+        Error(Ok r)
+    | _ -> Error(Error r)
+else
+    failwith ""
+"""
+
+[<Test>]
+let ``multiple multiline elifs`` () =
+    formatSourceString
+        false
+        """
+        if startWithMember sel then
+            (String.Join(String.Empty, "type T = ", Environment.NewLine, String(' ', startCol), sel), TypeMember)
+        elif String.startsWithOrdinal "and" (sel.TrimStart()) then
+            // Replace "and" by "type" or "let rec"
+            if startLine = endLine then
+                (pattern.Replace(sel, replacement, 1), p)
+            else
+                (String(' ', startCol)
+                 + pattern.Replace(sel, replacement, 1),
+                 p)
+        elif startLine = endLine then
+            (sel, Nothing)
+        else
+            failAndExit ()
+"""
+        config
+    |> prepend newline
+    |> should
+        equal
+        """
+if startWithMember sel then
+    (String.Join(String.Empty, "type T = ", Environment.NewLine, String(' ', startCol), sel), TypeMember)
+elif String.startsWithOrdinal "and" (sel.TrimStart()) then
+    // Replace "and" by "type" or "let rec"
+    if startLine = endLine then
+        (pattern.Replace(sel, replacement, 1), p)
+    else
+        (String(' ', startCol)
+         + pattern.Replace(sel, replacement, 1),
+         p)
+elif startLine = endLine then
+    (sel, Nothing)
+else
+    failAndExit ()
+"""
+
+[<Test>]
+let ``multiline but not that special if expression`` () =
+    formatSourceString
+        false
+        """
+if
+    List.exists
+        (function
+        | CompExpr _ -> true
+        | _ -> false)
+        es
+then
+    shortExpression ctx
+else
+    expressionFitsOnRestOfLine shortExpression longExpression ctx
+"""
+        config
+    |> prepend newline
+    |> should
+        equal
+        """
+if List.exists
+    (function
+    | CompExpr _ -> true
+    | _ -> false)
+    es then
+    shortExpression ctx
+else
+    expressionFitsOnRestOfLine shortExpression longExpression ctx
+"""

src/Fantomas/AstTransformer.fs

@@ -315,6 +315,26 @@ module private Ast =
                     |> finalContinuation
 
                 Continuation.sequence continuations finalContinuation
+            // don't collect nested elif expression as nodes.
+            // the ranges are often incorrect and using the else if or elif token is more reliable.
+            | SourceParser.ElIf ((ifExpr, thenExpr, _, range, _) :: es, elseExpr) ->
+                let elifs =
+                    es
+                    |> List.collect (fun (e1, e2, _, _, _) -> [ visit e1; visit e2 ])
+
+                let continuations : ((TriviaNodeAssigner list -> TriviaNodeAssigner list) -> TriviaNodeAssigner list) list =
+                    [ yield visit ifExpr
+                      yield visit thenExpr
+                      yield! elifs
+                      yield! (Option.toList elseExpr |> List.map visit) ]
+
+                let finalContinuation (nodes: TriviaNodeAssigner list list) : TriviaNodeAssigner list =
+                    mkNode SynExpr_IfThenElse range
+                    :: (List.collect id nodes)
+                    |> finalContinuation
+
+                Continuation.sequence continuations finalContinuation
+
             | SynExpr.IfThenElse (ifExpr, thenExpr, elseExpr, _, _, _, range) ->
                 let continuations : ((TriviaNodeAssigner list -> TriviaNodeAssigner list) -> TriviaNodeAssigner list) list =
                     [ yield visit ifExpr