Capture then + expr in new node (#3075)

* Update FCS to 050271d631956a4e0d0484a583d38236b727a46d, introduce new node to capture then + expr.

* Add changelog entry.

Author: nojaf

CHANGELOG.md

@@ -1,5 +1,13 @@
 # Changelog
 
+## 6.3.2 - 2024-04-12
+
+### Changed
+* Update FCS to 'Add SynExprSequentialTrivia', commit 050271d631956a4e0d0484a583d38236b727a46d [#3075](https://github.com/fsprojects/fantomas/pull/3075)
+
+### Fixed
+* Fantomas corrupts an explicit constructor with then clause. [#3074](https://github.com/fsprojects/fantomas/issues/3074)
+
 ## 6.3.1 - 2024-03-30
 
 ### Fixed

Directory.Build.props

@@ -46,7 +46,7 @@ Some common use cases include:
 
     <!-- Versions -->
     <PropertyGroup>
-        <FCSCommitHash>1da032a64321c77782e8d125afd3bf29863c3d9c</FCSCommitHash>
+        <FCSCommitHash>050271d631956a4e0d0484a583d38236b727a46d</FCSCommitHash>
     </PropertyGroup>
 
     <PropertyGroup>

src/Fantomas.Core.Tests/ASTTransformerTests.fs

@@ -27,7 +27,8 @@ let ``avoid stack-overflow in long array/list, 2485`` () =
                         true,
                         mkStringExpr (),
                         childExpr,
-                        Range.Zero
+                        Range.Zero,
+                        SynExprSequentialTrivia.Zero
                     ))
 
         SynExpr.ArrayOrListComputed(true, mkArray 0 (mkStringExpr ()), Range.Zero)

src/Fantomas.Core.Tests/ConstructorTests.fs

@@ -165,3 +165,40 @@ type StateMachine
         =
         StateMachine()
 """
+
+[<Test>]
+let ``explicit constructor with then keyword, 3074`` () =
+    formatSourceString
+        """
+type CreateBuildingViewModel =
+    new (items) as vm
+        =
+        let p = ""
+        {
+            inherit ResizeArray(seq {
+                yield p
+                yield! items
+            })
+        }
+        then
+            vm.program <- p
+"""
+        config
+    |> prepend newline
+    |> should
+        equal
+        """
+type CreateBuildingViewModel =
+    new(items) as vm =
+        let p = ""
+
+        { inherit
+            ResizeArray(
+                seq {
+                    yield p
+                    yield! items
+                }
+            ) }
+
+        then vm.program <- p
+"""

src/Fantomas.Core/ASTTransformer.fs

@@ -213,14 +213,18 @@ let mkAttributes (creationAide: CreationAide) (al: SynAttributeList list) : Mult
         let range = attributeLists |> List.map (fun al -> al.Range) |> combineRanges
         Some(MultipleAttributeListNode(attributeLists, range))
 
+/// Only used to get items of SynExpr.ArrayOrListComputed
+/// We can safely assume the SequentialTrivia.SeparatorRange is not going to be `then`.
 let (|Sequentials|_|) e =
     let rec visit (e: SynExpr) (finalContinuation: SynExpr list -> SynExpr list) : SynExpr list =
         match e with
-        | SynExpr.Sequential(_, _, e1, e2, _) -> visit e2 (fun xs -> e1 :: xs |> finalContinuation)
+        | SynExpr.Sequential(expr1 = e1; expr2 = e2) ->
+
+            visit e2 (fun xs -> e1 :: xs |> finalContinuation)
         | e -> finalContinuation [ e ]
 
     match e with
-    | SynExpr.Sequential(_, _, e1, e2, _) ->
+    | SynExpr.Sequential(expr1 = e1; expr2 = e2) ->
         let xs = visit e2 id
         Some(e1 :: xs)
     | _ -> None
@@ -332,12 +336,25 @@ let rec collectComputationExpressionStatements
 
         collectComputationExpressionStatements creationAide body (fun bodyStatements ->
             [ letOrUseBang; yield! andBangs; yield! bodyStatements ] |> finalContinuation)
-    | SynExpr.Sequential(_, _, e1, e2, _) ->
+    | SynExpr.Sequential(expr1 = e1; expr2 = e2; trivia = trivia) ->
         let continuations
             : ((ComputationExpressionStatement list -> ComputationExpressionStatement list)
                   -> ComputationExpressionStatement list) list =
-            [ collectComputationExpressionStatements creationAide e1
-              collectComputationExpressionStatements creationAide e2 ]
+            let c2 =
+                match trivia.SeparatorRange with
+                // detect then keyword in explicit constructor
+                | Some mThen when mThen.StartColumn + 4 = mThen.EndColumn ->
+                    let thenNode = stn "then" mThen
+                    let expr = mkExpr creationAide e2
+                    let m = unionRanges mThen e2.Range
+                    let node = ExprExplicitConstructorThenExpr(thenNode, expr, m)
+
+                    fun finalContinuation ->
+                        finalContinuation
+                            [ ComputationExpressionStatement.OtherStatement(Expr.ExplicitConstructorThenExpr node) ]
+                | _ -> collectComputationExpressionStatements creationAide e2
+
+            [ collectComputationExpressionStatements creationAide e1; c2 ]
 
         let finalContinuation (nodes: ComputationExpressionStatement list list) : ComputationExpressionStatement list =
             List.collect id nodes |> finalContinuation
@@ -2732,10 +2749,7 @@ let mkMemberDefn (creationAide: CreationAide) (md: SynMemberDefn) =
                 accessibility = ao)
             expr = expr
             trivia = { EqualsRange = Some mEq })) when (newIdent.idText = "new") ->
-        let exprNode, thenExprNode =
-            match expr with
-            | SynExpr.Sequential(_, false, e1, e2, _) -> mkExpr creationAide e1, Some(mkExpr creationAide e2)
-            | e -> mkExpr creationAide e, None
+        let exprNode = mkExpr creationAide expr
 
         MemberDefnExplicitCtorNode(
             mkXmlDoc px,
@@ -2746,7 +2760,6 @@ let mkMemberDefn (creationAide: CreationAide) (md: SynMemberDefn) =
             Option.map mkIdent ido,
             stn "=" mEq,
             exprNode,
-            thenExprNode,
             memberDefinitionRange
         )
         |> MemberDefn.ExplicitCtor

src/Fantomas.Core/CodePrinter.fs

@@ -1572,6 +1572,10 @@ let genExpr (e: Expr) =
             +> genSingleTextNode node.End
 
         expressionFitsOnRestOfLine short long |> genNode node
+    | Expr.ExplicitConstructorThenExpr node ->
+        genSingleTextNode node.Then
+        +> sepSpaceOrIndentAndNlnIfExpressionExceedsPageWidth (genExpr node.Expr)
+        |> genNode node
 
 let genQuoteExpr (node: ExprQuoteNode) =
     genSingleTextNode node.OpenToken
@@ -3786,15 +3790,7 @@ let genMemberDefn (md: MemberDefn) =
                  +> autoIndentAndNlnIfExpressionExceedsPageWidth (genLongParenPatParameter node.Pattern)
                  +> optSingle (fun alias -> sepSpace +> !- "as" +> sepSpace +> genSingleTextNode alias) node.Alias)
                 (fun isMultiline ctx ->
-                    let genExpr =
-                        genExpr node.Expr
-                        +> optSingle
-                            (fun thenExpr ->
-                                sepNln
-                                +> !- "then"
-                                +> sepSpaceOrIndentAndNlnIfExpressionExceedsPageWidth (genExpr thenExpr))
-                            node.ThenExpr
-
+                    let genExpr = genExpr node.Expr
                     let short = genSingleTextNode node.Equals +> sepSpace +> genExpr
 
                     let long ctx =
@@ -3810,7 +3806,7 @@ let genMemberDefn (md: MemberDefn) =
 
         genXml node.XmlDoc
         +> genAttributes node.Attributes
-        +> ifElse node.ThenExpr.IsSome long (expressionFitsOnRestOfLine short long)
+        +> expressionFitsOnRestOfLine short long
         |> genNode (MemberDefn.Node md)
     | MemberDefn.LetBinding node -> genBindings true node.Bindings |> genNode (MemberDefn.Node md)
     | MemberDefn.Interface node ->

src/Fantomas.Core/SyntaxOak.fs

@@ -1649,6 +1649,14 @@ type ExprBeginEndNode(beginNode: SingleTextNode, expr: Expr, endNode: SingleText
     member val Expr = expr
     member val End = endNode
 
+/// then <expr>
+/// Only valid in secondary constructors, original coming from SynExpr.Sequential(trivia = { SeparatorRange = Some mThen })
+type ExprExplicitConstructorThenExpr(thenNode: SingleTextNode, expr: Expr, range) =
+    inherit NodeBase(range)
+    override val Children: Node array = [| yield thenNode; yield Expr.Node expr |]
+    member val Then = thenNode
+    member val Expr = expr
+
 [<RequireQualifiedAccess; NoEquality; NoComparison>]
 type Expr =
     | Lazy of ExprLazyNode
@@ -1715,6 +1723,7 @@ type Expr =
     | Chain of ExprChain
     | DotLambda of ExprDotLambda
     | BeginEnd of ExprBeginEndNode
+    | ExplicitConstructorThenExpr of ExprExplicitConstructorThenExpr
 
     static member Node(x: Expr) : Node =
         match x with
@@ -1782,6 +1791,7 @@ type Expr =
         | Chain n -> n
         | DotLambda n -> n
         | BeginEnd n -> n
+        | ExplicitConstructorThenExpr n -> n
 
     member e.HasParentheses: bool =
         match e with
@@ -2399,7 +2409,6 @@ type MemberDefnExplicitCtorNode
         alias: SingleTextNode option,
         equals: SingleTextNode,
         expr: Expr,
-        thenExpr: Expr option,
         range
     ) =
     inherit NodeBase(range)
@@ -2412,8 +2421,7 @@ type MemberDefnExplicitCtorNode
            yield Pattern.Node pat
            yield! noa alias
            yield equals
-           yield Expr.Node expr
-           yield! noa (Option.map Expr.Node thenExpr) |]
+           yield Expr.Node expr |]
 
     member val XmlDoc = xmlDoc
     member val Attributes = attributes
@@ -2423,7 +2431,6 @@ type MemberDefnExplicitCtorNode
     member val Alias = alias
     member val Equals = equals
     member val Expr = expr
-    member val ThenExpr = thenExpr
 
 type MemberDefnInterfaceNode
     (interfaceNode: SingleTextNode, t: Type, withNode: SingleTextNode option, members: MemberDefn list, range) =