Long function signatures have indent if parameters are on separate li…

…ne. (#897)

* Long function signatures have indent if parameters are on separate line.

* Count the identifiers in the function definition to bypass futureNln check.

src/Fantomas.Tests/FunctionDefinitionTests.fs

@@ -542,4 +542,33 @@ let private addTaskToScheduler
             .Build()
 
     1
+"""
+
+[<Test>]
+let ``long function signature should align with equal sign, 883`` () =
+    formatSourceString false """let readModel (updateState : 'State -> EventEnvelope<'Event> list -> 'State) (initState : 'State) : ReadModel<'Event, 'State> =
+    ()
+"""  { config with IndentSpaceNum = 2; SpaceBeforeColon = true }
+    |> prepend newline
+    |> should equal """
+let readModel
+  (updateState : 'State -> EventEnvelope<'Event> list -> 'State)
+  (initState : 'State)
+  : ReadModel<'Event, 'State>
+  =
+  ()
+"""
+
+[<Test>]
+let ``long function signature should align with equal sign, no return type`` () =
+    formatSourceString false """let readModel (updateState : 'State -> EventEnvelope<'Event> list -> 'State) (initState : 'State) =
+    ()
+"""  { config with IndentSpaceNum = 2; SpaceBeforeColon = true; PageWidth = 80 }
+    |> prepend newline
+    |> should equal """
+let readModel
+  (updateState : 'State -> EventEnvelope<'Event> list -> 'State)
+  (initState : 'State)
+  =
+  ()
 """

src/Fantomas/CodePrinter.fs

@@ -544,6 +544,7 @@ and genLetBinding astContext pref b =
             ifElse astContext.IsFirstChild
                 (genAttributes astContext ats -- pref)
                 (!- pref +> genOnelinerAttributes astContext ats)
+
         let afterLetKeyword =
             opt sepSpace ao genAccess
             +> ifElse isMutable (!- "mutable ") sepNone
@@ -2748,10 +2749,10 @@ and genPatWithReturnType ao s ps tpso (t:SynType option) (astContext: ASTContext
 
     let hasBracket = ps |> Seq.map fst |> Seq.exists Option.isSome
     let genName = aoc -- s +> tpsoc +> sepSpace
+
     let genParametersInitial =
         colAutoNlnSkip0 (ifElse hasBracket sepSemi sepSpace) ps (genPatWithIdent astContext)
 
-
     let genReturnType, newlineBeforeReturnType =
         match t with
         | Some t -> genType astContext false t, sepNln
@@ -2760,17 +2761,32 @@ and genPatWithReturnType ao s ps tpso (t:SynType option) (astContext: ASTContext
     let genParametersWithNewlines =
         (sepNln +> col sepNln ps (genPatWithIdent astContext) +> newlineBeforeReturnType)
 
-    let isLongFunctionSignature ctx=
-        futureNlnCheck (genName +> genParametersInitial +> genReturnType) ctx
+    let isLongFunctionSignature (ctx: Context) =
+        let space = 1
+        let colon = if ctx.Config.SpaceBeforeColon then 3 else 2
+        let lengthByAST =
+            getSynAccessLength ao
+            + lengthWhenSome (fun _ -> space) ao
+            + s.Length
+            + space
+            + List.sumBy (snd >> getSynPatLength >> (+) space) ps
+            + lengthWhenSome (fun _ -> colon) t
+            + lengthWhenSome getSynTypeLength t
+
+        (ctx.Column + lengthByAST > ctx.Config.PageWidth)
+        || futureNlnCheck (genName +> genParametersInitial +> genReturnType) ctx
 
-    atCurrentColumn (fun ctx ->
+    fun ctx ->
         let isLong = isLongFunctionSignature ctx
+
         let expr =
             genName
             +> ifElse hasBracket sepOpenT sepNone
-            +> ifElse isLong genParametersWithNewlines genParametersInitial
+            +> ifElse isLong (indent +> genParametersWithNewlines  +> unindent) genParametersInitial
             +> ifElse hasBracket sepCloseT sepNone
-        expr ctx)
+
+        expr ctx
+
 and genConst (c:SynConst) (r:range) =
     match c with
     | SynConst.Unit ->

src/Fantomas/SourceTransformer.fs

@@ -1,5 +1,6 @@
 module internal Fantomas.SourceTransformer
 
+open FSharp.Compiler.SyntaxTree
 open Fantomas.Context
 open Fantomas.SourceParser
 
@@ -128,4 +129,47 @@ let addParenForTupleWhen f synExpr ctx =
         | FSharp.Compiler.SyntaxTree.SynExpr.Lambda _ -> true
         |_ -> false // "if .. then .. else" have precedence over ","
     let expr = f synExpr
-    ifElse (condition synExpr) (sepOpenT +> expr +> sepCloseT) expr ctx
+    ifElse (condition synExpr) (sepOpenT +> expr +> sepCloseT) expr ctx
+
+let lengthWhenSome f o =
+    match o with
+    | Some x -> f x
+    | None -> 0
+
+let getSynAccessLength ao =
+    lengthWhenSome (function | SynAccess.Internal -> 8 | SynAccess.Private -> 7 | SynAccess.Public -> 6) ao
+
+let rec getSynTypeLength (synType: SynType) =
+    match synType with
+    | TFun (t1, t2) ->
+        getSynTypeLength t1 + (* -> *) 2 + getSynTypeLength t2
+    | TVar(Typar(id, _)) ->
+        id.Length
+    | TApp(t, ts, _) ->
+        getSynTypeLength t + List.sumBy getSynTypeLength ts
+    | TLongIdent s ->
+        s.Length
+    | _ ->
+        0
+
+let rec getSynPatLength (synPat: SynPat) =
+    match synPat with
+    | PatLongIdent(ao, s, ps, _) ->
+        let accessLength = getSynAccessLength ao
+        let patternLength =
+            ps
+            |> List.sumBy (fun (ident, pat) ->
+                let identLength = lengthWhenSome String.length ident
+                identLength + getSynPatLength pat)
+        accessLength + patternLength + s.Length
+
+    | PatParen pat -> 2 + getSynPatLength pat
+
+    | PatNamed(ao,p,s) ->
+        let accessLength = getSynAccessLength ao
+        accessLength + getSynPatLength p + s.Length
+
+    | PatTyped (p,t) ->
+        getSynPatLength p + getSynTypeLength t
+
+    | _ -> 0