[WIP] Add basic support for "Consistent" Pattern Matching

fake-sample/script.fsx

@@ -11,33 +11,29 @@ open Fake.DotNet
 
 let sourceFiles = !! "*.fs"
 
-Target.create
-    "CheckFormat"
-    (fun _ ->
-        let result =
-            sourceFiles
-            |> Seq.map (sprintf "\"%s\"")
-            |> String.concat " "
-            |> sprintf "%s --check"
-            |> DotNet.exec id "fantomas"
+Target.create "CheckFormat" (fun _ ->
+    let result =
+        sourceFiles
+        |> Seq.map (sprintf "\"%s\"")
+        |> String.concat " "
+        |> sprintf "%s --check"
+        |> DotNet.exec id "fantomas"
 
-        if result.ExitCode = 0 then
-            Trace.log "No files need formatting"
-        elif result.ExitCode = 99 then
-            failwith "Some files need formatting, check output for more info"
-        else
-            Trace.logf "Errors while formatting: %A" result.Errors)
+    if result.ExitCode = 0 then
+        Trace.log "No files need formatting"
+    elif result.ExitCode = 99 then
+        failwith "Some files need formatting, check output for more info"
+    else
+        Trace.logf "Errors while formatting: %A" result.Errors)
 
-Target.create
-    "Format"
-    (fun _ ->
-        let result =
-            sourceFiles
-            |> Seq.map (sprintf "\"%s\"")
-            |> String.concat " "
-            |> DotNet.exec id "fantomas"
+Target.create "Format" (fun _ ->
+    let result =
+        sourceFiles
+        |> Seq.map (sprintf "\"%s\"")
+        |> String.concat " "
+        |> DotNet.exec id "fantomas"
 
-        if not result.OK then
-            printfn "Errors while formatting all files: %A" result.Messages)
+    if not result.OK then
+        printfn "Errors while formatting all files: %A" result.Messages)
 
 Target.runOrList ()

src/Fantomas.Core/FormatConfig.fs

@@ -26,6 +26,21 @@ type MultilineFormatterType =
         | "number_of_items" -> Some MultilineFormatterType.NumberOfItems
         | _ -> None
 
+type PatternMatchStyle =
+    | LineSpecific
+    | Consistent
+
+    static member ToConfigString(cfg: PatternMatchStyle) =
+        match cfg with
+        | LineSpecific -> "line_specific"
+        | Consistent -> "consistent"
+
+    static member OfConfigString(cfgString: string) =
+        match cfgString with
+        | "line_specific" -> Some LineSpecific
+        | "consistent" -> Some Consistent
+        | _ -> None
+
 type MultilineBracketStyle =
     | Cramped
     | Aligned
@@ -227,7 +242,12 @@ type FormatConfig =
 
       [<Category("Convention")>]
       [<DisplayName("Applies the Stroustrup style to the final (two) array or list argument(s) in a function application")>]
-      ExperimentalElmish: bool }
+      ExperimentalElmish: bool
+
+      [<Category("Indentation")>]
+      [<DisplayName("How to format pattern match expression")>]
+      [<Description("Possible options include each line judged separately (default), or consistent (either all single line or all multiline)")>]
+      ExperimentalPatternMatchStyle: PatternMatchStyle }
 
     member x.IsStroustrupStyle = x.MultilineBracketStyle = Stroustrup
 
@@ -268,4 +288,5 @@ type FormatConfig =
           MultilineBracketStyle = Cramped
           KeepMaxNumberOfBlankLines = 100
           NewlineBeforeMultilineComputationExpression = true
-          ExperimentalElmish = false }
+          ExperimentalElmish = false
+          ExperimentalPatternMatchStyle = LineSpecific }

src/Fantomas.Tests/EditorConfigurationTests.fs

@@ -543,3 +543,22 @@ fsharp_experimental_elmish = true
     let config = EditorConfig.readConfiguration fsharpFile.FSharpFile
 
     Assert.That(config.ExperimentalElmish, Is.True)
+
+[<Test>]
+let fsharp_consistent_pattern_matching_style () =
+    let rootDir = tempName ()
+
+    let editorConfig =
+        """
+[*.fs]
+fsharp_experimental_pattern_match_style = consistent
+"""
+
+    use configFixture =
+        new ConfigurationFile(defaultConfig, rootDir, content = editorConfig)
+
+    use fsharpFile = new FSharpFile(rootDir)
+
+    let config = EditorConfig.readConfiguration fsharpFile.FSharpFile
+
+    Assert.That(config.ExperimentalPatternMatchStyle, Is.EqualTo Consistent)

src/Fantomas/EditorConfig.fs

@@ -64,6 +64,8 @@ let (|Number|_|) (d: string) =
     | true, d -> Some(box d)
     | _ -> None
 
+let (|PatternMatchStyle|_|) pms = PatternMatchStyle.OfConfigString pms
+
 let (|MultilineFormatterType|_|) mft =
     MultilineFormatterType.OfConfigString mft
 
@@ -86,6 +88,7 @@ let parseOptionsFromEditorConfig
         | true, Number n -> n
         | true, Boolean b -> b
         | true, MultilineFormatterType mft -> box mft
+        | true, PatternMatchStyle pms -> box pms
         | true, EndOfLineStyle eol -> box eol
         | true, BracketStyle bs -> box bs
         | _ -> defaultValue)
@@ -105,6 +108,9 @@ let configToEditorConfig (config: FormatConfig) : string =
         | :? MultilineFormatterType as mft ->
             $"%s{toEditorConfigName recordField.PropertyName}=%s{MultilineFormatterType.ToConfigString mft}"
             |> Some
+        | :? PatternMatchStyle as pms ->
+            $"%s{toEditorConfigName recordField.PropertyName}=%s{PatternMatchStyle.ToConfigString pms}"
+            |> Some
         | :? EndOfLineStyle as eols ->
             $"%s{toEditorConfigName recordField.PropertyName}=%s{EndOfLineStyle.ToConfigString eols}"
             |> Some