Formatting Elmish inspired code (#922)

* Formatting Elmish code 🙈🙉🙊

* Elmish code take two

* Extracted the documentation from the unit tests. Clean up the code.
Support for arrays.

* Bumped to alpha 10

RELEASE_NOTES.md

@@ -1,4 +1,4 @@
-### 4.0.0-alpha-009 - 06/2020
+### 4.0.0-alpha-010 - 06/2020
 * WIP for [#705](https://github.com/fsprojects/fantomas/issues/705)
 * FCS 36
 

docs/Documentation.md

@@ -272,6 +272,7 @@ A default configuration file would look like
   "MaxFunctionBindingWidth":40,
   "MultilineBlockBracketsOnSameColumn":false,
   "NewlineBetweenTypeDefinitionAndMembers":false,
+  "MaxElmishWidth": 40,
   "StrictMode":false 
 }
 ```

docs/Formatting-Elmish-code.md

@@ -0,0 +1,74 @@
+# Formatting Elmish style guide
+
+This guide explains the main reasoning of how Fantomas formats "Elmish" inspired code.
+
+## Scope
+
+To keep things focused, the scope is currently limited to the Fable.React bindings:
+- https://github.com/fable-compiler/fable-react/blob/master/src/Fable.React.Standard.fs
+- https://github.com/fable-compiler/fable-react/blob/master/src/Fable.React.Props.fs
+
+Variants like Feliz and Fabulous might be covered in the future as well.
+
+## Key concepts
+
+There are two active patterns for [SynExpr](https://fsharp.github.io/FSharp.Compiler.Service/reference/fsharp-compiler-syntaxtree-synexpr.html) that capture the shapes in the Elmish DSL.
+
+See [SourceParser.fs](../src/Fantomas/SourceParser.fs)
+
+```fsharp
+let (|ElmishReactWithoutChildren|_|) e = ...
+
+let (|ElmishReactWithChildren|_|) e =
+````
+
+`ElmishReactWithoutChildren` captures unary tags like `<input />` or `<br />`.
+Translated in the F# DSL they match a function that takes a single list as arguments.
+
+```fsharp
+let i = input [ Type "hidden" ]
+```
+
+The props or attributes parameter is formatted like a normal list or array would be in default Fantomas.
+
+```fsharp
+// short
+myTag [ a1; a2 ]
+
+// long
+myTag [ a1
+        a2
+        a3 ]
+```
+
+The tag and attributes will always align.
+
+`ElmishReactWithChildren` captures the non-unary tags like `<p>...</p>` or `<div>...</div>`.
+Translated in the F# DSL they match a function that takes two lists as arguments.
+The first argument matches the same rules as the unary tag.
+
+While the second argument starts its opening bracket right after the closing of the attributes.
+The closing bracket of the children matches the start column of the tag.
+Unless the entire expression is short.
+
+Children have one extra indent starting from the parent tag column.
+
+
+```fsharp
+// short
+let myParagraph = p [] [ str "short" ]
+
+// long
+let myContainer =
+    div [ ClassName "container" ] [
+        h1 [] [ str "my title" ]
+    ]
+```
+
+When the children argument is empty, it is place right after the attributes.
+
+```fsharp
+let x =
+    div [ OnClick (fun _ -> prinftn "meh"
+          ClassName "container" ] []
+```

src/Fantomas.CoreGlobalTool.Tests/Fantomas.CoreGlobalTool.Tests.fsproj

@@ -4,7 +4,7 @@
     <TargetFramework>netcoreapp3.1</TargetFramework>
     <IsPackable>false</IsPackable>
     <GenerateProgramFile>false</GenerateProgramFile>
-    <Version>4.0.0-alpha-009</Version>
+    <Version>4.0.0-alpha-010</Version>
     <NoWarn>FS0988</NoWarn>
   </PropertyGroup>
   <ItemGroup>

src/Fantomas.CoreGlobalTool/Fantomas.CoreGlobalTool.fsproj

@@ -4,7 +4,7 @@
     <TargetFramework>netcoreapp3.1</TargetFramework>
     <ToolCommandName>fantomas</ToolCommandName>
     <PackAsTool>True</PackAsTool>
-    <Version>4.0.0-alpha-009</Version>
+    <Version>4.0.0-alpha-010</Version>
     <AssemblyName>fantomas-tool</AssemblyName>
   </PropertyGroup>
   <ItemGroup>