Validate formatted code after unit tests. Fixes fsprojects#842.

src/Fantomas.Tests/ControlStructureTests.fs

@@ -216,10 +216,9 @@ let x =
     |> prepend newline
     |> should equal """
 let x =
-    if try
-        true
-       with Failure _ -> false
-                               then
+    if (try
+            true
+        with Failure _ -> false) then
         ()
     else
         ()
@@ -239,11 +238,10 @@ let y =
     |> prepend newline
     |> should equal """
 let y =
-    if try
-        true
-       finally
-           false
-                 then
+    if (try
+            true
+        finally
+            false) then
         ()
     else
         ()

src/Fantomas.Tests/TestHelpers.fs

@@ -18,15 +18,54 @@ let newline = "\n"
 
 let sharedChecker = lazy(FSharpChecker.Create())
 
+let private safeToIgnoreWarnings =
+    [ "This construct is deprecated: it is only for use in the F# library"
+      "Identifiers containing '@' are reserved for use in F# code generation" ]
+
+let private isValidAndHasNoWarnings fileName source parsingOptions =
+    let allDefineOptions =
+        TokenParser.getOptimizedDefinesSets source
+        @ (TokenParser.getDefines source |> List.map List.singleton)
+        @ [[]]
+        |> List.distinct
+
+    allDefineOptions
+    |> List.map (fun conditionalCompilationDefines ->
+        async {
+            let parsingOptionsWithDefines = { parsingOptions with ConditionalCompilationDefines = conditionalCompilationDefines } // IsInteractive = false
+            // Run the first phase (untyped parsing) of the compiler
+            let sourceText = FSharp.Compiler.Text.SourceText.ofString source
+            let! untypedRes = sharedChecker.Value.ParseFile(fileName, sourceText, parsingOptionsWithDefines)
+
+            let errors =
+                untypedRes.Errors
+                |> Array.filter (fun e -> not (List.contains e.Message safeToIgnoreWarnings))
+            // FSharpErrorInfo contains both Errors and Warnings
+            // https://fsharp.github.io/FSharp.Compiler.Service/reference/fsharp-compiler-sourcecodeservices-fsharperrorinfo.html
+            return Array.isEmpty errors
+        }
+    )
+    |> Async.Parallel
+    |> Async.map (fun results -> Seq.fold (&&) true results)
+
 let formatSourceString isFsiFile (s : string) config = 
     // On Linux/Mac this will exercise different line endings
     let s = s.Replace("\r\n", Environment.NewLine)
     let fileName = if isFsiFile then "/src.fsi" else "/src.fsx"
+    let parsingOptions = FakeHelpers.createParsingOptionsFromFile fileName
+
+    async {
+        let! formatted =
+            CodeFormatter.FormatDocumentAsync(fileName, SourceOrigin.SourceString s, config, parsingOptions, sharedChecker.Value)
+
+        let! isValid = isValidAndHasNoWarnings fileName formatted parsingOptions
+        if not isValid then
+            failwithf "The formatted result is not valid F# code or contains warnings\n%s" formatted
+
+        return formatted.Replace("\r\n", "\n")
+    }
 
-    CodeFormatter.FormatDocumentAsync(fileName, SourceOrigin.SourceString s, config,
-                                      FakeHelpers.createParsingOptionsFromFile fileName, sharedChecker.Value)
     |> Async.RunSynchronously
-    |> fun s -> s.Replace("\r\n", "\n")
 
 let formatSourceStringWithDefines defines (s : string) config =
     // On Linux/Mac this will exercise different line endings

src/Fantomas/CodePrinter.fs

@@ -1965,12 +1965,12 @@ and genExpr astContext synExpr =
                     //           x
                     // bool expr x should be indented
                     +> ifElse hasCommentAfterIfKeyword (indent +> sepNln) sepNone
-                    +> genExpr astContext e1
-                    +> ifElse hasCommentAfterBoolExpr sepNln sepSpace
                     +> (match e1 with
                         | SynExpr.TryWith _
-                        | SynExpr.TryFinally _ -> atCurrentColumn (sepNln +> genThen synExpr.Range)
-                        | _ -> genThen synExpr.Range)
+                        | SynExpr.TryFinally _ -> sepOpenT +> genExpr astContext e1 +> sepCloseT
+                        | _ -> genExpr astContext e1)
+                    +> ifElse hasCommentAfterBoolExpr sepNln sepSpace
+                    +> genThen synExpr.Range
                     // f.ex if x then // meh
                     //          0
                     // 0 should be indented

src/Fantomas/Utils.fs

@@ -130,4 +130,8 @@ module Map =
         | None -> defaultValue
 
     let tryFindOrEmptyList (key:'t) (map: Map<'t, 'g list>) =
-        tryFindOrDefault [] key map
+        tryFindOrDefault [] key map
+
+module Async =
+    let map f computation =
+        async.Bind(computation, f >> async.Return)