handle AllowNullLiteral(false) correctly, fixes #383

closes #390

commit a9c9d60
Author: Max Malook <community@malook.de>
Date:   Wed Apr 29 04:43:26 2015 +0200

    handle AllowNullLiteral(false) correctly, fixes #383

commit 574b9b3
Author: Max Malook <community@malook.de>
Date:   Wed Apr 29 01:34:54 2015 +0200

    add tests to verify correct usage of new argument on AllowNullLiteralAttribute

src/fsharp/tc.fs

@@ -13982,7 +13982,7 @@ module EstablishTypeDefinitionCores = begin
             let hasCLIMutable = HasFSharpAttribute cenv.g cenv.g.attrib_CLIMutableAttribute attrs
 
             let hasStructLayoutAttr = HasFSharpAttribute cenv.g cenv.g.attrib_StructLayoutAttribute attrs
-            let hasAllowNullLiteralAttr = HasFSharpAttribute cenv.g cenv.g.attrib_AllowNullLiteralAttribute attrs
+            let hasAllowNullLiteralAttr = TryFindFSharpBoolAttribute cenv.g cenv.g.attrib_AllowNullLiteralAttribute attrs = Some(true)
 
             if hasAbstractAttr then 
                 tycon.TypeContents.tcaug_abstract <- true

tests/fsharp/typecheck/sigs/neg16.bsl

@@ -88,3 +88,5 @@ neg16.fs(110,16,110,20): typecheck error FS0879: Volatile fields must be marked
 neg16.fs(113,9,113,11): typecheck error FS0879: Volatile fields must be marked 'mutable' and cannot be thread-static
 
 neg16.fs(116,9,116,13): typecheck error FS0879: Volatile fields must be marked 'mutable' and cannot be thread-static
+
+neg16.fs(130,10,130,11): typecheck error FS0935: Types with the 'AllowNullLiteral' attribute may only inherit from or implement types which also allow the use of the null literal

tests/fsharp/typecheck/sigs/neg16.fs

@@ -122,3 +122,11 @@ module VolatileFieldSanityChecks = begin
 
 end
 
+module AllowNullLiteralWithArgumentTest = begin
+
+    type A() = class end
+
+    [<AllowNullLiteral(true)>] // expect an error here
+    type B() = inherit A()
+
+end

tests/fsharp/typecheck/sigs/pos16.fs

@@ -46,3 +46,10 @@ module UnitOfMeasurePrintfPositiveTests =
     let _ = sprintf "%g" 1.0M<metre>
     let _ = sprintf "%g" 1.0M<m>
     let _ = sprintf "%g" 1.0M<m/s>
+
+module AllowNullLiteralWithArgumentTest = 
+
+    type A() = class end
+
+    [<AllowNullLiteral(false)>]
+    type B() = inherit A()