From 686d9926e34bd65e9db8bf466fac662a06f260d2 Mon Sep 17 00:00:00 2001
From: Kevin Ransom <codecutter@hotmail.com>
Date: Sat, 17 Nov 2018 01:46:56 -0800
Subject: [PATCH] Add new implementation of IEnumerable<_> for dict

---
 src/FSharp.Profiles.props                     |  1 +
 src/FSharpSource.Profiles.targets             |  1 +
 .../FSharp.Core/fslib-extra-pervasives.fs     | 30 ++++++++++++++++++-
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/src/FSharp.Profiles.props b/src/FSharp.Profiles.props
index 915781c9534..3abfcb49be4 100644
--- a/src/FSharp.Profiles.props
+++ b/src/FSharp.Profiles.props
@@ -10,6 +10,7 @@
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(TargetFramework)' == 'netstandard1.6' or '$(TargetFramework)' == 'netcoreapp1.0'">
+    <DefineConstants>$(DefineConstants);NETSTANDARD</DefineConstants>
     <DefineConstants>$(DefineConstants);NETSTANDARD1_6</DefineConstants>
     <DefineConstants>$(DefineConstants);FX_NO_APP_DOMAINS</DefineConstants>
     <DefineConstants>$(DefineConstants);FX_NO_ARRAY_LONG_LENGTH</DefineConstants>
diff --git a/src/FSharpSource.Profiles.targets b/src/FSharpSource.Profiles.targets
index 9069ebdb955..3dc3cdd5fb3 100644
--- a/src/FSharpSource.Profiles.targets
+++ b/src/FSharpSource.Profiles.targets
@@ -13,6 +13,7 @@
   <!-- These should be distinguished in the future -->
 
   <PropertyGroup Condition="'$(TargetDotnetProfile)'=='coreclr'">
+    <DefineConstants>$(DefineConstants);NETSTANDARD</DefineConstants>
     <DefineConstants>$(DefineConstants);NETSTANDARD1_6</DefineConstants>
     <DefineConstants>$(DefineConstants);FX_NO_APP_DOMAINS</DefineConstants>
     <DefineConstants>$(DefineConstants);FX_NO_ARRAY_LONG_LENGTH</DefineConstants>
diff --git a/src/fsharp/FSharp.Core/fslib-extra-pervasives.fs b/src/fsharp/FSharp.Core/fslib-extra-pervasives.fs
index 63cb2d80718..b4271f4a267 100644
--- a/src/fsharp/FSharp.Core/fslib-extra-pervasives.fs
+++ b/src/fsharp/FSharp.Core/fslib-extra-pervasives.fs
@@ -43,7 +43,9 @@ module ExtraTopLevelOperators =
     [<DebuggerDisplay("Count = {Count}")>]
     [<DebuggerTypeProxy(typedefof<DictDebugView<_,_,_>>)>]
     type DictImpl<'SafeKey,'Key,'T>(t : Dictionary<'SafeKey,'T>, makeSafeKey : 'Key->'SafeKey, getKey : 'SafeKey->'Key) =
-
+#if NETSTANDARD
+        static let emptyEnumerator = (Array.empty<KeyValuePair<'Key, 'T>> :> seq<_>).GetEnumerator()
+#endif
         member x.Count = t.Count
 
         // Give a read-only view of the dictionary
@@ -110,8 +112,34 @@ module ExtraTopLevelOperators =
             member s.GetEnumerator() =
                 // We use an array comprehension here instead of seq {} as otherwise we get incorrect
                 // IEnumerator.Reset() and IEnumerator.Current semantics. 
+                // Coreclr has a bug with SZGenericEnumerators --- implement a correct enumerator.  On desktop use the desktop implementation because it's ngened.
+#if !NETSTANDARD               
                 let kvps = [| for (KeyValue (k,v)) in t -> KeyValuePair (getKey k, v) |] :> seq<_>
                 kvps.GetEnumerator()
+#else
+                let endIndex = t.Count
+                if endIndex = 0 then emptyEnumerator
+                else
+                    let kvps = [| for (KeyValue (k,v)) in t -> KeyValuePair (getKey k, v) |]
+                    let mutable index = -1
+                    let current () =
+                        if index < 0 then raise <| InvalidOperationException(SR.GetString(SR.enumerationNotStarted)) 
+                        if index >= endIndex then  raise <| InvalidOperationException(SR.GetString(SR.enumerationAlreadyFinished)) 
+                        kvps.[index]
+
+                    {new IEnumerator<_> with
+                        member __.Current = current ()
+                      interface System.Collections.IEnumerator with
+                            member __.Current = box(current())
+                            member __.MoveNext() =
+                                if index < endIndex then
+                                    index <- index + 1
+                                    index < endIndex
+                                else false
+                            member __.Reset() = index <- -1
+                      interface System.IDisposable with 
+                            member self.Dispose() = () }
+#endif
 
         interface System.Collections.IEnumerable with
             member s.GetEnumerator() =