Merge master to dev15.8 (#5087)

* Update README.md

* Update README.md

* Update README.md

* [RFCs FS-1051, FS-1052, FS-1053] support for span, readonly refs, byref-like structs (#4888)

* initial support for span, readonly refs, byref-like structs

* fix proto build

* make proto work with previous FSharp.Core

* make proto work with previous FSharp.Core

* update baselines

* integrate code cleanup

* integrate code cleanup

* integrate code cleanup

* integrate code cleanup

* fix build

* fix build

* implicit deref of byref returns

* add tests for Memory, ReadOnlySpan and ReadOnlyMemory

* fix tests

* simplify diff

* simplify diff

* remove duplicate error messages

* fix build

* test updates

* fix build

* fix build

* update baselines

* fix uses of NativePtr.toByRef

* switch to inference using byref pointer capabilities

* fix proto build

* update baselines, byref extension methods

* fix test errors

* emit in,out,modreq attributes correctly

* update tests

* fix build

* fix build

* fix tests

* fix tests

* get it right silly boy

* fix test

* minor cleanup

* add more tests

* clarify overloading behaviour + test case

* fix build break

* fix build of tests

* update tests

* add more tests

* byref fixes

* updates for subsumption calls, error message, assign-to-return-byref

* test updates, implicit deref on byref return for normal functions

* update baseline

* improve debug formatting, better error message on implicit deref, improve error messages

* add more tests for recursive functions

* update baselines

* fix baselines

* updates for new test cases

* updates for new test cases

* test updates and byref-to-byreflike

* deal with 'M() <- expr'

* restrict addresses of immutable top-level things

* fix IsByRefLike on struct

* update tests

* fix test

* fix test

* improve check for no-return-of-struct-field-addresses

* fix test case

* Provide fast generic comparer for bool values (#5076)

* provide fast generic comparer for bool values

* formatting

* no completion on name of value and function declaration (#5083)

* LOC CHECKIN | Microsoft/visualfsharp master | 20180604 | Termchange (#5082)

* fix merge

DEVGUIDE.md

@@ -223,7 +223,6 @@ To do this, build the non-buildfromsource version of FSharp.Compiler.Private (sr
 
     .\build net40
     copy /y src\fsharp\FSharp.Compiler.Private\obj\release\net40\FSComp.* src\buildfromsource\FSharp.Compiler.Private\
-
 
 #### Configuring proxy server
 

README.md

@@ -16,12 +16,12 @@ For historical reasons this repository is called "visualfsharp" and currently al
 
 ## Build Status
 
-|            | Ubuntu (Build) | Windows (Debug Build) | Windows (Release Tests 1) | Windows (Release Tests 2) | Windows  (Release Tests 3) |
-|:----------:|:----------------:|:----------------:|:------------------:|:-----------------------:|:---------------------:|
-|**master**  |[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/master/release_ubuntu14.04)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/master/job/release_ubuntu14.04/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/master/debug_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/master/job/debug_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/master/release_ci_part1_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/master/job/release_ci_part1_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/master/release_ci_part2_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/master/job/release_ci_part2_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/master/release_ci_part3_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/master/job/release_ci_part3_windows_nt/)|
-|**dev15.5**  |[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.5/release_ubuntu14.04)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.5/job/release_ubuntu14.04/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.5/debug_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.5/job/debug_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.5/release_ci_part1_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.5/job/release_ci_part1_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.5/release_ci_part2_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.5/job/release_ci_part2_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.5/release_ci_part3_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.5/job/release_ci_part3_windows_nt/)|
-|**dev15.6**  |[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.6/release_ubuntu14.04)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.6/job/release_ubuntu14.04/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.6/debug_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.6/job/debug_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.6/release_ci_part1_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.6/job/release_ci_part1_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.6/release_ci_part2_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.6/job/release_ci_part2_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.6/release_ci_part3_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.6/job/release_ci_part3_windows_nt/)|
-|**dev15.7**  |[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.7/release_ubuntu14.04)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.7/job/release_ubuntu14.04/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.7/debug_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.7/job/debug_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.7/release_ci_part1_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.7/job/release_ci_part1_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.7/release_ci_part2_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.7/job/release_ci_part2_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.7/release_ci_part3_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.7/job/release_ci_part3_windows_nt/)|
+|            | Ubuntu (Build) | Windows (Debug Build) | Windows (Release Tests 1) | Windows (Release Tests 2) | Windows  (Release Tests 3) | Windows  (Release Tests 4) |
+|:----------:|:----------------:|:----------------:|:------------------:|:-----------------------:|:---------------------:|:---------------------:|
+|**master**  |[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/master/release_ubuntu14.04)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/master/job/release_ubuntu14.04/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/master/debug_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/master/job/debug_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/master/release_ci_part1_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/master/job/release_ci_part1_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/master/release_ci_part2_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/master/job/release_ci_part2_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/master/release_ci_part3_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/master/job/release_ci_part3_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/master/release_ci_part4_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/master/job/release_ci_part4_windows_nt/)|
+**dev15.6**  |[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.6/release_ubuntu14.04)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.6/job/release_ubuntu14.04/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.6/debug_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.6/job/debug_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.6/release_ci_part1_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.6/job/release_ci_part1_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.6/release_ci_part2_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.6/job/release_ci_part2_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.6/release_ci_part3_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.6/job/release_ci_part3_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.6/release_ci_part4_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.6/job/release_ci_part4_windows_nt/)|
+**dev15.7**  |[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.7/release_ubuntu14.04)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.7/job/release_ubuntu14.04/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.7/debug_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.7/job/debug_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.7/release_ci_part1_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.7/job/release_ci_part1_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.7/release_ci_part2_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.7/job/release_ci_part2_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.7/release_ci_part3_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.7/job/release_ci_part3_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.7/release_ci_part4_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.7/job/release_ci_part4_windows_nt/)|
+**dev15.8**  |[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.8/release_ubuntu14.04)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.8/job/release_ubuntu14.04/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.8/debug_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.8/job/debug_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.8/release_ci_part1_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.8/job/release_ci_part1_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.8/release_ci_part2_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.8/job/release_ci_part2_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.8/release_ci_part3_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.8/job/release_ci_part3_windows_nt/)|[![Build Status](https://ci2.dot.net/buildStatus/icon?job=Microsoft_visualfsharp/dev15.8/release_ci_part4_windows_nt)](https://ci2.dot.net/job/Microsoft_visualfsharp/job/dev15.8/job/release_ci_part4_windows_nt/)|
 
 ## Help improve the Quality of the Tools by Using the Nightly Releases of Visual F# Tools
 To setup Visual Studio to use the latest nightly releases of the Visual F# Tools:

packages.config

@@ -39,6 +39,11 @@
   <package id="Microsoft.FSharp.TupleSample" version="1.0.0-alpha-161121"/>
   <package id="Microsoft.VSSDK.BuildTools" version="15.1.192" />
 
+  <!-- Testing Span -->
+  <package id="System.Memory" version="4.5.0-rc1" />
+  <package id="System.Runtime.CompilerServices.Unsafe" version="4.5.0-rc1" />
+  <package id="NETStandard.Library.NETFramework" version="2.0.0-preview2-25405-01" />
+
   <!-- Annoyingly the build of FSharp.Compiler.Server.Shared references a Visual Studio-specific attribute -->
   <!-- That DLL is logically part of the F# Compiler and F# Interactive but is shipped as part of the Visual F# IDE Tools -->
   <package id="Microsoft.VisualStudio.Shell.Immutable.10.0" version="10.0.30319" targetFramework="net46" />