added a 'latest' systemversion for vs2017

forgot to add the ".0" suffix


added unit tests for systemversion "latest"

modules/vstudio/tests/vc2010/test_globals.lua

@@ -253,3 +253,48 @@
 </PropertyGroup>
 		]]
 	end
+
+--
+-- Check that the "latest" systemversion works.
+-- note: we override the os.getWindowsRegistry method for reliable tests.
+--
+
+	function suite.windowsTargetPlatformVersionLatest_on2017()
+		p.action.set("vs2017")
+		systemversion "latest"
+		prepare()
+		local oldRegistry = os.getWindowsRegistry
+		os.getWindowsRegistry = function (key)
+			return "10.0.11111"
+		end
+		test.capture [[
+<PropertyGroup Label="Globals">
+	<ProjectGuid>{42B5DBC6-AE1F-903D-F75D-41E363076E92}</ProjectGuid>
+	<IgnoreWarnCompileDuplicatedFilename>true</IgnoreWarnCompileDuplicatedFilename>
+	<Keyword>Win32Proj</Keyword>
+	<RootNamespace>MyProject</RootNamespace>
+	<WindowsTargetPlatformVersion>10.0.11111.0</WindowsTargetPlatformVersion>
+</PropertyGroup>
+		]]
+		-- restore the registry function
+		os.getWindowsRegistry = oldRegistry
+	end
+
+--
+-- Check that the "latest" systemversion will not add <WindowsTargetPlatformVersion>
+-- when the action is less than 2017
+--
+
+	function suite.windowsTargetPlatformVersionLatest_on2015()
+		p.action.set("vs2015")
+		systemversion "10.0.10240.0"
+		prepare()
+		test.capture [[
+<PropertyGroup Label="Globals">
+	<ProjectGuid>{42B5DBC6-AE1F-903D-F75D-41E363076E92}</ProjectGuid>
+	<IgnoreWarnCompileDuplicatedFilename>true</IgnoreWarnCompileDuplicatedFilename>
+	<Keyword>Win32Proj</Keyword>
+	<RootNamespace>MyProject</RootNamespace>
+</PropertyGroup>
+		]]
+	end

modules/vstudio/vs2010_vcxproj.lua

@@ -2356,9 +2356,16 @@
 
 
 	function m.targetPlatformVersion(prj)
-		local min = project.systemversion(prj)
-		if min ~= nil and _ACTION >= "vs2015" then
-			m.element("WindowsTargetPlatformVersion", nil, min)
+		if _ACTION >= "vs2015" then
+			local min = project.systemversion(prj)
+			-- handle special "latest" version
+			if min == "latest" then
+				-- vs2015 and lower can't build against SDK 10
+				min = iif(_ACTION >= "vs2017", m.latestSDK10Version(), nil)
+			end
+			if min ~= nil then
+				m.element("WindowsTargetPlatformVersion", nil, min)
+			end
 		end
 	end
 
@@ -2484,6 +2491,15 @@
 		return m.conditionFromConfigText(vstudio.projectConfig(cfg))
 	end
 
+--
+-- Get the latest installed SDK 10 version from the registry.
+--
+
+	function m.latestSDK10Version()
+		local arch = iif(os.is64bit(), "\\WOW6432Node\\", "\\")
+		local version = os.getWindowsRegistry("HKLM:SOFTWARE" .. arch .."Microsoft\\Microsoft SDKs\\Windows\\v10.0\\ProductVersion")
+		return iif(version ~= nil, version .. ".0", nil)
+	end
 
 
 --