Introduce intrinsic to 'intersect' target frameworks

src/Build.UnitTests/Evaluation/Expander_Tests.cs

@@ -4295,6 +4295,19 @@ private void TestPropertyFunction(string expression, string propertyName, string
             result.ShouldBe(expected);
         }
 
+        [Theory]
+        [InlineData("net6.0", "netstandard2.0", "")]
+        [InlineData("net6.0-windows", "netstandard2.0", "")]
+        [InlineData("net6.0-windows", "net6.0", "net6.0-windows")]
+        [InlineData("netstandard2.0;net6.0", "net6.0", "net6.0")]
+        [InlineData("netstandard2.0;net6.0-windows", "net6.0", "net6.0-windows")]
+        [InlineData("netstandard2.0;net6.0-windows", "net6.0;netstandard2.0;net472", "netstandard2.0%3bnet6.0-windows")]
+        [InlineData("netstandard2.0;net472", "net6.0;netstandard2.0;net472", "netstandard2.0%3bnet472")]
+        public void PropertyFunctionFilterTargetFrameworks(string incoming, string filter, string expected)
+        {
+            TestPropertyFunction($"$([MSBuild]::FilterTargetFrameworks('{incoming}', '{filter}'))", "_", "_", expected);
+        }
+
         [Fact]
         public void ExpandItemVectorFunctions_GetPathsOfAllDirectoriesAbove()
         {

src/Build/Evaluation/IntrinsicFunctions.cs

@@ -549,6 +549,11 @@ internal static string GetTargetPlatformVersion(string tfm, int versionPartCount
             return NuGetFramework.Value.GetTargetPlatformVersion(tfm, versionPartCount);
         }
 
+        internal static string FilterTargetFrameworks(string incoming, string filter)
+        {
+            return NuGetFramework.Value.FilterTargetFrameworks(incoming, filter);
+        }
+
         internal static bool AreFeaturesEnabled(Version wave)
         {
             return ChangeWaves.AreFeaturesEnabled(wave);

src/Build/Utilities/NuGetFrameworkWrapper.cs

@@ -2,8 +2,11 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System;
+using System.Collections.Generic;
 using System.IO;
+using System.Linq;
 using System.Reflection;
+using System.Text;
 
 using Microsoft.Build.Framework;
 using Microsoft.Build.Shared;
@@ -27,6 +30,7 @@ internal class NuGetFrameworkWrapper
         private static PropertyInfo VersionProperty;
         private static PropertyInfo PlatformProperty;
         private static PropertyInfo PlatformVersionProperty;
+        private static PropertyInfo AllFrameworkVersionsProperty;
 
         public NuGetFrameworkWrapper()
         {
@@ -47,6 +51,7 @@ public NuGetFrameworkWrapper()
                 VersionProperty = NuGetFramework.GetProperty("Version");
                 PlatformProperty = NuGetFramework.GetProperty("Platform");
                 PlatformVersionProperty = NuGetFramework.GetProperty("PlatformVersion");
+                AllFrameworkVersionsProperty = NuGetFramework.GetProperty("AllFrameworkVersions");
             }
             catch
             {
@@ -91,5 +96,42 @@ private string GetNonZeroVersionParts(Version version, int minVersionPartCount)
             var nonZeroVersionParts = version.Revision == 0 ? version.Build == 0 ? version.Minor == 0 ? 1 : 2 : 3 : 4;
             return version.ToString(Math.Max(nonZeroVersionParts, minVersionPartCount));
         }
+
+        public string FilterTargetFrameworks(string incoming, string filter)
+        {
+            IEnumerable<(string originalTfm, object parsedTfm)> incomingFrameworks = ParseTfms(incoming);
+            IEnumerable<(string originalTfm, object parsedTfm)> filterFrameworks = ParseTfms(filter);
+            StringBuilder tfmList = new StringBuilder();
+
+            // An incoming target framework from 'incoming' is kept if it is compatible with any of the desired target frameworks on 'filter'
+            foreach (var l in incomingFrameworks)
+            {
+                if (filterFrameworks.Any(r =>
+                        (FrameworkProperty.GetValue(l.parsedTfm) as string).Equals(FrameworkProperty.GetValue(r.parsedTfm) as string, StringComparison.OrdinalIgnoreCase) &&
+                        (((Convert.ToBoolean(AllFrameworkVersionsProperty.GetValue(l.parsedTfm))) && (Convert.ToBoolean(AllFrameworkVersionsProperty.GetValue(r.parsedTfm)))) ||
+                         ((VersionProperty.GetValue(l.parsedTfm) as Version) == (VersionProperty.GetValue(r.parsedTfm) as Version)))))
+                {
+                    if (tfmList.Length == 0)
+                    {
+                        tfmList.Append(l.originalTfm);
+                    }
+                    else
+                    {
+                        tfmList.Append($";{l.originalTfm}");
+                    }
+                }
+            }
+
+            return tfmList.ToString();
+
+            IEnumerable<(string originalTfm, object parsedTfm)> ParseTfms(string desiredTargetFrameworks)
+            {
+                return desiredTargetFrameworks.Split(new char[] {';'}, StringSplitOptions.RemoveEmptyEntries).Select(tfm =>
+                {
+                    (string originalTfm, object parsedTfm) parsed = (tfm, Parse(tfm));
+                    return parsed;
+                });
+            }
+        }
     }
 }