Make the default route constraints linkable (#24727)

- Added a helper that gives the linker the ability to preserve the constructors of these types

Author: davidfowl

src/Http/Routing/src/ParameterPolicyActivator.cs

@@ -5,6 +5,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Linq;
 using System.Reflection;
@@ -86,6 +87,7 @@ public static T ResolveParameterPolicy<T>(
             }
         }
 
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2006:UnrecognizedReflectionPattern", Justification = "This type comes from the ConstraintMap.")]
         private static IParameterPolicy CreateParameterPolicy(IServiceProvider serviceProvider, Type parameterPolicyType, string argumentString)
         {
             ConstructorInfo activationConstructor = null;

src/Http/Routing/src/RouteOptions.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using Microsoft.AspNetCore.Routing.Constraints;
 
 namespace Microsoft.AspNetCore.Routing
@@ -82,38 +83,45 @@ public IDictionary<string, Type> ConstraintMap
 
         private static IDictionary<string, Type> GetDefaultConstraintMap()
         {
-            return new Dictionary<string, Type>(StringComparer.OrdinalIgnoreCase)
-            {
-                // Type-specific constraints
-                { "int", typeof(IntRouteConstraint) },
-                { "bool", typeof(BoolRouteConstraint) },
-                { "datetime", typeof(DateTimeRouteConstraint) },
-                { "decimal", typeof(DecimalRouteConstraint) },
-                { "double", typeof(DoubleRouteConstraint) },
-                { "float", typeof(FloatRouteConstraint) },
-                { "guid", typeof(GuidRouteConstraint) },
-                { "long", typeof(LongRouteConstraint) },
-
-                // Length constraints
-                { "minlength", typeof(MinLengthRouteConstraint) },
-                { "maxlength", typeof(MaxLengthRouteConstraint) },
-                { "length", typeof(LengthRouteConstraint) },
-
-                // Min/Max value constraints
-                { "min", typeof(MinRouteConstraint) },
-                { "max", typeof(MaxRouteConstraint) },
-                { "range", typeof(RangeRouteConstraint) },
-
-                // Regex-based constraints
-                { "alpha", typeof(AlphaRouteConstraint) },
-                { "regex", typeof(RegexInlineRouteConstraint) },
-
-                {"required", typeof(RequiredRouteConstraint) },
-
-                // Files
-                { "file", typeof(FileNameRouteConstraint) },
-                { "nonfile", typeof(NonFileNameRouteConstraint) },
-            };
+            var defaults = new Dictionary<string, Type>(StringComparer.OrdinalIgnoreCase);
+
+            // Type-specific constraints
+            AddConstraint<IntRouteConstraint>(defaults, "int");
+            AddConstraint<BoolRouteConstraint>(defaults, "bool");
+            AddConstraint<DateTimeRouteConstraint>(defaults, "datetime");
+            AddConstraint<DecimalRouteConstraint>(defaults, "decimal");
+            AddConstraint<DoubleRouteConstraint>(defaults, "double");
+            AddConstraint<FloatRouteConstraint>(defaults, "float");
+            AddConstraint<GuidRouteConstraint>(defaults, "guid");
+            AddConstraint<LongRouteConstraint>(defaults, "long");
+
+            // Length constraints
+            AddConstraint<MinLengthRouteConstraint>(defaults, "minlength");
+            AddConstraint<MaxLengthRouteConstraint>(defaults, "maxlength");
+            AddConstraint<LengthRouteConstraint>(defaults, "length");
+
+            // Min/Max value constraints
+            AddConstraint<MinRouteConstraint>(defaults, "min");
+            AddConstraint<MaxRouteConstraint>(defaults, "max");
+            AddConstraint<RangeRouteConstraint>(defaults, "range");
+
+            // Regex-based constraints
+            AddConstraint<AlphaRouteConstraint>(defaults, "alpha");
+            AddConstraint<RegexInlineRouteConstraint>(defaults, "regex");
+
+            AddConstraint<RequiredRouteConstraint>(defaults, "required");
+
+            // Files
+            AddConstraint<FileNameRouteConstraint>(defaults, "file");
+            AddConstraint<NonFileNameRouteConstraint>(defaults, "nonfile");
+
+            return defaults;
+        }
+
+        // This API could be exposed on RouteOptions
+        private static void AddConstraint<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)]TConstraint>(Dictionary<string, Type> constraintMap, string text) where TConstraint : IRouteConstraint
+        {
+            constraintMap[text] = typeof(TConstraint);
         }
     }
 }