Harden the PathString converter

src/Microsoft.AspNetCore.Http.Abstractions/PathString.cs

@@ -443,25 +443,35 @@ public override int GetHashCode()
         /// </summary>
         /// <param name="s"></param>
         public static implicit operator PathString(string s)
-        {
-            return new PathString(s);
-        }
+            => ConvertFromString(s);
 
         /// <summary>
         /// Implicitly calls ToString().
         /// </summary>
         /// <param name="path"></param>
         public static implicit operator string(PathString path)
-        {
-            return path.ToString();
-        }
+            => path.ToString();
+
+        internal static PathString ConvertFromString(string s)
+            => string.IsNullOrEmpty(s) ? new PathString(s) : FromUriComponent(s);
     }
 
     internal class PathStringConverter : TypeConverter
     {
+        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
+            => sourceType == typeof(string) 
+            ? true 
+            : base.CanConvertFrom(context, sourceType);
+
         public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
-        {
-            return new PathString((string)value);
-        }
+            => value is string 
+            ? PathString.ConvertFromString((string)value) 
+            : base.ConvertFrom(context, culture, value);
+
+        public override object ConvertTo(ITypeDescriptorContext context,
+           CultureInfo culture, object value, Type destinationType)
+            => destinationType == typeof(string) 
+            ? value.ToString() 
+            : base.ConvertTo(context, culture, value, destinationType);
     }
 }

test/Microsoft.AspNetCore.Http.Abstractions.Tests/PathStringTests.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
@@ -208,11 +208,27 @@ public void ToUriComponentEscapeCorrectly(string category, string input, string
         }
 
         [Fact]
-        public void PathStringConvertsFromString()
+        public void PathStringConvertsOnlyToAndFromString()
         {
             var converter = TypeDescriptor.GetConverter(typeof(PathString));
             PathString result = (PathString)converter.ConvertFromInvariantString("/foo");
             Assert.Equal("/foo", result.ToString());
+            Assert.Equal("/foo", converter.ConvertTo(result, typeof(string)));
+            Assert.True(converter.CanConvertFrom(typeof(string)));
+            Assert.False(converter.CanConvertFrom(typeof(int)));
+            Assert.False(converter.CanConvertFrom(typeof(bool)));
+            Assert.True(converter.CanConvertTo(typeof(string)));
+            Assert.False(converter.CanConvertTo(typeof(int)));
+            Assert.False(converter.CanConvertTo(typeof(bool)));
+        }
+
+        [Fact]
+        public void PathStringStaysEqualAfterAssignments()
+        {
+            PathString p1 = "/?";
+            string s1 = p1;
+            PathString p2 = s1;
+            Assert.Equal(p1, p2);
         }
     }
 }