Fix FontCollection glyph typeface caching

src/Avalonia.Base/Media/Fonts/EmbeddedFontCollection.cs

@@ -76,6 +76,9 @@ public override bool TryGetGlyphTypeface(string familyName, FontStyle style, Fon
                         glyphTypeface = syntheticGlyphTypeface;
                     }
 
+                    //Make sure we cache the found match
+                    glyphTypefaces.TryAdd(key, glyphTypeface);
+
                     return true;
                 }
             }

src/Avalonia.Base/Media/Fonts/SystemFontCollection.cs

@@ -81,6 +81,9 @@ public override bool TryGetGlyphTypeface(string familyName, FontStyle style, Fon
             //No exact match
             if (createdKey != key)
             {
+                //Add the created glyph typeface to the cache so we can match it.
+                glyphTypefaces.TryAdd(createdKey, glyphTypeface);
+
                 //Try to find nearest match if possible
                 if (TryGetNearestMatch(glyphTypefaces, key, out var nearestMatch))
                 {

tests/Avalonia.Skia.UnitTests/Media/EmbeddedFontCollectionTests.cs

@@ -1,4 +1,7 @@
 using System;
+using System.Collections;
+using System.Collections.Concurrent;
+using System.Collections.Generic;
 using Avalonia.Media;
 using Avalonia.Media.Fonts;
 using Avalonia.UnitTests;
@@ -89,5 +92,37 @@ public void Should_Get_Typeface_For_TypographicFamilyName()
                 Assert.Equal("Manrope", glyphTypeface2.TypographicFamilyName);
             }
         }
+
+        [Fact]
+        public void Should_Cache_Synthetic_GlyphTypeface()
+        {
+            using (UnitTestApplication.Start(TestServices.MockPlatformRenderInterface))
+            {
+                var source = new Uri(s_manrope, UriKind.Absolute);
+
+                var fontCollection = new TestEmbeddedFontCollection(source, source);
+
+                fontCollection.Initialize(new CustomFontManagerImpl());
+
+                Assert.True(fontCollection.TryGetGlyphTypeface("Manrope", FontStyle.Normal, FontWeight.ExtraBlack, FontStretch.Normal, out var glyphTypeface));
+
+                Assert.True(fontCollection.GlyphTypefaceCache.TryGetValue("Manrope", out var glyphTypefaces));
+
+                Assert.Equal(2, glyphTypefaces.Count);
+
+                fontCollection.TryGetGlyphTypeface("Manrope", FontStyle.Normal, FontWeight.ExtraBlack, FontStretch.Normal, out var otherGlyphTypeface);
+
+                Assert.Equal(glyphTypeface, otherGlyphTypeface);
+            }
+        }
+
+        private class TestEmbeddedFontCollection : EmbeddedFontCollection
+        {
+            public TestEmbeddedFontCollection(Uri key, Uri source) : base(key, source)
+            {
+            }
+
+            public IDictionary<string, ConcurrentDictionary<FontCollectionKey, IGlyphTypeface?>> GlyphTypefaceCache => _glyphTypefaceCache;
+        }
     }
 }

tests/Avalonia.Skia.UnitTests/Media/FontCollectionTests.cs

@@ -1,5 +1,8 @@
-using Avalonia.Media;
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using Avalonia.Media;
 using Avalonia.Media.Fonts;
+using Avalonia.UnitTests;
 using Xunit;
 
 namespace Avalonia.Skia.UnitTests.Media
@@ -24,5 +27,40 @@ public void Should_Get_Implicit_Typeface(string input, string familyName, FontSt
             Assert.Equal(weight, result.Weight);
             Assert.Equal(FontStretch.Normal, result.Stretch);
         }
+
+        [Win32Fact("Relies on some installed font family")]
+        public void Should_Cache_Nearest_Match()
+        {
+            using (UnitTestApplication.Start(TestServices.MockPlatformRenderInterface.With(fontManagerImpl: new FontManagerImpl())))
+            {
+                var fontManager = FontManager.Current;
+
+                var fontCollection = new TestSystemFontCollection(FontManager.Current);
+
+                Assert.True(fontCollection.TryGetGlyphTypeface("Arial", FontStyle.Normal, FontWeight.ExtraBlack, FontStretch.Normal, out var glyphTypeface));
+
+                Assert.True(glyphTypeface.FontSimulations == FontSimulations.Bold);
+
+                Assert.True(fontCollection.GlyphTypfaceCache.TryGetValue("Arial", out var glyphTypefaces));
+
+                Assert.Equal(2, glyphTypefaces.Count);
+
+                Assert.True(glyphTypefaces.ContainsKey(new FontCollectionKey(FontStyle.Normal, FontWeight.Black, FontStretch.Normal)));
+
+                fontCollection.TryGetGlyphTypeface("Arial", FontStyle.Normal, FontWeight.ExtraBlack, FontStretch.Normal, out var otherGlyphTypeface);
+
+                Assert.Equal(glyphTypeface, otherGlyphTypeface);
+            }
+        }
+
+        private class TestSystemFontCollection : SystemFontCollection
+        {
+            public TestSystemFontCollection(FontManager fontManager) : base(fontManager)
+            {
+
+            }
+
+            public IDictionary<string, ConcurrentDictionary<FontCollectionKey, IGlyphTypeface?>> GlyphTypfaceCache => _glyphTypefaceCache;
+        }
     }
 }