Fix null ref exception in LookupType5Format2SubTable

samples/DrawWithImageSharp/DrawWithImageSharp.csproj

@@ -46,7 +46,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="SixLabors.ImageSharp.Drawing" Version="2.0.0" />
+    <PackageReference Include="SixLabors.ImageSharp.Drawing" Version="2.0.1" />
     <PackageReference Include="System.ValueTuple" Version="4.5.0" />
   </ItemGroup>
 

src/SixLabors.Fonts/Tables/AdvancedTypographic/GSub/LookupType5SubTable.cs

@@ -150,7 +150,12 @@ public override bool TrySubstitution(
             return false;
         }
 
-        ClassSequenceRuleSetTable ruleSetTable = this.sequenceRuleSetTables[offset];
+        ClassSequenceRuleSetTable? ruleSetTable = this.sequenceRuleSetTables[offset];
+        if (ruleSetTable is null)
+        {
+            return false;
+        }
+
         SkippingGlyphIterator iterator = new(fontMetrics, collection, index, this.LookupFlags);
         foreach (ClassSequenceRuleTable ruleTable in ruleSetTable.SequenceRuleTables)
         {

src/SixLabors.Fonts/Tables/AdvancedTypographic/Shapers/IndicShaper.cs

@@ -52,9 +52,9 @@ public IndicShaper(ScriptClass script, Tag unicodeScriptTag, TextOptions textOpt
     {
         this.textOptions = textOptions;
 
-        if (IndicConfigurations.ContainsKey(script))
+        if (IndicConfigurations.TryGetValue(script, out ShapingConfiguration value))
         {
-            this.indicConfiguration = IndicConfigurations[script];
+            this.indicConfiguration = value;
         }
         else
         {

src/UnicodeTrieGenerator/Generator.UniversalShapingEngine.cs

@@ -528,12 +528,13 @@ or 0x2068
 
             if (category != null)
             {
-                if (!symbols.ContainsKey(category))
+                if (!symbols.TryGetValue(category, out int value))
                 {
-                    symbols[category] = numSymbols++;
+                    value = numSymbols++;
+                    symbols[category] = value;
                 }
 
-                builder.Set(codePoint.Code, (uint)symbols[category]);
+                builder.Set(codePoint.Code, (uint)value);
             }
 
             if (codePoint.IndicSyllabicCategory == ISC.VowelDependent && codePoint.Decomposition.Any())

tests/SixLabors.Fonts.Tests/Issues/Issues_363.cs

@@ -0,0 +1,18 @@
+// Copyright (c) Six Labors.
+// Licensed under the Six Labors Split License.
+
+namespace SixLabors.Fonts.Tests.Issues;
+
+public class Issues_363
+{
+    [Fact]
+    public void GSubFormat2NUllReferenceException()
+    {
+        Font font = new FontCollection().Add(TestFonts.BNazaninFile).CreateFont(12);
+
+        TextOptions textOptions = new(font);
+        string text = "تست فونت 1234";
+        FontRectangle rect = TextMeasurer.MeasureAdvance(text, textOptions);
+        Assert.NotEqual(default, rect);
+    }
+}

tests/SixLabors.Fonts.Tests/TestFonts.cs

@@ -245,6 +245,8 @@
 
     public static string THSarabunFile => GetFullPath("THSarabun.ttf");
 
+    public static string BNazaninFile => GetFullPath("BNazanin.ttf");
+
     public static Stream TwemojiMozillaData() => OpenStream(TwemojiMozillaFile);
 
     public static Stream SegoeuiEmojiData() => OpenStream(SegoeuiEmojiFile);
@@ -296,7 +298,7 @@
 
     private static string GetFullPath(string path)
     {
         string root = Path.GetDirectoryName(new Uri(typeof(TestFonts).GetTypeInfo().Assembly.CodeBase).LocalPath);
 
         string[] paths = new[]
         {