Fix: PascalCaseNamingConvention splits consecutive uppercase acronyms (AutoMapper #4593 backport)

src/AutoMapper/Configuration/INamingConvention.cs

@@ -24,7 +24,8 @@ public string[] Split(string input)
         int lower = 0;
         for(int index = 1; index < input.Length; index++)
         {
-            if (char.IsUpper(input[index]))
+            if (char.IsUpper(input[index]) &&
+                (!char.IsUpper(input[index - 1]) || (index + 1 < input.Length && !char.IsUpper(input[index + 1]))))
             {
                 result ??= [];
                 result.Add(input[lower..index]);

src/UnitTests/Bug/NamingConventions.cs

@@ -105,6 +105,24 @@ public void Should_map_from_pascal_to_lower()
     }
 }
 
+
+public class PascalCaseAcronymInPropertyName : AutoMapperSpecBase
+{
+    class Source { public Inner Form { get; set; } }
+    class Inner { public int XML { get; set; } }
+    class Dest { public int FormXML { get; set; } }
+
+    protected override MapperConfiguration CreateConfiguration() => new(cfg =>
+        cfg.CreateMap<Source, Dest>());
+
+    [Fact]
+    public void Should_flatten_acronym_property()
+    {
+        var result = Mapper.Map<Dest>(new Source { Form = new Inner { XML = 42 } });
+        result.FormXML.ShouldBe(42);
+    }
+}
+
 public class When_mapping_with_lowercase_naming_conventions_two_ways : AutoMapperSpecBase
 {
     private Dario _dario;