Change Auto charset to mean UTF-8 off-Windows (#23664)

Match Mono's behavior by changing the Auto character set to mean UTF-8 on non-Windows platforms (new behavior) and UCS-2/UTF-16 on Windows (current behavior).

Fixes #23464 
Fixes dotnet/corefx#32442

Impact of breaking change: It is highly unlikely that anyone is actively using current behavior since it is inconsistent with Mono and doesn't match any native system APIs on non-Windows platforms (they're all UTF-8 based).

We will need to update our documentation to reflect this updated behavior.

1 files changed, 9 insertions, 1 deletions

diff --git a/src/vm/methodtablebuilder.cpp b/src/vm/methodtablebuilder.cpp
index d4ce5b0df0..b9460264c3 100644
--- a/src/vm/methodtablebuilder.cpp
+++ b/src/vm/methodtablebuilder.cpp
@@ -11913,10 +11913,18 @@ BOOL HasLayoutMetadata(Assembly* pAssembly, IMDInternalImport* pInternalImport,
     {
         *pNLTType = nltAnsi;
     }
-    else if (IsTdUnicodeClass(clFlags) || IsTdAutoClass(clFlags))
+    else if (IsTdUnicodeClass(clFlags))
     {
         *pNLTType = nltUnicode;
     }
+    else if (IsTdAutoClass(clFlags))
+    {
+#ifdef PLATFORM_WINDOWS
+        *pNLTType = nltUnicode;
+#else
+        *pNLTType = nltAnsi; // We don't have a utf8 charset in metadata yet, but ANSI == UTF-8 off-Windows
+#endif
+    }
     else
     {
         pAssembly->ThrowTypeLoadException(pInternalImport, cl, IDS_CLASSLOAD_BADFORMAT);