Extend FAQ with full mode notes
Change-Id: Iad7d2e10c02b7497382e40733e7ac45517797f79
diff --git a/compatibility-faq.md b/compatibility-faq.md
index 8b15be4..f3dde4e 100644
--- a/compatibility-faq.md
+++ b/compatibility-faq.md
@@ -101,3 +101,19 @@
the fields to be renamed by R8 to the same name, but GSON serialization will
work as expected.
+# R8 full mode
+
+In full mode, R8 performs more aggressive optimizations, meaning that additional
+ProGuard configuration rules may be required. This section highlights some
+common issues that have been seen when using full mode.
+
+## Retrofit
+
+### Object instantiated with Retrofit's `create()` method is always replaced with `null`
+
+This happens because Retrofit uses reflection to return an object that
+implements a given interface. The issue can be resolved by using the most recent
+keep rules from the Retrofit library.
+
+See also https://github.com/square/retrofit/issues/3005 ("Insufficient keep
+rules for R8 in full mode").
