Document breaking change rule for stateless structs

Commit migrated from https://github.com/dotnet/corefx/commit/7444297ba077452d87bbbc5a4e5aab38069e2a54

diff --git a/docs/libraries/coding-guidelines/breaking-change-rules.md b/docs/libraries/coding-guidelines/breaking-change-rules.md
index 7da5726..6dafc1a 100644 (file)
--- a/docs/libraries/coding-guidelines/breaking-change-rules.md
+++ b/docs/libraries/coding-guidelines/breaking-change-rules.md
@@ -211,6 +211,10 @@ successfully bind to that overload, if simply passing an `int` value. However, i
 
 * Adding or removing `static` keyword from a member
 
+* Adding a field to a struct that previously had no state
+
+    Definite assignment rules allow use of uninitialized variables so long as the variable type is a stateless struct. If the struct is made stateful, code could now end up with uninitialized data. This is both potentially a source breaking and binary breaking change.
+
 ### Signatures
 ✓ **Allowed**
 * Adding `params` to a parameter