C++: Change note for StackVariable

Author: jbj

change-notes/1.24/analysis-cpp.md

@@ -0,0 +1,26 @@
+# Improvements to C/C++ analysis
+
+The following changes in version 1.24 affect C/C++ analysis in all applications.
+
+## General improvements
+
+## New queries
+
+| **Query**                   | **Tags**  | **Purpose**                                                        |
+|-----------------------------|-----------|--------------------------------------------------------------------|
+
+## Changes to existing queries
+
+| **Query**                  | **Expected impact**    | **Change**                                                       |
+|----------------------------|------------------------|------------------------------------------------------------------|
+
+## Changes to QL libraries
+
+* The new class `StackVariable` should be used in place of `LocalScopeVariable`
+  in most cases. The difference is that `StackVariable` does not include
+  variables declared with `static` or `thread_local`.
+  * As a rule of thumb, custom queries about the _values_ of variables should
+    be changed from `LocalScopeVariable` to `StackVariable`, while queries
+    about the _name or scope_ of variables should remain unchanged.
+  * The `LocalScopeVariableReachability` library is deprecated in favor of
+    `StackVariableReachability`. The functionality is the same.