Add notes about variable names and shadowing

Author: paveljanik

doc/developer-notes.md

@@ -331,6 +331,32 @@ Strings and formatting
 
   - *Rationale*: Bitcoin Core uses tinyformat, which is type safe. Leave them out to avoid confusion
 
+Variable names
+--------------
+
+The shadowing warning (`-Wshadow`) is enabled by default. It prevents issues rising
+from using a different variable with the same name.
+
+Please name variables so that their names do not shadow variables defined in the source code.
+
+E.g. in member initializers, prepend `_` to the argument name shadowing the
+member name:
+
+```c++
+class AddressBookPage
+{
+    Mode mode;
+}
+
+AddressBookPage::AddressBookPage(Mode _mode) :
+      mode(_mode)
+...
+```
+
+When using nested cycles, do not name the inner cycle variable the same as in
+upper cycle etc.
+
+
 Threads and synchronization
 ----------------------------