Merge #9544: [trivial] Add end of namespace comments. Improve consistency.

5a9b508 [trivial] Add end of namespace comments (practicalswift)

Tree-SHA512: 92b0fcae4d1d3f4da9e97569ae84ef2d6e09625a5815cd0e5f0eb6dd2ecba9852fa85c184c5ae9de5117050330ce995e9867b451fa8cd5512169025990541a2b

doc/developer-notes.md

@@ -68,7 +68,7 @@ public:
         return true;
     }
 }
-}
+} // namespace foo
 ```
 
 Doxygen comments
@@ -438,6 +438,21 @@ Source code organization
 
   - *Rationale*: Avoids symbol conflicts
 
+- Terminate namespaces with a comment (`// namespace mynamespace`). The comment
+  should be placed on the same line as the brace closing the namespace, e.g.
+
+```c++
+namespace mynamespace {
+    ...
+} // namespace mynamespace
+
+namespace {
+    ...
+} // namespace
+```
+
+  - *Rationale*: Avoids confusion about the namespace context
+
 GUI
 -----