Migrating interdependent-plugins.md from the wiki

docs/development/interdependent-plugins.md

@@ -0,0 +1,35 @@
+# Developing interdependent plugins
+
+Say you have two Kaleidoscope plugins or, more general, two Arduino libraries `A` and `B`. Let's assume `B` depends on `A` in a sense that `B` references symbols (functions/variables) defined in `A`. Both libraries define header files `a_header.h` and `b_header.h` that specify their exported symbols.
+
+The following sketch builds as expected.
+```cpp
+// my_sketch.ino
+#include "b_header.h"
+#include "a_header.h"
+...
+```
+
+If the header appear in opposite order the linker will throw undefined symbol errors regarding missing symbols from `A`.
+```cpp
+// my_sketch.ino
+#include "a_header.h"
+#include "b_header.h"
+...
+```
+The reason for this somewhat unexpected behavior is that the order of libraries' occurrence in the linker command line is crucial. The linker must see library `B` first to determine which symbols it needs to extract from `A`. If it encounters `A` first, it completely neglects its symbols as there are no references to it at that point.
+
+To be on the safe side and only if the sketch does not reference symbols from `A` directly, it is better to include the headers in the following way.
+```cpp
+// header_b.h
+#include "header_a.h"
+...
+```
+
+```cpp
+// my_sketch.ino
+// Do not include a_header.h directly. It is already included by b_header.h.
+#include "b_header.h"
+...
+```
+Note: I did no thorough research on how Arduino internally establishes the linker command line, e.g. with respect to a recursive traversal of the include-tree. This means, I am not sure how the link command line order is generated when header files that are included by the main `.ino` do include other files that provide definitions of library symbols in different orders. There might be additional pitfalls when header includes are more complex given a larger project.

docs/index.rst

@@ -84,6 +84,15 @@ Device drivers
    drivers/**
 
 
+Development tips
+----------------
+.. toctree::
+   :maxdepth: 1
+   :glob:
+
+   development/**
+
+
 What's new in v2.0
 ------------------
 .. toctree::