Add document detailing migration from old versions

3 files changed, 189 insertions, 1 deletions

diff --git a/docs/Makefile b/docs/Makefile
index e7143b25..0dbd97cf 100644
--- a/docs/Makefile
+++ b/docs/Makefile
@@ -1,4 +1,4 @@
-all: index.html concepts.html reference.html security.html \
+all: index.html concepts.html reference.html security.html migration.html \
 	generator_flow.png
 
 %.png: %.svg
diff --git a/docs/menu.rst b/docs/menu.rst
index a49b22c1..2c110def 100644
--- a/docs/menu.rst
+++ b/docs/menu.rst
@@ -4,8 +4,10 @@
     2) `Concepts`_
     3) `API reference`_
     4) `Security model`_
+    5) `Migration from older versions`_
     
 .. _`Overview`: index.html
 .. _`Concepts`: concepts.html
 .. _`API reference`: reference.html
 .. _`Security model`: security.html
+.. _`Migration from older versions`: migration.html
diff --git a/docs/migration.rst b/docs/migration.rst
new file mode 100644
index 00000000..9d41f5b1
--- /dev/null
+++ b/docs/migration.rst
@@ -0,0 +1,186 @@
+=====================================
+Nanopb: Migration from older versions
+=====================================
+
+.. include :: menu.rst
+
+This document details all the breaking changes that have been made to nanopb
+since its initial release. For each change, the rationale and required
+modifications of user applications are explained. Also any error indications
+are included, in order to make it easier to find this document.
+
+.. contents ::
+
+Nanopb-0.3.0 (2014-09-xx)
+=========================
+
+Separate field iterator logic to pb_common.c
+--------------------------------------------
+**Rationale:** Originally, the field iteration logic was simple enough to be
+duplicated in *pb_decode.c* and *pb_encode.c*. New field types have made the
+logic more complex, which required the creation of a new file to contain the
+common functionality.
+
+**Changes:** There is a new file, *pb_common.c*, which must be included in
+builds.
+
+**Required actions:** Add *pb_common.c* to build rules. This file is always
+required. Either *pb_decode.c* or *pb_encode.c* can still be left out if some
+functionality is not needed.
+
+**Error indications:** Linker error: undefined reference to
+*pb_field_iter_begin*, *pb_field_iter_next* or similar.
+
+Nanopb-0.2.9 (2014-08-09)
+=========================
+
+Change semantics of generator -e option
+---------------------------------------
+**Rationale:** Some compilers do not accept filenames with two dots (like
+in default extension .pb.c). The *-e* option to the generator allowed changing
+the extension, but not skipping the extra dot.
+
+**Changes:** The *-e* option in generator will no longer add the prepending
+dot. The default value has been adjusted accordingly to *.pb.c* to keep the
+default behaviour the same as before.
+
+**Required actions:** Only if using the generator -e option. Add dot before
+the parameter value on the command line.
+
+**Error indications:** File not found when trying to compile generated files.
+
+Nanopb-0.2.7 (2014-04-07)
+=========================
+
+Changed pointer-type bytes field datatype
+-----------------------------------------
+**Rationale:** In the initial pointer encoding support since nanopb-0.2.5,
+the bytes type used a separate *pb_bytes_ptr_t* type to represent *bytes*
+fields. This made it easy to encode data from a separate, user-allocated
+buffer. However, it made the internal logic more complex and was inconsistent
+with the other types.
+
+**Changes:** Dynamically allocated bytes fields now have the *pb_bytes_array_t*
+type, just like statically allocated ones.
+
+**Required actions:** Only if using pointer-type fields with the bytes datatype.
+Change any access to *msg->field.size* to *msg->field->size*. Change any
+allocation to reserve space of amount *PB_BYTES_ARRAY_T_ALLOCSIZE(n)*. If the
+data pointer was begin assigned from external source, implement the field using
+a callback function instead.
+
+**Error indications:** Compiler error: unknown type name *pb_bytes_ptr_t*.
+
+Nanopb-0.2.4 (2013-11-07)
+=========================
+
+Remove the NANOPB_INTERNALS compilation option
+----------------------------------------------
+**Rationale:** Having the option in the headers required the functions to
+be non-static, even if the option is not used. This caused errors on some
+static analysis tools.
+
+**Changes:** The *#ifdef* and associated functions were removed from the
+header.
+
+**Required actions:** Only if the *NANOPB_INTERNALS* option was previously
+used. Actions are as listed under nanopb-0.1.3 and nanopb-0.1.6.
+
+**Error indications:** Compiler warning: implicit declaration of function
+*pb_dec_string*, *pb_enc_string*, or similar.
+
+Nanopb-0.2.1 (2013-04-14)
+=========================
+
+Callback function signature
+---------------------------
+**Rationale:** Previously the auxilary data to field callbacks was passed
+as *void\**. This allowed passing of any data, but made it unnecessarily
+complex to return a pointer from callback.
+
+**Changes:** The callback function parameter was changed to *void\**.
+
+**Required actions:** You can continue using the old callback style by
+defining *PB_OLD_CALLBACK_STYLE*. Recommended action is to:
+
+  * Change the callback signatures to contain *void\** for decoders and
+    *void \* const \** for encoders.
+  * Change the callback function body to use *\*arg* instead of *arg*.
+
+**Error indications:** Compiler warning: assignment from incompatible
+pointer type, when initializing *funcs.encode* or *funcs.decode*.
+
+Nanopb-0.2.0 (2013-03-02)
+=========================
+
+Reformatted generated .pb.c file using macros
+---------------------------------------------
+**Rationale:** Previously the generator made a list of C *pb_field_t*
+initializers in the .pb.c file. This led to a need to regenerate all .pb.c
+files after even small changes to the *pb_field_t* definition.
+
+**Changes:** Macros were added to pb.h which allow for cleaner definition
+of the .pb.c contents. By changing the macro definitions, changes to the
+field structure are possible without breaking compatibility with old .pb.c
+files.
+
+**Required actions:** Regenerate all .pb.c files from the .proto sources.
+
+**Error indications:** Compiler warning: implicit declaration of function
+*pb_delta_end*.
+
+Changed pb_type_t definitions
+-----------------------------
+**Rationale:** The *pb_type_t* was previously an enumeration type. This
+caused warnings on some compilers when using bitwise operations to set flags
+inside the values.
+
+**Changes:** The *pb_type_t* was changed to *typedef uint8_t*. The values
+were changed to *#define*. Some value names were changed for consistency.
+
+**Required actions:** Only if you directly access the `pb_field_t` contents
+in your own code, something which is not usually done. Needed changes:
+
+  * Change *PB_HTYPE_ARRAY* to *PB_HTYPE_REPEATED*.
+  * Change *PB_HTYPE_CALLBACK* to *PB_ATYPE()* and *PB_ATYPE_CALLBACK*.
+
+**Error indications:** Compiler error: *PB_HTYPE_ARRAY* or *PB_HTYPE_CALLBACK*
+undeclared.
+
+Nanopb-0.1.6 (2012-09-02)
+=========================
+
+Refactored field decoder interface
+----------------------------------
+**Rationale:** Similarly to field encoders in nanopb-0.1.3.
+
+**Changes:** New functions with names *pb_decode_\** were added.
+
+**Required actions:** By defining NANOPB_INTERNALS, you can still keep using
+the old functions. Recommended action is to replace any calls with the newer
+*pb_decode_\** equivalents.
+
+**Error indications:** Compiler warning: implicit declaration of function
+*pb_dec_string*, *pb_dec_varint*, *pb_dec_submessage* or similar.
+
+Nanopb-0.1.3 (2012-06-12)
+=========================
+
+Refactored field encoder interface
+----------------------------------
+**Rationale:** The old *pb_enc_\** functions were designed mostly for the
+internal use by the core. Because they are internally accessed through
+function pointers, their signatures had to be common. This led to a confusing
+interface for external users.
+
+**Changes:** New functions with names *pb_encode_\** were added. These have
+easier to use interfaces. The old functions are now only thin wrappers for
+the new interface.
+
+**Required actions:** By defining NANOPB_INTERNALS, you can still keep using
+the old functions. Recommended action is to replace any calls with the newer
+*pb_encode_\** equivalents.
+
+**Error indications:** Compiler warning: implicit declaration of function
+*pb_enc_string*, *pb_enc_varint, *pb_enc_submessage* or similar.
+