Move package.xml format 1 to 2 migration to its own page (#4778) (#4782)

Signed-off-by: Shane Loretz <shane.loretz@gmail.com>
(cherry picked from commit 12cc86a)

Co-authored-by: Shane Loretz <sloretz@osrfoundation.org>

source/How-To-Guides/Migrating-from-ROS1.rst

@@ -8,6 +8,7 @@ If you are new to porting between ROS 1 and ROS 2, it is recommended to read thr
    :maxdepth: 1
 
    Migrating-from-ROS1/Migrating-Packages
+   Migrating-from-ROS1/Migrating-Package-XML
    Migrating-from-ROS1/Migrating-Interfaces
    Migrating-from-ROS1/Migrating-CPP-Packages
    Migrating-from-ROS1/Migrating-Python-Packages

source/How-To-Guides/Migrating-from-ROS1/Migrating-Package-XML.rst

@@ -0,0 +1,132 @@
+Migrating your package.xml to format 2
+======================================
+
+.. contents:: Table of Contents
+   :depth: 2
+   :local:
+
+ROS 2 requires ``package.xml`` files to use at least `format 2 <https://ros.org/reps/rep-0140.html>`__.
+This guide shows how to migrate a ``package.xml`` from format 1 to format 2.
+
+If the ``<package>`` tag at the start of your ``package.xml`` looks like either of the following, then it is using format 1 and you must migrate it.
+
+.. code-block:: xml
+
+    <package>
+
+.. code-block:: xml
+
+    <package format="1">
+
+
+Prerequisites
+-------------
+
+You should have a working ROS 1 installation.
+This enables you to check that the converted ``package.xml`` is valid by building and testing the package, since ROS 1 supports all ``package.xml`` format versions.
+
+Migrate from format 1 to 2
+--------------------------
+
+Format 1 and format 2 differ in how they specify dependencies.
+Read the `compatibility section in REP-0140 <https://www.ros.org/reps/rep-0140.html#compatibility>`__ for a summary of the differences.
+
+Add ``format`` attribute to ``<package>``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Add or set the ``format`` attribute to ``2`` to indicate that the ``package.xml`` uses format 2.
+
+.. code:: xml
+
+  <package format="2">
+
+Replace ``<run_depend>``
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+The ``<run_depend>`` tag is no longer allowed.
+If you have a dependency specified like this:
+
+.. code:: xml
+
+  <run_depend>foo</run_depend>
+
+then replace it with one or both of these tags:
+
+.. code:: xml
+
+  <build_export_depend>foo</build_export_depend>
+  <exec_depend>foo</exec_depend>
+
+If the dependency is needed when something in your package is executed, then use the ``<exec_depend>`` tag.
+If packages that depend on your package need the dependency when they are built, then use the ``<build_export_depend>`` tag.
+Use both tags if you are unsure.
+
+Convert some ``<build_depend>`` to ``<test_depend>``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In format 1 ``<test_depend>`` declares dependencies that are needed when running your package's tests.
+It still does that in format 2, but it additionally declares dependencies that are needed when building your package's tests.
+
+Because of the limitations of this tag in format 1, your package may have a test-only dependency specified as a ``<build_depend>`` like this:
+
+.. code:: xml
+
+  <build_depend>testfoo</build_depend>
+
+If so, change it to a ``<test_depend>``.
+
+.. code:: xml
+
+  <test_depend>testfoo</test_depend>
+
+.. note::
+
+    If you are using CMake, then make sure your test dependencies are only referenced within a ``if(BUILD_TESTING)`` block:
+
+    .. code:: cmake
+
+        if (BUILD_TESTING)
+            find_package(testfoo REQUIRED)
+        endif()
+
+Begin using ``<doc_depend>``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Use the new ``<doc_depend>`` tag to declare dependencies needed for building your package's documentation.
+For example, C++ packages might have this dependency:
+
+.. code:: xml
+
+  <doc_depend>doxygen</doc_depend>
+
+while Python packages might have this one:
+
+.. code:: xml
+
+  <doc_depend>python3-sphinx</doc_depend>
+
+See :doc:`the guide on documenting ROS 2 packages <../Documenting-a-ROS-2-Package>` for more information.
+
+Simplify dependencies with ``<depend>``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``<depend>`` is a new tag that makes ``package.xml`` files more concise.
+If your ``package.xml`` has these three tags for the same dependency:
+
+.. code::
+
+  <build_depend>foo</build_depend>
+  <build_export_depend>foo</build_export_depend>
+  <exec_depend>foo</exec_depend>
+
+then replace them with a single ``<depend>`` like this:
+
+.. code:: xml
+
+  <depend>foo</depend>
+
+Test your new ``package.xml``
+-----------------------------
+
+Build and test your package as you normally do using ``catkin_make``, ``cakin_make_isolated``, or the ``catkin`` build tool.
+If everything succeeds, then your ``package.xml`` is valid.

source/How-To-Guides/Migrating-from-ROS1/Migrating-Packages.rst

@@ -17,121 +17,11 @@ Prerequisites
 
 Before being able to migrate a ROS 1 package to ROS 2 all of its dependencies must be available in ROS 2.
 
-Package format version
-----------------------
+Package.xml format version
+--------------------------
 
-ROS 2 doesn't support format 1 of the package specification but only newer format versions (2 and higher).
-Therefore the ``package.xml`` file must be updated to at least format 2 if it uses format 1.
-Since ROS 1 supports all formats it is safe to perform that conversion in the ROS 1 package.
-
-Migrating from package format 1 to 2+
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-The differences between format 1 and format 2 only affect the package.xml with its dependencies.
-`REP-0140 <https://www.ros.org/reps/rep-0140.html>`__ defines these differences and provides their rationale.
-
-See :doc:`the rosdep documentation <../../Tutorials/Intermediate/Rosdep>` for more information about the various tags.
-
-**<package>**
-~~~~~~~~~~~~~
-
-The <package> tag determines which format to use, change it like this:
-
-.. code:: xml
-
-  <package format="2">
-
-**<depend>**
-~~~~~~~~~~~~~
-
-This is a new tag, intended to reduce unnecessary repetition.
-If your format 1 package contained:
-
-.. code:: xml
-
-  <build_depend>foo</build_depend>
-  <run_depend>foo</run_depend>
-
-It should be replaced with:
-
-.. code:: xml
-
-  <depend>foo</depend>
-
-In format 2, that is equivalent to:
-
-.. code:: xml
-
-  <build_depend>foo</build_depend>
-  <build_export_depend>foo</build_export_depend>
-  <exec_depend>foo</exec_depend>
-
-
-**<run_depend>**
-~~~~~~~~~~~~~~~~
-
-This tag is no longer allowed.
-Wherever found, it must be replaced:
-
-.. code:: xml
-
-  <run_depend>foo</run_depend>
-
-In format 2, that is equivalent to these two new tags:
-
-.. code:: xml
-
-  <build_export_depend>foo</build_export_depend>
-  <exec_depend>foo</exec_depend>
-
-If the dependency is only used at run-time, only the ``<exec_depend>`` is needed.
-If it is only exported to satisfy the build dependencies of other packages, use ``<build_export_depend>``.
-If both are needed, this may be a better choice:
-
-.. code:: xml
-
-  <depend>foo</depend>
-
-
-**<test_depend>**
-~~~~~~~~~~~~~~~~~
-
-In format 2, this tag can satisfy build dependencies, not just those needed for executing your tests.
-Unlike format 1, ``<test_depend>`` may now refer to a package also declared as some other type of dependency.
-
-Some test-only dependencies that formerly required a ``<build_depend>``, should now be expressed using ``<test_depend>``.
-For example:
-
-.. code:: xml
-
-  <build_depend>testfoo</build_depend>
-
-becomes:
-
-.. code:: xml
-
-  <test_depend>testfoo</test_depend>
-
-In your CMakeLists.txt make sure your test dependencies are only referenced within the conditional test block:
-
-.. code:: cmake
-
-  if (BUILD_TESTING)
-    find_package(testfoo REQUIRED)
-  endif()
-
-
-**<doc_depend>**
-~~~~~~~~~~~~~~~~
-
-This tag defines dependencies needed for building your documentation:
-
-.. code:: xml
-
-  <doc_depend>doxygen</doc_depend>
-  <doc_depend>python3-sphinx</doc_depend>
-
-This does not create binary package dependencies, unless they were also declared using some other dependency tag.
+ROS 2 only supports ``package.xml`` format versions 2 and higher.
+If your package's ``package.xml`` uses format 1, then update it using the :doc:`Package.xml format 1 to 2 migration guide <./Migrating-Package-XML>`.
 
 Dependency names
 ----------------