bitbake-user-manual: add REQUIRED_VERSION and adjust PREFERRED_VERSION entry

Add REQUIRED_VERSION, add a reference to it in PREFERRED_VERSION and
adjust the opening statement to read slightly better.

Signed-off-by: Paul Eggleton <paul.eggleton@microsoft.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 16 insertions, 2 deletions

diff --git a/doc/bitbake-user-manual/bitbake-user-manual-ref-variables.rst b/doc/bitbake-user-manual/bitbake-user-manual-ref-variables.rst
index 1528b0406..489fa15fa 100644
--- a/doc/bitbake-user-manual/bitbake-user-manual-ref-variables.rst
+++ b/doc/bitbake-user-manual/bitbake-user-manual-ref-variables.rst
@@ -1096,8 +1096,8 @@ overview of their function and contents.
          PREFERRED_PROVIDER_aaa = "bbb"
 
    :term:`PREFERRED_VERSION`
-      If there are multiple versions of recipes available, this variable
-      determines which recipe should be given preference. You must always
+      If there are multiple versions of a recipe available, this variable
+      determines which version should be given preference. You must always
       suffix the variable with the :term:`PN` you want to
       select, and you should set :term:`PV` accordingly for
       precedence.
@@ -1117,6 +1117,10 @@ overview of their function and contents.
          end of the string. You cannot use the wildcard character in any other
          location of the string.
 
+      If a recipe with the specified version is not available, a warning
+      message will be shown. See :term:`REQUIRED_VERSION` if you want this
+      to be an error instead.
+
    :term:`PREMIRRORS`
       Specifies additional paths from which BitBake gets source code. When
       the build system searches for source code, it first tries the local
@@ -1227,6 +1231,16 @@ overview of their function and contents.
       The directory in which a local copy of a ``google-repo`` directory is
       stored when it is synced.
 
+   :term:`REQUIRED_VERSION`
+      If there are multiple versions of a recipe available, this variable
+      determines which version should be given preference. ``REQUIRED_VERSION``
+      works in exactly the same manner as :term:`PREFERRED_VERSION`, except
+      that if the specified version is not available then an error message
+      is shown and the build fails immediately.
+
+      If both ``REQUIRED_VERSION`` and ``PREFERRED_VERSION`` are set for
+      the same recipe, the ``REQUIRED_VERSION`` value applies.
+
    :term:`RPROVIDES`
       A list of package name aliases that a package also provides. These
       aliases are useful for satisfying runtime dependencies of other