are advised to not set the variable @code{V} inside the @file{Makefile.am}
file, to allow the user to override the value for subdirectories as well.
- The current implementation of this feature relies on a non-POSIX, but in
- practice rather widely supported @file{Makefile} construct of nested
- variable expansion @samp{$(@var{var1}$(V))}. Do not use the
- @option{silent-rules} option if your package needs to build with
- @command{make} implementations that do not support it. The
- @option{silent-rules} option turns off warnings about recursive variable
- expansion, which are in turn enabled by @option{-Wportability}
- (@pxref{automake Invocation}).
+ The current implementation of this feature normally uses nested
+ variable expansion @samp{$(@var{var1}$(V))}, a @file{Makefile} feature
+ that is not required by POSIX 2008 but is widely supported in
-practice. On the rare @command{make} implementations that do not
-support nested variable expansion, whether rules are silent is always
-determined at configure time, and cannot be overridden at make time.
-Future versions of POSIX are likely to require nested variable
-expansion, so this minor limitation should go away with time.
++practice. The @option{silent-rules} option thus turns off warnings
++about recursive variable expansion, which are in turn enabled by
++@option{-Wportability} (@pxref{automake Invocation}). On the rare
++@command{make} implementations that do not support nested variable
++expansion, whether rules are silent is always determined at configure
++time, and cannot be overridden at make time. Future versions of POSIX
++are likely to require nested variable expansion, so this minor
++limitation should go away with time.
@vindex @code{AM_V_GEN}
@vindex @code{AM_V_at}