doc: update Vala documentation

From https://bugs.gnu.org/70557#29.

* doc/automake.texi (Vala Support): Update the URL for Vala.
Drop the mention of a version requirement, as no current system
  will have a too-old version of Vala.
Note the restriction on conditional inclusion of source files in
  *_SOURCES.

diff --git a/doc/automake.texi b/doc/automake.texi
index d30905e0f0e2f42932aa7f29f87325efba43eb07..2b897204e3db3703bf4ad35c9b78a92f39ba4497 100644 (file)
--- a/doc/automake.texi
+++ b/doc/automake.texi
@@ -7017,24 +7017,29 @@ the @code{_LDFLAGS} variable for the program.
 
 
 @node Vala Support
-@comment  node-name,  next,  previous,  up
 @section Vala Support
 
-@cindex Vala Support
+@cindex Vala support
 @cindex Support for Vala
+@cindex GNU Make, required by Vala
 
-Automake provides initial support for Vala
-(@uref{https://www.vala-project.org/}).
-This requires valac version 0.7.0 or later, and currently requires
-the user to use GNU @command{make}.
+Automake supports Vala (@uref{https://vala.dev/}).
+Vala support requires the user to use GNU @command{make}.
 
 @example
 foo_SOURCES = foo.vala bar.vala zardoz.c
 @end example
 
 Any @file{.vala} file listed in a @code{_SOURCES} variable will be
-compiled into C code by the Vala compiler. The generated @file{.c} files
-are distributed. The end user does not need to have a Vala compiler installed.
+compiled into C code by the Vala compiler.  The generated @file{.c}
+files are distributed. The end user does not need to have a Vala
+compiler installed.
+
+Because all C files must be generated, and the Vala compiler compiles
+all the @file{.vala} files for a target at once, it is not possible to
+add files to a @code{_SOURCES} variable that cannot be compiled
+together; for example, alternative platform-specific definitions of
+the same methods.
 
 Automake ships with an Autoconf macro called @code{AM_PROG_VALAC}
 that will locate the Vala compiler and optionally check its version