[Emacs-diffs] master 4d97e1a: Export major version of latest Emacs supported by emacs-module.h.

[Philipp Stephani]

branch: master
commit 4d97e1a9ea35c3a1d9f03abb7a822d57f384c1a5
Author: Philipp Stephani <address@hidden>
Commit: Philipp Stephani <address@hidden>

    Export major version of latest Emacs supported by emacs-module.h.
    
    This is useful if module authors want to support multiple versions of
    emacs-module.h.
    
    * configure.ac (emacs_major_version): Define substitution.
    
    * src/emacs-module.h.in (EMACS_MAJOR_VERSION): Define macro.
    
    * doc/lispref/internals.texi (Module Initialization): Document
    EMACS_MAJOR_VERSION preprocessor macro.
    
    * test/data/emacs-module/mod-test.c (emacs_module_init): Verify
    behavior of EMACS_MAJOR_VERSION.
---
 configure.ac                      |  2 ++
 doc/lispref/internals.texi        | 11 +++++++++++
 etc/NEWS                          |  3 +++
 src/emacs-module.h.in             |  2 ++
 test/data/emacs-module/mod-test.c |  5 +++++
 5 files changed, 23 insertions(+)

diff --git a/configure.ac b/configure.ac
index 810c321..79fe0c9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3697,6 +3697,8 @@ AC_SUBST_FILE([module_env_snippet_27])
 module_env_snippet_25="$srcdir/src/module-env-25.h"
 module_env_snippet_26="$srcdir/src/module-env-26.h"
 module_env_snippet_27="$srcdir/src/module-env-27.h"
+emacs_major_version="${PACKAGE_VERSION%%.*}"
+AC_SUBST(emacs_major_version)
 
 ### Use -lpng if available, unless '--with-png=no'.
 HAVE_PNG=no
diff --git a/doc/lispref/internals.texi b/doc/lispref/internals.texi
index 5ae71af..cfeb492 100644
--- a/doc/lispref/internals.texi
+++ b/doc/lispref/internals.texi
@@ -1191,6 +1191,17 @@ grow with new Emacs releases.  Given the version of 
Emacs, the module
 can use only the parts of the module @acronym{API} that existed in
 that version, since those parts are identical in later versions.
 
address@hidden defines a preprocessor macro
address@hidden  It expands to an integer literal which is
+the latest major version of Emacs supported by the header.
address@hidden Info}.  Note that the value of
address@hidden is a compile-time constant and does not
+represent the version of Emacs that is currently running and has
+loaded your module.  If you want your module to be compatible with
+various versions of @file{emacs-module.h} as well as various versions
+of Emacs, you can use conditional compilation based on
address@hidden
+
 We recommend that modules always perform the compatibility
 verification, unless they do their job entirely in the initialization
 function, and don't access any Lisp objects or use any Emacs functions
diff --git a/etc/NEWS b/etc/NEWS
index cf6f4fe..9b32d72 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1933,6 +1933,9 @@ convert between timespec structures and Emacs Lisp time 
values.
 'extract_big_integer' to create and extract arbitrary-size integer
 values.
 
+** emacs-module.h now defines a macro EMACS_MAJOR_VERSION that expands
+to the major version of the latest Emacs supported by the header.
+
 
 * Changes in Emacs 27.1 on Non-Free Operating Systems
 
diff --git a/src/emacs-module.h.in b/src/emacs-module.h.in
index fbc62a6..9955e30 100644
--- a/src/emacs-module.h.in
+++ b/src/emacs-module.h.in
@@ -32,6 +32,8 @@ along with GNU Emacs.  If not, see 
<https://www.gnu.org/licenses/>.  */
 #include <gmp.h>
 #endif
 
+#define EMACS_MAJOR_VERSION @emacs_major_version@
+
 #if defined __cplusplus && __cplusplus >= 201103L
 # define EMACS_NOEXCEPT noexcept
 #else
diff --git a/test/data/emacs-module/mod-test.c 
b/test/data/emacs-module/mod-test.c
index b7007bd..a9154fa 100644
--- a/test/data/emacs-module/mod-test.c
+++ b/test/data/emacs-module/mod-test.c
@@ -445,6 +445,11 @@ bind_function (emacs_env *env, const char *name, 
emacs_value Sfun)
 int
 emacs_module_init (struct emacs_runtime *ert)
 {
+  /* Check that EMACS_MAJOR_VERSION is defined and an integral
+     constant.  */
+  char dummy[EMACS_MAJOR_VERSION];
+  assert (27 <= sizeof dummy);
+
   if (ert->size < sizeof *ert)
     {
       fprintf (stderr, "Runtime size of runtime structure (%"pT" bytes) "