Promote function type aliases to the public module API.

Previously module authors had to define type aliases for module
functions and finalizers themselves.  This commit adds and documents
aliases so that this is no longer necessary.

* src/emacs-module.h.in: Add 'emacs_function' and 'emacs_finalizer'
type aliases.

* src/emacs-module.c: Remove old 'emacs_subr' and 'emacs_finalizer'
type aliases.
(struct Lisp_Module_Function, module_make_function): Switch from
'emacs_subr' to 'emacs_function'.

* doc/lispref/internals.texi (Module Functions): Document and use
'emacs_function' type alias.
(Module Values): Document 'emacs_finalizer' type alias.

* etc/NEWS: Mention change.

2 files changed, 17 insertions, 12 deletions

diff --git a/src/emacs-module.c b/src/emacs-module.c
index ff1a05450ce..76229137d87 100644
--- a/src/emacs-module.c
+++ b/src/emacs-module.c
@@ -122,12 +122,6 @@ To add a new module function, proceed as follows:
 /* Function prototype for the module init function.  */
 typedef int (*emacs_init_function) (struct emacs_runtime *);
 
-/* Function prototype for module user-pointer finalizers.  These
-   should not throw C++ exceptions, so emacs-module.h declares the
-   corresponding interfaces with EMACS_NOEXCEPT.  There is only C code
-   in this module, though, so this constraint is not enforced here.  */
-typedef void (*emacs_finalizer) (void *);
-
 
 /* Memory management.  */
 
@@ -466,10 +460,6 @@ module_non_local_exit_throw (emacs_env *env, emacs_value tag, emacs_value value)
                                    value_to_lisp (value));
 }
 
-/* Function prototype for the module Lisp functions.  */
-typedef emacs_value (*emacs_subr) (emacs_env *, ptrdiff_t,
-                                   emacs_value *, void *);
-
 /* Module function.  */
 
 /* A function environment is an auxiliary structure returned by
@@ -486,7 +476,7 @@ struct Lisp_Module_Function
 
   /* Fields ignored by GC.  */
   ptrdiff_t min_arity, max_arity;
-  emacs_subr subr;
+  emacs_function subr;
   void *data;
 } GCALIGNED_STRUCT;
 
@@ -505,7 +495,7 @@ allocate_module_function (void)
 
 static emacs_value
 module_make_function (emacs_env *env, ptrdiff_t min_arity, ptrdiff_t max_arity,
-                      emacs_subr func, const char *docstring, void *data)
+                      emacs_function func, const char *docstring, void *data)
 {
   MODULE_FUNCTION_BEGIN (NULL);
 
diff --git a/src/emacs-module.h.in b/src/emacs-module.h.in
index ecbfe28c72c..fbeaebd7956 100644
--- a/src/emacs-module.h.in
+++ b/src/emacs-module.h.in
@@ -78,6 +78,21 @@ struct emacs_runtime
     EMACS_ATTRIBUTE_NONNULL(1);
 };
 
+/* Type aliases for function pointer types used in the module API.
+   Note that we don't use these aliases directly in the API to be able
+   to mark the function arguments as 'noexcept' before C++20.
+   However, users can use them if they want.  */
+
+/* Function prototype for the module Lisp functions.  These must not
+   throw C++ exceptions.  */
+typedef emacs_value (*emacs_function) (emacs_env *env, ptrdiff_t nargs,
+                                       emacs_value *args,
+                                       void *data)
+  EMACS_NOEXCEPT EMACS_ATTRIBUTE_NONNULL (1);
+
+/* Function prototype for module user-pointer finalizers.  These must
+   not throw C++ exceptions.  */
+typedef void (*emacs_finalizer) (void *data) EMACS_NOEXCEPT;
 
 /* Possible Emacs function call outcomes.  */
 enum emacs_funcall_exit