add modules using Daniel Colascione ideas

See [1] for Daniel's proposal.

* src/module.c: new file
* src/emacs_module.h: module API
* src/Makefile.in: hardcode libltdl link flag and module.c compilation
* modules/basic/basic.c: sample module
* modules/basic/Makefile: module Makefile for linux

1: https://lists.gnu.org/archive/html/emacs-devel/2015-02/msg00960.html

modules/basic/Makefile

@@ -0,0 +1,15 @@
+ROOT = ../..
+
+CFLAGS  =
+LDFLAGS =
+
+all: basic.so basic.doc
+
+%.so: %.o
+	gcc -shared $(LDFLAGS) -o $@ $<
+
+%.o: %.c
+	gcc -ggdb3 -Wall -I$(ROOT)/src $(CFLAGS) -fPIC -c $<
+
+%.doc: %.c
+	$(ROOT)/lib-src/make-docfile $< > $@

modules/basic/basic.c

@@ -0,0 +1,64 @@
+/*
+
+  basic.c - sample module
+
+  This module provides a simple `basic-sum' function.
+
+  I've used the following prefixes throughout the code:
+  - Sfoo: subr (function wraper)
+  - Qfoo: symbol value
+  - Ffoo: function value
+
+*/
+
+#include <emacs_module.h>
+
+int plugin_is_GPL_compatible;
+
+/* C function we want to expose to emacs */
+static int64_t sum (int64_t a, int64_t b)
+{
+  return a + b;
+}
+
+/* Proper module subr that wraps the C function */
+static emacs_value Fsum (emacs_env *env, int nargs, emacs_value args[])
+{
+  int64_t a = env->fixnum_to_int (env, args[0]);
+  int64_t b = env->fixnum_to_int (env, args[1]);
+
+  int64_t r = sum(a, b);
+
+  return env->make_fixnum (env, r);
+}
+
+/* Binds NAME to FUN */
+static void bind_function (emacs_env *env, const char *name, emacs_value Ffun)
+{
+  emacs_value Qfset = env->intern (env, "fset");
+  emacs_value Qsym = env->intern (env, name);
+  emacs_value args[] = { Qsym, Ffun };
+
+  env->funcall (env, Qfset, 2, args);
+}
+
+/* Provide FEATURE to Emacs */
+static void provide (emacs_env *env, const char *feature)
+{
+  emacs_value Qfeat = env->intern (env, feature);
+  emacs_value Qprovide = env->intern (env, "provide");
+  emacs_value args[] = { Qfeat };
+
+  env->funcall (env, Qprovide, 1, args);
+}
+
+int emacs_module_init (struct emacs_runtime *ert)
+{
+  emacs_env *env = ert->get_environment (ert);
+  emacs_value Ssum = env->make_function (env, 2, 2, Fsum);
+
+  bind_function (env, "basic-sum", Ssum);
+  provide (env, "basic");
+
+  return 0;
+}

src/Makefile.in

@@ -367,7 +367,7 @@ base_obj = dispnew.o frame.o scroll.o xdisp.o menu.o $(XMENU_OBJ) window.o \
 	minibuf.o fileio.o dired.o \
 	cmds.o casetab.o casefiddle.o indent.o search.o regex.o undo.o \
 	alloc.o data.o doc.o editfns.o callint.o \
-	eval.o floatfns.o fns.o font.o print.o lread.o \
+	eval.o floatfns.o fns.o font.o print.o lread.o module.o \
 	syntax.o $(UNEXEC_OBJ) bytecode.o \
 	process.o gnutls.o callproc.o \
 	region-cache.o sound.o atimer.o \
@@ -427,7 +427,7 @@ LIBES = $(LIBS) $(W32_LIBS) $(LIBS_GNUSTEP) $(LIBX_BASE) $(LIBIMAGE) \
    $(LIBS_TERMCAP) $(GETLOADAVG_LIBS) $(SETTINGS_LIBS) $(LIBSELINUX_LIBS) \
    $(FREETYPE_LIBS) $(FONTCONFIG_LIBS) $(LIBOTF_LIBS) $(M17N_FLT_LIBS) \
    $(LIBGNUTLS_LIBS) $(LIB_PTHREAD) \
-   $(GFILENOTIFY_LIBS) $(LIB_MATH) $(LIBZ)
+   $(GFILENOTIFY_LIBS) $(LIB_MATH) $(LIBZ) -lltdl
 
 all: emacs$(EXEEXT) $(OTHER_FILES)
 .PHONY: all

src/emacs.c

@@ -1430,6 +1430,9 @@ Using an Emacs configured with --with-x-toolkit=lucid does not have this problem
       syms_of_terminal ();
       syms_of_term ();
       syms_of_undo ();
+
+      syms_of_module ();
+
 #ifdef HAVE_SOUND
       syms_of_sound ();
 #endif

src/emacs_module.h

@@ -0,0 +1,124 @@
+/*
+  emacs_module.h - Module API
+  Copyright (C) 2015 Free Software Foundation, Inc.
+
+  This file is part of GNU Emacs.
+
+  GNU Emacs is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  GNU Emacs is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef EMACS_MODULE_H
+#define EMACS_MODULE_H
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+/* Current environement */
+typedef struct emacs_env_25 emacs_env;
+typedef void* emacs_value;
+
+/* Struct passed to a module init function (emacs_module_init) */
+struct emacs_runtime {
+  size_t size;
+  emacs_env* (*get_environment)(struct emacs_runtime *ert);
+};
+
+
+/* Function prototype for the module init function */
+typedef int (*emacs_init_function)(struct emacs_runtime *ert);
+
+/* Function prototype for the module Lisp functions */
+typedef emacs_value (*emacs_subr)(emacs_env *env,
+                                  int nargs,
+                                  emacs_value args[]);
+struct emacs_env_25 {
+  /*
+   * Structure size (for version checking)
+   */
+
+  size_t size;
+
+  /*
+   * Memory management
+   */
+
+  emacs_value (*make_global_reference)(emacs_env *env,
+                                       emacs_value any_reference);
+
+  void (*free_global_reference)(emacs_env *env,
+                                emacs_value global_reference);
+
+  /*
+   * Error handling
+   */
+
+  bool (*error_check)(emacs_env *env);
+
+  void (*clear_error)(emacs_env *env);
+
+  bool (*get_error)(emacs_env *env,
+                    emacs_value *error_symbol_out,
+                    emacs_value *error_data_out);
+
+  void (*signal_error)(emacs_env *env,
+                       emacs_value error_symbol,
+                       emacs_value error_data);
+
+  /*
+   * Function registration
+   */
+
+  emacs_value (*make_function)(emacs_env *env,
+                               int min_arity,
+                               int max_arity,
+                               emacs_subr function);
+
+  emacs_value (*funcall)(emacs_env *env,
+                         emacs_value function,
+                         int nargs,
+                         emacs_value args[]);
+
+  emacs_value (*intern)(emacs_env *env,
+                        const char *symbol_name);
+
+  /*
+   * Type conversion
+   */
+
+  emacs_value (*type_of)(emacs_env *env,
+                         emacs_value value);
+
+  int64_t (*fixnum_to_int)(emacs_env *env,
+                           emacs_value value);
+
+  emacs_value (*make_fixnum)(emacs_env *env,
+                             int64_t value);
+
+  double (*float_to_c_double)(emacs_env *env,
+                              emacs_value value);
+
+  emacs_value (*make_float)(emacs_env *env,
+                            double value);
+
+  bool (*copy_string_contents)(emacs_env *env,
+                               emacs_value value,
+                               char *buffer,
+                               size_t* length_inout);
+
+  emacs_value (*make_string)(emacs_env *env,
+                             const char *contents);
+};
+
+#endif /* EMACS_MODULE_H */

src/lisp.h

@@ -4021,6 +4021,8 @@ Lisp_Object backtrace_top_function (void);
 extern bool let_shadows_buffer_binding_p (struct Lisp_Symbol *symbol);
 extern bool let_shadows_global_binding_p (Lisp_Object symbol);
 
+/* Defined in module.c.  */
+void syms_of_module (void);
 
 /* Defined in editfns.c.  */
 extern void insert1 (Lisp_Object);