bug#25082: [PATCH] Add support to emacsclient for command-lline options in ALTERNATE_EDITOR/--alternate-editor

[Reuben Thomas <rrt@sc3d.org>]

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The attached patch adds support to emacsclient for command-line options
when specifying the alternate editor, so that for example one can now say:

ALTERNATE_EDITOR="emacs -Q -nw"

I have added documentation to NEWS. It did not seem necessary to change the
man page, as nowhere does it imply that you can't do this, and I
implemented the feature when I found that it didn't work as I expected;
other similar environment variables with which users may be familiar, such
as EDITOR and VISUAL, already work like this.

-- 
http://rrt.sc3d.org

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From 20f8b12cb667d99bd62dda338558c797f29f6861 Mon Sep 17 00:00:00 2001
From: Reuben Thomas <rrt@sc3d.org>
Date: Thu, 1 Dec 2016 15:21:57 +0000
Subject: [PATCH 5/5] Add support for arguments in ALTERNATE_EDITOR to
 emacsclient

* lib-src/emacsclient.c (fail): Parse ALTERNATE_EDITOR, or
corresponding command-line argument, into space-separated tokens.
* etc/NEWS: Document.
---
 etc/NEWS              |  4 +++
 lib-src/emacsclient.c | 73 ++++++++++++++++++++++++++++++++++++++-------------
 2 files changed, 59 insertions(+), 18 deletions(-)

diff --git a/etc/NEWS b/etc/NEWS
index 33b8a42..c4f4569 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -268,6 +268,10 @@ variable of this kind to swap modifiers in Emacs.
 ---
 ** New input methods: 'cyrillic-tuvan', 'polish-prefix'.
 
+++
+** emacsclient now accepts command-line options in ALTERNATE_EDITOR
+and --alternate-editor. For example, ALTERNATE_EDITOR="emacs -Q -nw".
+
 \f
 * Editing Changes in Emacs 26.1
 
diff --git a/lib-src/emacsclient.c b/lib-src/emacsclient.c
index 2909d63..b561db6 100644
--- a/lib-src/emacsclient.c
+++ b/lib-src/emacsclient.c
@@ -109,6 +109,9 @@ char *w32_getenv (const char *);
 /* Name used to invoke this program.  */
 const char *progname;
 
+/* The first argument to main.  */
+int main_argc;
+
 /* The second argument to main.  */
 char **main_argv;
 
@@ -192,6 +195,35 @@ xmalloc (size_t size)
   return result;
 }
 
+/* Like realloc but get fatal error if memory is exhausted.  */
+
+static void *
+xrealloc (void *ptr, size_t size)
+{
+  void *result = realloc (ptr, size);
+  if (result == NULL)
+    {
+      perror ("realloc");
+      exit (EXIT_FAILURE);
+    }
+  return result;
+}
+
+/* Like strdup but get a fatal error if memory is exhausted. */
+char *xstrdup (const char *);
+
+char *
+xstrdup (const char *s)
+{
+  char *result = strdup (s);
+  if (result == NULL)
+    {
+      perror ("strdup");
+      exit (EXIT_FAILURE);
+    }
+  return result;
+}
+
 /* From sysdep.c */
 #if !defined (HAVE_GET_CURRENT_DIR_NAME) || defined (BROKEN_GET_CURRENT_DIR_NAME)
 
@@ -255,21 +287,6 @@ get_current_dir_name (void)
 
 #ifdef WINDOWSNT
 
-/* Like strdup but get a fatal error if memory is exhausted. */
-char *xstrdup (const char *);
-
-char *
-xstrdup (const char *s)
-{
-  char *result = strdup (s);
-  if (result == NULL)
-    {
-      perror ("strdup");
-      exit (EXIT_FAILURE);
-    }
-  return result;
-}
-
 #define REG_ROOT "SOFTWARE\\GNU\\Emacs"
 
 char *w32_get_resource (HKEY, const char *, LPDWORD);
@@ -651,7 +668,7 @@ Report bugs with M-x report-emacs-bug.\n");
 }
 
 /* Try to run a different command, or --if no alternate editor is
-   defined-- exit with an errorcode.
+   defined-- exit with an decoderde.
    Uses argv, but gets it from the global variable main_argv.  */
 
 static _Noreturn void
@@ -659,9 +676,27 @@ fail (void)
 {
   if (alternate_editor)
     {
-      int i = optind - 1;
+      size_t extra_args_size = (main_argc - optind + 1) * sizeof (char *);
+      size_t new_argv_size = extra_args_size;
+      char **new_argv = NULL;
+      /* Needed because strtok overwrites its input.  */
+      char *s = xstrdup (alternate_editor);
+      unsigned toks = 0;
+      char *tok = strtok(s, " ");
+
+      /* Unpack alternate_editor's space-separated tokens into new_argv.  */
+      do
+        {
+          toks++;
+          new_argv = xrealloc (new_argv, new_argv_size + toks * sizeof (char *));
+          new_argv[toks - 1] = tok;
+        }
+      while ((tok = strtok (NULL, " ")));
+
+      /* Append main_argv arguments to new_argv.  */
+      memcpy (&new_argv[toks], main_argv + optind, extra_args_size);
 
-      execvp (alternate_editor, main_argv + i);
+      execvp (s, new_argv);
       message (true, "%s: error executing alternate editor \"%s\"\n",
 	       progname, alternate_editor);
     }
@@ -674,6 +709,7 @@ fail (void)
 int
 main (int argc, char **argv)
 {
+  main_argc = argc;
   main_argv = argv;
   progname = argv[0];
   message (true, "%s: Sorry, the Emacs server is supported only\n"
@@ -1607,6 +1643,7 @@ main (int argc, char **argv)
   int start_daemon_if_needed;
   int exit_status = EXIT_SUCCESS;
 
+  main_argc = argc;
   main_argv = argv;
   progname = argv[0];
 
-- 
2.7.4