fish: edit: centralize the EDITOR handling

Allow null as value for the editor parameter of edit_file_editor, which
will then get it from the EDITOR envvar (falling back on vi).

This is basically code motion from the two edit_file_editor users to it.

edit/edit.c

@@ -333,15 +333,9 @@ edit (const char *filename, const char *root)
 
   if (perl_expr != NULL) {
     r = edit_file_perl (g, filename, perl_expr, backup_extension, verbose);
-  } else {
-    const char *editor;
-
-    editor = getenv ("EDITOR");
-    if (editor == NULL)
-      editor = "vi";
-
-    r = edit_file_editor (g, filename, editor, backup_extension, verbose);
-  }
+  } else
+    r = edit_file_editor (g, filename, NULL /* use $EDITOR */,
+                          backup_extension, verbose);
 
   switch (r) {
   case -1:

fish/edit.c

@@ -47,11 +47,8 @@ run_edit (const char *cmd, size_t argc, char *argv[])
     editor = "vi";
   else if (STRCASEEQ (cmd, "emacs"))
     editor = "emacs -nw";
-  else {
-    editor = getenv ("EDITOR");
-    if (editor == NULL)
-      editor = "vi"; /* could be cruel here and choose ed(1) */
-  }
+  else
+    editor = NULL; /* use $EDITOR */
 
   /* Handle 'win:...' prefix. */
   remotefilename = win_prefix (argv[0]);

fish/file-edit.c

@@ -52,6 +52,12 @@ edit_file_editor (guestfs_h *g, const char *filename, const char *editor,
   int r;
   struct utimbuf times;
 
+  if (editor == NULL) {
+    editor = getenv ("EDITOR");
+    if (editor == NULL)
+      editor = "vi";
+  }
+
   /* Download the file and write it to a temporary. */
   if (do_download (g, filename, &tmpfilename) == -1)
     return -1;

fish/file-edit.h

@@ -25,6 +25,9 @@
  * Edit 'filename' using the specified 'editor' application.
  * If 'backup_extension' is not null, then a copy of 'filename' is saved
  * with 'backup_extension' appended to its file name.
+ * If 'editor' is null, then the EDITOR environment variable
+ * will be queried for the editor application, leaving "vi" as fallback
+ * if not set.
  *
  * Returns -1 for failure, 0 on success, 1 if the editor did not change
  * the file (e.g. the user closed the editor without saving).