[RFC] Make "directories" a variable

[dje at google dot com (Doug Evans)]

Hi.

I needed to be able to reference source_path from python,
but it's not possible today because it's not a parameter
(in the python gdb.parameter sense, and the alternative
of adding a patch to allow capturing the output of "show dir"
feels like a hack).

This patch makes it a parameter,
and I'm looking for early feedback on this approach.

I like the addition of "set directories mumble", but that's just me,
and I know better than to be wedded to it. :-)
An alternative is to making directories a variable without a setter,
or have "set dir mumble" flag an error and referring the user to
the "dir" command.
The way I look at it, "dir" is just a wrapper around "set dir".
Today "set dir" is "private/protected" (so to speak), and the public
interface is the "dir" command.
I don't have a strong opinion on making "set dir" "public", but
I do think, though, that source_path should be a parameter.

There's no current entry for "directory search list" in
enum var_types, but there are at least two variables that
are directory search lists (directories and libthread-db-search-path).
Adding enum var_dir_search_list (or some such) is a reasonable way to go.
I haven't done that yet pending approval of making "directories" a
parameter.

Tom suggested in IRC returning a list in python.
I don't have a strong opinion on that either,
it's trivial for the user to work with either form.

doc updates also deferred pending positive feedback.

2009-10-05  Doug Evans  <dje@google.com>

	Make "directories" a variable so gdb.parameter ("directories")
	works from python.
	* source.c (source_path_1): New static global.
	(strip_builtin_search_dir): New function.
	(set_directories_command): New function.
	(show_directories_1): Renamed from show_directories,
	all callers updated.
	(show_directories_command): New function.
	(_initialize_source): Remove "directories" add_cmd, replace with
	add_setshow_optional_filename_cmd.

	* testsuite/gdb.base/help.exp (show directories): Update expected
	output.

Index: source.c
===================================================================
RCS file: /cvs/src/src/gdb/source.c,v
retrieving revision 1.104
diff -u -p -u -p -r1.104 source.c
--- source.c	22 Sep 2009 22:34:17 -0000	1.104
+++ source.c	6 Oct 2009 01:50:12 -0000
@@ -66,7 +66,10 @@ static void line_info (char *, int);
 
 static void source_info (char *, int);
 
-static void show_directories (char *, int);
+/* "set directories foo" stores the value here,
+   which is later copied to SOURCE_PATH by set_directories.  */
+
+static char *source_path_1;
 
 /* Path of directories to search for source files.
    Same format as the PATH environment variable's value.  */
@@ -302,14 +305,73 @@ select_source_symtab (struct symtab *s)
   error (_("Can't find a default source file"));
 }
 
+/* Subroutine of set_directories_command to simplify it.
+   Strip one $cdir or $cwd from PATH (by storing '\0').
+   Returns non-zero if a path element was removed, zero otherwise.  */
+
+static int
+strip_builtin_search_dir (char *path)
+{
+  char *p;
+  char *compare_here;
+  char *strip_here;
+
+  p = strrchr (path, DIRNAME_SEPARATOR);
+  if (p != NULL)
+    {
+      compare_here = p + 1;
+      strip_here = p;
+    }
+  else
+    {
+      compare_here = path;
+      strip_here = path;
+    }
+
+  if (strcmp (compare_here, "$cdir") == 0
+      || strcmp (compare_here, "$cwd") == 0)
+    {
+      *strip_here = '\0';
+      return 1;
+    }
+
+  return 0;
+}
+
 static void
-show_directories (char *ignore, int from_tty)
+set_directories_command (char *args, int from_tty, struct cmd_list_element *c)
+{
+  /* "set dir mumble" doesn't prepend paths, it resets the entire
+     path list.  The theory is that set(show(dir)) should be a no-op.  */
+
+  /* We preserve the invariant that $cdir:$cwd is always at the end of
+     the list.  This is done by stripping any trailing $cdir:$cwd from
+     SOURCE_PATH_1, and using the same code as the "dir" command.
+     This code doesn't make an assumption on the ordering of cdir/cwd.  */
+  if (strip_builtin_search_dir (source_path_1))
+    (void) strip_builtin_search_dir (source_path_1);
+
+  xfree (source_path);
+  init_source_path ();
+  if (*source_path_1 != '\0')
+    mod_path (source_path_1, &source_path);
+}
+
+static void
+show_directories_1 (char *ignore, int from_tty)
 {
   puts_filtered ("Source directories searched: ");
   puts_filtered (source_path);
   puts_filtered ("\n");
 }
 
+static void
+show_directories_command (struct ui_file *file, int from_tty,
+			  struct cmd_list_element *c, const char *value)
+{
+  show_directories_1 (NULL, from_tty);
+}
+
 /* Forget what we learned about line positions in source files, and
    which directories contain them; must check again now since files
    may be found in a different directory now.  */
@@ -381,7 +443,7 @@ directory_command (char *dirname, int fr
       forget_cached_source_info ();
     }
   if (from_tty)
-    show_directories ((char *) 0, from_tty);
+    show_directories_1 ((char *) 0, from_tty);
 }
 
 /* Add a path given with the -d command line switch.
@@ -1926,6 +1988,7 @@ void
 _initialize_source (void)
 {
   struct cmd_list_element *c;
+
   current_source_symtab = 0;
   init_source_path ();
 
@@ -1948,16 +2011,27 @@ With no argument, reset the search path 
 
   set_cmd_completer (c, filename_completer);
 
-  add_cmd ("directories", no_class, show_directories, _("\
-Current search path for finding source files.\n\
+  add_setshow_optional_filename_cmd ("directories",
+				     class_files,
+				     &source_path_1,
+				     _("\
+Set the search path for finding source files."),
+				     _("\
+Show the search path for finding source files."),
+				     _("\
 $cwd in the path means the current working directory.\n\
-$cdir in the path means the compilation directory of the source file."),
-	   &showlist);
+$cdir in the path means the compilation directory of the source file.\n\
+GDB ensures the search path always ends with $cdir:$cwd by\n\
+appending these paths if necessary.\n\
+Setting the value to an empty string sets it to $cdir:$cwd, the default."),
+			    set_directories_command,
+			    show_directories_command,
+			    &setlist, &showlist);
 
   if (xdb_commands)
     {
       add_com_alias ("D", "directory", class_files, 0);
-      add_cmd ("ld", no_class, show_directories, _("\
+      add_cmd ("ld", no_class, show_directories_1, _("\
 Current search path for finding source files.\n\
 $cwd in the path means the current working directory.\n\
 $cdir in the path means the compilation directory of the source file."),
Index: testsuite/gdb.base/help.exp
===================================================================
RCS file: /cvs/src/src/gdb/testsuite/gdb.base/help.exp,v
retrieving revision 1.35
diff -u -p -u -p -r1.35 help.exp
--- testsuite/gdb.base/help.exp	13 Aug 2009 14:58:27 -0000	1.35
+++ testsuite/gdb.base/help.exp	6 Oct 2009 01:50:13 -0000
@@ -513,7 +513,7 @@ gdb_test "help show confirm" "Show wheth
 # test help show convenience
 gdb_test "help show convenience" "Debugger convenience \\(\"\\\$foo\"\\) variables\.\[\r\n\]+These variables are created when you assign them values;\[\r\n\]+thus, \"print \\\$foo=1\" gives \"\\\$foo\" the value 1\.  Values may be any type\.\[\r\n\]+A few convenience variables are given values automatically:\[\r\n\]+\"\\\$_\"holds the last address examined with \"x\" or \"info lines\",\[\r\n\]+\"\\\$__\" holds the contents of the last address examined with \"x\"\." "help show convenience"
 # test help show directories
-gdb_test "help show directories" "Current search path for finding source files\.\[\r\n\]+\\\$cwd in the path means the current working directory\.\[\r\n\]+\\\$cdir in the path means the compilation directory of the source file\." "help show directories"
+gdb_test "help show directories" "Show the search path for finding source files\.\[\r\n\]+\\\$cwd in the path means the current working directory\.\[\r\n\]+\\\$cdir in the path means the compilation directory of the source file\..*" "help show directories"
 # test help show editing
 gdb_test "help show editing" "Show editing of command lines as they are typed\.\[\r\n\]+Use \"on\" to enable the editing, and \"off\" to disable it\.\[\r\n\]+Without an argument, command line editing is enabled\.  To edit, use\[\r\n\]+EMACS-like or VI-like commands like control-P or ESC\." "help show editing"
 # test help show environment