RFA: interactive command to enable parser debugging

[Tom Tromey <tromey@redhat.com>]

I've been looking at a few possible parser bugs lately, and I wanted to
be able to set "yydebug" interactively.

This patch adds a "set debug parser" command that can be used to do this.
This seems ok to me because we define YYDEBUG in c-exp.y.

I did not modify the other parsers to respect this flag.  I leave that
to the relevant language maintainers.

This needs a doc review.

Let me know what you think.  Barring objection I will commit it once the
doc patch is satisfactory.

Tom

2010-02-09  Tom Tromey  <tromey@redhat.com>

	* parser-defs.h (parser_debug): Declare.
	* parse.c (_initialize_parse): Install "debug parser" set/show
	command.
	(parser_debug): New global.
	(show_parserdebug): New function.
	* c-exp.y (c_parse): Set yydebug.

2010-02-09  Tom Tromey  <tromey@redhat.com>

	* gdb.texinfo (Debugging Output): Document set debug parser and
	show debug parser.

diff --git a/gdb/c-exp.y b/gdb/c-exp.y
index 459177a..095ec40 100644
--- a/gdb/c-exp.y
+++ b/gdb/c-exp.y
@@ -2555,6 +2555,9 @@ c_parse (void)
   gdb_assert (! macro_original_text);
   make_cleanup (scan_macro_cleanup, 0);
 
+  make_cleanup_restore_integer (&yydebug);
+  yydebug = parser_debug;
+
   /* Initialize some state used by the lexer.  */
   last_was_structop = 0;
   saw_name_at_eof = 0;
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 2145f2b..c645fa2 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -18848,6 +18848,11 @@ is off.
 @item show debug overload
 Displays the current state of displaying @value{GDBN} C@t{++} overload
 debugging info.
+@item show debug parser
+Show the current state of expression parser debugging.
+@item set debug parser
+Turns on or off the display of expression parser debugging output.
+The default is off.
 @cindex packets, reporting on stdout
 @cindex serial connections, debugging
 @cindex debug remote protocol
diff --git a/gdb/parse.c b/gdb/parse.c
index 1c73d75..d54053b 100644
--- a/gdb/parse.c
+++ b/gdb/parse.c
@@ -109,6 +109,18 @@ show_expressiondebug (struct ui_file *file, int from_tty,
   fprintf_filtered (file, _("Expression debugging is %s.\n"), value);
 }
 
+
+/* Non-zero if an expression parser should set yydebug.  */
+int parser_debug;
+
+static void
+show_parserdebug (struct ui_file *file, int from_tty,
+		  struct cmd_list_element *c, const char *value)
+{
+  fprintf_filtered (file, _("Parser debugging is %s.\n"), value);
+}
+
+
 static void free_funcalls (void *ignore);
 
 static int prefixify_expression (struct expression *);
@@ -1388,4 +1400,12 @@ When non-zero, the internal representation of expressions will be printed."),
 			    NULL,
 			    show_expressiondebug,
 			    &setdebuglist, &showdebuglist);
+  add_setshow_boolean_cmd ("parser", class_maintenance,
+			    &parser_debug, _("\
+Set parser debugging."), _("\
+Show parser debugging."), _("\
+When non-zero, expression parser tracing will be enabled."),
+			    NULL,
+			    show_parserdebug,
+			    &setdebuglist, &showdebuglist);
 }
diff --git a/gdb/parser-defs.h b/gdb/parser-defs.h
index 6fcf7ae..c4eb1a0 100644
--- a/gdb/parser-defs.h
+++ b/gdb/parser-defs.h
@@ -29,6 +29,8 @@
 
 struct block;
 
+extern int parser_debug;
+
 extern struct expression *expout;
 extern int expout_size;
 extern int expout_ptr;