RFA: add to_string argument to gdb.execute

[Tom Tromey <tromey at redhat dot com>]

I plan to check this in.  It needs a doc review.

This adds a to_string argument to gdb.execute, so you can capture
command output in a python string.

I've gone back and forth on how I wanted to implement this idea, but in
the end I settled on this approach as very simple and useful.

This patch also adds keyword arguments to gdb.execute.  I think our rule
should be that any function with 2 or more arguments should take keyword
arguments; we violate this in a couple of places.

There is still room for a bigger change, involving structured output
from gdb.  My plan there is to expose MI commands to Python, and make a
new kind of ui_out that creates Python objects.  I think this approach
has several nice points: we know it will be fairly complete (because MI
is), and we already have documentation.

Built and regtested on x86-64 (compile farm).

Tom

2010-06-10  Tom Tromey  <tromey@redhat.com>

	PR python/10808:
	* python/python.c (execute_gdb_command): Add keywords.  Accept
	"to_string" argument.
	(struct restore_ui_file_closure): New.
	(restore_ui_file): New function.
	(make_cleanup_restore_ui_file): Likewise.
	(GdbMethods) <execute>: Update.

2010-06-10  Tom Tromey  <tromey@redhat.com>

	PR python/10808:
	* gdb.texinfo (Basic Python): Document new gdb.execute argument.

2010-06-10  Tom Tromey  <tromey@redhat.com>

	PR python/10808:
	* gdb.python/python.exp: Add new tests.

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index fa7a0ec..e7af24a 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -20045,15 +20045,20 @@ methods and classes added by @value{GDBN} are placed in this module.
 use in all scripts evaluated by the @code{python} command.
 
 @findex gdb.execute
-@defun execute command [from_tty]
+@defun execute command [from_tty] [to_string]
 Evaluate @var{command}, a string, as a @value{GDBN} CLI command.
 If a GDB exception happens while @var{command} runs, it is
 translated as described in @ref{Exception Handling,,Exception Handling}.
-If no exceptions occur, this function returns @code{None}.
 
 @var{from_tty} specifies whether @value{GDBN} ought to consider this
 command as having originated from the user invoking it interactively.
 It must be a boolean value.  If omitted, it defaults to @code{False}.
+
+By default, any output produced by @var{command} is sent to
+@value{GDBN}'s standard output.  If the @var{to_string} parameter is
+@code{True}, then output will be collected by @code{gdb.execute} and
+returned as a string.  The default is @code{False}, in which case the
+return value is @code{None}.
 @end defun
 
 @findex gdb.breakpoints
diff --git a/gdb/python/python.c b/gdb/python/python.c
index 31880c1..c4d4a55 100644
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -309,36 +309,94 @@ gdbpy_target_wide_charset (PyObject *self, PyObject *args)
   return PyUnicode_Decode (cset, strlen (cset), host_charset (), NULL);
 }
 
+struct restore_ui_file_closure
+{
+  struct ui_file **variable;
+  struct ui_file *value;
+};
+
+static void
+restore_ui_file (void *p)
+{
+  struct restore_ui_file_closure *closure = p;
+
+  *(closure->variable) = closure->value;
+}
+
+/* Remember the current value of *VARIABLE and make it restored when
+   the cleanup is run.  */
+struct cleanup *
+make_cleanup_restore_ui_file (struct ui_file **variable)
+{
+  struct restore_ui_file_closure *c = XNEW (struct restore_ui_file_closure);
+
+  c->variable = variable;
+  c->value = *variable;
+
+  return make_cleanup_dtor (restore_ui_file, (void *) c, xfree);
+}
+
 /* A Python function which evaluates a string using the gdb CLI.  */
 
 static PyObject *
-execute_gdb_command (PyObject *self, PyObject *args)
+execute_gdb_command (PyObject *self, PyObject *args, PyObject *kw)
 {
   char *arg;
-  PyObject *from_tty_obj = NULL;
-  int from_tty;
-  int cmp;
+  PyObject *from_tty_obj = NULL, *to_string_obj = NULL;
+  int from_tty, to_string;
   volatile struct gdb_exception except;
+  static char *keywords[] = {"command", "from_tty", "to_string", NULL };
+  char *result = NULL;
 
-  if (! PyArg_ParseTuple (args, "s|O!", &arg, &PyBool_Type, &from_tty_obj))
+  if (! PyArg_ParseTupleAndKeywords (args, kw, "s|O!O!", keywords, &arg,
+				     &PyBool_Type, &from_tty_obj,
+				     &PyBool_Type, &to_string_obj))
     return NULL;
 
   from_tty = 0;
   if (from_tty_obj)
     {
-      cmp = PyObject_IsTrue (from_tty_obj);
+      int cmp = PyObject_IsTrue (from_tty_obj);
       if (cmp < 0)
-	  return NULL;
+	return NULL;
       from_tty = cmp;
     }
 
+  to_string = 0;
+  if (to_string_obj)
+    {
+      int cmp = PyObject_IsTrue (to_string_obj);
+      if (cmp < 0)
+	return NULL;
+      to_string = cmp;
+    }
+
   TRY_CATCH (except, RETURN_MASK_ALL)
     {
       /* Copy the argument text in case the command modifies it.  */
       char *copy = xstrdup (arg);
       struct cleanup *cleanup = make_cleanup (xfree, copy);
+      struct ui_file *str_file = NULL;
+
+      if (to_string)
+	{
+	  str_file = mem_fileopen ();
+
+	  make_cleanup_restore_ui_file (&gdb_stdout);
+	  make_cleanup_restore_ui_file (&gdb_stderr);
+	  make_cleanup_ui_file_delete (str_file);
+
+	  gdb_stdout = str_file;
+	  gdb_stderr = str_file;
+	}
 
       execute_command (copy, from_tty);
+
+      if (str_file)
+	result = ui_file_xstrdup (str_file, NULL);
+      else
+	result = NULL;
+
       do_cleanups (cleanup);
     }
   GDB_PY_HANDLE_EXCEPTION (except);
@@ -346,6 +404,12 @@ execute_gdb_command (PyObject *self, PyObject *args)
   /* Do any commands attached to breakpoint we stopped at.  */
   bpstat_do_actions ();
 
+  if (result)
+    {
+      PyObject *r = PyString_FromString (result);
+      xfree (result);
+      return r;
+    }
   Py_RETURN_NONE;
 }
 
@@ -737,7 +801,7 @@ static PyMethodDef GdbMethods[] =
 {
   { "history", gdbpy_history, METH_VARARGS,
     "Get a value from history" },
-  { "execute", execute_gdb_command, METH_VARARGS,
+  { "execute", (PyCFunction) execute_gdb_command, METH_VARARGS | METH_KEYWORDS,
     "Execute a gdb command" },
   { "parameter", gdbpy_parameter, METH_VARARGS,
     "Return a gdb parameter's value" },
diff --git a/gdb/testsuite/gdb.python/python.exp b/gdb/testsuite/gdb.python/python.exp
index b345ad2..f7f11cc 100644
--- a/gdb/testsuite/gdb.python/python.exp
+++ b/gdb/testsuite/gdb.python/python.exp
@@ -80,3 +80,7 @@ gdb_test "source $srcdir/$subdir/source2.py" "yes"
 
 gdb_test "python print gdb.current_objfile()" "None"
 gdb_test "python print gdb.objfiles()" "\\\[\\\]"
+
+gdb_test_no_output \
+    "python x = gdb.execute('printf \"%d\", 23', to_string = True)"
+gdb_test "python print x" "23"