[python] fix latest round of MI buglets

[Tom Tromey <tromey at redhat dot com>]

I'm checking this in on the python branch.

This adds some test cases for things Vladimir mentioned in his latest
email, and also has fixes for the problems.

I also fixed a crash I found while writing the new tests.

Tom

2009-08-26  Tom Tromey  <tromey@redhat.com>

	* varobj.c (dynamic_varobj_has_child_method): New function.
	(value_get_print_value): Use it.
	(install_new_value_visualizer): Do nothing if value==NULL.

2009-08-26  Tom Tromey  <tromey@redhat.com>

	* gdb.python/python-prettyprint.c (main): Add 'container2'.  Add
	extra dummy add_item call.
	* gdb.python/python-mi.exp: Add new tests.  Use
	mi_create_dynamic_varobj.
	* lib/mi-support.exp (mi_create_dynamic_varobj): New proc.

diff --git a/gdb/testsuite/gdb.python/python-mi.exp b/gdb/testsuite/gdb.python/python-mi.exp
index 095ee78..fc74fcf 100644
--- a/gdb/testsuite/gdb.python/python-mi.exp
+++ b/gdb/testsuite/gdb.python/python-mi.exp
@@ -48,7 +48,7 @@ mi_gdb_test "python execfile ('${srcdir}/${subdir}/${testfile}.py')" ""
 mi_continue_to_line [gdb_get_line_number {MI breakpoint here} ${testfile}.c] \
   "step to breakpoint"
 
-mi_create_floating_varobj container c \
+mi_create_dynamic_varobj container c \
   "create container varobj, no pretty-printing"
 
 mi_list_varobj_children container {
@@ -61,7 +61,7 @@ mi_delete_varobj container "delete varobj"
 
 mi_gdb_test "-enable-pretty-printing" ""
 
-mi_create_floating_varobj container c \
+mi_create_dynamic_varobj container c \
   "create container varobj"
 
 mi_list_varobj_children container {
@@ -150,6 +150,16 @@ mi_list_varobj_children container {
 
 mi_next "next over update 4"
 
+
+# Regression test: examine an object that has no children, then update
+# it to ensure that we don't print the children.
+mi_create_dynamic_varobj container2 c2 \
+  "create second container varobj"
+
+mi_gdb_test "-var-update container2" \
+  "\\^done,changelist=.." \
+  "update varobj, no children requested"
+
 # This should only show the first child, because the update range has
 # been set.
 mi_varobj_update_dynamic container \
diff --git a/gdb/testsuite/gdb.python/python-prettyprint.c b/gdb/testsuite/gdb.python/python-prettyprint.c
index 6bbbf1d..deca2e9 100644
--- a/gdb/testsuite/gdb.python/python-prettyprint.c
+++ b/gdb/testsuite/gdb.python/python-prettyprint.c
@@ -162,6 +162,7 @@ main ()
   struct ss  ssa[2];
   string x = make_string ("this is x");
   zzz_type c = make_container ("container");
+  zzz_type c2 = make_container ("container2");
   const struct string_repr cstring = { { "const string" } };
   /* Clearing by being `static' could invoke an other GDB C++ bug.  */
   struct nullstr nullstr;
@@ -206,6 +207,7 @@ main ()
   add_item (&c, 1011);
   c.elements[0] = 1023;
 
+  add_item (&c, 2222);		/* dummy */
   do_nothing ();
 #endif
 
diff --git a/gdb/testsuite/lib/mi-support.exp b/gdb/testsuite/lib/mi-support.exp
index 64bc28e..3a42704 100644
--- a/gdb/testsuite/lib/mi-support.exp
+++ b/gdb/testsuite/lib/mi-support.exp
@@ -1214,6 +1214,14 @@ proc mi_create_varobj_checked { name expression type testname } {
         $testname
 }
 
+# Same as mi_create_floating_varobj, but assumes the test is creating
+# a dynamic varobj that has children, so the value must be "{...}".
+proc mi_create_dynamic_varobj {name expression testname} {
+    mi_gdb_test "-var-create $name @ $expression" \
+        "\\^done,name=\"$name\",numchild=\"\(-1\|\[0-9\]+\)\",value=\"{\\.\\.\\.}\",type=.*" \
+        $testname
+}
+
 # Deletes the specified NAME. 
 proc mi_delete_varobj { name testname } {
     mi_gdb_test "-var-delete $name" \
diff --git a/gdb/varobj.c b/gdb/varobj.c
index 357c990..cbab433 100644
--- a/gdb/varobj.c
+++ b/gdb/varobj.c
@@ -923,6 +923,23 @@ install_dynamic_child (struct varobj *var,
     }
 }
 
+#if HAVE_PYTHON
+
+static int
+dynamic_varobj_has_child_method (struct varobj *var)
+{
+  struct cleanup *back_to;
+  PyObject *printer = var->pretty_printer;
+  int result;
+
+  back_to = varobj_ensure_python_env (var);
+  result = PyObject_HasAttr (printer, gdbpy_children_cst);
+  do_cleanups (back_to);
+  return result;
+}
+
+#endif
+
 static int
 update_dynamic_varobj_children (struct varobj *var,
 				VEC (varobj_p) **changed,
@@ -1363,8 +1380,9 @@ static void
 install_new_value_visualizer (struct varobj *var)
 {
 #if HAVE_PYTHON
-  /* If the constructor is None, then we want the raw value.  */
-  if (var->constructor != Py_None)
+  /* If the constructor is None, then we want the raw value.  If VAR
+     does not have a value, just skip this.  */
+  if (var->constructor != Py_None && var->value)
     {
       struct cleanup *cleanup;
       PyObject *pretty_printer = NULL;
@@ -2385,12 +2403,7 @@ value_get_print_value (struct value *value, enum varobj_display_formats format,
       {
 	/* First check to see if we have any children at all.  If so,
 	   we simply return {...}.  */
-	if (var->num_children == -1)
-	  {
-	    int dummy;
-	    update_dynamic_varobj_children (var, NULL, NULL, &dummy, 0, 0);
-	  }
-	if (var->num_children > 0 || var->saved_item)
+	if (dynamic_varobj_has_child_method (var))
 	  return xstrdup ("{...}");
 
 	if (PyObject_HasAttr (value_formatter, gdbpy_to_string_cst))