Use unique_xmalloc_ptr in Python code

This changes some utility functions in the Python code to return
unique_xmalloc_ptr, and then fixes up the callers.

I chose unique_xmalloc_ptr rather than std::string because at a few
call points the xmalloc'd string is released and ownership transferred
elsewhere.

This patch found a few existing memory leaks.  For example,
py-unwind.c called gdbpy_obj_to_string but never freed the result.

Built and regression tested on the buildbot.

2016-11-09  Tom Tromey  <tom@tromey.com>

	* varobj.h (varobj_get_display_hint): Change return type.
	* varobj.c (varobj_get_display_hint): Return unique_xmalloc_ptr.
	(varobj_value_get_print_value): Update.
	* python/python.c (gdbpy_before_prompt_hook, gdbpy_print_stack)
	(gdbpy_apply_type_printers): Update.
	* python/python-internal.h (unicode_to_target_string)
	(python_string_to_target_string, python_string_to_host_string)
	(gdbpy_obj_to_string, gdbpy_exception_to_string)
	(gdbpy_get_display_hint): Change return types.
	* python/py-varobj.c (py_varobj_iter_next): Update.
	* python/py-value.c (valpy_getitem, convert_value_from_python):
	Update.
	* python/py-utils.c (unicode_to_encoded_string)
	(unicode_to_target_string, python_string_to_target_string)
	(python_string_to_host_string, gdbpy_obj_to_string)
	(gdbpy_exception_to_string): Return unique_xmalloc_ptr.
	* python/py-unwind.c (pyuw_parse_register_id): Update.
	* python/py-type.c (typy_getitem): Update.
	* python/py-prettyprint.c (gdbpy_get_display_hint)
	(print_stack_unless_memory_error, print_children)
	(gdbpy_apply_val_pretty_printer): Update.
	* python/py-param.c (set_parameter_value): Update.
	(get_doc_string, call_doc_function): Return unique_xmalloc_ptr.
	(get_set_value, get_show_value, compute_enum_values, parmpy_init):
	Update.
	* python/py-infthread.c (thpy_set_name): Update.
	* python/py-function.c (fnpy_call, fnpy_init): Update.
	* python/py-framefilter.c (extract_sym): Change "name" to
	unique_xmalloc_ptr.
	(enumerate_args, enumerate_locals): Update.
	(py_print_frame): Use unique_xmalloc_ptr.
	* python/py-frame.c (frapy_read_var): Update.  Remove cleanup.
	* python/py-cmd.c (cmdpy_function, cmdpy_completer, cmdpy_init):
	Update.
	* python/py-breakpoint.c (bppy_set_condition): Use
	unique_xmalloc_ptr.
	(bppy_init): Likewise.  Remove cleanup.
	(local_setattro): Update.
	* mi/mi-cmd-var.c (print_varobj, mi_cmd_var_list_children)
	(varobj_update_one): Update.

gdb/python/py-utils.c

@@ -107,10 +107,10 @@ python_string_to_unicode (PyObject *obj)
    conversion, NULL will be returned and a python exception will be set.
 
    The caller is responsible for xfree'ing the string.  */
-static char *
+static gdb::unique_xmalloc_ptr<char>
 unicode_to_encoded_string (PyObject *unicode_str, const char *charset)
 {
-  char *result;
+  gdb::unique_xmalloc_ptr<char> result;
   PyObject *string;
 
   /* Translate string to named charset.  */
@@ -119,9 +119,9 @@ unicode_to_encoded_string (PyObject *unicode_str, const char *charset)
     return NULL;
 
 #ifdef IS_PY3K
-  result = xstrdup (PyBytes_AsString (string));
+  result.reset (xstrdup (PyBytes_AsString (string)));
 #else
-  result = xstrdup (PyString_AsString (string));
+  result.reset (xstrdup (PyString_AsString (string)));
 #endif
 
   Py_DECREF (string);
@@ -140,12 +140,11 @@ unicode_to_encoded_python_string (PyObject *unicode_str, const char *charset)
   return PyUnicode_AsEncodedString (unicode_str, charset, NULL);
 }
 
-/* Returns a newly allocated string with the contents of the given unicode
-   string object converted to the target's charset.  If an error occurs during
-   the conversion, NULL will be returned and a python exception will be set.
-
-   The caller is responsible for xfree'ing the string.  */
-char *
+/* Returns a newly allocated string with the contents of the given
+   unicode string object converted to the target's charset.  If an
+   error occurs during the conversion, NULL will be returned and a
+   python exception will be set.  */
+gdb::unique_xmalloc_ptr<char>
 unicode_to_target_string (PyObject *unicode_str)
 {
   return unicode_to_encoded_string (unicode_str,
@@ -164,20 +163,18 @@ unicode_to_target_python_string (PyObject *unicode_str)
 }
 
 /* Converts a python string (8-bit or unicode) to a target string in
-   the target's charset.  Returns NULL on error, with a python exception set.
-
-   The caller is responsible for xfree'ing the string.  */
-char *
+   the target's charset.  Returns NULL on error, with a python
+   exception set.  */
+gdb::unique_xmalloc_ptr<char>
 python_string_to_target_string (PyObject *obj)
 {
   PyObject *str;
-  char *result;
 
   str = python_string_to_unicode (obj);
   if (str == NULL)
     return NULL;
 
-  result = unicode_to_target_string (str);
+  gdb::unique_xmalloc_ptr<char> result (unicode_to_target_string (str));
   Py_DECREF (str);
   return result;
 }
@@ -203,20 +200,19 @@ python_string_to_target_python_string (PyObject *obj)
 }
 
 /* Converts a python string (8-bit or unicode) to a target string in
-   the host's charset.  Returns NULL on error, with a python exception set.
-
-   The caller is responsible for xfree'ing the string.  */
-char *
+   the host's charset.  Returns NULL on error, with a python exception
+   set.  */
+gdb::unique_xmalloc_ptr<char>
 python_string_to_host_string (PyObject *obj)
 {
   PyObject *str;
-  char *result;
 
   str = python_string_to_unicode (obj);
   if (str == NULL)
     return NULL;
 
-  result = unicode_to_encoded_string (str, host_charset ());
+  gdb::unique_xmalloc_ptr<char>
+    result (unicode_to_encoded_string (str, host_charset ()));
   Py_DECREF (str);
   return result;
 }
@@ -243,20 +239,21 @@ gdbpy_is_string (PyObject *obj)
 }
 
 /* Return the string representation of OBJ, i.e., str (obj).
-   Space for the result is malloc'd, the caller must free.
    If the result is NULL a python error occurred, the caller must clear it.  */
 
-char *
+gdb::unique_xmalloc_ptr<char>
 gdbpy_obj_to_string (PyObject *obj)
 {
   PyObject *str_obj = PyObject_Str (obj);
 
   if (str_obj != NULL)
     {
+      gdb::unique_xmalloc_ptr<char> msg;
+
 #ifdef IS_PY3K
-      char *msg = python_string_to_host_string (str_obj);
+      msg = python_string_to_host_string (str_obj);
 #else
-      char *msg = xstrdup (PyString_AsString (str_obj));
+      msg.reset (xstrdup (PyString_AsString (str_obj)));
 #endif
 
       Py_DECREF (str_obj);
@@ -269,14 +266,11 @@ gdbpy_obj_to_string (PyObject *obj)
 /* Return the string representation of the exception represented by
    TYPE, VALUE which is assumed to have been obtained with PyErr_Fetch,
    i.e., the error indicator is currently clear.
-   Space for the result is malloc'd, the caller must free.
    If the result is NULL a python error occurred, the caller must clear it.  */
 
-char *
+gdb::unique_xmalloc_ptr<char>
 gdbpy_exception_to_string (PyObject *ptype, PyObject *pvalue)
 {
-  char *str;
-
   /* There are a few cases to consider.
      For example:
      pvalue is a string when PyErr_SetString is used.
@@ -288,11 +282,9 @@ gdbpy_exception_to_string (PyObject *ptype, PyObject *pvalue)
      gdb.GdbError ("message").  */
 
   if (pvalue && pvalue != Py_None)
-    str = gdbpy_obj_to_string (pvalue);
+    return gdbpy_obj_to_string (pvalue);
   else
-    str = gdbpy_obj_to_string (ptype);
-
-  return str;
+    return gdbpy_obj_to_string (ptype);
 }
 
 /* Convert a GDB exception to the appropriate Python exception.