[PATCH 5/6] Safe wrappers for some string conversions

[Tom Tromey <tom@tromey.com>]

This adds a couple of new Python wrappers for "safe-style" string
conversions.  This allows some FIXME removal.

Note that I've added a new gdbpy_borrowed_ref constructor, from
gdbpy_opt_borrowed_ref.  This is checked at runtime to preserve the
invariant.
---
 gdb/python/py-frame.c        |  9 ++-------
 gdb/python/py-ref.h          |  7 +++++++
 gdb/python/py-tui.c          |  7 +------
 gdb/python/py-utils.c        | 20 ++++++++++++++++++++
 gdb/python/python-internal.h |  4 ++++
 5 files changed, 34 insertions(+), 13 deletions(-)

diff --git a/gdb/python/py-frame.c b/gdb/python/py-frame.c
index e4dd9e9252e..e34d4b5d2e9 100644
--- a/gdb/python/py-frame.c
+++ b/gdb/python/py-frame.c
@@ -355,13 +355,8 @@ frame_object::read_var (gdbpy_borrowed_ref<> args,
     var = symbol_object_to_symbol (sym_obj);
   else if (gdbpy_is_string (sym_obj))
     {
-      gdb::unique_xmalloc_ptr<char>
-	var_name (python_string_to_target_string (sym_obj));
-
-      /* FIXME: Python safety.  python_string_to_target_string should
-	 throw on error.  */
-      if (var_name == nullptr)
-	throw gdb_python_exception ();
+      gdb::unique_xmalloc_ptr<char> var_name
+	= safe_python_string_to_target_string (sym_obj);
 
       if (block_obj != nullptr)
 	{
diff --git a/gdb/python/py-ref.h b/gdb/python/py-ref.h
index 3d0373b7001..7cbfb03b103 100644
--- a/gdb/python/py-ref.h
+++ b/gdb/python/py-ref.h
@@ -108,6 +108,13 @@ class gdbpy_borrowed_ref : public gdbpy_opt_borrowed_ref<T>
     gdb_assert (this->m_obj != nullptr);
   }
 
+  template<typename U>
+  gdbpy_borrowed_ref (gdbpy_opt_borrowed_ref<U> obj)
+    : gdbpy_opt_borrowed_ref<T> (obj)
+  {
+    gdb_assert (this->m_obj != nullptr);
+  }
+
   gdbpy_borrowed_ref (std::nullptr_t) = delete;
 
   /* Allow a (checked) conversion to any subclass of T.  */
diff --git a/gdb/python/py-tui.c b/gdb/python/py-tui.c
index 388e441ed55..be8c22aac27 100644
--- a/gdb/python/py-tui.c
+++ b/gdb/python/py-tui.c
@@ -506,13 +506,8 @@ gdbpy_tui_window::set_title (gdbpy_opt_borrowed_ref<> new_title)
     gdbpy_err_format (PyExc_TypeError,
 		      _("Cannot delete \"title\" attribute."));
 
-  /* FIXME: Python safety.  Ideally python_string_to_host_string would
-     throw on error, but this can't be done until more of the code has
-     been converted.  */
   gdb::unique_xmalloc_ptr<char> value
-    = python_string_to_host_string (new_title);
-  if (value == nullptr)
-    throw gdb_python_exception ();
+    = safe_python_string_to_host_string (new_title);
 
   window->set_title (value.get ());
 }
diff --git a/gdb/python/py-utils.c b/gdb/python/py-utils.c
index 1c68b206601..40433256c62 100644
--- a/gdb/python/py-utils.c
+++ b/gdb/python/py-utils.c
@@ -119,6 +119,16 @@ python_string_to_target_string (PyObject *obj)
   return unicode_to_target_string (str.get ());
 }
 
+/* Wrapper for python_string_to_target_string that throws on failure.  */
+gdb::unique_xmalloc_ptr<char>
+safe_python_string_to_target_string (gdbpy_borrowed_ref<> obj)
+{
+  gdb::unique_xmalloc_ptr<char> result = python_string_to_target_string (obj);
+  if (result == nullptr)
+    throw gdb_python_exception ();
+  return result;
+}
+
 /* 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.
@@ -147,6 +157,16 @@ python_string_to_host_string (PyObject *obj)
   return unicode_to_encoded_string (str.get (), host_charset ());
 }
 
+/* Wrapper for python_string_to_host_string that throws on failure.  */
+gdb::unique_xmalloc_ptr<char>
+safe_python_string_to_host_string (gdbpy_borrowed_ref<> obj)
+{
+  gdb::unique_xmalloc_ptr<char> result = python_string_to_host_string (obj);
+  if (result == nullptr)
+    throw gdb_python_exception ();
+  return result;
+}
+
 /* See python/python-internal.h.  */
 
 gdbpy_ref<>
diff --git a/gdb/python/python-internal.h b/gdb/python/python-internal.h
index 5515820411b..ee1a19131bd 100644
--- a/gdb/python/python-internal.h
+++ b/gdb/python/python-internal.h
@@ -1017,8 +1017,12 @@ void gdbpy_print_stack_or_quit ();
 gdbpy_ref<> python_string_to_unicode (PyObject *obj);
 gdb::unique_xmalloc_ptr<char> unicode_to_target_string (PyObject *unicode_str);
 gdb::unique_xmalloc_ptr<char> python_string_to_target_string (PyObject *obj);
+gdb::unique_xmalloc_ptr<char> safe_python_string_to_target_string
+    (gdbpy_borrowed_ref<> obj);
 gdbpy_ref<> python_string_to_target_python_string (PyObject *obj);
 gdb::unique_xmalloc_ptr<char> python_string_to_host_string (PyObject *obj);
+gdb::unique_xmalloc_ptr<char> safe_python_string_to_host_string
+    (gdbpy_borrowed_ref<> obj);
 
 /* Convert a host string STR to a python string.  */
 

-- 
2.49.0