-Wwrite-strings: Add a PyArg_ParseTupleAndKeywords "const char *" overload

-Wwrite-strings flags code like:

   static char *keywords[] = {"command", "from_tty", "to_string", NULL };

as needing "(char *)" casts, because string literals are "const char []".

We can get rid of the casts by changing the array type like this:

 -  static char *keywords[] = {"command", "from_tty", "to_string", NULL };
 +  static const char *keywords[] = {"command", "from_tty", "to_string", NULL };

However, passing the such array to PyArg_ParseTupleAndKeywords no longer
works OOTB, because PyArg_ParseTupleAndKeywords expects a "char **":

  PyArg_ParseTupleAndKeywords(PyObject *args, PyObject *kw,
                              const char *format,
			      char *keywords[], ...);

and "const char **" is not implicitly convertible to "char **".  C++
is more tolerant that C here WRT aliasing, and a const_cast<char **>
is fine.  However, to avoid having all callers do the cast themselves,
this commit defines a gdb_PyArg_ParseTupleAndKeywords function here
with a corresponding 'keywords' parameter type that does the cast in a
single place.

gdb/ChangeLog:
2017-04-05  Pedro Alves  <palves@redhat.com>

	* python/python-internal.h (gdb_PyArg_ParseTupleAndKeywords): New
	static inline function.
	* python/py-arch.c (archpy_disassemble): Constify 'keywords'
	array and use gdb_PyArg_ParseTupleAndKeywords.
	* python/py-cmd.c (cmdpy_init): Likewise.
	* python/py-finishbreakpoint.c (bpfinishpy_init): Likewise.
	* python/py-inferior.c (infpy_read_memory, infpy_write_memory)
	(infpy_search_memory): Likewise.
	* python/py-objfile.c (objfpy_add_separate_debug_file)
	(gdbpy_lookup_objfile): Likewise.
	* python/py-symbol.c (gdbpy_lookup_symbol)
	(gdbpy_lookup_global_symbol): Likewise.
	* python/py-type.c (gdbpy_lookup_type): Likewise.
	* python/py-value.c (valpy_lazy_string, valpy_string): Likewise.
	* python/python.c (execute_gdb_command, gdbpy_write, gdbpy_flush):
	Likewise.

1 files changed, 6 insertions, 6 deletions

diff --git a/gdb/python/py-value.c b/gdb/python/py-value.c
index 9c0470f..b5a0ef8 100644
--- a/gdb/python/py-value.c
+++ b/gdb/python/py-value.c
@@ -431,11 +431,11 @@ valpy_lazy_string (PyObject *self, PyObject *args, PyObject *kw)
   gdb_py_longest length = -1;
   struct value *value = ((value_object *) self)->value;
   const char *user_encoding = NULL;
-  static char *keywords[] = { "encoding", "length", NULL };
+  static const char *keywords[] = { "encoding", "length", NULL };
   PyObject *str_obj = NULL;
 
-  if (!PyArg_ParseTupleAndKeywords (args, kw, "|s" GDB_PY_LL_ARG, keywords,
-				    &user_encoding, &length))
+  if (!gdb_PyArg_ParseTupleAndKeywords (args, kw, "|s" GDB_PY_LL_ARG,
+					keywords, &user_encoding, &length))
     return NULL;
 
   if (length < -1)
@@ -526,10 +526,10 @@ valpy_string (PyObject *self, PyObject *args, PyObject *kw)
   const char *user_encoding = NULL;
   const char *la_encoding = NULL;
   struct type *char_type;
-  static char *keywords[] = { "encoding", "errors", "length", NULL };
+  static const char *keywords[] = { "encoding", "errors", "length", NULL };
 
-  if (!PyArg_ParseTupleAndKeywords (args, kw, "|ssi", keywords,
-				    &user_encoding, &errors, &length))
+  if (!gdb_PyArg_ParseTupleAndKeywords (args, kw, "|ssi", keywords,
+					&user_encoding, &errors, &length))
     return NULL;
 
   TRY