[PATCH 14/18] -Wwrite-strings: Add a PyArg_ParseTupleAndKeywords "const char *" overload

[Pedro Alves <palves@redhat.com>]

-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 like this:

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

However, passing the 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 **>
would be fine.

However, to avoid having all callers add the 'const_cast<char **>'
themselves, this commit define a PyArg_ParseTupleAndKeywords overload
here with a corresponding 'keywords' parameter type that does the cast
in a single place.

As in the PyGetSetDef patch, I'd be fine with naming this
gdb_PyArg_ParseTupleAndKeywords instead, if people would find having
our own overload confusing.

BTW, this API issue was discussed years ago in the python-dev list:

 https://mail.python.org/pipermail/python-dev/2006-February/060689.html

... and an overload for C++ was suggested in there somewhere.
Unfortunately, it was never added.

gdb/ChangeLog:
yyyy-mm-dd  Pedro Alves  <palves@redhat.com>

	* python/py-arch.c (archpy_disassemble): Constify 'keywords'
	array.
	* python/py-cmd.c (cmdpy_init): Constify 'keywords' array.
	* python/py-finishbreakpoint.c (bpfinishpy_init): Constify
	'keywords' array.
	* python/py-inferior.c (infpy_read_memory, infpy_write_memory)
	(infpy_search_memory): Constify 'keywords' array.
	* python/py-objfile.c (objfpy_add_separate_debug_file)
	(gdbpy_lookup_objfile): Constify 'keywords' array.
	* python/py-symbol.c (gdbpy_lookup_symbol)
	(gdbpy_lookup_global_symbol): Constify 'keywords' array.
	* python/py-type.c (gdbpy_lookup_type): Constify 'keywords' array.
	* python/py-value.c (valpy_lazy_string, valpy_string): Constify
	'keywords' array.
	* python/python.c (execute_gdb_command, gdbpy_write, gdbpy_flush):
	Constify 'keywords' array.
	* python/python-internal.h (PyArg_ParseTupleAndKeywords): New
	function overload.
---
 gdb/python/py-arch.c             |  2 +-
 gdb/python/py-breakpoint.c       |  4 ++--
 gdb/python/py-cmd.c              |  6 +++---
 gdb/python/py-finishbreakpoint.c |  2 +-
 gdb/python/py-inferior.c         |  6 +++---
 gdb/python/py-objfile.c          |  4 ++--
 gdb/python/py-symbol.c           |  4 ++--
 gdb/python/py-type.c             |  2 +-
 gdb/python/py-value.c            |  4 ++--
 gdb/python/python-internal.h     | 25 +++++++++++++++++++++++++
 gdb/python/python.c              |  6 +++---
 11 files changed, 45 insertions(+), 20 deletions(-)

diff --git a/gdb/python/py-arch.c b/gdb/python/py-arch.c
index 71d2989..48fae32 100644
--- a/gdb/python/py-arch.c
+++ b/gdb/python/py-arch.c
@@ -116,7 +116,7 @@ archpy_name (PyObject *self, PyObject *args)
 static PyObject *
 archpy_disassemble (PyObject *self, PyObject *args, PyObject *kw)
 {
-  static char *keywords[] = { "start_pc", "end_pc", "count", NULL };
+  static const char *keywords[] = { "start_pc", "end_pc", "count", NULL };
   CORE_ADDR start, end = 0;
   CORE_ADDR pc;
   gdb_py_ulongest start_temp;
diff --git a/gdb/python/py-breakpoint.c b/gdb/python/py-breakpoint.c
index 724a7ed..2043d42 100644
--- a/gdb/python/py-breakpoint.c
+++ b/gdb/python/py-breakpoint.c
@@ -637,8 +637,8 @@ bppy_get_ignore_count (PyObject *self, void *closure)
 static int
 bppy_init (PyObject *self, PyObject *args, PyObject *kwargs)
 {
-  static char *keywords[] = { "spec", "type", "wp_class", "internal",
-			      "temporary", NULL };
+  static const char *keywords[] = { "spec", "type", "wp_class", "internal",
+				    "temporary", NULL };
   const char *spec;
   int type = bp_breakpoint;
   int access_type = hw_write;
diff --git a/gdb/python/py-cmd.c b/gdb/python/py-cmd.c
index 3aaf7f9..8f61d9c 100644
--- a/gdb/python/py-cmd.c
+++ b/gdb/python/py-cmd.c
@@ -490,8 +490,8 @@ cmdpy_init (PyObject *self, PyObject *args, PyObject *kw)
   char *docstring = NULL;
   struct cmd_list_element **cmd_list;
   char *cmd_name, *pfx_name;
-  static char *keywords[] = { "name", "command_class", "completer_class",
-			      "prefix", NULL };
+  static const char *keywords[] = { "name", "command_class", "completer_class",
+				    "prefix", NULL };
   PyObject *is_prefix = NULL;
   int cmp;
 
@@ -506,7 +506,7 @@ cmdpy_init (PyObject *self, PyObject *args, PyObject *kw)
 
   if (! PyArg_ParseTupleAndKeywords (args, kw, "si|iO",
 				     keywords, &name, &cmdtype,
-			  &completetype, &is_prefix))
+				     &completetype, &is_prefix))
     return -1;
 
   if (cmdtype != no_class && cmdtype != class_run
diff --git a/gdb/python/py-finishbreakpoint.c b/gdb/python/py-finishbreakpoint.c
index 106fe34..9d43d55 100644
--- a/gdb/python/py-finishbreakpoint.c
+++ b/gdb/python/py-finishbreakpoint.c
@@ -156,7 +156,7 @@ bpfinishpy_post_stop_hook (struct gdbpy_breakpoint_object *bp_obj)
 static int
 bpfinishpy_init (PyObject *self, PyObject *args, PyObject *kwargs)
 {
-  static char *keywords[] = { "frame", "internal", NULL };
+  static const char *keywords[] = { "frame", "internal", NULL };
   struct finish_breakpoint_object *self_bpfinish =
       (struct finish_breakpoint_object *) self;
   PyObject *frame_obj = NULL;
diff --git a/gdb/python/py-inferior.c b/gdb/python/py-inferior.c
index 46a0aad..8b4782b 100644
--- a/gdb/python/py-inferior.c
+++ b/gdb/python/py-inferior.c
@@ -435,7 +435,7 @@ infpy_read_memory (PyObject *self, PyObject *args, PyObject *kw)
   CORE_ADDR addr, length;
   gdb_byte *buffer = NULL;
   PyObject *addr_obj, *length_obj, *result;
-  static char *keywords[] = { "address", "length", NULL };
+  static const char *keywords[] = { "address", "length", NULL };
 
   if (! PyArg_ParseTupleAndKeywords (args, kw, "OO", keywords,
 				     &addr_obj, &length_obj))
@@ -494,7 +494,7 @@ infpy_write_memory (PyObject *self, PyObject *args, PyObject *kw)
   const gdb_byte *buffer;
   CORE_ADDR addr, length;
   PyObject *addr_obj, *length_obj = NULL;
-  static char *keywords[] = { "address", "buffer", "length", NULL };
+  static const char *keywords[] = { "address", "buffer", "length", NULL };
 #ifdef IS_PY3K
   Py_buffer pybuf;
 
@@ -643,7 +643,7 @@ infpy_search_memory (PyObject *self, PyObject *args, PyObject *kw)
 {
   struct gdb_exception except = exception_none;
   CORE_ADDR start_addr, length;
-  static char *keywords[] = { "address", "length", "pattern", NULL };
+  static const char *keywords[] = { "address", "length", "pattern", NULL };
   PyObject *start_addr_obj, *length_obj;
   Py_ssize_t pattern_size;
   const gdb_byte *buffer;
diff --git a/gdb/python/py-objfile.c b/gdb/python/py-objfile.c
index 105d88a..ad1ec4f 100644
--- a/gdb/python/py-objfile.c
+++ b/gdb/python/py-objfile.c
@@ -432,7 +432,7 @@ objfpy_is_valid (PyObject *self, PyObject *args)
 static PyObject *
 objfpy_add_separate_debug_file (PyObject *self, PyObject *args, PyObject *kw)
 {
-  static char *keywords[] = { "file_name", NULL };
+  static const char *keywords[] = { "file_name", NULL };
   objfile_object *obj = (objfile_object *) self;
   const char *file_name;
 
@@ -559,7 +559,7 @@ objfpy_lookup_objfile_by_build_id (const char *build_id)
 PyObject *
 gdbpy_lookup_objfile (PyObject *self, PyObject *args, PyObject *kw)
 {
-  static char *keywords[] = { "name", "by_build_id", NULL };
+  static const char *keywords[] = { "name", "by_build_id", NULL };
   const char *name;
   PyObject *by_build_id_obj = NULL;
   int by_build_id;
diff --git a/gdb/python/py-symbol.c b/gdb/python/py-symbol.c
index b71cfb4..de44c06 100644
--- a/gdb/python/py-symbol.c
+++ b/gdb/python/py-symbol.c
@@ -373,7 +373,7 @@ gdbpy_lookup_symbol (PyObject *self, PyObject *args, PyObject *kw)
   int domain = VAR_DOMAIN;
   struct field_of_this_result is_a_field_of_this;
   const char *name;
-  static char *keywords[] = { "name", "block", "domain", NULL };
+  static const char *keywords[] = { "name", "block", "domain", NULL };
   struct symbol *symbol = NULL;
   PyObject *block_obj = NULL, *sym_obj, *bool_obj;
   const struct block *block = NULL;
@@ -443,7 +443,7 @@ gdbpy_lookup_global_symbol (PyObject *self, PyObject *args, PyObject *kw)
 {
   int domain = VAR_DOMAIN;
   const char *name;
-  static char *keywords[] = { "name", "domain", NULL };
+  static const char *keywords[] = { "name", "domain", NULL };
   struct symbol *symbol = NULL;
   PyObject *sym_obj;
 
diff --git a/gdb/python/py-type.c b/gdb/python/py-type.c
index f071006..4f4ede1 100644
--- a/gdb/python/py-type.c
+++ b/gdb/python/py-type.c
@@ -1347,7 +1347,7 @@ type_object_to_type (PyObject *obj)
 PyObject *
 gdbpy_lookup_type (PyObject *self, PyObject *args, PyObject *kw)
 {
-  static char *keywords[] = { "name", "block", NULL };
+  static const char *keywords[] = { "name", "block", NULL };
   const char *type_name = NULL;
   struct type *type = NULL;
   PyObject *block_obj = NULL;
diff --git a/gdb/python/py-value.c b/gdb/python/py-value.c
index bb42e8b..1a82af5 100644
--- a/gdb/python/py-value.c
+++ b/gdb/python/py-value.c
@@ -431,7 +431,7 @@ 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,
@@ -526,7 +526,7 @@ 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))
diff --git a/gdb/python/python-internal.h b/gdb/python/python-internal.h
index 8fc89cd..76f7443 100644
--- a/gdb/python/python-internal.h
+++ b/gdb/python/python-internal.h
@@ -318,6 +318,31 @@ struct gdb_PyGetSetDef : PyGetSetDef
 
 #define PyGetSetDef gdb_PyGetSetDef
 
+/* The 'keywords' parameter of PyArg_ParseTupleAndKeywords has type
+   'char **'.  However, string literals are const in C++, and so to
+   avoid casting at every keyword array definition, we'll need to make
+   the keywords array an array of 'const char *'.  To avoid having all
+   callers add a 'const_cast<char **>' themselves when passing such an
+   array through 'char **', we define a PyArg_ParseTupleAndKeywords
+   overload here with a corresponding 'keywords' parameter type that
+   does the cast in a single place.  */
+
+static inline int
+PyArg_ParseTupleAndKeywords (PyObject *args, PyObject *kw,
+			     const char *format, const char **keywords, ...)
+{
+  va_list ap;
+  int res;
+
+  va_start (ap, keywords);
+  res = PyArg_VaParseTupleAndKeywords (args, kw, format,
+				       const_cast<char **> (keywords),
+				       ap);
+  va_end (ap);
+
+  return res;
+}
+
 /* In order to be able to parse symtab_and_line_to_sal_object function
    a real symtab_and_line structure is needed.  */
 #include "symtab.h"
diff --git a/gdb/python/python.c b/gdb/python/python.c
index a7aff53..5a46493 100644
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -572,7 +572,7 @@ execute_gdb_command (PyObject *self, PyObject *args, PyObject *kw)
   const char *arg;
   PyObject *from_tty_obj = NULL, *to_string_obj = NULL;
   int from_tty, to_string;
-  static char *keywords[] = {"command", "from_tty", "to_string", NULL };
+  static const char *keywords[] = { "command", "from_tty", "to_string", NULL };
 
   if (! PyArg_ParseTupleAndKeywords (args, kw, "s|O!O!", keywords, &arg,
 				     &PyBool_Type, &from_tty_obj,
@@ -1047,7 +1047,7 @@ static PyObject *
 gdbpy_write (PyObject *self, PyObject *args, PyObject *kw)
 {
   const char *arg;
-  static char *keywords[] = {"text", "stream", NULL };
+  static const char *keywords[] = { "text", "stream", NULL };
   int stream_type = 0;
 
   if (! PyArg_ParseTupleAndKeywords (args, kw, "s|i", keywords, &arg,
@@ -1088,7 +1088,7 @@ gdbpy_write (PyObject *self, PyObject *args, PyObject *kw)
 static PyObject *
 gdbpy_flush (PyObject *self, PyObject *args, PyObject *kw)
 {
-  static char *keywords[] = {"stream", NULL };
+  static const char *keywords[] = { "stream", NULL };
   int stream_type = 0;
 
   if (! PyArg_ParseTupleAndKeywords (args, kw, "|i", keywords,
-- 
2.5.5