-Wwrite-strings: Wrap PyGetSetDef for construction with string literals

Unfortunately, PyGetSetDef's 'name' and 'doc' members are 'char *'
instead of 'const char *', meaning that in order to list-initialize
PyGetSetDef arrays using string literals requires writing explicit
'char *' casts.  For example:

    static PyGetSetDef value_object_getset[] = {
   -  { "address", valpy_get_address, NULL, "The address of the value.",
   +  { (char *) "address", valpy_get_address, NULL,
   +    (char *) "The address of the value.",
	NULL },
   -  { "is_optimized_out", valpy_get_is_optimized_out, NULL,
   -    "Boolean telling whether the value is optimized "
   +  { (char *) "is_optimized_out", valpy_get_is_optimized_out, NULL,
   +    (char *) "Boolean telling whether the value is optimized "
	"out (i.e., not available).",
	NULL },
   -  { "type", valpy_get_type, NULL, "Type of the value.", NULL },
   -  { "dynamic_type", valpy_get_dynamic_type, NULL,
   -    "Dynamic type of the value.", NULL },
   -  { "is_lazy", valpy_get_is_lazy, NULL,
   -    "Boolean telling whether the value is lazy (not fetched yet\n\
   +  { (char *) "type", valpy_get_type, NULL,
   +    (char *) "Type of the value.", NULL },
   +  { (char *) "dynamic_type", valpy_get_dynamic_type, NULL,
   +    (char *) "Dynamic type of the value.", NULL },
   +  { (char *) "is_lazy", valpy_get_is_lazy, NULL,
   +    (char *) "Boolean telling whether the value is lazy (not fetched yet\n\
    from the inferior).  A lazy value is fetched when needed, or when\n\
    the \"fetch_lazy()\" method is called.", NULL },
      {NULL}  /* Sentinel */

We have ~20 such arrays, and I first wrote a patch that fixed all of
them like that...  It's not pretty...

One way to make these a bit less ugly would be add a new macro that
hides the casts, like:

  #define GDBPY_GSDEF(NAME, GET, SET, DOC, CLOSURE) \
     { (char *) NAME, GET, SET, (char *) DOC, CLOSURE }

and then use it like:

    static PyGetSetDef value_object_getset[] = {
       GDBPY_GSDEF ("address", valpy_get_address, NULL,
       		    "The address of the value.", NULL),
       GDBPY_GSDEF ("is_optimized_out", valpy_get_is_optimized_out, NULL,
       		    "Boolean telling whether the value is optimized ", NULL),
      {NULL}  /* Sentinel */
    };

But since we have C++11, which gives us constexpr and list
initialization, I thought of a way that requires no changes where the
arrays are initialized:

We add a new type that extends PyGetSetDef (called gdb_PyGetSetDef),
and add constexpr constructors that accept const 'name' and 'doc', and
then list/aggregate initialization simply "calls" these matching
constructors instead.

I put "calls" in quotes, because given "constexpr", it's all done at
compile time, and there's no overhead either in binary size or at run
time.  In fact, we get identical binaries, before/after this change.

Unlike the fixes that fix some old Python API to match the API of more
recent Python, this switches to using explicit "gdb_PyGetSetDef"
everywhere, just to be clear that we are using our own version of it.

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

	* python/python-internal.h (gdb_PyGetSetDef): New type.
	* python/py-block.c (block_object_getset)
	(breakpoint_object_getset): Now a gdb_PyGetSetDef array.
	* python/py-event.c (event_object_getset)
	(finish_breakpoint_object_getset): Likewise.
	* python/py-inferior.c (inferior_object_getset): Likewise.
	* python/py-infthread.c (thread_object_getset): Likewise.
	* python/py-lazy-string.c (lazy_string_object_getset): Likewise.
	* python/py-linetable.c (linetable_entry_object_getset): Likewise.
	* python/py-objfile.c (objfile_getset): Likewise.
	* python/py-progspace.c (pspace_getset): Likewise.
	* python/py-record-btrace.c (btpy_insn_getset, btpy_call_getset):
	Likewise.
	* python/py-record.c (recpy_record_getset): Likewise.
	* python/py-symbol.c (symbol_object_getset): Likewise.
	* python/py-symtab.c (symtab_object_getset, sal_object_getset):
	Likewise.
	* python/py-type.c (type_object_getset, field_object_getset):
	Likewise.
	* python/py-value.c (value_object_getset): Likewise.

gdb/ChangeLog

@@ -1,3 +1,26 @@
+2017-04-05  Pedro Alves  <palves@redhat.com>
+
+	* python/python-internal.h (gdb_PyGetSetDef): New type.
+	* python/py-block.c (block_object_getset)
+	(breakpoint_object_getset): Now a gdb_PyGetSetDef array.
+	* python/py-event.c (event_object_getset)
+	(finish_breakpoint_object_getset): Likewise.
+	* python/py-inferior.c (inferior_object_getset): Likewise.
+	* python/py-infthread.c (thread_object_getset): Likewise.
+	* python/py-lazy-string.c (lazy_string_object_getset): Likewise.
+	* python/py-linetable.c (linetable_entry_object_getset): Likewise.
+	* python/py-objfile.c (objfile_getset): Likewise.
+	* python/py-progspace.c (pspace_getset): Likewise.
+	* python/py-record-btrace.c (btpy_insn_getset, btpy_call_getset):
+	Likewise.
+	* python/py-record.c (recpy_record_getset): Likewise.
+	* python/py-symbol.c (symbol_object_getset): Likewise.
+	* python/py-symtab.c (symtab_object_getset, sal_object_getset):
+	Likewise.
+	* python/py-type.c (type_object_getset, field_object_getset):
+	Likewise.
+	* python/py-value.c (value_object_getset): Likewise.
+
 2017-04-05  Pedro Alves  <palves@redhat.com>
 
 	* python/python-internal.h (gdb_PyObject_CallMethod)

gdb/python/py-block.c

@@ -461,7 +461,7 @@ Return true if this block is valid, false if not." },
   {NULL}  /* Sentinel */
 };
 
-static PyGetSetDef block_object_getset[] = {
+static gdb_PyGetSetDef block_object_getset[] = {
   { "start", blpy_get_start, NULL, "Start address of the block.", NULL },
   { "end", blpy_get_end, NULL, "End address of the block.", NULL },
   { "function", blpy_get_function, NULL,

gdb/python/py-breakpoint.c

@@ -1048,7 +1048,7 @@ local_setattro (PyObject *self, PyObject *name, PyObject *v)
   return PyObject_GenericSetAttr ((PyObject *)self, name, v);
 }
 
-static PyGetSetDef breakpoint_object_getset[] = {
+static gdb_PyGetSetDef breakpoint_object_getset[] = {
   { "enabled", bppy_get_enabled, bppy_set_enabled,
     "Boolean telling whether the breakpoint is enabled.", NULL },
   { "silent", bppy_get_silent, bppy_set_silent,

gdb/python/py-event.c

@@ -114,7 +114,7 @@ evpy_emit_event (PyObject *event,
   return 0;
 }
 
-static PyGetSetDef event_object_getset[] =
+static gdb_PyGetSetDef event_object_getset[] =
 {
   { "__dict__", gdb_py_generic_dict, NULL,
     "The __dict__ for this event.", &event_object_type },

gdb/python/py-finishbreakpoint.c

@@ -426,7 +426,7 @@ gdbpy_initialize_finishbreakpoints (void)
   return 0;
 }
 
-static PyGetSetDef finish_breakpoint_object_getset[] = {
+static gdb_PyGetSetDef finish_breakpoint_object_getset[] = {
   { "return_value", bpfinishpy_get_returnvalue, NULL,
   "gdb.Value object representing the return value, if any. \
 None otherwise.", NULL },

gdb/python/py-inferior.c

@@ -827,7 +827,7 @@ gdbpy_initialize_inferior (void)
 				 &membuf_object_type);
 }
 
-static PyGetSetDef inferior_object_getset[] =
+static gdb_PyGetSetDef inferior_object_getset[] =
 {
   { "num", infpy_get_num, NULL, "ID of inferior, as assigned by GDB.", NULL },
   { "pid", infpy_get_pid, NULL, "PID of inferior, as assigned by the OS.",

gdb/python/py-infthread.c

@@ -304,7 +304,7 @@ gdbpy_initialize_thread (void)
 				 (PyObject *) &thread_object_type);
 }
 
-static PyGetSetDef thread_object_getset[] =
+static gdb_PyGetSetDef thread_object_getset[] =
 {
   { "name", thpy_get_name, thpy_set_name,
     "The name of the thread, as set by the user or the OS.", NULL },

gdb/python/py-lazy-string.c

@@ -300,7 +300,7 @@ static PyMethodDef lazy_string_object_methods[] = {
 };
 
 
-static PyGetSetDef lazy_string_object_getset[] = {
+static gdb_PyGetSetDef lazy_string_object_getset[] = {
   { "address", stpy_get_address, NULL, "Address of the string.", NULL },
   { "encoding", stpy_get_encoding, NULL, "Encoding of the string.", NULL },
   { "length", stpy_get_length, NULL, "Length of the string.", NULL },

gdb/python/py-linetable.c

@@ -550,7 +550,7 @@ PyTypeObject ltpy_iterator_object_type = {
 };
 
 
-static PyGetSetDef linetable_entry_object_getset[] = {
+static gdb_PyGetSetDef linetable_entry_object_getset[] = {
   { "line", ltpy_entry_get_line, NULL,
     "The line number in the source file.", NULL },
   { "pc", ltpy_entry_get_pc, NULL,

gdb/python/py-objfile.c

@@ -670,7 +670,7 @@ Add FILE_NAME to the list of files containing debug info for the objfile." },
   { NULL }
 };
 
-static PyGetSetDef objfile_getset[] =
+static gdb_PyGetSetDef objfile_getset[] =
 {
   { "__dict__", gdb_py_generic_dict, NULL,
     "The __dict__ for this objfile.", &objfile_object_type },

gdb/python/py-progspace.c

@@ -378,7 +378,7 @@ gdbpy_initialize_pspace (void)
 
 
 
-static PyGetSetDef pspace_getset[] =
+static gdb_PyGetSetDef pspace_getset[] =
 {
   { "__dict__", gdb_py_generic_dict, NULL,
     "The __dict__ for this progspace.", &pspace_object_type },

gdb/python/py-record-btrace.c

@@ -903,7 +903,7 @@ recpy_bt_goto (PyObject *self, PyObject *args)
 
 /* BtraceInstruction members.  */
 
-struct PyGetSetDef btpy_insn_getset[] =
+struct gdb_PyGetSetDef btpy_insn_getset[] =
 {
   { "number", btpy_number, NULL, "instruction number", NULL},
   { "error", btpy_insn_error, NULL, "error number for gaps", NULL},
@@ -920,7 +920,7 @@ executed speculatively", NULL},
 
 /* BtraceFunctionCall members.  */
 
-static PyGetSetDef btpy_call_getset[] =
+static gdb_PyGetSetDef btpy_call_getset[] =
 {
   { "number", btpy_number, NULL, "function call number", NULL},
   { "level", btpy_call_level, NULL, "call stack level", NULL},

gdb/python/py-record.c

@@ -175,7 +175,7 @@ Rewind to given location."},
 
 /* Record member list.  */
 
-static PyGetSetDef recpy_record_getset[] = {
+static gdb_PyGetSetDef recpy_record_getset[] = {
   { "ptid", recpy_ptid, NULL, "Current thread.", NULL },
   { "method", recpy_method, NULL, "Current recording method.", NULL },
   { "format", recpy_format, NULL, "Current recording format.", NULL },

gdb/python/py-symbol.c

@@ -560,7 +560,7 @@ gdbpy_initialize_symbols (void)
 
 
 
-static PyGetSetDef symbol_object_getset[] = {
+static gdb_PyGetSetDef symbol_object_getset[] = {
   { "type", sympy_get_type, NULL,
     "Type of the symbol.", NULL },
   { "symtab", sympy_get_symtab, NULL,

gdb/python/py-symtab.c

@@ -544,7 +544,7 @@ gdbpy_initialize_symtabs (void)
 
 
 
-static PyGetSetDef symtab_object_getset[] = {
+static gdb_PyGetSetDef symtab_object_getset[] = {
   { "filename", stpy_get_filename, NULL,
     "The symbol table's source filename.", NULL },
   { "objfile", stpy_get_objfile, NULL, "The symtab's objfile.",
@@ -606,7 +606,7 @@ PyTypeObject symtab_object_type = {
   symtab_object_getset		  /*tp_getset */
 };
 
-static PyGetSetDef sal_object_getset[] = {
+static gdb_PyGetSetDef sal_object_getset[] = {
   { "symtab", salpy_get_symtab, NULL, "Symtab object.", NULL },
   { "pc", salpy_get_pc, NULL, "Return the symtab_and_line's pc.", NULL },
   { "last", salpy_get_last, NULL,

gdb/python/py-type.c

@@ -1413,7 +1413,7 @@ gdbpy_initialize_types (void)
 
 
 
-static PyGetSetDef type_object_getset[] =
+static gdb_PyGetSetDef type_object_getset[] =
 {
   { "code", typy_get_code, NULL,
     "The code for this type.", NULL },
@@ -1587,7 +1587,7 @@ PyTypeObject type_object_type =
   0,				  /* tp_new */
 };
 
-static PyGetSetDef field_object_getset[] =
+static gdb_PyGetSetDef field_object_getset[] =
 {
   { "__dict__", gdb_py_generic_dict, NULL,
     "The __dict__ for this field.", &field_object_type },

gdb/python/py-value.c

@@ -1767,7 +1767,7 @@ gdbpy_initialize_values (void)
 
 
 
-static PyGetSetDef value_object_getset[] = {
+static gdb_PyGetSetDef value_object_getset[] = {
   { "address", valpy_get_address, NULL, "The address of the value.",
     NULL },
   { "is_optimized_out", valpy_get_is_optimized_out, NULL,

gdb/python/python-internal.h

@@ -286,6 +286,36 @@ gdb_PySys_SetPath (const GDB_PYSYS_SETPATH_CHAR *path)
 
 #define PySys_SetPath gdb_PySys_SetPath
 
+/* Wrap PyGetSetDef to allow convenient construction with string
+   literals.  Unfortunately, PyGetSetDef's 'name' and 'doc' members
+   are 'char *' instead of 'const char *', meaning that in order to
+   list-initialize PyGetSetDef arrays with string literals (and
+   without the wrapping below) would require writing explicit 'char *'
+   casts.  Instead, we extend PyGetSetDef and add constexpr
+   constructors that accept const 'name' and 'doc', hiding the ugly
+   casts here in a single place.  */
+
+struct gdb_PyGetSetDef : PyGetSetDef
+{
+  constexpr gdb_PyGetSetDef (const char *name_, getter get_, setter set_,
+			     const char *doc_, void *closure_)
+    : PyGetSetDef {const_cast<char *> (name_), get_, set_,
+		   const_cast<char *> (doc_), closure_}
+  {}
+
+  /* Alternative constructor that allows omitting the closure in list
+     initialization.  */
+  constexpr gdb_PyGetSetDef (const char *name_, getter get_, setter set_,
+			     const char *doc_)
+    : gdb_PyGetSetDef {name_, get_, set_, doc_, NULL}
+  {}
+
+  /* Constructor for the sentinel entries.  */
+  constexpr gdb_PyGetSetDef (std::nullptr_t)
+    : gdb_PyGetSetDef {NULL, NULL, NULL, NULL, NULL}
+  {}
+};
+
 /* 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"