gdb: startup commands to control Python extension language

Add two new commands to GDB that can be placed into the early
initialization to control how Python starts up.  The new options are:

  set python ignore-environment on|off
  set python dont-write-bytecode auto|on|off

  show python ignore-environment
  show python dont-write-bytecode

These can be used from GDB's startup file to control how the Python
extension language behaves.  These options are equivalent to the -E
and -B flags to python respectively, their descriptions from the
Python man page:

  -E     Ignore environment variables like PYTHONPATH and PYTHONHOME
         that modify the  behavior  of  the  interpreter.

  -B     Don't write .pyc files on import.

gdb/ChangeLog:

	* NEWS: Mention new commands.
	* python/python.c (python_ignore_environment): New static global.
	(show_python_ignore_environment): New function.
	(set_python_ignore_environment): New function.
	(python_dont_write_bytecode): New static global.
	(show_python_dont_write_bytecode): New function.
	(set_python_dont_write_bytecode): New function.
	(_initialize_python): Register new commands.

gdb/doc/ChangeLog:

	* python.texinfo (Python Commands): Mention new commands.

gdb/testsuite/ChangeLog:

	* gdb.python/py-startup-opt.exp: New file.

1 files changed, 98 insertions, 0 deletions

diff --git a/gdb/python/python.c b/gdb/python/python.c
index 1d0d86d..c46d68b 100644
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -1578,6 +1578,80 @@ python_command (const char *arg, int from_tty)
 
 #endif /* HAVE_PYTHON */
 
+/* When this is turned on before Python is initialised then Python will
+   ignore any environment variables related to Python.  This is equivalent
+   to passing `-E' to the python program.  */
+static bool python_ignore_environment = false;
+
+/* Implement 'show python ignore-environment'.  */
+
+static void
+show_python_ignore_environment (struct ui_file *file, int from_tty,
+				struct cmd_list_element *c, const char *value)
+{
+  fprintf_filtered (file, _("Python's ignore-environment setting is %s.\n"),
+		    value);
+}
+
+/* Implement 'set python ignore-environment'.  This sets Python's internal
+   flag no matter when the command is issued, however, if this is used
+   after Py_Initialize has been called then most of the environment will
+   already have been read.  */
+
+static void
+set_python_ignore_environment (const char *args, int from_tty,
+			       struct cmd_list_element *c)
+{
+#ifdef HAVE_PYTHON
+  Py_IgnoreEnvironmentFlag = python_ignore_environment ? 1 : 0;
+#endif
+}
+
+/* When this is turned on before Python is initialised then Python will
+   not write `.pyc' files on import of a module.  */
+static enum auto_boolean python_dont_write_bytecode = AUTO_BOOLEAN_AUTO;
+
+/* Implement 'show python dont-write-bytecode'.  */
+
+static void
+show_python_dont_write_bytecode (struct ui_file *file, int from_tty,
+				 struct cmd_list_element *c, const char *value)
+{
+  if (python_dont_write_bytecode == AUTO_BOOLEAN_AUTO)
+    {
+      const char *auto_string
+	= (python_ignore_environment
+	   || getenv ("PYTHONDONTWRITEBYTECODE") == nullptr) ? "off" : "on";
+
+      fprintf_filtered (file,
+			_("Python's dont-write-bytecode setting is %s (currently %s).\n"),
+			value, auto_string);
+    }
+  else
+    fprintf_filtered (file, _("Python's dont-write-bytecode setting is %s.\n"),
+		      value);
+}
+
+/* Implement 'set python dont-write-bytecode'.  This sets Python's internal
+   flag no matter when the command is issued, however, if this is used
+   after Py_Initialize has been called then many modules could already
+   have been imported and their byte code written out.  */
+
+static void
+set_python_dont_write_bytecode (const char *args, int from_tty,
+				struct cmd_list_element *c)
+{
+#ifdef HAVE_PYTHON
+  if (python_dont_write_bytecode == AUTO_BOOLEAN_AUTO)
+    Py_DontWriteBytecodeFlag
+      = (!python_ignore_environment
+	 && getenv ("PYTHONDONTWRITEBYTECODE") != nullptr) ? 1 : 0;
+  else
+    Py_DontWriteBytecodeFlag
+      = python_dont_write_bytecode == AUTO_BOOLEAN_TRUE ? 1 : 0;
+#endif /* HAVE_PYTHON */
+}
+
 
 
 /* Lists for 'set python' commands.  */
@@ -1880,6 +1954,30 @@ message == an error message without a stack will be printed."),
 			NULL, NULL,
 			&user_set_python_list,
 			&user_show_python_list);
+
+  add_setshow_boolean_cmd ("ignore-environment", no_class,
+			   &python_ignore_environment, _("\
+Set whether the Python interpreter should ignore environment variables."), _(" \
+Show whether the Python interpreter showlist ignore environment variables."), _(" \
+When enabled GDB's Python interpreter will ignore any Python related\n	\
+flags in the environment.  This is equivalent to passing `-E' to a\n	\
+python executable."),
+			   set_python_ignore_environment,
+			   show_python_ignore_environment,
+			   &user_set_python_list,
+			   &user_show_python_list);
+
+  add_setshow_auto_boolean_cmd ("dont-write-bytecode", no_class,
+				&python_dont_write_bytecode, _("\
+Set whether the Python interpreter should ignore environment variables."), _(" \
+Show whether the Python interpreter showlist ignore environment variables."), _(" \
+When enabled GDB's Python interpreter will ignore any Python related\n	\
+flags in the environment.  This is equivalent to passing `-E' to a\n	\
+python executable."),
+				set_python_dont_write_bytecode,
+				show_python_dont_write_bytecode,
+				&user_set_python_list,
+				&user_show_python_list);
 }
 
 #ifdef HAVE_PYTHON