Allow breakpoint commands to be set from Python

This changes the Python API so that breakpoint commands can be set by
writing to the "commands" attribute.

ChangeLog
2018-05-04  Tom Tromey  <tom@tromey.com>

	PR python/22731:
	* NEWS: Mention that breakpoint commands are writable.
	* python/py-breakpoint.c (bppy_set_commands): New function.
	(breakpoint_object_getset) <"commands">: Use it.

doc/ChangeLog
2018-05-04  Tom Tromey  <tom@tromey.com>

	PR python/22731:
	* python.texi (Breakpoints In Python): Mention that "commands" is
	writable.

testsuite/ChangeLog
2018-05-04  Tom Tromey  <tom@tromey.com>

	PR python/22731:
	* gdb.python/py-breakpoint.exp: Test setting breakpoint commands.

gdb/ChangeLog

@@ -1,3 +1,10 @@
+2018-05-04  Tom Tromey  <tom@tromey.com>
+
+	PR python/22731:
+	* NEWS: Mention that breakpoint commands are writable.
+	* python/py-breakpoint.c (bppy_set_commands): New function.
+	(breakpoint_object_getset) <"commands">: Use it.
+
 2018-05-04  Tom Tromey  <tom@tromey.com>
 
 	* tracepoint.c (actions_command): Update.

gdb/NEWS

@@ -31,6 +31,9 @@ set|show record btrace cpu
 
   ** Type alignment is now exposed via the "align" attribute of a gdb.Type.
 
+  ** The commands attached to a breakpoint can be set by assigning to
+     the breakpoint's "commands" field.
+
 * New targets
 
 RiscV ELF			riscv*-*-elf

gdb/doc/ChangeLog

@@ -1,3 +1,9 @@
+2018-05-04  Tom Tromey  <tom@tromey.com>
+
+	PR python/22731:
+	* python.texi (Breakpoints In Python): Mention that "commands" is
+	writable.
+
 2018-05-02  Tom Tromey  <tom@tromey.com>
 
 	PR python/20084:

gdb/doc/python.texi

@@ -5136,7 +5136,7 @@ value is @code{None}.  This attribute is writable.
 This attribute holds the commands attached to the breakpoint.  If
 there are commands, this attribute's value is a string holding all the
 commands, separated by newlines.  If there are no commands, this
-attribute is @code{None}.  This attribute is not writable.
+attribute is @code{None}.  This attribute is writable.
 @end defvar
 
 @node Finish Breakpoints in Python

gdb/python/py-breakpoint.c

@@ -510,6 +510,49 @@ bppy_get_commands (PyObject *self, void *closure)
   return host_string_to_python_string (stb.c_str ());
 }
 
+/* Set the commands attached to a breakpoint.  Returns 0 on success.
+   Returns -1 on error, with a python exception set.  */
+static int
+bppy_set_commands (PyObject *self, PyObject *newvalue, void *closure)
+{
+  gdbpy_breakpoint_object *self_bp = (gdbpy_breakpoint_object *) self;
+  struct breakpoint *bp = self_bp->bp;
+  struct gdb_exception except = exception_none;
+
+  BPPY_SET_REQUIRE_VALID (self_bp);
+
+  gdb::unique_xmalloc_ptr<char> commands
+    (python_string_to_host_string (newvalue));
+  if (commands == nullptr)
+    return -1;
+
+  TRY
+    {
+      bool first = true;
+      char *save_ptr = nullptr;
+      auto reader
+	= [&] ()
+	  {
+	    const char *result = strtok_r (first ? commands.get () : nullptr,
+					   "\n", &save_ptr);
+	    first = false;
+	    return result;
+	  };
+
+      counted_command_line lines = read_command_lines_1 (reader, 1, nullptr);
+      breakpoint_set_commands (self_bp->bp, std::move (lines));
+    }
+  CATCH (ex, RETURN_MASK_ALL)
+    {
+      except = ex;
+    }
+  END_CATCH
+
+  GDB_PY_SET_HANDLE_EXCEPTION (except);
+
+  return 0;
+}
+
 /* Python function to get the breakpoint type.  */
 static PyObject *
 bppy_get_type (PyObject *self, void *closure)
@@ -1185,7 +1228,7 @@ when setting this property.", NULL },
   { "condition", bppy_get_condition, bppy_set_condition,
     "Condition of the breakpoint, as specified by the user,\
 or None if no condition set."},
-  { "commands", bppy_get_commands, NULL,
+  { "commands", bppy_get_commands, bppy_set_commands,
     "Commands of the breakpoint, as specified by the user."},
   { "type", bppy_get_type, NULL,
     "Type of breakpoint."},

gdb/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2018-05-04  Tom Tromey  <tom@tromey.com>
+
+	PR python/22731:
+	* gdb.python/py-breakpoint.exp: Test setting breakpoint commands.
+
 2018-05-04  Tom Tromey  <tom@tromey.com>
 
 	PR gdb/11750:

gdb/testsuite/gdb.python/py-breakpoint.exp

@@ -197,8 +197,16 @@ proc_with_prefix test_bkpt_cond_and_cmds { } {
 
     gdb_py_test_silent_cmd "python blist = gdb.breakpoints()" \
 	"Get Breakpoint List" 0
-    gdb_test "python print (blist\[len(blist)-1\].commands)" \
+    gdb_py_test_silent_cmd "python last_bp = blist\[len(blist)-1\]" \
+	"Find last breakpoint" 0
+    gdb_test "python print (last_bp.commands)" \
 	"print \"Command for breakpoint has been executed.\".*print result"
+
+    gdb_test_no_output "python last_bp.commands = 'echo hi\\necho there'" \
+	"set commands"
+    # Note the length is 3 because the string ends in a \n.
+    gdb_test "python print (len(last_bp.commands.split('\\n')))" "3" \
+	"check number of lines in commands"
 }
 
 proc_with_prefix test_bkpt_invisible { } {