Add "undefined-command" error code at end of ^error result...

... when trying to execute an undefined GDB/MI command. When trying
to execute a GDB/MI command which does not exist, the current error
result record looks like this:

    -unsupported
    ^error,msg="Undefined MI command: unsupported"

The only indication that the command does not exist is the error
message. It would be a little fragile for a consumer to rely solely
on the contents of the error message in order to determine whether
a command exists or not.

This patch improves the situation by adding concept of error
code, starting with one well-defined error code ("undefined-command")
identifying errors due to a non-existant command. Here is the new
output:

    -unsupported
    ^error,msg="Undefined MI command: unsupported",code="undefined-command"

This error code is only displayed when the corresponding error
condition is met. Otherwise, the error record remains unchanged.
For instance:

    -symbol-list-lines foo.adb
    ^error,msg="-symbol-list-lines: Unknown source file name."

For frontends to be able to know whether they can rely on this
variable, a new entry "undefined-command-error-code" has been
added to the "-list-features" command.  Another option would be
to always generate an error="..." variable (for the default case,
we could decide for instance that the error code is the empty string).
But it seems more efficient to provide that info in "-list-features"
and then only add the error code when meaningful.

gdb/ChangeLog:

        (from Pedro Alves  <palves@redhat.com>)
        (from Joel Brobecker  <brobecker@adacore.com>)
        * exceptions.h (enum_errors) <UNDEFINED_COMMAND_ERROR>: New enum.
        * mi/mi-parse.c (mi_parse): Throw UNDEFINED_COMMAND_ERROR instead
        of a regular error when the GDB/MI command does not exist.
        * mi/mi-main.c (mi_cmd_list_features): Add
        "undefined-command-error-code".
        (mi_print_exception): Print an "undefined-command"
        error code if EXCEPTION.ERROR is UNDEFINED_COMMAND_ERROR.
        * NEWS: Add entry documenting the new "code" variable in
        "^error" result records.

gdb/doc/ChangeLog:

        * gdb.texinfo (GDB/MI Result Records): Fix the syntax of the
        "^error" result record concerning the error message.  Document
        the error code that may also be part of that result record.
        (GDB/MI Miscellaneous Commands): Document the
        "undefined-command-error-code" element in the output of
        the "-list-features" GDB/MI command.

gdb/testsuite/ChangeLog:

        * gdb.mi/mi-undefined-cmd.exp: New testcase.

1 files changed, 33 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.mi/mi-undefined-cmd.exp b/gdb/testsuite/gdb.mi/mi-undefined-cmd.exp
new file mode 100644
index 0000000..8df0a76
--- /dev/null
+++ b/gdb/testsuite/gdb.mi/mi-undefined-cmd.exp
@@ -0,0 +1,33 @@
+# Copyright 2013 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+load_lib mi-support.exp
+set MIFLAGS "-i=mi"
+
+gdb_exit
+if [mi_gdb_start] {
+    continue
+}
+
+
+# First, verify that the debugger correctly advertises support
+# for the "undefined-command" error code...
+mi_gdb_test "-list-features" \
+            "\\^done,features=\\\[.*\"undefined-command-error-code\".*\\\]" \
+            "-list-features should include \"undefined-command-error-code\""
+
+mi_gdb_test "-undefined-command" \
+            "\\^error,.*,code=\"undefined-command\"" \
+            "error code when executing undefined command"