inadvertent language switch during breakpoint_re_set_one

Trying to insert a breakpoint using *FUNC'address with an Ada program
and then running the program until reaching that breakpoint currently
yields the following behavior:

    (gdb) break *a'address
    Breakpoint 1 at 0x40240c: file a.adb, line 1.
    (gdb) run
    [1]  + 27222 suspended (tty output) /[...]/gdb -q simple_main

Unsuspending GDB then shows it was suspended trying to report
the following error:

    Starting program: /home/takamaka.a/brobecke/ex/simple/a
    Error in re-setting breakpoint 1: Unmatched single quote.
    Error in re-setting breakpoint 1: Unmatched single quote.
    Error in re-setting breakpoint 1: Unmatched single quote.
    [Inferior 1 (process 32470) exited normally]

The "a'address" is Ada speak for function A's address ("A" by
itself means the result of calling A with no arguments). The
transcript above shows that we're having problems trying to
parse the breakpoint location while re-setting it.  As a result,
we also fail to stop at the breakpoint.

Normally, breakpoint locations are evaluated with the current_language
being set to the language of the breakpoint. But, unfortunately for us,
what happened in this case is that parse_exp_in_context_1 calls
get_selected_block which eventually leads to a call to select_frame
because the current_frame hadn't been set yet.  select_frame then
finds that our language_mode is auto, and therefore changes the
current_language to match the language of the frame we just selected.
In our case, the language chosen was 'c', which of course is not
able to parse an Ada expression, hence the error.

This patch prevents this by forcing the language_mode to manual
before we call breakpoint_re_set_one.

gdb/ChangeLog:

        * breakpoint.c (breakpoint_re_set): Temporarily force language_mode
        to language_mode_manual while calling breakpoint_re_set_one.

gdb/testsuite/ChangeLog:

        * gdb.ada/bp_fun_addr: New testcase.

Tested on x86_64-linux.

5 files changed, 76 insertions, 0 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 01f4c00..082a435 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2018-06-01  Joel Brobecker  <brobecker@adacore.com>
+
+	* breakpoint.c (breakpoint_re_set): Temporarily force language_mode
+	to language_mode_manual while calling breakpoint_re_set_one.
+
 2018-06-01  Tom Tromey  <tom@tromey.com>
 
 	* valops.c (value_cast_structs, destructor_name_p): Update.
diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index f3101af..00c538e 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -13868,6 +13868,19 @@ breakpoint_re_set (void)
     scoped_restore save_input_radix = make_scoped_restore (&input_radix);
     scoped_restore_current_pspace_and_thread restore_pspace_thread;
 
+    /* breakpoint_re_set_one sets the current_language to the language
+       of the breakpoint it is resetting (see prepare_re_set_context)
+       before re-evaluating the breakpoint's location.  This change can
+       unfortunately get undone by accident if the language_mode is set
+       to auto, and we either switch frames, or more likely in this context,
+       we select the current frame.
+
+       We prevent this by temporarily turning the language_mode to
+       language_mode_manual.  We restore it once all breakpoints
+       have been reset.  */
+    scoped_restore save_language_mode = make_scoped_restore (&language_mode);
+    language_mode = language_mode_manual;
+
     /* Note: we must not try to insert locations until after all
        breakpoints have been re-set.  Otherwise, e.g., when re-setting
        breakpoint 1, we'd insert the locations of breakpoint 2, which
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 9fb10b5..8cef172 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2018-06-01  Joel Brobecker  <brobecker@adacore.com>
+
+	* gdb.ada/bp_fun_addr: New testcase.
+
 2018-06-01  Tom Tromey  <tom@tromey.com>
 
 	* gdb.xml/tdesc-regs.exp (load_description): Update expected
diff --git a/gdb/testsuite/gdb.ada/bp_fun_addr.exp b/gdb/testsuite/gdb.ada/bp_fun_addr.exp
new file mode 100644
index 0000000..b037d43
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/bp_fun_addr.exp
@@ -0,0 +1,35 @@
+# Copyright 2016-2018 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 "ada.exp"
+
+if { [skip_ada_tests] } { return -1 }
+
+standard_ada_testfile a
+
+if {[gdb_compile_ada "${srcfile}" "${binfile}" executable {debug}] != ""} {
+    return -1
+}
+
+clean_restart ${testfile}
+
+gdb_test "break *a'address" \
+         "Breakpoint \[0-9\]+ at.*: file .*a.adb, line \[0-9\]+."
+
+gdb_run_cmd
+gdb_test "" \
+         "Breakpoint $decimal, a \\(\\).*" \
+         "run until breakpoint at a'address"
+
diff --git a/gdb/testsuite/gdb.ada/bp_fun_addr/a.adb b/gdb/testsuite/gdb.ada/bp_fun_addr/a.adb
new file mode 100644
index 0000000..00e2e86
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/bp_fun_addr/a.adb
@@ -0,0 +1,19 @@
+--  Copyright 2016-2018 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/>.
+
+procedure A is
+begin
+   null;
+end A;