Fix bug in DAP handling of 'pause' requests

While working on cancellation, I noticed that a DAP 'pause' request
would set the "do not emit the continue" flag.  This meant that a
subsequent request that should provoke a 'continue' event would
instead suppress the event.

I then tried writing a more obvious test case for this, involving an
inferior call -- and discovered that gdb.events.cont does not fire for
an inferior call.

This patch installs a new event listener for gdb.events.inferior_call
and arranges for this to emit continue and stop events when
appropriate.  It also fixes the original bug, by adding a check to
exec_and_expect_stop.

gdb/python/lib/gdb/dap/events.py

@@ -128,8 +128,9 @@ def exec_and_expect_stop(cmd, reason):
     """Indicate that a stop is expected, then execute CMD"""
     global _expected_stop
     _expected_stop = reason
-    global _suppress_cont
-    _suppress_cont = True
+    if reason != StopKinds.PAUSE:
+        global _suppress_cont
+        _suppress_cont = True
     # FIXME if the call fails should we clear _suppress_cont?
     exec_and_log(cmd)
 
@@ -156,6 +157,26 @@ def _on_stop(event):
     send_event("stopped", obj)
 
 
+# This keeps a bit of state between the start of an inferior call and
+# the end.  If the inferior was already running when the call started
+# (as can happen if a breakpoint condition calls a function), then we
+# do not want to emit 'continued' or 'stop' events for the call.  Note
+# that, for some reason, gdb.events.cont does not fire for an infcall.
+_infcall_was_running = False
+
+
+@in_gdb_thread
+def _on_inferior_call(event):
+    global _infcall_was_running
+    if isinstance(event, gdb.InferiorCallPreEvent):
+        _infcall_was_running = inferior_running
+        if not _infcall_was_running:
+            _cont(None)
+    else:
+        if not _infcall_was_running:
+            _on_stop(None)
+
+
 gdb.events.stop.connect(_on_stop)
 gdb.events.exited.connect(_on_exit)
 gdb.events.new_thread.connect(_new_thread)
@@ -163,3 +184,4 @@ gdb.events.thread_exited.connect(_thread_exited)
 gdb.events.cont.connect(_cont)
 gdb.events.new_objfile.connect(_new_objfile)
 gdb.events.free_objfile.connect(_objfile_removed)
+gdb.events.inferior_call.connect(_on_inferior_call)

gdb/testsuite/gdb.dap/pause.c

@@ -0,0 +1,44 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2011-2023 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/>.  */
+
+#include <unistd.h>
+
+int
+do_nothing ()
+{
+  return 91;
+}
+
+int
+return_false ()
+{
+  return 0;
+}
+
+void
+sleep_a_bit ()
+{
+  sleep (1);			/* STOP */
+}
+
+int
+main ()
+{
+  while (1)
+    sleep_a_bit ();
+  return 0;
+}

gdb/testsuite/gdb.dap/pause.exp

@@ -19,7 +19,7 @@ require allow_dap_tests
 
 load_lib dap-support.exp
 
-standard_testfile attach.c
+standard_testfile
 
 if {[build_executable ${testfile}.exp $testfile $srcfile] == -1} {
     return
@@ -29,6 +29,18 @@ if {[dap_launch $testfile] == ""} {
     return
 }
 
+# Set a conditional breakpoint that will never fire.  This is done to
+# test the state-tracking in events -- an inferior call from a
+# breakpoint condition should not cause any sort of stop or continue
+# events.
+set line [gdb_get_line_number "STOP"]
+dap_check_request_and_response "set conditional breakpoint" \
+    setBreakpoints \
+    [format {o source [o path [%s]] \
+		 breakpoints [a [o line [i %d] \
+				     condition [s "return_false()"]]]} \
+	 [list s $srcfile] $line]
+
 dap_check_request_and_response "start inferior" configurationDone
 dap_wait_for_event_and_check "inferior started" thread "body reason" started
 
@@ -45,4 +57,20 @@ dap_check_request_and_response pause pause \
 dap_wait_for_event_and_check "stopped by pause" stopped \
     "body reason" pause
 
+set result [dap_request_and_response evaluate {o expression [s do_nothing()]}]
+gdb_assert {[dict get [lindex $result 0] body result] == 91} \
+    "check result of evaluation"
+
+set seen fail
+foreach event [lindex $result 1] {
+    if {[dict get $event type] != "event"} {
+	continue
+    }
+    if {[dict get $event event] == "continued"} {
+	set seen pass
+	break
+    }
+}
+gdb_assert {$seen == "pass"} "continue event from inferior call"
+
 dap_shutdown