[PATCH 22/25] Add "stop at main" extension to DAP launch request

[Tom Tromey <tromey@adacore.com>]

Co-workers who work on a program that uses DAP asked for the ability
to have gdb stop at the main subprogram when launching.  This patch
implements this extension.
---
 gdb/doc/gdb.texinfo                    |  5 +++++
 gdb/python/lib/gdb/dap/launch.py       | 13 +++++++++++-
 gdb/testsuite/gdb.dap/stop-at-main.exp | 37 ++++++++++++++++++++++++++++++++++
 gdb/testsuite/lib/dap-support.exp      |  9 +++++++--
 4 files changed, 61 insertions(+), 3 deletions(-)

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index f66dd4df3cf..eb95273d93d 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -39018,6 +39018,11 @@ inferior will be set to exactly as passed in.  @xref{Environment}.
 @item program
 If provided, this is a string that specifies the program to use.  This
 corresponds to the @code{file} command.  @xref{Files}.
+
+@item stopAtBeginningOfMainSubprogram
+If provided, this must be a boolean.  When @samp{True}, @value{GDBN}
+will set a temporary breakpoint at the program's main procedure, using
+the same approach as the @code{start} command.  @xref{Starting}.
 @end table
 
 @value{GDBN} defines some parameters that can be passed to the
diff --git a/gdb/python/lib/gdb/dap/launch.py b/gdb/python/lib/gdb/dap/launch.py
index 2fec3267cbb..aee8c2f9ae6 100644
--- a/gdb/python/lib/gdb/dap/launch.py
+++ b/gdb/python/lib/gdb/dap/launch.py
@@ -20,7 +20,7 @@ from typing import Mapping, Optional, Sequence
 
 from .events import ExecutionInvoker
 from .server import request, capability
-from .startup import send_gdb, send_gdb_with_response, in_gdb_thread
+from .startup import send_gdb, send_gdb_with_response, in_gdb_thread, exec_and_log
 
 
 _program = None
@@ -36,6 +36,14 @@ def _set_args_env(args, env):
             inf.set_env(name, value)
 
 
+@in_gdb_thread
+def _break_at_main():
+    inf = gdb.selected_inferior()
+    main = inf.main_name
+    if main is not None:
+        exec_and_log("tbreak " + main)
+
+
 # Any parameters here are necessarily extensions -- DAP requires this
 # from implementations.  Any additions or changes here should be
 # documented in the gdb manual.
@@ -45,12 +53,15 @@ def launch(
     program: Optional[str] = None,
     args: Sequence[str] = (),
     env: Optional[Mapping[str, str]] = None,
+    stopAtBeginningOfMainSubprogram: bool = False,
     **extra,
 ):
     if program is not None:
         global _program
         _program = program
         send_gdb(f"file {_program}")
+    if stopAtBeginningOfMainSubprogram:
+        send_gdb(_break_at_main)
     if len(args) > 0 or env is not None:
         send_gdb(lambda: _set_args_env(args, env))
 
diff --git a/gdb/testsuite/gdb.dap/stop-at-main.exp b/gdb/testsuite/gdb.dap/stop-at-main.exp
new file mode 100644
index 00000000000..80a9b81e152
--- /dev/null
+++ b/gdb/testsuite/gdb.dap/stop-at-main.exp
@@ -0,0 +1,37 @@
+# Copyright 2022-2023 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/>.
+
+# Test the stop-at-main extension.
+
+require allow_dap_tests
+
+load_lib dap-support.exp
+
+standard_testfile attach.c
+
+if {[build_executable ${testfile}.exp $testfile $srcfile] == -1} {
+    return
+}
+
+if {[dap_launch $testfile {} {} 1] == ""} {
+    return
+}
+
+dap_check_request_and_response "start inferior" configurationDone
+# We didn't explicitly set a breakpoint, so if we hit one, it worked.
+dap_wait_for_event_and_check "stopped at function breakpoint" stopped \
+    "body reason" breakpoint
+
+dap_shutdown
diff --git a/gdb/testsuite/lib/dap-support.exp b/gdb/testsuite/lib/dap-support.exp
index e1fada8b703..92484bfdb8d 100644
--- a/gdb/testsuite/lib/dap-support.exp
+++ b/gdb/testsuite/lib/dap-support.exp
@@ -241,8 +241,9 @@ proc _dap_initialize {name} {
 # request.  If specified, ARGS is a list of command-line arguments,
 # and ENV is a list of pairs of the form {VAR VALUE} that is used to
 # populate the inferior's environment.  After this is called, gdb will
-# be ready to accept breakpoint requests.
-proc dap_launch {file {args {}} {env {}}} {
+# be ready to accept breakpoint requests.  If STOP_AT_MAIN is nonzero,
+# pass "stopAtBeginningOfMainSubprogram" to the launch request.
+proc dap_launch {file {args {}} {env {}} {stop_at_main 0}} {
     if {[_dap_initialize "startup - initialize"] == ""} {
 	return ""
     }
@@ -269,6 +270,10 @@ proc dap_launch {file {args {}} {env {}}} {
 	append params " \[o $envlist\]"
     }
 
+    if {$stop_at_main} {
+	append params { stopAtBeginningOfMainSubprogram [l true]}
+    }
+
     return [dap_check_request_and_response "startup - launch" launch $params]
 }
 

-- 
2.40.0