[llvm] [Dexter] llvm-lit: Always log DAP messages to stderr (PR #158586)

[Orlando Cazalet-Hyams via llvm-commits]

https://github.com/OCHyams created https://github.com/llvm/llvm-project/pull/158586

This will help diagnose flaky buildbots. The stderr output is only shown by lit if the test fails.

---

More flakiness not addressed by recent fixes:
* https://lab.llvm.org/buildbot/#/builders/181/builds/27846
* https://lab.llvm.org/buildbot/#/builders/181/builds/27634 (https://github.com/llvm/llvm-project/issues/158306)

>From 54900222ff34db244dc3de2c1b1d054d2348dff0 Mon Sep 17 00:00:00 2001
From: Orlando Cazalet-Hyams <orlando.hyams at sony.com>
Date: Mon, 15 Sep 2025 10:09:28 +0100
Subject: [PATCH] [Dexter] llvm-lit: Always log DAP messages to stderr

This will help diagnose flaky buildbots. The stderr output is only shown by
lit if the test fails.
---
 .../debuginfo-tests/dexter/dex/debugger/DAP.py           | 9 ++++++++-
 .../debuginfo-tests/dexter/dex/debugger/Debuggers.py     | 6 +++++-
 cross-project-tests/lit.cfg.py                           | 6 ++++--
 3 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/cross-project-tests/debuginfo-tests/dexter/dex/debugger/DAP.py b/cross-project-tests/debuginfo-tests/dexter/dex/debugger/DAP.py
index 4e64f880487f5..a849990678d42 100644
--- a/cross-project-tests/debuginfo-tests/dexter/dex/debugger/DAP.py
+++ b/cross-project-tests/debuginfo-tests/dexter/dex/debugger/DAP.py
@@ -59,10 +59,17 @@ def _custom_enter(self):
         if self.log_file == "-":
             self.out_handle = sys.stdout
             return
+        if self.log_file == "-e":
+            self.out_handle = sys.stderr
+            return
         self.out_handle = open(self.log_file, "w+", encoding="utf-8")
 
     def _custom_exit(self):
-        if self.out_handle is not None and self.log_file != "-":
+        if (
+            self.out_handle is not None
+            and self.log_file != "-"
+            and self.log_file != "-e"
+        ):
             self.out_handle.close()
         self.open = False
 
diff --git a/cross-project-tests/debuginfo-tests/dexter/dex/debugger/Debuggers.py b/cross-project-tests/debuginfo-tests/dexter/dex/debugger/Debuggers.py
index ef23dcf6bebbc..eedd68fcdb1ba 100644
--- a/cross-project-tests/debuginfo-tests/dexter/dex/debugger/Debuggers.py
+++ b/cross-project-tests/debuginfo-tests/dexter/dex/debugger/Debuggers.py
@@ -186,7 +186,11 @@ def handle_debugger_tool_base_options(context, defaults):  # noqa
                 '<d>could not find</> <r>"{}"</>'.format(options.lldb_executable)
             )
 
-    if options.dap_message_log is not None and options.dap_message_log != "-":
+    if (
+        options.dap_message_log is not None
+        and options.dap_message_log != "-"
+        and options.dap_message_log != "-e"
+    ):
         options.dap_message_log = os.path.abspath(options.dap_message_log)
 
 
diff --git a/cross-project-tests/lit.cfg.py b/cross-project-tests/lit.cfg.py
index f042c27aece9f..e702a7739f511 100644
--- a/cross-project-tests/lit.cfg.py
+++ b/cross-project-tests/lit.cfg.py
@@ -121,7 +121,7 @@ def configure_dexter_substitutions():
         tools.append(
             ToolSubst(
                 "%dexter_lldb_args",
-                f'--lldb-executable "{lldb_dap_path}" --debugger lldb-dap',
+                f'--lldb-executable "{lldb_dap_path}" --debugger lldb-dap --dap-message-log=-e',
             )
         )
 
@@ -148,7 +148,9 @@ def configure_dexter_substitutions():
         dexter_regression_test_c_builder = "clang"
         dexter_regression_test_cxx_builder = "clang++"
         dexter_regression_test_debugger = "lldb-dap"
-        dexter_regression_test_additional_flags = f'--lldb-executable "{lldb_dap_path}"'
+        dexter_regression_test_additional_flags = (
+            f'--lldb-executable "{lldb_dap_path}" --dap-message-log=-e'
+        )
         dexter_regression_test_c_flags = "-O0 -glldb -std=gnu11"
         dexter_regression_test_cxx_flags = "-O0 -glldb -std=gnu++11"