[lldb-dap] Add a CMake variable for defining a welcome message (#78811)

lldb-dap instances managed by other extensions benefit from having a
welcome message with, for example, a basic user guide or a
troubleshooting message.
This PR adds a cmake variable for defining such message in a simple way.
This message appears upon initialization but before initCommands are
executed, as they might cause a failure and prevent the message from
being displayed.

Author: walter-erquinigo

lldb/tools/lldb-dap/CMakeLists.txt

@@ -46,6 +46,12 @@ add_lldb_tool(lldb-dap
     Support
   )
 
+if(LLDB_DAP_WELCOME_MESSAGE)
+  target_compile_definitions(lldb-dap
+    PRIVATE
+    -DLLDB_DAP_WELCOME_MESSAGE=\"${LLDB_DAP_WELCOME_MESSAGE}\")
+endif()
+
 if(LLDB_BUILD_FRAMEWORK)
   # In the build-tree, we know the exact path to the framework directory.
   # The installed framework can be in different locations.

lldb/tools/lldb-dap/lldb-dap.cpp

@@ -108,6 +108,14 @@ typedef void (*RequestCallback)(const llvm::json::Object &command);
 
 enum LaunchMethod { Launch, Attach, AttachForSuspendedLaunch };
 
+/// Prints a welcome message on the editor if the preprocessor variable
+/// LLDB_DAP_WELCOME_MESSAGE is defined.
+static void PrintWelcomeMessage() {
+#ifdef LLDB_DAP_WELCOME_MESSAGE
+  g_dap.SendOutput(OutputType::Console, LLDB_DAP_WELCOME_MESSAGE);
+#endif
+}
+
 lldb::SBValueList *GetTopLevelScope(int64_t variablesReference) {
   switch (variablesReference) {
   case VARREF_LOCALS:
@@ -657,6 +665,8 @@ void request_attach(const llvm::json::Object &request) {
   g_dap.SetFrameFormat(GetString(arguments, "customFrameFormat"));
   g_dap.SetThreadFormat(GetString(arguments, "customThreadFormat"));
 
+  PrintWelcomeMessage();
+
   // This is a hack for loading DWARF in .o files on Mac where the .o files
   // in the debug map of the main executable have relative paths which require
   // the lldb-dap binary to have its working directory set to that relative
@@ -666,7 +676,7 @@ void request_attach(const llvm::json::Object &request) {
 
   // Run any initialize LLDB commands the user specified in the launch.json
   if (llvm::Error err = g_dap.RunInitCommands()) {
-    response["success"] = false;
+    kkkk response["success"] = false;
     EmplaceSafeString(response, "message", llvm::toString(std::move(err)));
     g_dap.SendJSON(llvm::json::Value(std::move(response)));
     return;
@@ -1838,10 +1848,12 @@ void request_launch(const llvm::json::Object &request) {
   g_dap.SetFrameFormat(GetString(arguments, "customFrameFormat"));
   g_dap.SetThreadFormat(GetString(arguments, "customThreadFormat"));
 
+  PrintWelcomeMessage();
+
   // This is a hack for loading DWARF in .o files on Mac where the .o files
-  // in the debug map of the main executable have relative paths which require
-  // the lldb-dap binary to have its working directory set to that relative
-  // root for the .o files in order to be able to load debug info.
+  // in the debug map of the main executable have relative paths which
+  // require the lldb-dap binary to have its working directory set to that
+  // relative root for the .o files in order to be able to load debug info.
   if (!debuggerRoot.empty())
     llvm::sys::fs::set_current_path(debuggerRoot);