[lldb-dap] Add 'source' references to stack frames without source files.

This adds 'source' references to all stack frames. When opening a stack frame users will see the disassembly of the frame if the source is not available.

This works around the odd behavior of navigating frames without the VSCode disassembly view open, which causes 'step' to step in the first frame with a source instead of the active frame.

Author: ashgti

lldb/tools/lldb-dap/Handler/SourceRequestHandler.cpp

@@ -9,7 +9,15 @@
 #include "DAP.h"
 #include "EventHelper.h"
 #include "JSONUtils.h"
+#include "LLDBUtils.h"
 #include "RequestHandler.h"
+#include "lldb/API/SBFrame.h"
+#include "lldb/API/SBInstructionList.h"
+#include "lldb/API/SBProcess.h"
+#include "lldb/API/SBStream.h"
+#include "lldb/API/SBTarget.h"
+#include "lldb/API/SBThread.h"
+#include "llvm/Support/JSON.h"
 
 namespace lldb_dap {
 
@@ -74,8 +82,37 @@ namespace lldb_dap {
 void SourceRequestHandler::operator()(const llvm::json::Object &request) {
   llvm::json::Object response;
   FillResponse(request, response);
-  llvm::json::Object body{{"content", ""}};
-  response.try_emplace("body", std::move(body));
+  const auto *arguments = request.getObject("arguments");
+  const auto *source = arguments->getObject("source");
+  llvm::json::Object body;
+  int64_t source_ref = GetUnsigned(
+      source, "sourceReference", GetUnsigned(arguments, "sourceReference", 0));
+
+  if (source_ref) {
+    lldb::SBProcess process = dap.target.GetProcess();
+    // Upper 32 bits is the thread index ID
+    lldb::SBThread thread =
+        process.GetThreadByIndexID(GetLLDBThreadIndexID(source_ref));
+    // Lower 32 bits is the frame index
+    lldb::SBFrame frame = thread.GetFrameAtIndex(GetLLDBFrameID(source_ref));
+    if (!frame.IsValid()) {
+      response["success"] = false;
+      response["message"] = "source not found";
+    } else {
+      lldb::SBInstructionList insts =
+          frame.GetSymbol().GetInstructions(dap.target);
+      lldb::SBStream stream;
+      insts.GetDescription(stream);
+      body["content"] = stream.GetData();
+      body["mimeType"] = "text/x-lldb.disassembly";
+      response.try_emplace("body", std::move(body));
+    }
+  } else {
+    response["success"] = false;
+    response["message"] =
+        "invalid arguments, expected source.sourceReference to be set";
+  }
+
   dap.SendJSON(llvm::json::Value(std::move(response)));
 }
 

lldb/tools/lldb-dap/JSONUtils.cpp

@@ -45,7 +45,6 @@
 #include "llvm/Support/ScopedPrinter.h"
 #include "llvm/Support/raw_ostream.h"
 #include <chrono>
-#include <climits>
 #include <cstddef>
 #include <iomanip>
 #include <optional>
@@ -698,14 +697,22 @@ llvm::json::Value CreateSource(llvm::StringRef source_path) {
   return llvm::json::Value(std::move(source));
 }
 
-static std::optional<llvm::json::Value> CreateSource(lldb::SBFrame &frame) {
+static llvm::json::Value CreateSource(lldb::SBFrame &frame,
+                                      llvm::StringRef frame_name) {
   auto line_entry = frame.GetLineEntry();
   // A line entry of 0 indicates the line is compiler generated i.e. no source
   // file is associated with the frame.
   if (line_entry.GetFileSpec().IsValid() && line_entry.GetLine() != 0)
     return CreateSource(line_entry);
 
-  return {};
+  llvm::json::Object source;
+  EmplaceSafeString(source, "name", frame_name);
+  source.try_emplace("sourceReference", MakeDAPFrameID(frame));
+  // If we don't have a filespec then we don't have the original source. Mark
+  // the source as deemphasized since users will only be able to view assembly
+  // for these frames.
+  EmplaceSafeString(source, "presentationHint", "deemphasize");
+  return std::move(source);
 }
 
 // "StackFrame": {
@@ -799,21 +806,22 @@ llvm::json::Value CreateStackFrame(lldb::SBFrame &frame,
 
   EmplaceSafeString(object, "name", frame_name);
 
-  auto source = CreateSource(frame);
-
-  if (source) {
-    object.try_emplace("source", *source);
-    auto line_entry = frame.GetLineEntry();
-    auto line = line_entry.GetLine();
-    if (line && line != LLDB_INVALID_LINE_NUMBER)
-      object.try_emplace("line", line);
-    else
-      object.try_emplace("line", 0);
+  object.try_emplace("source", CreateSource(frame, frame_name));
+  auto line_entry = frame.GetLineEntry();
+  if (line_entry.IsValid() &&
+      (line_entry.GetLine() != 0 ||
+       line_entry.GetLine() != LLDB_INVALID_LINE_NUMBER)) {
+    object.try_emplace("line", line_entry.GetLine());
     auto column = line_entry.GetColumn();
     object.try_emplace("column", column);
   } else {
-    object.try_emplace("line", 0);
-    object.try_emplace("column", 0);
+    lldb::addr_t inst_offset = frame.GetPCAddress().GetOffset() -
+                               frame.GetSymbol().GetStartAddress().GetOffset();
+    lldb::addr_t inst_line =
+        inst_offset / (frame.GetThread().GetProcess().GetAddressByteSize() / 2);
+    // lines are base-1 indexed
+    object.try_emplace("line", inst_line + 1);
+    object.try_emplace("column", 1);
   }
 
   const auto pc = frame.GetPC();