[lldb-dap] Show hidden frames as "subtle"

This commit takes advantage of the recently introduced
`SBFrame::IsHidden` to show those hidden frames as "subtle" frames in
the UI. E.g., VS Code renders such frames grayed out in the stack trace

Author: vogelsgesang

lldb/test/API/tools/lldb-dap/stackTrace/subtleFrames/Makefile

@@ -0,0 +1,3 @@
+CXX_SOURCES := main.c
+
+include Makefile.rules

lldb/test/API/tools/lldb-dap/stackTrace/subtleFrames/TestDAP_subtleFrames.py

@@ -0,0 +1,29 @@
+"""
+Test lldb-dap stack trace response
+"""
+
+
+import dap_server
+from lldbsuite.test.decorators import *
+import os
+
+import lldbdap_testcase
+from lldbsuite.test import lldbtest, lldbutil
+
+
+class TestDAP_subtleFrames(lldbdap_testcase.DAPTestCaseBase):
+    def test_subtleFrames(self):
+        """
+        Test that internal stack frames (such as the ones used by `std::function`)
+        are marked as "subtle".
+        """
+        program = self.getBuildArtifact("a.out")
+        self.build_and_launch(program)
+        source = "main.cpp"
+        self.set_source_breakpoints(source, [line_number(source, "BREAK HERE")])
+        self.continue_to_next_stop()
+
+        backtrace = self.get_stackFrames()[0]
+        for f in backtrace:
+            if "__function" in f["name"]:
+                self.assertEqual(f["presentationHint"], "subtle")

lldb/test/API/tools/lldb-dap/stackTrace/subtleFrames/main.cpp

@@ -0,0 +1,13 @@
+#include <functional>
+#include <iostream>
+
+void greet() {
+  // BREAK HERE
+  std::cout << "Hello\n";
+}
+
+int main() {
+  std::function<void()> func{greet};
+  func();
+  return 0;
+}

lldb/tools/lldb-dap/JSONUtils.cpp

@@ -763,6 +763,9 @@ llvm::json::Value CreateStackFrame(lldb::SBFrame &frame) {
     object.try_emplace("instructionPointerReference", formatted_addr);
   }
 
+  if (frame.IsArtificial() || frame.IsHidden())
+    object.try_emplace("presentationHint", "subtle");
+
   return llvm::json::Value(std::move(object));
 }