[lldb-dap] Treat empty thread names as unset (llvm#141529)

When a target thread returned an empty but not `nullptr` string as its
name, the thread would show up with an empty name in lldb-dap.

I don't know how this works on macOS and Linux, but on Windows,
[`TargetThreadWindows::GetName`](https://github.com/llvm/llvm-project/blob/deedc8a181b9598d188b2175357bce990a271d5d/lldb/source/Plugins/Process/Windows/Common/TargetThreadWindows.cpp#L178-L204)
returns a non-null pointer to an empty string, because on MSVC's STL,
`std::string{}.c_str()` returns a pointer to inside the object (the SSO
storage).

This changes the check in `CreateThread`, when no custom thread
formatter is set, to check for the length of the thread and queue name
instead of it being `nullptr`.

Author: Nerixyz

lldb/test/API/tools/lldb-dap/threads/Makefile

@@ -1,4 +1,4 @@
-C_SOURCES := main.c
+CXX_SOURCES := main.cpp
 
 ENABLE_THREADS := YES
 

lldb/test/API/tools/lldb-dap/threads/TestDAP_threads.py

@@ -1,5 +1,5 @@
 """
-Test lldb-dap setBreakpoints request
+Test lldb-dap threads request
 """
 
 from lldbsuite.test.decorators import *
@@ -9,7 +9,6 @@
 
 
 class TestDAP_threads(lldbdap_testcase.DAPTestCaseBase):
-    @skipIfWindows
     def test_correct_thread(self):
         """
         Tests that the correct thread is selected if we continue from
@@ -19,7 +18,7 @@ def test_correct_thread(self):
         """
         program = self.getBuildArtifact("a.out")
         self.build_and_launch(program)
-        source = "main.c"
+        source = "main.cpp"
         breakpoint_line = line_number(source, "// break here")
         lines = [breakpoint_line]
         # Set breakpoint in the thread function
@@ -42,8 +41,10 @@ def test_correct_thread(self):
         )
         self.assertFalse(stopped_event[0]["body"]["preserveFocusHint"])
         self.assertTrue(stopped_event[0]["body"]["threadCausedFocus"])
+        # All threads should be named Thread {index}
+        threads = self.dap_server.get_threads()
+        self.assertTrue(all(len(t["name"]) > 0 for t in threads))
 
-    @skipIfWindows
     def test_thread_format(self):
         """
         Tests the support for custom thread formats.
@@ -54,7 +55,7 @@ def test_thread_format(self):
             customThreadFormat="This is thread index #${thread.index}",
             stopCommands=["thread list"],
         )
-        source = "main.c"
+        source = "main.cpp"
         breakpoint_line = line_number(source, "// break here")
         lines = [breakpoint_line]
         # Set breakpoint in the thread function
@@ -63,8 +64,18 @@ def test_thread_format(self):
             len(breakpoint_ids), len(lines), "expect correct number of breakpoints"
         )
         self.continue_to_breakpoints(breakpoint_ids)
-        # We are stopped at the second thread
+        # We are stopped at the first thread
         threads = self.dap_server.get_threads()
         print("got thread", threads)
-        self.assertEqual(threads[0]["name"], "This is thread index #1")
-        self.assertEqual(threads[1]["name"], "This is thread index #2")
+        if self.getPlatform() == "windows":
+            # Windows creates a thread pool once WaitForSingleObject is called
+            # by thread.join(). As we are in the thread function, we can't be
+            # certain that join() has been called yet and a thread pool has
+            # been created, thus we only check for the first two threads.
+            names = list(sorted(t["name"] for t in threads))[:2]
+            self.assertEqual(
+                names, ["This is thread index #1", "This is thread index #2"]
+            )
+        else:
+            self.assertEqual(threads[0]["name"], "This is thread index #1")
+            self.assertEqual(threads[1]["name"], "This is thread index #2")

lldb/test/API/tools/lldb-dap/threads/main.c

@@ -0,0 +1,18 @@
+#include <cstdio>
+#include <thread>
+
+int state_var;
+
+void thread() {
+  state_var++; // break here
+}
+
+int main(int argc, char **argv) {
+  std::thread t1(thread);
+  t1.join();
+  std::thread t2(thread);
+  t2.join();
+
+  printf("state_var is %d\n", state_var);
+  return 0;
+}

lldb/test/API/tools/lldb-dap/threads/main.cpp

@@ -764,12 +764,12 @@ llvm::json::Value CreateThread(lldb::SBThread &thread, lldb::SBFormat &format) {
   if (format && thread.GetDescriptionWithFormat(format, stream).Success()) {
     thread_str = stream.GetData();
   } else {
-    const char *thread_name = thread.GetName();
-    const char *queue_name = thread.GetQueueName();
+    llvm::StringRef thread_name(thread.GetName());
+    llvm::StringRef queue_name(thread.GetQueueName());
 
-    if (thread_name) {
-      thread_str = std::string(thread_name);
-    } else if (queue_name) {
+    if (!thread_name.empty()) {
+      thread_str = thread_name.str();
+    } else if (!queue_name.empty()) {
       auto kind = thread.GetQueue().GetKind();
       std::string queue_kind_label = "";
       if (kind == lldb::eQueueKindSerial) {