[lldb] Add alternative SBThread::GetStopDescription

the function signature for `GetStopDescription` is
`lldb::SBThread::GetStopDescription(char *dst_or_null, size_t len)`
to get a description you need to call the function first time to get the
buffer size. and again to get the description.
This is little worse from the python size as the signature is
`lldb.SBThread.GetStopDescription(int: len) -> list[str]` the user has
to pass the max size as possible with no way of checking if it is enough.

This patch adds a new api
`lldb.SBThread.GetStopDescription(desc: lldb.SBStream()) -> bool`
`bool lldb::SBThread::GetStopDescription(lldb::SBStream &description)`
which handles this case.

Author: da-viper

lldb/bindings/lua/lua-typemaps.swig

@@ -121,9 +121,16 @@ LLDB_NUMBER_TYPEMAP(enum SWIGTYPE);
   $1 = (char *)malloc($2);
 }
 
+// Remove the default type check for this match.
+// because if the match function has an overload and a typemap,
+// it will typecheck against the original function instead of the
+// typemap.
+%typemap(typecheck, precedence=SWIG_TYPECHECK_POINTER) (char *dst_or_null, size_t dst_len) ""
+
 %typemap(argout) (char *dst_or_null, size_t dst_len) {
   lua_pop(L, 1); // Blow away the previous result
-  lua_pushlstring(L, (const char *)$1, $result);
+  llvm::StringRef ref($1);
+  lua_pushlstring(L, (const char *)$1, ref.size());
   free($1);
   // SWIG_arg was already incremented
 }

lldb/bindings/python/python-typemaps.swig

@@ -224,6 +224,13 @@ AND call SWIG_fail at the same time, because it will result in a double free.
   }
   $1 = (char *)malloc($2);
 }
+
+// Remove the default type check for this match.
+// because if the match function has an overload and a typemap,
+// it will typecheck against the original function instead of the
+// typemap.
+%typemap(typecheck, precedence=SWIG_TYPECHECK_POINTER) (char *dst_or_null, size_t dst_len) ""
+
 %typemap(argout) (char *dst_or_null, size_t dst_len) {
   Py_XDECREF($result); /* Blow away any previous result */
   llvm::StringRef ref($1);

lldb/include/lldb/API/SBThread.h

@@ -81,6 +81,14 @@ class LLDB_API SBThread {
   SBThreadCollection
   GetStopReasonExtendedBacktraces(InstrumentationRuntimeType type);
 
+  /// Gets a human-readable description of why the thread stopped.
+  ///
+  /// \param stream Output stream to receive the stop description text
+  /// \return
+  ///   true if obtained and written to the stream,
+  //    false if there was an error retrieving the description.
+  bool GetStopDescription(lldb::SBStream &stream) const;
+
   size_t GetStopDescription(char *dst_or_null, size_t dst_len);
 
   SBValue GetStopReturnValue();

lldb/source/API/SBThread.cpp

@@ -239,11 +239,34 @@ SBThread::GetStopReasonExtendedBacktraces(InstrumentationRuntimeType type) {
   return threads;
 }
 
-size_t SBThread::GetStopDescription(char *dst, size_t dst_len) {
-  LLDB_INSTRUMENT_VA(this, dst, dst_len);
+bool SBThread::GetStopDescription(lldb::SBStream &stream) const {
+  LLDB_INSTRUMENT_VA(this, stream);
+
+  if (!m_opaque_sp)
+    return false;
+
+  llvm::Expected<StoppedExecutionContext> exe_ctx =
+      GetStoppedExecutionContext(m_opaque_sp);
+  if (!exe_ctx) {
+    LLDB_LOG_ERROR(GetLog(LLDBLog::API), exe_ctx.takeError(), "{0}");
+    return false;
+  }
+
+  if (!exe_ctx->HasThreadScope())
+    return false;
+
+  Stream &strm = stream.ref();
+  const std::string stop_desc = exe_ctx->GetThreadPtr()->GetStopDescription();
+  strm.PutCString(stop_desc);
+
+  return true;
+}
+
+size_t SBThread::GetStopDescription(char *dst_or_null, size_t dst_len) {
+  LLDB_INSTRUMENT_VA(this, dst_or_null, dst_len);
 
-  if (dst)
-    *dst = 0;
+  if (dst_or_null)
+    *dst_or_null = 0;
 
   llvm::Expected<StoppedExecutionContext> exe_ctx =
       GetStoppedExecutionContext(m_opaque_sp);
@@ -259,8 +282,8 @@ size_t SBThread::GetStopDescription(char *dst, size_t dst_len) {
   if (thread_stop_desc.empty())
     return 0;
 
-  if (dst)
-    return ::snprintf(dst, dst_len, "%s", thread_stop_desc.c_str()) + 1;
+  if (dst_or_null)
+    return ::snprintf(dst_or_null, dst_len, "%s", thread_stop_desc.c_str()) + 1;
 
   // NULL dst passed in, return the length needed to contain the
   // description.

lldb/test/API/lua_api/TestThreadAPI.lua

@@ -0,0 +1,25 @@
+_T = require('lua_lldb_test').create_test('TestThreadAPI')
+
+function _T:TestGetStopDescription()
+    local target = self:create_target()
+    local breakpoint = target:BreakpointCreateByName("main", "a.out")
+    assertTrue(breakpoint:IsValid() and breakpoint:GetNumLocations() == 1)
+
+    local process = target:LaunchSimple({ 'arg1', 'arg2' }, nil, nil)
+    local thread = get_stopped_thread(process, lldb.eStopReasonBreakpoint)
+    assertNotNil(thread)
+    assertTrue(thread:IsValid())
+
+    assertEqual("breakpoint", thread:GetStopDescription(string.len("breakpoint") + 1))
+    assertEqual("break", thread:GetStopDescription(string.len("break") + 1))
+    assertEqual("b", thread:GetStopDescription(string.len("b") + 1))
+    assertEqual("breakpoint 1.1", thread:GetStopDescription(string.len("breakpoint 1.1") + 100))
+
+    -- Test stream variation
+    local stream = lldb.SBStream()
+    assertTrue(thread:GetStopDescription(stream))
+    assertNotNil(stream)
+    assertEqual("breakpoint 1.1", stream:GetData())
+end
+
+os.exit(_T:run())

lldb/test/API/python_api/default-constructor/sb_thread.py

@@ -10,6 +10,7 @@ def fuzz_obj(obj):
     obj.GetStopReasonDataCount()
     obj.GetStopReasonDataAtIndex(100)
     obj.GetStopDescription(256)
+    obj.GetStopDescription(lldb.SBStream())
     obj.GetThreadID()
     obj.GetIndexID()
     obj.GetName()

lldb/test/API/python_api/thread/TestThreadAPI.py

@@ -138,6 +138,11 @@ def get_stop_description(self):
             "breakpoint 1.1", thread.GetStopDescription(len("breakpoint 1.1") + 100)
         )
 
+        # Test the stream variation
+        stream = lldb.SBStream()
+        self.assertTrue(thread.GetStopDescription(stream))
+        self.assertEqual("breakpoint 1.1", stream.GetData())
+
     def step_out_of_malloc_into_function_b(self, exe_name):
         """Test Python SBThread.StepOut() API to step out of a malloc call where the call site is at function b()."""
         exe = self.getBuildArtifact(exe_name)

lldb/tools/lldb-rpc-gen/RPCCommon.cpp

@@ -118,6 +118,7 @@ static constexpr llvm::StringRef MethodsWithPointerPlusLen[] = {
     "_ZN4lldb8SBTarget15GetInstructionsEyPKvm",
     "_ZN4lldb8SBTarget25GetInstructionsWithFlavorEyPKcPKvm",
     "_ZN4lldb8SBThread18GetStopDescriptionEPcm",
+    "_ZNK4lldb8SBThread18GetStopDescriptionERNS_8SBStreamE",
     // The below mangled names are used for dummy methods in shell tests
     // that test the emitters' output. If you're adding any new mangled names
     // from the actual SB API to this list please add them above.