[lldb] Add matching based on Python callbacks for data formatters.

This patch adds a new matching method for data formatters, in addition
to the existing exact typename and regex-based matching. The new method
allows users to specify the name of a Python callback function that
takes a `SBType` object and decides whether the type is a match or not.

Here is an overview of the changes performed:

- Add a new `eFormatterMatchCallback` matching type, and logic to handle
  it in `TypeMatcher` and `SBTypeNameSpecifier`.

- Extend `FormattersMatchCandidate` instances with a pointer to the
  current `ScriptInterpreter` and the `TypeImpl` corresponding to the
  candidate type, so we can run registered callbacks and pass the type
  to them. All matcher search functions now receive a
  `FormattersMatchCandidate` instead of a type name.

- Add some glue code to ScriptInterpreterPython and the SWIG bindings to
  allow calling a formatter matching callback. Most of this code is
  modeled after the equivalent code for watchpoint callback functions.

- Add an API test for the new callback-based matching feature.

For more context, please check the RFC thread where this feature was
originally discussed:
https://discourse.llvm.org/t/rfc-python-callback-for-data-formatters-type-matching/64204/11

Differential Revision: https://reviews.llvm.org/D135648

2 files changed, 30 insertions, 0 deletions

diff --git a/lldb/bindings/python/python-swigsafecast.swig b/lldb/bindings/python/python-swigsafecast.swig
index eb684133abef..aa5e8e50a2d9 100644
--- a/lldb/bindings/python/python-swigsafecast.swig
+++ b/lldb/bindings/python/python-swigsafecast.swig
@@ -97,6 +97,10 @@ PythonObject ToSWIGWrapper(lldb::ExecutionContextRefSP ctx_sp) {
                       SWIGTYPE_p_lldb__SBExecutionContext);
 }
 
+PythonObject ToSWIGWrapper(lldb::TypeImplSP type_impl_sp) {
+  return ToSWIGHelper(new lldb::SBType(type_impl_sp), SWIGTYPE_p_lldb__SBType);
+}
+
 PythonObject ToSWIGWrapper(const TypeSummaryOptions &summary_options) {
   return ToSWIGHelper(new lldb::SBTypeSummaryOptions(summary_options),
                       SWIGTYPE_p_lldb__SBTypeSummaryOptions);
diff --git a/lldb/bindings/python/python-wrapper.swig b/lldb/bindings/python/python-wrapper.swig
index 626fc47bebb9..adac8a405ab9 100644
--- a/lldb/bindings/python/python-wrapper.swig
+++ b/lldb/bindings/python/python-wrapper.swig
@@ -90,6 +90,32 @@ bool lldb_private::LLDBSwigPythonWatchpointCallbackFunction(
   return stop_at_watchpoint;
 }
 
+// This function is called by
+// ScriptInterpreterPython::FormatterMatchingCallbackFunction and it's used when
+// a data formatter provides the name of a callback to inspect a candidate type
+// before considering a match.
+bool lldb_private::LLDBSwigPythonFormatterCallbackFunction(
+    const char *python_function_name, const char *session_dictionary_name,
+    lldb::TypeImplSP type_impl_sp) {
+
+  PyErr_Cleaner py_err_cleaner(true);
+
+  auto dict = PythonModule::MainModule().ResolveName<PythonDictionary>(
+      session_dictionary_name);
+  auto pfunc = PythonObject::ResolveNameWithDictionary<PythonCallable>(
+      python_function_name, dict);
+
+  if (!pfunc.IsAllocated())
+    return false;
+
+  PythonObject result =
+      pfunc(ToSWIGWrapper(type_impl_sp), dict);
+
+  // Only if everything goes okay and the function returns True we'll consider
+  // it a match.
+  return result.get() == Py_True;
+}
+
 bool lldb_private::LLDBSwigPythonCallTypeScript(
     const char *python_function_name, const void *session_dictionary,
     const lldb::ValueObjectSP &valobj_sp, void **pyfunct_wrapper,