Temporarily disable libc++ std::function formatter due to performance issue

[shafik]

Summary

We have been seeing increased reports of performance issue around large project and formatting std::function variables especially in functions signatures in back traces. There are some possible fixes but exploring those fixes may take time and it is better to temporarily disable the formatter due to its impact and re-enable it once we have a fix.

[aprantl]

packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/function/TestLibCxxFunction.py

26 ↗

(On Diff #213080)

I didn't know that worked! Please also add a comment that explains *why* this test is skipped.

[shafik]

Adding as suggested.

[shafik]

@aprantl I did not know either until I looked at decorators.py and it says:

# @skipIf, skip for all platform/compiler/arch,

[JDevlieghere]

Please also add a comment to formatters::LibcxxFunctionSummaryProvider saying that it's currently not being registered.

lldb/trunk/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/function/TestLibCxxFunction.py

class LibCxxFunctionTestCase(TestBase):
     mydir = TestBase.compute_mydir(__file__)
 
     def get_variable(self, name):
         var = self.frame().FindVariable(name)
         var.SetPreferDynamicValue(lldb.eDynamicCanRunTarget)
         var.SetPreferSyntheticValue(True)
         return var
 
+    # Temporarily skipping for everywhere b/c we are disabling the std::function formatter
+    # due to performance issues but plan on turning it back on once they are addressed.
+    @skipIf
     @add_test_categories(["libc++"])
     def test(self):
         """Test that std::function as defined by libc++ is correctly printed by LLDB"""
         self.build()
         self.runCmd("file " + self.getBuildArtifact("a.out"), CURRENT_EXECUTABLE_SET)
 
         bkpt = self.target().FindBreakpointByID(
             lldbutil.run_break_set_by_source_regexp(

lldb/trunk/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp

AddCXXSynthetic(
       stl_synth_flags, true);
   AddCXXSynthetic(
       cpp_category_sp,
       lldb_private::formatters::LibcxxSharedPtrSyntheticFrontEndCreator,
       "weak_ptr synthetic children",
       ConstString("^(std::__[[:alnum:]]+::)weak_ptr<.+>(( )?&)?$"),
       stl_synth_flags, true);
 
-  AddCXXSummary(
-      cpp_category_sp, lldb_private::formatters::LibcxxFunctionSummaryProvider,
-      "libc++ std::function summary provider",
-      ConstString("^std::__[[:alnum:]]+::function<.+>$"), stl_summary_flags,
-      true);
-
   stl_summary_flags.SetDontShowChildren(false);
   stl_summary_flags.SetSkipPointers(false);
   AddCXXSummary(cpp_category_sp,
                 lldb_private::formatters::LibcxxContainerSummaryProvider,
                 "libc++ std::bitset summary provider",
                 ConstString("^std::__[[:alnum:]]+::bitset<.+>(( )?&)?$"),
                 stl_summary_flags, true);
   AddCXXSummary(cpp_category_sp,