Summary

LLDB type formatters (pretty printers) do not format STL types correctly when using the in-source libcxx in flutter

Expected outcome

STL types should automatically be formatted when using the LLDB debugger with Flutter Engine sources.

(std::vector<std::basic_string<char> >) severities = size=4 {
  [0] = "INFO"
  [1] = "WARNING"
  [2] = "ERROR"
  [3] = "IMPORTANT"
}

Actual outcome

STL types are formatted using LLDB's default display

(std::vector<std::basic_string<char> >) severities = {
  __begin_ = 0x0000555559cae0a0
  __end_ = 0x0000555559cae100
  __cap_ = 0x0000555559cae100
  __padding1_548_ = {}
  __alloc_ = {}
  __padding2_548_ = {}
}

Steps to reproduce

1. Build the flutter engine unittests with Linux
2. Change to the build output folder (eg src/out/host_debug_unopt )
3. Run

   $ lldb ./exe.unstripped/fml_unittests -- --gtest_filter=LoggingTest.SanityTests
   (lldb) breakpoint set --file logging_unittests.cc --line 81
   (lldb) run
   (lldb) frame variable severities