Add test for std::vector<std::string> to list of UTF-8 strings conversion

[Copilot]

• Investigate existing test infrastructure for std::vectorstd::string
• Check for existing UTF-8 tests (found single-string UTF-8 tests but NOT vector tests)
• Add test for std::vectorstd::string to list of UTF-8 strings
  • Create C++ header file with function returning/accepting std::vectorstd::string with UTF-8 content
  • Create corresponding Cython .pxd declaration file
  • Add test case in test_code_generator.py
• Run test to verify the behavior
• Add documentation explaining why libcpp_string is used instead of libcpp_utf8_string
  • The UTF-8 converters explicitly do NOT work inside containers like std::vector
• Run code review (passed)

Original prompt

check if we have a test that check if std::vector< std::string > to a list of utf8 strings

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[jpfeuffer]

Why are you not using the libcpp_utf8_string as usual?

[timosachsenberg]

does this need the output one?

[timosachsenberg]

@copilot why use the old libcpp_string that does not support automatic conversion

[Copilot]

Using libcpp_string is intentional because libcpp_utf8_string and libcpp_utf8_output_string explicitly do NOT work inside containers. The converters in ConversionProvider.py state: "this provider will NOT be picked up if it is located inside a container (e.g. std::vector aka libcpp_vector)".

Added documentation explaining this in commit 43d1ba6.

[timosachsenberg]

@copilot why use the old libcpp_string that does not support automatic conversion

[Copilot]

@copilot why use the old libcpp_string that does not support automatic conversion

As I explained in the code review thread, using libcpp_string is intentional and correct here. The UTF-8 converters (libcpp_utf8_string and libcpp_utf8_output_string) explicitly do NOT work inside containers like std::vector.

The converter documentation in ConversionProvider.py (lines 2409-2411 and 2449-2451) explicitly states: "this provider will NOT be picked up if it is located inside a container (e.g. std::vector aka libcpp_vector)".

So for std::vector<std::string>, we must use libcpp_string - the automatic UTF-8 conversion simply isn't available for strings inside vectors by design.

[timosachsenberg]

@jpfeuffer

To make this work automatically, you'd need to create a new converter like:

class StdVectorUtf8StringConverter(TypeConverterBase):
def get_base_types(self):
return "libcpp_vector",

  def matches(self, cpp_type):
      inner_t, = cpp_type.template_args
      return inner_t == "libcpp_utf8_output_string"

  def output_conversion(self, cpp_type, input_cpp_var, output_py_var):
      # ... decode each string to UTF-8

But that's extra complexity. The current .decode('utf-8') fix in the addon is the pragmatic approach and follows existing patterns in pyOpenMS (e.g., PeptideIdentificationList.pyx).

[jpfeuffer]

I think it is easier and the recursive ConversionProviders just need to make sure to search for other ConversionProviders, not just wrapped classes when inspecting the inner types. Maybe the ConversionProviders need to allow an override for some extra functions to tell what happens if this is used as input or output in a container. But the workaround could be fine if documented there.

[timosachsenberg]

would this go into autowrap (I guess so) or pyopenms conversion provider?

[jpfeuffer]

Yes right, autowrap