Read-only memoryview fields in a cdef class lead to AssertionError

[zhanghjumich]

Hi,

I am using Cython 0.28.2 from Anaconda and noticed that the following code will lead to AssertionError during Cython compilation:

cdef struct B:
    int a
    int b

cdef class A:
    cdef const B[:] c

% cythonize test.pyx
Compiling test.pyx because it changed.
[1/1] Cythonizing test.pyx
Traceback (most recent call last):
  File "/home/zhanghj/.local/opt/conda/bin/cythonize", line 11, in <module>
    sys.exit(main())
  File "/home/zhanghj/.local/opt/conda/lib/python3.6/site-packages/Cython/Build/Cythonize.py", line 196, in main
    cython_compile(path, options)
  File "/home/zhanghj/.local/opt/conda/lib/python3.6/site-packages/Cython/Build/Cythonize.py", line 90, in cython_compile
    **options.options)
  File "/home/zhanghj/.local/opt/conda/lib/python3.6/site-packages/Cython/Build/Dependencies.py", line 1026, in cythonize
    cythonize_one(*args)
  File "/home/zhanghj/.local/opt/conda/lib/python3.6/site-packages/Cython/Build/Dependencies.py", line 1129, in cythonize_one
    result = compile_single(pyx_file, options, full_module_name=full_module_name)
  File "/home/zhanghj/.local/opt/conda/lib/python3.6/site-packages/Cython/Compiler/Main.py", line 649, in compile_single
    return run_pipeline(source, options, full_module_name)
  File "/home/zhanghj/.local/opt/conda/lib/python3.6/site-packages/Cython/Compiler/Main.py", line 499, in run_pipeline
    err, enddata = Pipeline.run_pipeline(pipeline, source)
  File "/home/zhanghj/.local/opt/conda/lib/python3.6/site-packages/Cython/Compiler/Pipeline.py", line 354, in run_pipeline
    data = run(phase, data)
  File "/home/zhanghj/.local/opt/conda/lib/python3.6/site-packages/Cython/Compiler/Pipeline.py", line 334, in run
    return phase(data)
  File "/home/zhanghj/.local/opt/conda/lib/python3.6/site-packages/Cython/Compiler/Pipeline.py", line 52, in generate_pyx_code_stage
    module_node.process_implementation(options, result)
  File "/home/zhanghj/.local/opt/conda/lib/python3.6/site-packages/Cython/Compiler/ModuleNode.py", line 142, in process_implementation
    self.generate_c_code(env, options, result)
  File "/home/zhanghj/.local/opt/conda/lib/python3.6/site-packages/Cython/Compiler/ModuleNode.py", line 397, in generate_c_code
    globalstate.use_utility_code(utilcode)
  File "Cython/Compiler/Code.py", line 1601, in Cython.Compiler.Code.GlobalState.use_utility_code
  File "Cython/Compiler/Code.py", line 674, in Cython.Compiler.Code.LazyUtilityCode.put_code
  File "/home/zhanghj/.local/opt/conda/lib/python3.6/site-packages/Cython/Compiler/PyrexTypes.py", line 888, in lazy_utility_callback
    context['dtype_typeinfo'] = Buffer.get_type_information_cname(code, self.dtype)
  File "/home/zhanghj/.local/opt/conda/lib/python3.6/site-packages/Cython/Compiler/Buffer.py", line 674, in get_type_information_cname
    assert len(fields) > 0
AssertionError

% cython --version
Cython version 0.28.2

Thank you

[brhumphe]

This is still an issue on 0.29.14. Attempting to assign anything to the memory view definition also generates the same error:

from struct import pack

cdef packed struct B:
    int a
    int b
    
cdef const B[:] c

cdef bytes data = pack('ii', 1, 2)
# Adding this line will cause the assertion error. Any type of assignment seems to do it.
c = data

[franklsf95]

+1 also observed on 0.29.21. Any fix?

[scoder]

Does this also fail in Cython 3.0?

[franklsf95]

@scoder yes, just tested on Cython 3.0a6:

❯ cython --version
Cython version 3.0a6
❯ cython -3 a.pyx
Traceback (most recent call last):
  File "/Users/lsf/miniconda3/envs/cython-test/bin/cython", line 8, in <module>
    sys.exit(setuptools_main())
  File "/Users/lsf/miniconda3/envs/cython-test/lib/python3.9/site-packages/Cython/Compiler/Main.py", line 711, in setuptools_main
    return main(command_line = 1)
  File "/Users/lsf/miniconda3/envs/cython-test/lib/python3.9/site-packages/Cython/Compiler/Main.py", line 729, in main
    result = compile(sources, options)
  File "/Users/lsf/miniconda3/envs/cython-test/lib/python3.9/site-packages/Cython/Compiler/Main.py", line 628, in compile
    return compile_multiple(source, options)
  File "/Users/lsf/miniconda3/envs/cython-test/lib/python3.9/site-packages/Cython/Compiler/Main.py", line 605, in compile_multiple
    result = run_pipeline(source, options, context=context)
  File "/Users/lsf/miniconda3/envs/cython-test/lib/python3.9/site-packages/Cython/Compiler/Main.py", line 503, in run_pipeline
    err, enddata = Pipeline.run_pipeline(pipeline, source)
  File "/Users/lsf/miniconda3/envs/cython-test/lib/python3.9/site-packages/Cython/Compiler/Pipeline.py", line 356, in run_pipeline
    data = run(phase, data)
  File "/Users/lsf/miniconda3/envs/cython-test/lib/python3.9/site-packages/Cython/Compiler/Pipeline.py", line 336, in run
    return phase(data)
  File "/Users/lsf/miniconda3/envs/cython-test/lib/python3.9/site-packages/Cython/Compiler/Pipeline.py", line 52, in generate_pyx_code_stage
    module_node.process_implementation(options, result)
  File "/Users/lsf/miniconda3/envs/cython-test/lib/python3.9/site-packages/Cython/Compiler/ModuleNode.py", line 167, in process_implementation
    self.generate_c_code(env, options, result)
  File "/Users/lsf/miniconda3/envs/cython-test/lib/python3.9/site-packages/Cython/Compiler/ModuleNode.py", line 469, in generate_c_code
    globalstate.use_utility_code(utilcode)
  File "/Users/lsf/miniconda3/envs/cython-test/lib/python3.9/site-packages/Cython/Compiler/Code.py", line 1713, in use_utility_code
    utility_code.put_code(self)
  File "/Users/lsf/miniconda3/envs/cython-test/lib/python3.9/site-packages/Cython/Compiler/Code.py", line 684, in put_code
    utility = self.callback(globalstate.rootwriter)
  File "/Users/lsf/miniconda3/envs/cython-test/lib/python3.9/site-packages/Cython/Compiler/PyrexTypes.py", line 936, in lazy_utility_callback
    context['dtype_typeinfo'] = Buffer.get_type_information_cname(code, self.dtype)
  File "/Users/lsf/miniconda3/envs/cython-test/lib/python3.9/site-packages/Cython/Compiler/Buffer.py", line 675, in get_type_information_cname
    assert len(fields) > 0
AssertionError

[scoder]

Thanks for the short reproducer and for testing it.