Pylance-release: TypeError: Cannot read property 'category' of undefined

[martinjohndyer]

A combination of property deleters and the abc.ABCMeta class produces the above error in the Pylance logs when trying to access a property of an instance of the class. I actually discovered this while using the Time class from Astropy, but I realise that's a very complicated class. Hopefully the snippet below makes this clearer.

Environment data

• Language Server version: 2020.7.1
• OS and version: Ubuntu 18.04
• Python version (& distribution if applicable, e.g. Anaconda): 3.6.9

Expected behaviour

No error

Actual behaviour

Problem: "An internal error occurred while performing type checking", see logs below.

Logs

[Info  - 15:55:10] Pylance language server 2020.7.1 starting
[Info  - 15:55:10] Server root directory: /home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server
[Info  - 15:55:10] Setting pythonPath for service "<default>": "/usr/bin/python3"
[Info  - 15:55:10] stubPath typings is not a valid directory.
[Info  - 15:55:10] Assuming Python version 3.6
[Info  - 15:55:10] Assuming Python platform Linux
[Info  - 15:55:10] Searching for source files
[Info  - 15:55:10] No source files found.
IntelliCode model /home/martin/.vscode/extensions/visualstudioexptteam.vscodeintellicode-1.2.9/cache/15708AE89896CA5DF1690433B7A8D93D28B7_215F8B4FAB1F4663ABD624559FD205B9
Loading ONNX runtime...
Loaded ONNX runtime. Creating IntelliCode session...
2020-07-15 14:55:10.630057549 [I:onnxruntime:, inference_session.cc:174 ConstructorCommon] Creating and using per session threadpools since use_per_session_threads_ is true
2020-07-15 14:55:10.630517091 [W:onnxruntime:, graph.cc:814 Graph] Initializer embeddings_matrix:0_quantized appears in graph inputs and will not be treated as constant value/weight. This may fail some of the graph optimizations, like const folding. Move it out of graph inputs if there is no need to override it, by either re-generating the model with latest exporter/converter or with the tool onnxruntime/tools/python/remove_initializer_from_input.py.
2020-07-15 14:55:10.630533944 [W:onnxruntime:, graph.cc:814 Graph] Initializer embeddings_matrix:0_scale appears in graph inputs and will not be treated as constant value/weight. This may fail some of the graph optimizations, like const folding. Move it out of graph inputs if there is no need to override it, by either re-generating the model with latest exporter/converter or with the tool onnxruntime/tools/python/remove_initializer_from_input.py.
2020-07-15 14:55:10.630543198 [W:onnxruntime:, graph.cc:814 Graph] Initializer embeddings_matrix:0_zero_point appears in graph inputs and will not be treated as constant value/weight. This may fail some of the graph optimizations, like const folding. Move it out of graph inputs if there is no need to override it, by either re-generating the model with latest exporter/converter or with the tool onnxruntime/tools/python/remove_initializer_from_input.py.
2020-07-15 14:55:10.630565238 [W:onnxruntime:, graph.cc:814 Graph] Initializer fixed_quantization_range_uint8 appears in graph inputs and will not be treated as constant value/weight. This may fail some of the graph optimizations, like const folding. Move it out of graph inputs if there is no need to override it, by either re-generating the model with latest exporter/converter or with the tool onnxruntime/tools/python/remove_initializer_from_input.py.
2020-07-15 14:55:10.630572752 [W:onnxruntime:, graph.cc:814 Graph] Initializer fixed_zero appears in graph inputs and will not be treated as constant value/weight. This may fail some of the graph optimizations, like const folding. Move it out of graph inputs if there is no need to override it, by either re-generating the model with latest exporter/converter or with the tool onnxruntime/tools/python/remove_initializer_from_input.py.
2020-07-15 14:55:10.631386163 [I:onnxruntime:, inference_session.cc:830 Initialize] Initializing session.
2020-07-15 14:55:10.631401230 [I:onnxruntime:, inference_session.cc:848 Initialize] Adding default CPU execution provider.
2020-07-15 14:55:10.632458538 [I:onnxruntime:, reshape_fusion.cc:37 ApplyImpl] Total fused reshape node count: 0
2020-07-15 14:55:10.632797834 [I:onnxruntime:, reshape_fusion.cc:37 ApplyImpl] Total fused reshape node count: 0
2020-07-15 14:55:10.633824886 [V:onnxruntime:, inference_session.cc:671 TransformGraph] Node placements
2020-07-15 14:55:10.633837746 [V:onnxruntime:, inference_session.cc:673 TransformGraph] All nodes have been placed on [CPUExecutionProvider].
2020-07-15 14:55:10.633873744 [I:onnxruntime:, session_state.cc:25 SetGraph] SaveMLValueNameIndexMapping
2020-07-15 14:55:10.633977172 [I:onnxruntime:, session_state.cc:70 SetGraph] Done saving OrtValue mappings.
2020-07-15 14:55:10.634601250 [I:onnxruntime:, session_state_initializer.cc:178 SaveInitializedTensors] Saving initialized tensors.
2020-07-15 14:55:10.661032241 [I:onnxruntime:, session_state_initializer.cc:223 SaveInitializedTensors] Done saving initialized tensors
2020-07-15 14:55:10.663214588 [I:onnxruntime:, inference_session.cc:919 Initialize] Session successfully initialized.
Created IntelliCode session.
[Info  - 15:55:10] Background analysis root directory: /home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server
[Info  - 15:55:10] Background analysis started
[BG] analyzing: /home/martin/test2.py ...
[BG]   parsing: /home/martin/test2.py (85ms)
[BG]   parsing: /home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/typeshed-fallback/stdlib/2and3/builtins.pyi (166ms)
[BG]   binding: /home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/typeshed-fallback/stdlib/2and3/builtins.pyi (86ms)
[BG]   binding: /home/martin/test2.py (3ms)
[BG]   checking: /home/martin/test2.py ...
[BG]     parsing: /home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/typeshed-fallback/stdlib/3/abc.pyi (8ms)
[BG]     binding: /home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/typeshed-fallback/stdlib/3/abc.pyi (1ms)
[BG]     parsing: /home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/typeshed-fallback/stdlib/3/typing.pyi (55ms)
[BG]     binding: /home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/typeshed-fallback/stdlib/3/typing.pyi (16ms)
[Error - 15:55:11] An internal error occurred while while performing type checking for /home/martin/test2.py: TypeError: Cannot read property 'category' of undefined
    at $t (/home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/pyright.bundle.js:1:307871)
    at qt (/home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/pyright.bundle.js:1:305811)
    at /home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/pyright.bundle.js:1:304752
    at Wt (/home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/pyright.bundle.js:1:305039)
    at $t (/home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/pyright.bundle.js:1:310097)
    at Gt (/home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/pyright.bundle.js:1:307557)
    at $t (/home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/pyright.bundle.js:1:307959)
    at Xt (/home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/pyright.bundle.js:1:315783)
    at Jt (/home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/pyright.bundle.js:1:315366)
    at Ce (/home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/pyright.bundle.js:1:218159)
[BG]   checking: /home/martin/test2.py (130ms)
[BG] analyzing: /home/martin/test2.py (473ms)
[Error - 15:55:11] Error performing analysis: TypeError: Cannot read property 'category' of undefined
    at $t (/home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/pyright.bundle.js:1:307871)
    at qt (/home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/pyright.bundle.js:1:305811)
    at /home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/pyright.bundle.js:1:304752
    at Wt (/home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/pyright.bundle.js:1:305039)
    at $t (/home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/pyright.bundle.js:1:310097)
    at Gt (/home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/pyright.bundle.js:1:307557)
    at $t (/home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/pyright.bundle.js:1:307959)
    at Xt (/home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/pyright.bundle.js:1:315783)
    at Jt (/home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/pyright.bundle.js:1:315366)
    at Ce (/home/martin/.vscode/extensions/ms-python.vscode-pylance-2020.7.1/server/pyright.bundle.js:1:218159)

Trying to hover over the instance or property gives the following extra readout with the same error:

[Error - 15:55:59] Request textDocument/hover failed.
  Message: Request textDocument/hover failed with message: Cannot read property 'category' of undefined
  Code: -32603

Code Snippet / Additional information

The errors are very easy to produce under normal conditions if Astropy is installed:

from astropy.time import Time

time = Time('2020-01-01 00:00:00')
print(time.unix)

Delving into Astropy I eventually settled on this basic example that creates the errors above:

import abc

class MyClass(metaclass=abc.ABCMeta):
    def __init__(self, value=None):
        self._cache = {'value': value}

    @property
    def cache(self):
        return self._cache

    @cache.deleter
    def cache(self):
        self._cache = {key: None for key in self._cache}

    def __getattr__(self, attr):
        cache = self.cache
        if attr in cache:
            return cache[attr]
        else:
            return self.__getattribute__(attr)


myclass = MyClass('test')
print(myclass.value)
del myclass.cache
print(myclass.value)

I have no idea why the combination of the property deleter and the ABCMeta class produces the above errors, but hopefully that snipped is a start for someone to have a look into this.

[erictraut]

@bschnurr, this is a crash in the heart of the type checker, so I'll take it.

[erictraut]

Thanks for the reporting the bug. Your simplified example was very helpful. This will be fixed in an upcoming version of Pylance.

[jakebailey]

This didn't make it into 2020.7.2 (fixed just as we were releasing), but will likely be in the next one.

[jakebailey]

This issue has been fixed in version 2020.7.3, which we've just released. You can find the changelog here: https://github.com/microsoft/pylance-release/blob/master/CHANGELOG.md#202073-21-july-2020