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Morgan Bartholomewandintellij-monorepo-bot
c2f7a647e3
- moved functions to `PyTypeUtil` - improved naming and documentation - improved hitbox for unnecessary - added tests to suites Merge-request: IJ-MR-174646 Merged-by: Morgan Bartholomew <morgan.bartholomew@jetbrains.com> GitOrigin-RevId: 4cecc6eb9a22cd8cc4d4019e0ff6f22faebe8cae
36 lines
1.5 KiB
HTML
36 lines
1.5 KiB
HTML
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<p>Reports <code>typing.cast</code> calls where the source and target types are unrelated.</p>
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<p>An error is reported when neither the source type is a subtype of the target, nor the target type is a subtype of the source.
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Such casts often indicate a logical error, as an instance of one type cannot be assumed to be an instance of the other,
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and <code>typing.cast</code> does not dynamically validate the type.</p>
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<p>This check applies even to types that could theoretically have a common descendant.
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For example, it will flag a cast between two sibling classes <code>Left</code> and <code>Right</code> that both inherit from <code>Top</code>,
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because there is no direct inheritance relationship between them.</p>
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<p><b>Example:</b></p>
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<pre><code>
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from typing import cast
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# Non-overlapping types — likely a mistake
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<b>cast(int, "a")</b> # 'str' -> 'int'
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<b>cast(list[int], ["a"])</b> # 'list[str]' -> 'list[int]'
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# Recommended explicit escape hatch is to use a "double cast"
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cast(int, <b>cast(object, "a")</b>) # ok
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# Legitimate overlapping cases
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cast(int, object()) # a valid down cast
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cast(object, 1) # a valid up cast
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# While the following is an invalid cast, as <code>list</code> is invariant. It's not currently supported by this inspection
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int_list = [1, 2, 3]
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cast(list[object], int_list)
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</code></pre>
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<!-- tooltip end -->
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<p>The inspection relies on static type information; when a type is unknown, no warning is reported.
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Variance of generic types is not yet considered.</p>
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