Resolve the false positive dead_code lint when type is only used via destructuring #133128
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| @@ -12,10 +12,10 @@ fn field_read(f: Foo) -> usize { | |||
| } | |||
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| enum XYZ { | |||
| X, //~ ERROR variants `X` and `Y` are never constructed | |||
| X, //~ ERROR variant `X` is never constructed | |||
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Hmm, I'm not sure about this change. Because the old statement that Y is never constructed is correct. And if a variant appears in a pattern but is never constructed I think it should be warned about, because that could genuinely indicate dead code.
So now I'm questioning the whole premise of #132874 and this PR. If anything, I think let Foo(_x) = get_thing::<Foo>(); should be made to give a warning. Does that seem reasonable?
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Also, it would be better if the commits were squashed together because they are all part of the same logical change. (But that may be moot if the PR doesn't go ahead.)
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(Also, you've done a nice job on the code and test changes, they look good if we are willing to go in this direction.)
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Thank you for your review. I understood that the code given in the issue #132874 should be warned as you explained.
Now, I'm thinking that there's a possibility that the issue owner actually found a bug, but the MRE in the issue was over-generalized because he said he found the issue when using zerocopy::FromBytes::read_from_bytes and that function contains extra language features (derive macro, trait) that have been missed in the MRE.
So, I'm asking to give us another MRE closer to the original code.
#132874 (comment)
Fixes #132874
Resolves the false positive dead_code lint when type is only used via destructuring reported by the issue #132874 .
The existing code seems to have forgotten to mark the variant itself as a live symbol while it marks the variants fields. This PR adds the code to mark the variant itself as a live symbol in order to resolve the false positive dead code.