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C-bugCategory: Clippy is not doing the correct thingCategory: Clippy is not doing the correct thingI-false-positiveIssue: The lint was triggered on code it shouldn't haveIssue: The lint was triggered on code it shouldn't haveI-suggestion-causes-errorIssue: The suggestions provided by this Lint cause an ICE/error when appliedIssue: The suggestions provided by this Lint cause an ICE/error when applied
Description
Summary
Modifying a union field that is behind ManuallyDrop incorrectly triggers the "immediately dereferencing a reference" lint, causing Clippy to suggest broken code.
Reproducer
use std::mem::ManuallyDrop;
struct Data {
num: u64,
}
union DataWithPadding {
data: ManuallyDrop<Data>,
with_padding: [u8; size_of::<Data>()],
}
fn main() {
let mut a = DataWithPadding {
with_padding: [0; size_of::<DataWithPadding>()],
};
unsafe {
(*(&raw mut a.data)).num = 42;
// Clippy suggests `(a.data).num = 42;`, which doesn't work
println!("{:?}", a.with_padding);
}
}
Version
rustc 1.87.0-nightly (8c392966a 2025-03-01)
binary: rustc
commit-hash: 8c392966a013fd8a09e6b78b3c8d6e442bc278e1
commit-date: 2025-03-01
host: x86_64-pc-windows-msvc
release: 1.87.0-nightly
LLVM version: 20.1.0
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C-bugCategory: Clippy is not doing the correct thingCategory: Clippy is not doing the correct thingI-false-positiveIssue: The lint was triggered on code it shouldn't haveIssue: The lint was triggered on code it shouldn't haveI-suggestion-causes-errorIssue: The suggestions provided by this Lint cause an ICE/error when appliedIssue: The suggestions provided by this Lint cause an ICE/error when applied