feat(allocator/vec): remove ManuallyDrop wrapper

[Dunqing]

Partially revert #6623, It still keeps the check for non-drop element of Vec

[Dunqing]

• refactor(allocator/vec2): rename parameters and method name to align with std #9858 : 2 dependent PRs (#9855 , #9857 )
• feat(allocator/vec2): align the retain method with the standard implementation #9752
• feat(allocator/vec): remove ManuallyDrop wrapper #9742 👈 (View in Graphite)
• feat(allocator): remove drop operations from Vec2 #9679
• feat(allocator): replace allocator_ap2's Vec with Vec2 #9656
• feat(allocator): add Vec2::retain_mut method #9655
• feat(allocator): connect Vec2 module and make it compile #9647
• refactor(allocator/vec): disable lint warnings in vec2 files #9730
• docs(allocator/vec): fix link in doc comment for Vec2 #9729
• refactor(allocator/vec): comment out feature-gated methods #9728
• main

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[codspeed-hq]

CodSpeed Performance Report

Merging #9742 will not alter performance

_{Comparing 03-13-feat_allocator_vec_remove_manuallydrop_wrapper (caa477c) with main (65643bc)}

Summary

✅ 33 untouched benchmarks

[overlookmotel]

Apart from the 2 comments below, this looks good.

We definitely need to keep the const { Self::ASSERT_T_IS_NOT_DROP } assertions. Vec itself is non-drop, but these assertions also make sure that T (what you put in the Vec) is also non-drop.

This prevents memory leaks because otherwise there'd be nothing stopping you creating, for example, a Vec<'a, std::string::String>.

{
    let mut vec = Vec::new_in(&allocator);
    vec.push("foobar".to_string());
    // `vec` gets dropped here, but `Vec` doesn't implement `Drop`,
    // so it doesn't drop the `String`.
    // The 6 bytes of heap memory owned by the `String` is not reclaimed = memory leak.
}

const { Self::ASSERT_T_IS_NOT_DROP } is a compile-time check which prevents this. The example above will refuse to compile due to this assertion.

[overlookmotel]

Merge activity

• Mar 14, 3:51 AM EDT: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Mar 14, 3:52 AM EDT: A user added this pull request to the Graphite merge queue.
• Mar 14, 4:06 AM EDT: A user merged this pull request with the Graphite merge queue.