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Box sometimes forgets to drop its allocator when the Box is conditionally initialized. #131082
Description
I tried this code:
#![feature(allocator_api)]
use std::alloc::{Allocator, AllocError, Layout, Global};
use std::ptr::NonNull;
struct LoudDropAllocator;
unsafe impl Allocator for LoudDropAllocator {
fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
Global.allocate(layout)
}
unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
Global.deallocate(ptr, layout);
}
}
impl Drop for LoudDropAllocator {
fn drop(&mut self) {
println!("dropping allocator...");
}
}
struct HasDrop;
impl Drop for HasDrop {
fn drop(&mut self) {}
}
fn foo() {
println!("foo()");
let b = Box::new_in(HasDrop, LoudDropAllocator);
if true {
drop(*b);
} else {
drop(b);
}
}
fn bar() {
println!("bar()");
let b = Box::new_in(HasDrop, LoudDropAllocator);
if true {
drop(*b);
} else {
// drop(b);
}
}
fn main() {
foo();
bar();
}I expected the program to output:
foo()
dropping allocator...
bar()
dropping allocator...
Instead it output:
foo()
bar()
dropping allocator...
Seems like there's something wrong with the drop flags.
Making HasDrop not implement Drop causes the program to behave as expected.
Meta
Reproducible on the playground with version 1.83.0-nightly (2024-09-30 fb4aebddd18d258046dd)
Activity
beepster4096 commentedon Oct 1, 2024
@rustbot claim
[-]Box sometimes leaks its allocator when its contents are conditionally initialized.[/-][+]Box sometimes forgets to drop its allocator when the Box is conditionally initialized.[/+]beepster4096 commentedon Oct 1, 2024
Likely caused by #100036. Tried it out on godbolt, and it doesn't reproduce before 1.72. (with RUSTC_BOOTSTRAP=1)
add mir-opt test for rust-lang#131082
Rollup merge of rust-lang#131146 - beepster4096:box_drop_flags, r=wes…
Rollup merge of rust-lang#143672 - beepster4096:box_drop_flags_again,…
Rollup merge of rust-lang#143672 - beepster4096:box_drop_flags_again,…
Auto merge of #143672 - beepster4096:box_drop_flags_again, r=oli-obk
Rollup merge of rust-lang#143672 - beepster4096:box_drop_flags_again,…
Rollup merge of rust-lang#143672 - beepster4096:box_drop_flags_again,…
Unrolled build for #143672
Rollup merge of #143672 - beepster4096:box_drop_flags_again, r=oli-obk