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Commit3033120

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Rollup merge ofrust-lang#127659 - saethlin:manually-drop-bufwriter, r=joboet
Use ManuallyDrop in BufWriter::into_partsThe fact that `mem::forget` takes by value means that it interacts very poorly with Stacked Borrows; generally users think of calling it as a no-op, but in Stacked Borrows, the field retagging tends to cause surprise tag invalidation.
2 parents6b67c66 +c8b79dd commit3033120

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2 files changed

+17
-7
lines changed

2 files changed

+17
-7
lines changed

‎std/src/io/buffered/bufwriter.rs‎

Lines changed: 7 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -3,7 +3,7 @@ use crate::fmt;
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usecrate::io::{
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self,ErrorKind,IntoInnerError,IoSlice,Seek,SeekFrom,Write,DEFAULT_BUF_SIZE,
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};
6-
usecrate::mem;
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usecrate::mem::{self,ManuallyDrop};
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usecrate::ptr;
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/// Wraps a writer and buffers its output.
@@ -164,13 +164,13 @@ impl<W: Write> BufWriter<W> {
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/// assert_eq!(&buffered_data.unwrap(), b"ata");
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/// ```
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#[stable(feature ="bufwriter_into_parts", since ="1.56.0")]
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pubfninto_parts(mutself) ->(W,Result<Vec<u8>,WriterPanicked>){
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let buf = mem::take(&mutself.buf);
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let buf =if !self.panicked{Ok(buf)}else{Err(WriterPanicked{ buf})};
167+
pubfninto_parts(self) ->(W,Result<Vec<u8>,WriterPanicked>){
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letmut this =ManuallyDrop::new(self);
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let buf = mem::take(&mut this.buf);
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let buf =if !this.panicked{Ok(buf)}else{Err(WriterPanicked{ buf})};
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171-
// SAFETY: forget(self) prevents double dropping inner
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let inner =unsafe{ ptr::read(&self.inner)};
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mem::forget(self);
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// SAFETY: double-drops are prevented by putting `this` in a ManuallyDrop that is never dropped
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let inner =unsafe{ ptr::read(&this.inner)};
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(inner, buf)
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}

‎std/src/io/buffered/tests.rs‎

Lines changed: 10 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1067,3 +1067,13 @@ fn bufreader_full_initialize() {
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// But we initialized the whole buffer!
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assert_eq!(reader.initialized(), reader.capacity());
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}
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/// This is a regression test for https://github.com/rust-lang/rust/issues/127584.
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#[test]
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fnbufwriter_aliasing(){
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usecrate::io::{BufWriter,Cursor};
1075+
letmut v =vec![0;1024];
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let c =Cursor::new(&mut v);
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let w =BufWriter::new(Box::new(c));
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let _ = w.into_parts();
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}

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