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Auto merge of #74699 - notriddle:fd-non-negative, r=m-ou-se
Mark `-1` as an available niche for file descriptors Based on discussion from <https://internals.rust-lang.org/t/can-the-standard-library-shrink-option-file/12768>, the file descriptor `-1` is chosen based on the POSIX API designs that use it as a sentinel to report errors. A bigger niche could've been chosen, particularly on Linux, but would not necessarily be portable. This PR also adds a test case to ensure that the -1 niche (which is kind of hacky and has no obvious test case) works correctly. It requires the "upper" bound, which is actually -1, to be expressed in two's complement.
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b0e5c7d1fe
@ -12,6 +12,11 @@ use crate::sys_common::AsInner;
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use libc::{c_int, c_void};
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#[derive(Debug)]
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#[rustc_layout_scalar_valid_range_start(0)]
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// libstd/os/raw/mod.rs assures me that every libstd-supported platform has a
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// 32-bit c_int. Below is -2, in two's complement, but that only works out
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// because c_int is 32 bits.
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#[rustc_layout_scalar_valid_range_end(0xFF_FF_FF_FE)]
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pub struct FileDesc {
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fd: c_int,
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}
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@ -63,7 +68,9 @@ const fn max_iov() -> usize {
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impl FileDesc {
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pub fn new(fd: c_int) -> FileDesc {
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FileDesc { fd }
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assert_ne!(fd, -1i32);
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// SAFETY: we just asserted that the value is in the valid range and isn't `-1` (the only value bigger than `0xFF_FF_FF_FE` unsigned)
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unsafe { FileDesc { fd } }
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}
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pub fn raw(&self) -> c_int {
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@ -3,7 +3,7 @@ use core::mem::ManuallyDrop;
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#[test]
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fn limit_vector_count() {
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let stdout = ManuallyDrop::new(FileDesc { fd: 1 });
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let stdout = ManuallyDrop::new(unsafe { FileDesc { fd: 1 } });
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let bufs = (0..1500).map(|_| IoSlice::new(&[])).collect::<Vec<_>>();
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assert!(stdout.write_vectored(&bufs).is_ok());
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}
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@ -15,12 +15,19 @@
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// padding and overall computed sizes can be quite different.
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#![feature(start)]
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#![feature(rustc_attrs)]
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#![allow(dead_code)]
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use std::num::NonZeroU32;
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pub enum MyOption<T> { None, Some(T) }
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#[rustc_layout_scalar_valid_range_start(0)]
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#[rustc_layout_scalar_valid_range_end(0xFF_FF_FF_FE)]
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pub struct MyNotNegativeOne {
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_i: i32,
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}
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impl<T> Default for MyOption<T> {
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fn default() -> Self { MyOption::None }
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}
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@ -77,17 +84,18 @@ fn start(_: isize, _: *const *const u8) -> isize {
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let _a: MyOption<bool> = Default::default();
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let _b: MyOption<char> = Default::default();
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let _c: MyOption<std::cmp::Ordering> = Default::default();
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let _b: MyOption<MyOption<u8>> = Default::default();
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let _d: MyOption<MyOption<u8>> = Default::default();
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let _e: Enum4<(), char, (), ()> = Enum4::One(());
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let _f: Enum4<(), (), bool, ()> = Enum4::One(());
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let _g: Enum4<(), (), (), MyOption<u8>> = Enum4::One(());
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let _h: MyOption<MyNotNegativeOne> = Default::default();
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// Unions do not currently participate in niche filling.
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let _h: MyOption<Union2<NonZeroU32, u32>> = Default::default();
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let _i: MyOption<Union2<NonZeroU32, u32>> = Default::default();
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// ...even when theoretically possible.
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let _i: MyOption<Union1<NonZeroU32>> = Default::default();
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let _j: MyOption<Union2<NonZeroU32, NonZeroU32>> = Default::default();
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let _j: MyOption<Union1<NonZeroU32>> = Default::default();
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let _k: MyOption<Union2<NonZeroU32, NonZeroU32>> = Default::default();
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0
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}
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@ -43,6 +43,12 @@ print-type-size variant `Three`: 0 bytes
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print-type-size field `.0`: 0 bytes
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print-type-size variant `Four`: 0 bytes
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print-type-size field `.0`: 0 bytes
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print-type-size type: `MyNotNegativeOne`: 4 bytes, alignment: 4 bytes
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print-type-size field `._i`: 4 bytes
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print-type-size type: `MyOption<MyNotNegativeOne>`: 4 bytes, alignment: 4 bytes
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print-type-size variant `Some`: 4 bytes
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print-type-size field `.0`: 4 bytes
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print-type-size variant `None`: 0 bytes
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print-type-size type: `MyOption<char>`: 4 bytes, alignment: 4 bytes
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print-type-size variant `Some`: 4 bytes
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print-type-size field `.0`: 4 bytes
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