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Make from_bits in bitflags! safe; add from_bits_truncate #14208

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Make from_bits in bitflags! safe; add from_bits_truncate #14208

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4 changes: 1 addition & 3 deletions src/libnative/io/file_unix.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -493,9 +493,7 @@ fn mkstat(stat: &libc::stat) -> io::FileStat {
io::FileStat {
size: stat.st_size as u64,
kind: kind,
perm: unsafe {
io::FilePermission::from_bits(stat.st_mode as u32) & io::AllPermissions
},
perm: io::FilePermission::from_bits_truncate(stat.st_mode as u32),
created: mktime(stat.st_ctime as u64, stat.st_ctime_nsec as u64),
modified: mktime(stat.st_mtime as u64, stat.st_mtime_nsec as u64),
accessed: mktime(stat.st_atime as u64, stat.st_atime_nsec as u64),
Expand Down
4 changes: 1 addition & 3 deletions src/libnative/io/file_win32.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -492,9 +492,7 @@ fn mkstat(stat: &libc::stat) -> io::FileStat {
io::FileStat {
size: stat.st_size as u64,
kind: kind,
perm: unsafe {
io::FilePermission::from_bits(stat.st_mode as u32) & io::AllPermissions
},
perm: io::FilePermission::from_bits_truncate(stat.st_mode as u32),
created: stat.st_ctime as u64,
modified: stat.st_mtime as u64,
accessed: stat.st_atime as u64,
Expand Down
4 changes: 1 addition & 3 deletions src/librustuv/file.rs
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Expand Up @@ -285,9 +285,7 @@ impl FsRequest {
FileStat {
size: stat.st_size as u64,
kind: kind,
perm: unsafe {
io::FilePermission::from_bits(stat.st_mode as u32) & io::AllPermissions
},
perm: io::FilePermission::from_bits_truncate(stat.st_mode as u32),
created: to_msec(stat.st_birthtim),
modified: to_msec(stat.st_mtim),
accessed: to_msec(stat.st_atim),
Expand Down
37 changes: 30 additions & 7 deletions src/libstd/bitflags.rs
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Expand Up @@ -136,10 +136,20 @@ macro_rules! bitflags(
self.bits
}

/// Convert from underlying bit representation. Unsafe because the
/// bits are not guaranteed to represent valid flags.
pub unsafe fn from_bits(bits: $T) -> $BitFlags {
$BitFlags { bits: bits }
/// Convert from underlying bit representation, unless that
/// representation contains bits that do not correspond to a flag.
pub fn from_bits(bits: $T) -> ::std::option::Option<$BitFlags> {
if (bits & !$BitFlags::all().bits()) != 0 {
::std::option::None
} else {
::std::option::Some($BitFlags { bits: bits })
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Maybe use std::option; could make it cleaner.

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I didn't want to import the module as part of the macro, since that can pollute the macro client's namespace -- so I think the type signature, at least, needs to stay as is.

(Note that macros.rs in libstd follows the same pattern.)

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Fair enough, I have to admit I’m not used to declaring macros.

}
}

/// Convert from underlying bit representation, dropping any bits
/// that do not correspond to flags.
pub fn from_bits_truncate(bits: $T) -> $BitFlags {
$BitFlags { bits: bits } & $BitFlags::all()
}

/// Returns `true` if no flags are currently stored.
Expand Down Expand Up @@ -209,6 +219,7 @@ macro_rules! bitflags(

#[cfg(test)]
mod tests {
use option::{Some, None};
use ops::{BitOr, BitAnd, Sub, Not};

bitflags!(
Expand All @@ -231,9 +242,21 @@ mod tests {

#[test]
fn test_from_bits() {
assert!(unsafe { Flags::from_bits(0x00000000) } == Flags::empty());
assert!(unsafe { Flags::from_bits(0x00000001) } == FlagA);
assert!(unsafe { Flags::from_bits(0x00000111) } == FlagABC);
assert!(Flags::from_bits(0) == Some(Flags::empty()));
assert!(Flags::from_bits(0x1) == Some(FlagA));
assert!(Flags::from_bits(0x10) == Some(FlagB));
assert!(Flags::from_bits(0x11) == Some(FlagA | FlagB));
assert!(Flags::from_bits(0x1000) == None);
}

#[test]
fn test_from_bits_truncate() {
assert!(Flags::from_bits_truncate(0) == Flags::empty());
assert!(Flags::from_bits_truncate(0x1) == FlagA);
assert!(Flags::from_bits_truncate(0x10) == FlagB);
assert!(Flags::from_bits_truncate(0x11) == (FlagA | FlagB));
assert!(Flags::from_bits_truncate(0x1000) == Flags::empty());
assert!(Flags::from_bits_truncate(0x1001) == FlagA);
}

#[test]
Expand Down