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Auto merge of #51564 - SimonSapin:try-int, r=alexcrichton
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Implement always-fallible TryFrom for usize/isize conversions that are infallible on some platforms

This reverts commit 837d6c7 "Remove TryFrom impls that might become conditionally-infallible with a portability lint".

This fixes #49415 by adding (restoring) missing `TryFrom` impls for integer conversions to or from `usize` or `isize`, by making them always fallible at the type system level (that is, with `Error=TryFromIntError`) even though they happen to be infallible on some platforms (for some values of `size_of::<usize>()`).

They had been removed to allow the possibility to conditionally having some of them be infallible `From` impls instead, depending on the platforms, and have the [portability lint](rust-lang/rfcs#1868) warn when they are used in code that is not already opting into non-portability. For example `#[allow(some_lint)] usize::from(x: u64)` would be valid on code that only targets 64-bit platforms.

This PR gives up on this possiblity for two reasons:

* Based on discussion with @aturon, it seems that the portability lint is not happening any time soon. It’s better to have the conversions be available *at all* than keep blocking them for so long. Portability-lint-gated platform-specific APIs can always be added separately later.

* For code that is fine with fallibility, the alternative would force it to opt into "non-portability" even though there would be no real portability issue.
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@bors
bors committed Jul 3, 2018
2 parents 81d5c3e + e7c122c commit 0fb6e39
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Showing 4 changed files with 191 additions and 101 deletions.
75 changes: 2 additions & 73 deletions src/libcore/iter/range.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -91,7 +91,7 @@ macro_rules! step_impl_unsigned {
#[inline]
#[allow(unreachable_patterns)]
fn add_usize(&self, n: usize) -> Option<Self> {
match <$t>::private_try_from(n) {
match <$t>::try_from(n) {
Ok(n_as_t) => self.checked_add(n_as_t),
Err(_) => None,
}
Expand Down Expand Up @@ -123,7 +123,7 @@ macro_rules! step_impl_signed {
#[inline]
#[allow(unreachable_patterns)]
fn add_usize(&self, n: usize) -> Option<Self> {
match <$unsigned>::private_try_from(n) {
match <$unsigned>::try_from(n) {
Ok(n_as_unsigned) => {
// Wrapping in unsigned space handles cases like
// `-120_i8.add_usize(200) == Some(80_i8)`,
Expand Down Expand Up @@ -461,74 +461,3 @@ impl<A: Step> DoubleEndedIterator for ops::RangeInclusive<A> {

#[stable(feature = "fused", since = "1.26.0")]
impl<A: Step> FusedIterator for ops::RangeInclusive<A> {}

/// Compensate removal of some impls per
/// https://github.com/rust-lang/rust/pull/49305#issuecomment-376293243
trait PrivateTryFromUsize: Sized {
fn private_try_from(n: usize) -> Result<Self, ()>;
}

impl<T> PrivateTryFromUsize for T where T: TryFrom<usize> {
#[inline]
fn private_try_from(n: usize) -> Result<Self, ()> {
T::try_from(n).map_err(|_| ())
}
}

// no possible bounds violation
macro_rules! try_from_unbounded {
($($target:ty),*) => {$(
impl PrivateTryFromUsize for $target {
#[inline]
fn private_try_from(value: usize) -> Result<Self, ()> {
Ok(value as $target)
}
}
)*}
}

// unsigned to signed (only positive bound)
#[cfg(any(target_pointer_width = "32", target_pointer_width = "64"))]
macro_rules! try_from_upper_bounded {
($($target:ty),*) => {$(
impl PrivateTryFromUsize for $target {
#[inline]
fn private_try_from(u: usize) -> Result<$target, ()> {
if u > (<$target>::max_value() as usize) {
Err(())
} else {
Ok(u as $target)
}
}
}
)*}
}


#[cfg(target_pointer_width = "16")]
mod ptr_try_from_impls {
use super::PrivateTryFromUsize;

try_from_unbounded!(u16, u32, u64, u128);
try_from_unbounded!(i32, i64, i128);
}

#[cfg(target_pointer_width = "32")]
mod ptr_try_from_impls {
use super::PrivateTryFromUsize;

try_from_upper_bounded!(u16);
try_from_unbounded!(u32, u64, u128);
try_from_upper_bounded!(i32);
try_from_unbounded!(i64, i128);
}

#[cfg(target_pointer_width = "64")]
mod ptr_try_from_impls {
use super::PrivateTryFromUsize;

try_from_upper_bounded!(u16, u32);
try_from_unbounded!(u64, u128);
try_from_upper_bounded!(i32, i64);
try_from_unbounded!(i128);
}
70 changes: 60 additions & 10 deletions src/libcore/num/mod.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -4213,6 +4213,21 @@ impl From<!> for TryFromIntError {
}
}

// no possible bounds violation
macro_rules! try_from_unbounded {
($source:ty, $($target:ty),*) => {$(
#[unstable(feature = "try_from", issue = "33417")]
impl TryFrom<$source> for $target {
type Error = TryFromIntError;

#[inline]
fn try_from(value: $source) -> Result<Self, Self::Error> {
Ok(value as $target)
}
}
)*}
}

// only negative bounds
macro_rules! try_from_lower_bounded {
($source:ty, $($target:ty),*) => {$(
Expand Down Expand Up @@ -4311,44 +4326,79 @@ try_from_both_bounded!(i128, u64, u32, u16, u8);
try_from_upper_bounded!(usize, isize);
try_from_lower_bounded!(isize, usize);

try_from_upper_bounded!(usize, u8);
try_from_upper_bounded!(usize, i8, i16);
try_from_both_bounded!(isize, u8);
try_from_both_bounded!(isize, i8);

#[cfg(target_pointer_width = "16")]
mod ptr_try_from_impls {
use super::TryFromIntError;
use convert::TryFrom;

// Fallible across platfoms, only implementation differs
try_from_upper_bounded!(usize, u8);
try_from_unbounded!(usize, u16, u32, u64, u128);
try_from_upper_bounded!(usize, i8, i16);
try_from_unbounded!(usize, i32, i64, i128);

try_from_both_bounded!(isize, u8);
try_from_lower_bounded!(isize, u16, u32, u64, u128);
try_from_both_bounded!(isize, i8);
try_from_unbounded!(isize, i16, i32, i64, i128);

rev!(try_from_upper_bounded, usize, u32, u64, u128);
rev!(try_from_lower_bounded, usize, i8, i16);
rev!(try_from_both_bounded, usize, i32, i64, i128);

rev!(try_from_upper_bounded, isize, u16, u32, u64, u128);
rev!(try_from_both_bounded, isize, i32, i64, i128);
}

#[cfg(target_pointer_width = "32")]
mod ptr_try_from_impls {
use super::TryFromIntError;
use convert::TryFrom;

// Fallible across platfoms, only implementation differs
try_from_both_bounded!(isize, u16);
try_from_upper_bounded!(usize, u8, u16);
try_from_unbounded!(usize, u32, u64, u128);
try_from_upper_bounded!(usize, i8, i16, i32);
try_from_unbounded!(usize, i64, i128);

try_from_both_bounded!(isize, u8, u16);
try_from_lower_bounded!(isize, u32, u64, u128);
try_from_both_bounded!(isize, i8, i16);
try_from_unbounded!(isize, i32, i64, i128);

rev!(try_from_unbounded, usize, u32);
rev!(try_from_upper_bounded, usize, u64, u128);
rev!(try_from_lower_bounded, usize, i8, i16, i32);
rev!(try_from_both_bounded, usize, i64, i128);

rev!(try_from_unbounded, isize, u16);
rev!(try_from_upper_bounded, isize, u32, u64, u128);
rev!(try_from_unbounded, isize, i32);
rev!(try_from_both_bounded, isize, i64, i128);
}

#[cfg(target_pointer_width = "64")]
mod ptr_try_from_impls {
use super::TryFromIntError;
use convert::TryFrom;

// Fallible across platfoms, only implementation differs
try_from_both_bounded!(isize, u16, u32);
try_from_upper_bounded!(usize, u8, u16, u32);
try_from_unbounded!(usize, u64, u128);
try_from_upper_bounded!(usize, i8, i16, i32, i64);
try_from_unbounded!(usize, i128);

try_from_both_bounded!(isize, u8, u16, u32);
try_from_lower_bounded!(isize, u64, u128);
try_from_both_bounded!(isize, i8, i16, i32);
try_from_unbounded!(isize, i64, i128);

rev!(try_from_unbounded, usize, u32, u64);
rev!(try_from_upper_bounded, usize, u128);
rev!(try_from_lower_bounded, usize, i8, i16, i32, i64);
rev!(try_from_both_bounded, usize, i128);

rev!(try_from_unbounded, isize, u16, u32);
rev!(try_from_upper_bounded, isize, u64, u128);
rev!(try_from_unbounded, isize, i32, i64);
rev!(try_from_both_bounded, isize, i128);
}

#[doc(hidden)]
Expand Down
127 changes: 127 additions & 0 deletions src/libcore/tests/num/mod.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,15 @@ mod flt2dec;
mod dec2flt;
mod bignum;


/// Adds the attribute to all items in the block.
macro_rules! cfg_block {
($(#[$attr:meta]{$($it:item)*})*) => {$($(
#[$attr]
$it
)*)*}
}

/// Groups items that assume the pointer width is either 16/32/64, and has to be altered if
/// support for larger/smaller pointer widths are added in the future.
macro_rules! assume_usize_width {
Expand Down Expand Up @@ -330,6 +339,42 @@ assume_usize_width! {

test_impl_try_from_always_ok! { test_try_u16usize, u16, usize }
test_impl_try_from_always_ok! { test_try_i16isize, i16, isize }

test_impl_try_from_always_ok! { test_try_usizeu64, usize, u64 }
test_impl_try_from_always_ok! { test_try_usizeu128, usize, u128 }
test_impl_try_from_always_ok! { test_try_usizei128, usize, i128 }

test_impl_try_from_always_ok! { test_try_isizei64, isize, i64 }
test_impl_try_from_always_ok! { test_try_isizei128, isize, i128 }

cfg_block!(
#[cfg(target_pointer_width = "16")] {
test_impl_try_from_always_ok! { test_try_usizeu16, usize, u16 }
test_impl_try_from_always_ok! { test_try_isizei16, isize, i16 }
test_impl_try_from_always_ok! { test_try_usizeu32, usize, u32 }
test_impl_try_from_always_ok! { test_try_usizei32, usize, i32 }
test_impl_try_from_always_ok! { test_try_isizei32, isize, i32 }
test_impl_try_from_always_ok! { test_try_usizei64, usize, i64 }
}

#[cfg(target_pointer_width = "32")] {
test_impl_try_from_always_ok! { test_try_u16isize, u16, isize }
test_impl_try_from_always_ok! { test_try_usizeu32, usize, u32 }
test_impl_try_from_always_ok! { test_try_isizei32, isize, i32 }
test_impl_try_from_always_ok! { test_try_u32usize, u32, usize }
test_impl_try_from_always_ok! { test_try_i32isize, i32, isize }
test_impl_try_from_always_ok! { test_try_usizei64, usize, i64 }
}

#[cfg(target_pointer_width = "64")] {
test_impl_try_from_always_ok! { test_try_u16isize, u16, isize }
test_impl_try_from_always_ok! { test_try_u32usize, u32, usize }
test_impl_try_from_always_ok! { test_try_u32isize, u32, isize }
test_impl_try_from_always_ok! { test_try_i32isize, i32, isize }
test_impl_try_from_always_ok! { test_try_u64usize, u64, usize }
test_impl_try_from_always_ok! { test_try_i64isize, i64, isize }
}
);
}

/// Conversions where max of $source can be represented as $target,
Expand Down Expand Up @@ -378,6 +423,24 @@ assume_usize_width! {
test_impl_try_from_signed_to_unsigned_upper_ok! { test_try_isizeu64, isize, u64 }
test_impl_try_from_signed_to_unsigned_upper_ok! { test_try_isizeu128, isize, u128 }
test_impl_try_from_signed_to_unsigned_upper_ok! { test_try_isizeusize, isize, usize }

cfg_block!(
#[cfg(target_pointer_width = "16")] {
test_impl_try_from_signed_to_unsigned_upper_ok! { test_try_isizeu16, isize, u16 }
test_impl_try_from_signed_to_unsigned_upper_ok! { test_try_isizeu32, isize, u32 }
}

#[cfg(target_pointer_width = "32")] {
test_impl_try_from_signed_to_unsigned_upper_ok! { test_try_isizeu32, isize, u32 }

test_impl_try_from_signed_to_unsigned_upper_ok! { test_try_i32usize, i32, usize }
}

#[cfg(target_pointer_width = "64")] {
test_impl_try_from_signed_to_unsigned_upper_ok! { test_try_i32usize, i32, usize }
test_impl_try_from_signed_to_unsigned_upper_ok! { test_try_i64usize, i64, usize }
}
);
}

/// Conversions where max of $source can not be represented as $target,
Expand Down Expand Up @@ -419,9 +482,29 @@ test_impl_try_from_unsigned_to_signed_upper_err! { test_try_u128i64, u128, i64 }
test_impl_try_from_unsigned_to_signed_upper_err! { test_try_u128i128, u128, i128 }

assume_usize_width! {
test_impl_try_from_unsigned_to_signed_upper_err! { test_try_u64isize, u64, isize }
test_impl_try_from_unsigned_to_signed_upper_err! { test_try_u128isize, u128, isize }

test_impl_try_from_unsigned_to_signed_upper_err! { test_try_usizei8, usize, i8 }
test_impl_try_from_unsigned_to_signed_upper_err! { test_try_usizei16, usize, i16 }
test_impl_try_from_unsigned_to_signed_upper_err! { test_try_usizeisize, usize, isize }

cfg_block!(
#[cfg(target_pointer_width = "16")] {
test_impl_try_from_unsigned_to_signed_upper_err! { test_try_u16isize, u16, isize }
test_impl_try_from_unsigned_to_signed_upper_err! { test_try_u32isize, u32, isize }
}

#[cfg(target_pointer_width = "32")] {
test_impl_try_from_unsigned_to_signed_upper_err! { test_try_u32isize, u32, isize }
test_impl_try_from_unsigned_to_signed_upper_err! { test_try_usizei32, usize, i32 }
}

#[cfg(target_pointer_width = "64")] {
test_impl_try_from_unsigned_to_signed_upper_err! { test_try_usizei32, usize, i32 }
test_impl_try_from_unsigned_to_signed_upper_err! { test_try_usizei64, usize, i64 }
}
);
}

/// Conversions where min/max of $source can not be represented as $target.
Expand Down Expand Up @@ -481,6 +564,34 @@ test_impl_try_from_same_sign_err! { test_try_i128i64, i128, i64 }

assume_usize_width! {
test_impl_try_from_same_sign_err! { test_try_usizeu8, usize, u8 }
test_impl_try_from_same_sign_err! { test_try_u128usize, u128, usize }
test_impl_try_from_same_sign_err! { test_try_i128isize, i128, isize }

cfg_block!(
#[cfg(target_pointer_width = "16")] {
test_impl_try_from_same_sign_err! { test_try_u32usize, u32, usize }
test_impl_try_from_same_sign_err! { test_try_u64usize, u64, usize }

test_impl_try_from_same_sign_err! { test_try_i32isize, i32, isize }
test_impl_try_from_same_sign_err! { test_try_i64isize, i64, isize }
}

#[cfg(target_pointer_width = "32")] {
test_impl_try_from_same_sign_err! { test_try_u64usize, u64, usize }
test_impl_try_from_same_sign_err! { test_try_usizeu16, usize, u16 }

test_impl_try_from_same_sign_err! { test_try_i64isize, i64, isize }
test_impl_try_from_same_sign_err! { test_try_isizei16, isize, i16 }
}

#[cfg(target_pointer_width = "64")] {
test_impl_try_from_same_sign_err! { test_try_usizeu16, usize, u16 }
test_impl_try_from_same_sign_err! { test_try_usizeu32, usize, u32 }

test_impl_try_from_same_sign_err! { test_try_isizei16, isize, i16 }
test_impl_try_from_same_sign_err! { test_try_isizei32, isize, i32 }
}
);
}

/// Conversions where neither the min nor the max of $source can be represented by
Expand Down Expand Up @@ -525,6 +636,22 @@ test_impl_try_from_signed_to_unsigned_err! { test_try_i128u64, i128, u64 }
assume_usize_width! {
test_impl_try_from_signed_to_unsigned_err! { test_try_isizeu8, isize, u8 }
test_impl_try_from_signed_to_unsigned_err! { test_try_i128usize, i128, usize }

cfg_block! {
#[cfg(target_pointer_width = "16")] {
test_impl_try_from_signed_to_unsigned_err! { test_try_i32usize, i32, usize }
test_impl_try_from_signed_to_unsigned_err! { test_try_i64usize, i64, usize }
}
#[cfg(target_pointer_width = "32")] {
test_impl_try_from_signed_to_unsigned_err! { test_try_i64usize, i64, usize }

test_impl_try_from_signed_to_unsigned_err! { test_try_isizeu16, isize, u16 }
}
#[cfg(target_pointer_width = "64")] {
test_impl_try_from_signed_to_unsigned_err! { test_try_isizeu16, isize, u16 }
test_impl_try_from_signed_to_unsigned_err! { test_try_isizeu32, isize, u32 }
}
}
}

macro_rules! test_float {
Expand Down
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