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Auto merge of #132542 - RalfJung:const_panic, r=tgross35

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add const_panic macro to make it easier to fall back to non-formatting panic in const

Suggested by `@tgross35`

r? `@tgross35`
This commit is contained in:
bors 2024-11-03 16:20:51 +00:00
commit e3a918ece0
8 changed files with 142 additions and 129 deletions
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43
library/core/src/char/methods.rs
View File

@ -1,7 +1,7 @@
//! impl char {}
use super::*;
use crate::intrinsics::const_eval_select;
use crate::macros::const_panic;
use crate::slice;
use crate::str::from_utf8_unchecked_mut;
use crate::unicode::printable::is_printable;
@ -1773,17 +1773,7 @@ const fn len_utf16(code: u32) -> usize {
#[cfg_attr(bootstrap, rustc_const_stable(feature = "const_char_encode_utf8", since = "1.83.0"))]
#[doc(hidden)]
#[inline]
#[rustc_allow_const_fn_unstable(const_eval_select)]
pub const fn encode_utf8_raw(code: u32, dst: &mut [u8]) -> &mut [u8] {
const fn panic_at_const(_code: u32, _len: usize, _dst_len: usize) {
// Note that we cannot format in constant expressions.
panic!("encode_utf8: buffer does not have enough bytes to encode code point");
}
fn panic_at_rt(code: u32, len: usize, dst_len: usize) {
panic!(
"encode_utf8: need {len} bytes to encode U+{code:04X} but buffer has just {dst_len}",
);
}
let len = len_utf8(code);
match (len, &mut *dst) {
(1, [a, ..]) => {
@ -1804,8 +1794,15 @@ fn panic_at_rt(code: u32, len: usize, dst_len: usize) {
*c = (code >> 6 & 0x3F) as u8 | TAG_CONT;
*d = (code & 0x3F) as u8 | TAG_CONT;
}
// FIXME(const-hack): We would prefer to have streamlined panics when formatters become const-friendly.
_ => const_eval_select((code, len, dst.len()), panic_at_const, panic_at_rt),
_ => {
const_panic!(
"encode_utf8: buffer does not have enough bytes to encode code point",
"encode_utf8: need {len} bytes to encode U+{code:04X} but buffer has just {dst_len}",
code: u32 = code,
len: usize = len,
dst_len: usize = dst.len(),
)
}
};
// SAFETY: `<&mut [u8]>::as_mut_ptr` is guaranteed to return a valid pointer and `len` has been tested to be within bounds.
unsafe { slice::from_raw_parts_mut(dst.as_mut_ptr(), len) }
@ -1826,15 +1823,6 @@ fn panic_at_rt(code: u32, len: usize, dst_len: usize) {
#[doc(hidden)]
#[inline]
pub const fn encode_utf16_raw(mut code: u32, dst: &mut [u16]) -> &mut [u16] {
const fn panic_at_const(_code: u32, _len: usize, _dst_len: usize) {
// Note that we cannot format in constant expressions.
panic!("encode_utf16: buffer does not have enough bytes to encode code point");
}
fn panic_at_rt(code: u32, len: usize, dst_len: usize) {
panic!(
"encode_utf16: need {len} bytes to encode U+{code:04X} but buffer has just {dst_len}",
);
}
let len = len_utf16(code);
match (len, &mut *dst) {
(1, [a, ..]) => {
@ -1845,8 +1833,15 @@ fn panic_at_rt(code: u32, len: usize, dst_len: usize) {
*a = (code >> 10) as u16 | 0xD800;
*b = (code & 0x3FF) as u16 | 0xDC00;
}
// FIXME(const-hack): We would prefer to have streamlined panics when formatters become const-friendly.
_ => const_eval_select((code, len, dst.len()), panic_at_const, panic_at_rt),
_ => {
const_panic!(
"encode_utf16: buffer does not have enough bytes to encode code point",
"encode_utf16: need {len} bytes to encode U+{code:04X} but buffer has just {dst_len}",
code: u32 = code,
len: usize = len,
dst_len: usize = dst.len(),
)
}
};
// SAFETY: `<&mut [u16]>::as_mut_ptr` is guaranteed to return a valid pointer and `len` has been tested to be within bounds.
unsafe { slice::from_raw_parts_mut(dst.as_mut_ptr(), len) }

61
library/core/src/macros/mod.rs
View File

@ -12,6 +12,54 @@ macro_rules! panic {
};
}
/// Helper macro for panicking in a `const fn`.
/// Invoke as:
/// ```rust,ignore (just an example)
/// core::macros::const_panic!("boring message", "flavored message {a} {b:?}", a: u32 = foo.len(), b: Something = bar);
/// ```
/// where the first message will be printed in const-eval,
/// and the second message will be printed at runtime.
// All uses of this macro are FIXME(const-hack).
#[unstable(feature = "panic_internals", issue = "none")]
#[doc(hidden)]
pub macro const_panic {
($const_msg:literal, $runtime_msg:literal, $($arg:ident : $ty:ty = $val:expr),* $(,)?) => {{
#[inline]
#[track_caller]
fn runtime($($arg: $ty),*) -> ! {
$crate::panic!($runtime_msg);
}
#[inline]
#[track_caller]
const fn compiletime($(_: $ty),*) -> ! {
$crate::panic!($const_msg);
}
// Wrap call to `const_eval_select` in a function so that we can
// add the `rustc_allow_const_fn_unstable`. This is okay to do
// because both variants will panic, just with different messages.
#[rustc_allow_const_fn_unstable(const_eval_select)]
#[inline(always)]
#[track_caller]
#[cfg_attr(bootstrap, rustc_const_stable(feature = "const_panic", since = "CURRENT_RUSTC_VERSION"))]
const fn do_panic($($arg: $ty),*) -> ! {
$crate::intrinsics::const_eval_select(($($arg),* ,), compiletime, runtime)
}
do_panic($($val),*)
}},
// We support leaving away the `val` expressions for *all* arguments
// (but not for *some* arguments, that's too tricky).
($const_msg:literal, $runtime_msg:literal, $($arg:ident : $ty:ty),* $(,)?) => {
$crate::macros::const_panic!(
$const_msg,
$runtime_msg,
$($arg: $ty = $arg),*
)
},
}
/// Asserts that two expressions are equal to each other (using [`PartialEq`]).
///
/// Assertions are always checked in both debug and release builds, and cannot
@ -196,6 +244,19 @@ macro_rules! assert_ne {
},
}
/// A version of `assert` that prints a non-formatting message in const contexts.
///
/// See [`const_panic!`].
#[unstable(feature = "panic_internals", issue = "none")]
#[doc(hidden)]
pub macro const_assert {
($condition: expr, $const_msg:literal, $runtime_msg:literal, $($arg:tt)*) => {{
if !$crate::intrinsics::likely($condition) {
$crate::macros::const_panic!($const_msg, $runtime_msg, $($arg)*)
}
}}
}
/// A macro for defining `#[cfg]` match-like statements.
///
/// It is similar to the `if/elif` C preprocessor macro by allowing definition of a cascade of

20
library/core/src/num/f128.rs
View File

@ -14,6 +14,7 @@
use crate::convert::FloatToInt;
#[cfg(not(test))]
use crate::intrinsics;
use crate::macros::const_assert;
use crate::mem;
use crate::num::FpCategory;
@ -1263,17 +1264,14 @@ pub fn total_cmp(&self, other: &Self) -> crate::cmp::Ordering {
#[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
#[must_use = "method returns a new number and does not mutate the original value"]
pub const fn clamp(mut self, min: f128, max: f128) -> f128 {
#[inline] // inline to avoid LLVM crash
const fn assert_at_const(min: f128, max: f128) {
// Note that we cannot format in constant expressions.
assert!(min <= max, "min > max, or either was NaN");
}
#[inline] // inline to avoid codegen regression
fn assert_at_rt(min: f128, max: f128) {
assert!(min <= max, "min > max, or either was NaN. min = {min:?}, max = {max:?}");
}
// FIXME(const-hack): We would prefer to have streamlined panics when formatters become const-friendly.
intrinsics::const_eval_select((min, max), assert_at_const, assert_at_rt);
const_assert!(
min <= max,
"min > max, or either was NaN",
"min > max, or either was NaN. min = {min:?}, max = {max:?}",
min: f128,
max: f128,
);
if self < min {
self = min;
}

20
library/core/src/num/f16.rs
View File

@ -14,6 +14,7 @@
use crate::convert::FloatToInt;
#[cfg(not(test))]
use crate::intrinsics;
use crate::macros::const_assert;
use crate::mem;
use crate::num::FpCategory;
@ -1238,17 +1239,14 @@ pub fn total_cmp(&self, other: &Self) -> crate::cmp::Ordering {
#[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
#[must_use = "method returns a new number and does not mutate the original value"]
pub const fn clamp(mut self, min: f16, max: f16) -> f16 {
#[inline] // inline to avoid LLVM crash
const fn assert_at_const(min: f16, max: f16) {
// Note that we cannot format in constant expressions.
assert!(min <= max, "min > max, or either was NaN");
}
#[inline] // inline to avoid codegen regression
fn assert_at_rt(min: f16, max: f16) {
assert!(min <= max, "min > max, or either was NaN. min = {min:?}, max = {max:?}");
}
// FIXME(const-hack): We would prefer to have streamlined panics when formatters become const-friendly.
intrinsics::const_eval_select((min, max), assert_at_const, assert_at_rt);
const_assert!(
min <= max,
"min > max, or either was NaN",
"min > max, or either was NaN. min = {min:?}, max = {max:?}",
min: f16,
max: f16,
);
if self < min {
self = min;
}

19
library/core/src/num/f32.rs
View File

@ -14,6 +14,7 @@
use crate::convert::FloatToInt;
#[cfg(not(test))]
use crate::intrinsics;
use crate::macros::const_assert;
use crate::mem;
use crate::num::FpCategory;
@ -1407,16 +1408,14 @@ pub fn total_cmp(&self, other: &Self) -> crate::cmp::Ordering {
#[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
#[inline]
pub const fn clamp(mut self, min: f32, max: f32) -> f32 {
const fn assert_at_const(min: f32, max: f32) {
// Note that we cannot format in constant expressions.
assert!(min <= max, "min > max, or either was NaN");
}
#[inline] // inline to avoid codegen regression
fn assert_at_rt(min: f32, max: f32) {
assert!(min <= max, "min > max, or either was NaN. min = {min:?}, max = {max:?}");
}
// FIXME(const-hack): We would prefer to have streamlined panics when formatters become const-friendly.
intrinsics::const_eval_select((min, max), assert_at_const, assert_at_rt);
const_assert!(
min <= max,
"min > max, or either was NaN",
"min > max, or either was NaN. min = {min:?}, max = {max:?}",
min: f32,
max: f32,
);
if self < min {
self = min;
}

19
library/core/src/num/f64.rs
View File

@ -14,6 +14,7 @@
use crate::convert::FloatToInt;
#[cfg(not(test))]
use crate::intrinsics;
use crate::macros::const_assert;
use crate::mem;
use crate::num::FpCategory;
@ -1407,16 +1408,14 @@ pub fn total_cmp(&self, other: &Self) -> crate::cmp::Ordering {
#[rustc_const_unstable(feature = "const_float_methods", issue = "130843")]
#[inline]
pub const fn clamp(mut self, min: f64, max: f64) -> f64 {
const fn assert_at_const(min: f64, max: f64) {
// Note that we cannot format in constant expressions.
assert!(min <= max, "min > max, or either was NaN");
}
#[inline] // inline to avoid codegen regression
fn assert_at_rt(min: f64, max: f64) {
assert!(min <= max, "min > max, or either was NaN. min = {min:?}, max = {max:?}");
}
// FIXME(const-hack): We would prefer to have streamlined panics when formatters become const-friendly.
intrinsics::const_eval_select((min, max), assert_at_const, assert_at_rt);
const_assert!(
min <= max,
"min > max, or either was NaN",
"min > max, or either was NaN. min = {min:?}, max = {max:?}",
min: f64,
max: f64,
);
if self < min {
self = min;
}

21
library/core/src/num/mod.rs
View File

@ -2,6 +2,7 @@
#![stable(feature = "rust1", since = "1.0.0")]
use crate::macros::const_panic;
use crate::str::FromStr;
use crate::ub_checks::assert_unsafe_precondition;
use crate::{ascii, intrinsics, mem};
@ -1452,24 +1453,16 @@ pub const fn can_not_overflow<T>(radix: u32, is_signed_ty: bool, digits: &[u8])
radix <= 16 && digits.len() <= mem::size_of::<T>() * 2 - is_signed_ty as usize
}
#[track_caller]
const fn from_str_radix_panic_ct(_radix: u32) -> ! {
panic!("from_str_radix_int: must lie in the range `[2, 36]`");
}
#[track_caller]
fn from_str_radix_panic_rt(radix: u32) -> ! {
panic!("from_str_radix_int: must lie in the range `[2, 36]` - found {}", radix);
}
#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
#[cfg_attr(feature = "panic_immediate_abort", inline)]
#[cold]
#[track_caller]
#[rustc_allow_const_fn_unstable(const_eval_select)]
const fn from_str_radix_panic(radix: u32) {
// The only difference between these two functions is their panic message.
intrinsics::const_eval_select((radix,), from_str_radix_panic_ct, from_str_radix_panic_rt);
const fn from_str_radix_panic(radix: u32) -> ! {
const_panic!(
"from_str_radix_int: must lie in the range `[2, 36]`",
"from_str_radix_int: must lie in the range `[2, 36]` - found {radix}",
radix: u32 = radix,
)
}
macro_rules! from_str_radix {

68
library/core/src/slice/index.rs
View File

@ -1,6 +1,6 @@
//! Indexing implementations for `[T]`.
use crate::intrinsics::const_eval_select;
use crate::macros::const_panic;
use crate::ub_checks::assert_unsafe_precondition;
use crate::{ops, range};
@ -31,67 +31,37 @@ fn index_mut(&mut self, index: I) -> &mut I::Output {
#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
#[cfg_attr(feature = "panic_immediate_abort", inline)]
#[track_caller]
#[rustc_allow_const_fn_unstable(const_eval_select)]
const fn slice_start_index_len_fail(index: usize, len: usize) -> ! {
// FIXME(const-hack): once integer formatting in panics is possible, we
// should use the same implementation at compiletime and runtime.
const_eval_select((index, len), slice_start_index_len_fail_ct, slice_start_index_len_fail_rt)
}
#[inline]
#[track_caller]
fn slice_start_index_len_fail_rt(index: usize, len: usize) -> ! {
panic!("range start index {index} out of range for slice of length {len}");
}
#[inline]
#[track_caller]
const fn slice_start_index_len_fail_ct(_: usize, _: usize) -> ! {
panic!("slice start index is out of range for slice");
const_panic!(
"slice start index is out of range for slice",
"range start index {index} out of range for slice of length {len}",
index: usize,
len: usize,
)
}
#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
#[cfg_attr(feature = "panic_immediate_abort", inline)]
#[track_caller]
#[rustc_allow_const_fn_unstable(const_eval_select)]
const fn slice_end_index_len_fail(index: usize, len: usize) -> ! {
// FIXME(const-hack): once integer formatting in panics is possible, we
// should use the same implementation at compiletime and runtime.
const_eval_select((index, len), slice_end_index_len_fail_ct, slice_end_index_len_fail_rt)
}
#[inline]
#[track_caller]
fn slice_end_index_len_fail_rt(index: usize, len: usize) -> ! {
panic!("range end index {index} out of range for slice of length {len}");
}
#[inline]
#[track_caller]
const fn slice_end_index_len_fail_ct(_: usize, _: usize) -> ! {
panic!("slice end index is out of range for slice");
const_panic!(
"slice end index is out of range for slice",
"range end index {index} out of range for slice of length {len}",
index: usize,
len: usize,
)
}
#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
#[cfg_attr(feature = "panic_immediate_abort", inline)]
#[track_caller]
#[rustc_allow_const_fn_unstable(const_eval_select)]
const fn slice_index_order_fail(index: usize, end: usize) -> ! {
// FIXME(const-hack): once integer formatting in panics is possible, we
// should use the same implementation at compiletime and runtime.
const_eval_select((index, end), slice_index_order_fail_ct, slice_index_order_fail_rt)
}
#[inline]
#[track_caller]
fn slice_index_order_fail_rt(index: usize, end: usize) -> ! {
panic!("slice index starts at {index} but ends at {end}");
}
#[inline]
#[track_caller]
const fn slice_index_order_fail_ct(_: usize, _: usize) -> ! {
panic!("slice index start is larger than end");
const_panic!(
"slice index start is larger than end",
"slice index starts at {index} but ends at {end}",
index: usize,
end: usize,
)
}
#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]