[RFC 2011] Library code · rust-lang/rust@664e8a9 (original) (raw)
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// Contains the machinery necessary to print useful assert! messages. Not intended for public
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// usage, not even nightly use-cases.
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//
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// Based on https://github.com/dtolnay/case-studies/tree/master/autoref-specialization. When
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// 'specialization' is robust enough (5 years? 10 years? Never?), Capture can be specialized
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// to [Printable].
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#![allow(missing_debug_implementations)]
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#![doc(hidden)]
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#![unstable(feature = "generic_assert_internals", issue = "44838")]
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use crate::{
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fmt::{Debug, Formatter},
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marker::PhantomData,
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};
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// ***** TryCapture - Generic *****
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/// Marker used by [Capture]
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#[unstable(feature = "generic_assert_internals", issue = "44838")]
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pub struct TryCaptureWithoutDebug;
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/// Catches an arbitrary E and modifies to accordingly
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#[unstable(feature = "generic_assert_internals", issue = "44838")]
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pub trait TryCaptureGeneric<E, M> {
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/// Similar to [TryCapturePrintable] but generic to any E.
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fn try_capture(&self, to: &mut Capture<E, M>);
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}
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impl TryCaptureGeneric<E, TryCaptureWithoutDebug> for &Wrapper<&E> {
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#[inline]
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fn try_capture(&self, _: &mut Capture<E, TryCaptureWithoutDebug>) {}
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}
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impl Debug for Capture<E, TryCaptureWithoutDebug> {
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fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), core::fmt::Error> {
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f.write_str("N/A")
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}
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}
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// ***** TryCapture - Printable *****
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/// Marker used by [Capture]
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#[unstable(feature = "generic_assert_internals", issue = "44838")]
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pub struct TryCaptureWithDebug;
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/// Catches an arbitrary E: Printable and modifies to accordingly
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#[unstable(feature = "generic_assert_internals", issue = "44838")]
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pub trait TryCapturePrintable<E, M> {
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/// Similar as [TryCaptureGeneric] but specialized to any E: Printable.
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fn try_capture(&self, to: &mut Capture<E, M>);
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}
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impl TryCapturePrintable<E, TryCaptureWithDebug> for Wrapper<&E>
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where
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E: Printable,
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{
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#[inline]
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fn try_capture(&self, to: &mut Capture<E, TryCaptureWithDebug>) {
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to.elem = Some(*self.0);
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}
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}
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impl Debug for Capture<E, TryCaptureWithDebug>
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where
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E: Printable,
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{
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fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), core::fmt::Error> {
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match self.elem {
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None => f.write_str("N/A"),
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Some(ref value) => Debug::fmt(value, f),
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}
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}
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}
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// ***** Others *****
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/// All possible captured assert! elements
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///
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/// # Types
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///
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/// * E: Element that is going to be displayed.
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/// * M: Marker used to differentiate [Capture]s in regards to [Debug].
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#[unstable(feature = "generic_assert_internals", issue = "44838")]
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pub struct Capture<E, M> {
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// If None, then E does not implements [Printable] or E wasn't evaluated (assert!( ... )
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// short-circuited).
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//
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// If Some, then E implements [Printable] and was evaluated.
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pub elem: Option,
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phantom: PhantomData,
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}
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impl<M, T> Capture<M, T> {
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#[inline]
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pub const fn new() -> Self {
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Self { elem: None, phantom: PhantomData }
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}
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}
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/// Necessary for the implementations of TryCapture*
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#[unstable(feature = "generic_assert_internals", issue = "44838")]
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pub struct Wrapper(pub T);
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/// Tells which elements can be copied and displayed
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#[unstable(feature = "generic_assert_internals", issue = "44838")]
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pub trait Printable: Copy + Debug {}
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impl Printable for T where T: Copy + Debug {}
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