[rustc.git] / compiler / rustc_transmute / src / maybe_transmutable / mod.rs

use crate::Map;
use crate::{Answer, Reason};

#[cfg(test)]
mod tests;

mod query_context;
use query_context::QueryContext;

use crate::layout::{self, dfa, Byte, Dfa, Nfa, Tree, Uninhabited};
pub(crate) struct MaybeTransmutableQuery<L, C>
where
    C: QueryContext,
{
    src: L,
    dst: L,
    scope: <C as QueryContext>::Scope,
    assume: crate::Assume,
    context: C,
}

impl<L, C> MaybeTransmutableQuery<L, C>
where
    C: QueryContext,
{
    pub(crate) fn new(
        src: L,
        dst: L,
        scope: <C as QueryContext>::Scope,
        assume: crate::Assume,
        context: C,
    ) -> Self {
        Self { src, dst, scope, assume, context }
    }

    pub(crate) fn map_layouts<F, M>(
        self,
        f: F,
    ) -> Result<MaybeTransmutableQuery<M, C>, Answer<<C as QueryContext>::Ref>>
    where
        F: FnOnce(
            L,
            L,
            <C as QueryContext>::Scope,
            &C,
        ) -> Result<(M, M), Answer<<C as QueryContext>::Ref>>,
    {
        let Self { src, dst, scope, assume, context } = self;

        let (src, dst) = f(src, dst, scope, &context)?;

        Ok(MaybeTransmutableQuery { src, dst, scope, assume, context })
    }
}

#[cfg(feature = "rustc")]
mod rustc {
    use super::*;
    use crate::layout::tree::Err;

    use rustc_middle::ty::Ty;
    use rustc_middle::ty::TyCtxt;

    impl<'tcx> MaybeTransmutableQuery<Ty<'tcx>, TyCtxt<'tcx>> {
        /// This method begins by converting `src` and `dst` from `Ty`s to `Tree`s,
        /// then computes an answer using those trees.
        #[instrument(level = "debug", skip(self), fields(src = ?self.src, dst = ?self.dst))]
        pub fn answer(self) -> Answer<<TyCtxt<'tcx> as QueryContext>::Ref> {
            let query_or_answer = self.map_layouts(|src, dst, scope, &context| {
                // Convert `src` and `dst` from their rustc representations, to `Tree`-based
                // representations. If these conversions fail, conclude that the transmutation is
                // unacceptable; the layouts of both the source and destination types must be
                // well-defined.
                let src = Tree::from_ty(src, context).map_err(|err| match err {
                    // Answer `Yes` here, because "Unknown Type" will already be reported by
                    // rustc. No need to spam the user with more errors.
                    Err::Unknown => Answer::Yes,
                    Err::Unspecified => Answer::No(Reason::SrcIsUnspecified),
                })?;

                let dst = Tree::from_ty(dst, context).map_err(|err| match err {
                    Err::Unknown => Answer::Yes,
                    Err::Unspecified => Answer::No(Reason::DstIsUnspecified),
                })?;

                Ok((src, dst))
            });

            match query_or_answer {
                Ok(query) => query.answer(),
                Err(answer) => answer,
            }
        }
    }
}

impl<C> MaybeTransmutableQuery<Tree<<C as QueryContext>::Def, <C as QueryContext>::Ref>, C>
where
    C: QueryContext,
{
    /// Answers whether a `Tree` is transmutable into another `Tree`.
    ///
    /// This method begins by de-def'ing `src` and `dst`, and prunes private paths from `dst`,
    /// then converts `src` and `dst` to `Nfa`s, and computes an answer using those NFAs.
    #[inline(always)]
    #[instrument(level = "debug", skip(self), fields(src = ?self.src, dst = ?self.dst))]
    pub(crate) fn answer(self) -> Answer<<C as QueryContext>::Ref> {
        let assume_visibility = self.assume.visibility;
        let query_or_answer = self.map_layouts(|src, dst, scope, context| {
            // Remove all `Def` nodes from `src`, without checking their visibility.
            let src = src.prune(&|def| true);

            tracing::trace!(?src, "pruned src");

            // Remove all `Def` nodes from `dst`, additionally...
            let dst = if assume_visibility {
                // ...if visibility is assumed, don't check their visibility.
                dst.prune(&|def| true)
            } else {
                // ...otherwise, prune away all unreachable paths through the `Dst` layout.
                dst.prune(&|def| context.is_accessible_from(def, scope))
            };

            tracing::trace!(?dst, "pruned dst");

            // Convert `src` from a tree-based representation to an NFA-based representation.
            // If the conversion fails because `src` is uninhabited, conclude that the transmutation
            // is acceptable, because instances of the `src` type do not exist.
            let src = Nfa::from_tree(src).map_err(|Uninhabited| Answer::Yes)?;

            // Convert `dst` from a tree-based representation to an NFA-based representation.
            // If the conversion fails because `src` is uninhabited, conclude that the transmutation
            // is unacceptable, because instances of the `dst` type do not exist.
            let dst =
                Nfa::from_tree(dst).map_err(|Uninhabited| Answer::No(Reason::DstIsPrivate))?;

            Ok((src, dst))
        });

        match query_or_answer {
            Ok(query) => query.answer(),
            Err(answer) => answer,
        }
    }
}

impl<C> MaybeTransmutableQuery<Nfa<<C as QueryContext>::Ref>, C>
where
    C: QueryContext,
{
    /// Answers whether a `Nfa` is transmutable into another `Nfa`.
    ///
    /// This method converts `src` and `dst` to DFAs, then computes an answer using those DFAs.
    #[inline(always)]
    #[instrument(level = "debug", skip(self), fields(src = ?self.src, dst = ?self.dst))]
    pub(crate) fn answer(self) -> Answer<<C as QueryContext>::Ref> {
        let query_or_answer = self
            .map_layouts(|src, dst, scope, context| Ok((Dfa::from_nfa(src), Dfa::from_nfa(dst))));

        match query_or_answer {
            Ok(query) => query.answer(),
            Err(answer) => answer,
        }
    }
}

impl<C> MaybeTransmutableQuery<Dfa<<C as QueryContext>::Ref>, C>
where
    C: QueryContext,
{
    /// Answers whether a `Nfa` is transmutable into another `Nfa`.
    ///
    /// This method converts `src` and `dst` to DFAs, then computes an answer using those DFAs.
    pub(crate) fn answer(self) -> Answer<<C as QueryContext>::Ref> {
        MaybeTransmutableQuery {
            src: &self.src,
            dst: &self.dst,
            scope: self.scope,
            assume: self.assume,
            context: self.context,
        }
        .answer()
    }
}

impl<'l, C> MaybeTransmutableQuery<&'l Dfa<<C as QueryContext>::Ref>, C>
where
    C: QueryContext,
{
    pub(crate) fn answer(&mut self) -> Answer<<C as QueryContext>::Ref> {
        self.answer_memo(&mut Map::default(), self.src.start, self.dst.start)
    }

    #[inline(always)]
    #[instrument(level = "debug", skip(self))]
    fn answer_memo(
        &self,
        cache: &mut Map<(dfa::State, dfa::State), Answer<<C as QueryContext>::Ref>>,
        src_state: dfa::State,
        dst_state: dfa::State,
    ) -> Answer<<C as QueryContext>::Ref> {
        if let Some(answer) = cache.get(&(src_state, dst_state)) {
            answer.clone()
        } else {
            let answer = if dst_state == self.dst.accepting {
                // truncation: `size_of(Src) >= size_of(Dst)`
                Answer::Yes
            } else if src_state == self.src.accepting {
                // extension: `size_of(Src) >= size_of(Dst)`
                if let Some(dst_state_prime) = self.dst.byte_from(dst_state, Byte::Uninit) {
                    self.answer_memo(cache, src_state, dst_state_prime)
                } else {
                    Answer::No(Reason::DstIsTooBig)
                }
            } else {
                let src_quantification = if self.assume.validity {
                    // if the compiler may assume that the programmer is doing additional validity checks,
                    // (e.g.: that `src != 3u8` when the destination type is `bool`)
                    // then there must exist at least one transition out of `src_state` such that the transmute is viable...
                    there_exists
                } else {
                    // if the compiler cannot assume that the programmer is doing additional validity checks,
                    // then for all transitions out of `src_state`, such that the transmute is viable...
                    // then there must exist at least one transition out of `src_state` such that the transmute is viable...
                    for_all
                };

                src_quantification(
                    self.src.bytes_from(src_state).unwrap_or(&Map::default()),
                    |(&src_validity, &src_state_prime)| {
                        if let Some(dst_state_prime) = self.dst.byte_from(dst_state, src_validity) {
                            self.answer_memo(cache, src_state_prime, dst_state_prime)
                        } else if let Some(dst_state_prime) =
                            self.dst.byte_from(dst_state, Byte::Uninit)
                        {
                            self.answer_memo(cache, src_state_prime, dst_state_prime)
                        } else {
                            Answer::No(Reason::DstIsBitIncompatible)
                        }
                    },
                )
            };
            cache.insert((src_state, dst_state), answer.clone());
            answer
        }
    }
}

impl<R> Answer<R>
where
    R: layout::Ref,
{
    pub(crate) fn and(self, rhs: Self) -> Self {
        match (self, rhs) {
            (Self::No(reason), _) | (_, Self::No(reason)) => Self::No(reason),
            (Self::Yes, Self::Yes) => Self::Yes,
            (Self::IfAll(mut lhs), Self::IfAll(ref mut rhs)) => {
                lhs.append(rhs);
                Self::IfAll(lhs)
            }
            (constraint, Self::IfAll(mut constraints))
            | (Self::IfAll(mut constraints), constraint) => {
                constraints.push(constraint);
                Self::IfAll(constraints)
            }
            (lhs, rhs) => Self::IfAll(vec![lhs, rhs]),
        }
    }

    pub(crate) fn or(self, rhs: Self) -> Self {
        match (self, rhs) {
            (Self::Yes, _) | (_, Self::Yes) => Self::Yes,
            (Self::No(lhr), Self::No(rhr)) => Self::No(lhr),
            (Self::IfAny(mut lhs), Self::IfAny(ref mut rhs)) => {
                lhs.append(rhs);
                Self::IfAny(lhs)
            }
            (constraint, Self::IfAny(mut constraints))
            | (Self::IfAny(mut constraints), constraint) => {
                constraints.push(constraint);
                Self::IfAny(constraints)
            }
            (lhs, rhs) => Self::IfAny(vec![lhs, rhs]),
        }
    }
}

pub fn for_all<R, I, F>(iter: I, f: F) -> Answer<R>
where
    R: layout::Ref,
    I: IntoIterator,
    F: FnMut(<I as IntoIterator>::Item) -> Answer<R>,
{
    use std::ops::ControlFlow::{Break, Continue};
    let (Continue(result) | Break(result)) =
        iter.into_iter().map(f).try_fold(Answer::Yes, |constraints, constraint| {
            match constraint.and(constraints) {
                Answer::No(reason) => Break(Answer::No(reason)),
                maybe => Continue(maybe),
            }
        });
    result
}

pub fn there_exists<R, I, F>(iter: I, f: F) -> Answer<R>
where
    R: layout::Ref,
    I: IntoIterator,
    F: FnMut(<I as IntoIterator>::Item) -> Answer<R>,
{
    use std::ops::ControlFlow::{Break, Continue};
    let (Continue(result) | Break(result)) = iter.into_iter().map(f).try_fold(
        Answer::No(Reason::DstIsBitIncompatible),
        |constraints, constraint| match constraint.or(constraints) {
            Answer::Yes => Break(Answer::Yes),
            maybe => Continue(maybe),
        },
    );
    result
}
Commit	Line	Data
064997fb FG	1	use crate::Map;
	2	use crate::{Answer, Reason};
	3
	4	#[cfg(test)]
	5	mod tests;
	6
	7	mod query_context;
	8	use query_context::QueryContext;
	9
	10	use crate::layout::{self, dfa, Byte, Dfa, Nfa, Tree, Uninhabited};
	11	pub(crate) struct MaybeTransmutableQuery<L, C>
	12	where
	13	C: QueryContext,
	14	{
	15	src: L,
	16	dst: L,
	17	scope: <C as QueryContext>::Scope,
	18	assume: crate::Assume,
	19	context: C,
	20	}
	21
	22	impl<L, C> MaybeTransmutableQuery<L, C>
	23	where
	24	C: QueryContext,
	25	{
	26	pub(crate) fn new(
	27	src: L,
	28	dst: L,
	29	scope: <C as QueryContext>::Scope,
	30	assume: crate::Assume,
	31	context: C,
	32	) -> Self {
	33	Self { src, dst, scope, assume, context }
	34	}
	35
	36	pub(crate) fn map_layouts<F, M>(
	37	self,
	38	f: F,
	39	) -> Result<MaybeTransmutableQuery<M, C>, Answer<<C as QueryContext>::Ref>>
	40	where
	41	F: FnOnce(
	42	L,
	43	L,
	44	<C as QueryContext>::Scope,
	45	&C,
	46	) -> Result<(M, M), Answer<<C as QueryContext>::Ref>>,
	47	{
	48	let Self { src, dst, scope, assume, context } = self;
	49
	50	let (src, dst) = f(src, dst, scope, &context)?;
	51
	52	Ok(MaybeTransmutableQuery { src, dst, scope, assume, context })
	53	}
	54	}
	55
	56	#[cfg(feature = "rustc")]
	57	mod rustc {
	58	use super::*;
	59	use crate::layout::tree::Err;
	60
	61	use rustc_middle::ty::Ty;
	62	use rustc_middle::ty::TyCtxt;
	63
	64	impl<'tcx> MaybeTransmutableQuery<Ty<'tcx>, TyCtxt<'tcx>> {
65	/// This method begins by converting `src` and `dst` from `Ty`s to `Tree`s,
66	/// then computes an answer using those trees.
67	#[instrument(level = "debug", skip(self), fields(src = ?self.src, dst = ?self.dst))]
68	pub fn answer(self) -> Answer<<TyCtxt<'tcx> as QueryContext>::Ref> {
69	let query_or_answer = self.map_layouts(\|src, dst, scope, &context\| {
70	// Convert `src` and `dst` from their rustc representations, to `Tree`-based
71	// representations. If these conversions fail, conclude that the transmutation is
72	// unacceptable; the layouts of both the source and destination types must be
73	// well-defined.
74	let src = Tree::from_ty(src, context).map_err(\|err\| match err {
75	// Answer `Yes` here, because "Unknown Type" will already be reported by
76	// rustc. No need to spam the user with more errors.
77	Err::Unknown => Answer::Yes,
78	Err::Unspecified => Answer::No(Reason::SrcIsUnspecified),
79	})?;
80
81	let dst = Tree::from_ty(dst, context).map_err(\|err\| match err {
82	Err::Unknown => Answer::Yes,
83	Err::Unspecified => Answer::No(Reason::DstIsUnspecified),
84	})?;
85
86	Ok((src, dst))
87	});
88
89	match query_or_answer {
90	Ok(query) => query.answer(),
91	Err(answer) => answer,
92	}
93	}
94	}
95	}
96
97	impl<C> MaybeTransmutableQuery<Tree<<C as QueryContext>::Def, <C as QueryContext>::Ref>, C>
98	where
99	C: QueryContext,
100	{
101	/// Answers whether a `Tree` is transmutable into another `Tree`.
102	///
103	/// This method begins by de-def'ing `src` and `dst`, and prunes private paths from `dst`,
104	/// then converts `src` and `dst` to `Nfa`s, and computes an answer using those NFAs.
105	#[inline(always)]
106	#[instrument(level = "debug", skip(self), fields(src = ?self.src, dst = ?self.dst))]
107	pub(crate) fn answer(self) -> Answer<<C as QueryContext>::Ref> {
108	let assume_visibility = self.assume.visibility;
109	let query_or_answer = self.map_layouts(\|src, dst, scope, context\| {
110	// Remove all `Def` nodes from `src`, without checking their visibility.
111	let src = src.prune(&\|def\| true);
112
113	tracing::trace!(?src, "pruned src");
114
115	// Remove all `Def` nodes from `dst`, additionally...
116	let dst = if assume_visibility {
117	// ...if visibility is assumed, don't check their visibility.
118	dst.prune(&\|def\| true)
119	} else {
120	// ...otherwise, prune away all unreachable paths through the `Dst` layout.
121	dst.prune(&\|def\| context.is_accessible_from(def, scope))
122	};
123
124	tracing::trace!(?dst, "pruned dst");
125
126	// Convert `src` from a tree-based representation to an NFA-based representation.
127	// If the conversion fails because `src` is uninhabited, conclude that the transmutation
128	// is acceptable, because instances of the `src` type do not exist.
129	let src = Nfa::from_tree(src).map_err(\|Uninhabited\| Answer::Yes)?;
130
131	// Convert `dst` from a tree-based representation to an NFA-based representation.
132	// If the conversion fails because `src` is uninhabited, conclude that the transmutation
133	// is unacceptable, because instances of the `dst` type do not exist.
134	let dst =
135	Nfa::from_tree(dst).map_err(\|Uninhabited\| Answer::No(Reason::DstIsPrivate))?;
136
137	Ok((src, dst))
138	});
139
140	match query_or_answer {
141	Ok(query) => query.answer(),
142	Err(answer) => answer,
143	}
144	}
145	}
146
147	impl<C> MaybeTransmutableQuery<Nfa<<C as QueryContext>::Ref>, C>
148	where
149	C: QueryContext,
150	{
151	/// Answers whether a `Nfa` is transmutable into another `Nfa`.
152	///
153	/// This method converts `src` and `dst` to DFAs, then computes an answer using those DFAs.
154	#[inline(always)]
155	#[instrument(level = "debug", skip(self), fields(src = ?self.src, dst = ?self.dst))]
156	pub(crate) fn answer(self) -> Answer<<C as QueryContext>::Ref> {
157	let query_or_answer = self
158	.map_layouts(\|src, dst, scope, context\| Ok((Dfa::from_nfa(src), Dfa::from_nfa(dst))));
159
160	match query_or_answer {
161	Ok(query) => query.answer(),
162	Err(answer) => answer,
163	}
164	}
165	}
166
167	impl<C> MaybeTransmutableQuery<Dfa<<C as QueryContext>::Ref>, C>
168	where
169	C: QueryContext,
170	{
171	/// Answers whether a `Nfa` is transmutable into another `Nfa`.
172	///
173	/// This method converts `src` and `dst` to DFAs, then computes an answer using those DFAs.
174	pub(crate) fn answer(self) -> Answer<<C as QueryContext>::Ref> {
175	MaybeTransmutableQuery {
176	src: &self.src,
177	dst: &self.dst,
178	scope: self.scope,
179	assume: self.assume,
180	context: self.context,
181	}
182	.answer()
183	}
184	}
185
186	impl<'l, C> MaybeTransmutableQuery<&'l Dfa<<C as QueryContext>::Ref>, C>
187	where
188	C: QueryContext,
189	{
190	pub(crate) fn answer(&mut self) -> Answer<<C as QueryContext>::Ref> {
191	self.answer_memo(&mut Map::default(), self.src.start, self.dst.start)
192	}
193
194	#[inline(always)]
195	#[instrument(level = "debug", skip(self))]
196	fn answer_memo(
197	&self,
198	cache: &mut Map<(dfa::State, dfa::State), Answer<<C as QueryContext>::Ref>>,
199	src_state: dfa::State,
200	dst_state: dfa::State,
201	) -> Answer<<C as QueryContext>::Ref> {
202	if let Some(answer) = cache.get(&(src_state, dst_state)) {
203	answer.clone()
204	} else {
205	let answer = if dst_state == self.dst.accepting {
206	// truncation: `size_of(Src) >= size_of(Dst)`
207	Answer::Yes
208	} else if src_state == self.src.accepting {
209	// extension: `size_of(Src) >= size_of(Dst)`
210	if let Some(dst_state_prime) = self.dst.byte_from(dst_state, Byte::Uninit) {
211	self.answer_memo(cache, src_state, dst_state_prime)
212	} else {
213	Answer::No(Reason::DstIsTooBig)
214	}
215	} else {
216	let src_quantification = if self.assume.validity {
217	// if the compiler may assume that the programmer is doing additional validity checks,
218	// (e.g.: that `src != 3u8` when the destination type is `bool`)
219	// then there must exist at least one transition out of `src_state` such that the transmute is viable...
220	there_exists
221	} else {
222	// if the compiler cannot assume that the programmer is doing additional validity checks,
223	// then for all transitions out of `src_state`, such that the transmute is viable...
224	// then there must exist at least one transition out of `src_state` such that the transmute is viable...
225	for_all
226	};
227
228	src_quantification(
229	self.src.bytes_from(src_state).unwrap_or(&Map::default()),
230	\|(&src_validity, &src_state_prime)\| {
231	if let Some(dst_state_prime) = self.dst.byte_from(dst_state, src_validity) {
232	self.answer_memo(cache, src_state_prime, dst_state_prime)
233	} else if let Some(dst_state_prime) =
234	self.dst.byte_from(dst_state, Byte::Uninit)
235	{
236	self.answer_memo(cache, src_state_prime, dst_state_prime)
237	} else {
238	Answer::No(Reason::DstIsBitIncompatible)
239	}
240	},
241	)
242	};
243	cache.insert((src_state, dst_state), answer.clone());
244	answer
245	}
246	}
247	}
248
249	impl<R> Answer<R>
250	where
251	R: layout::Ref,
252	{
253	pub(crate) fn and(self, rhs: Self) -> Self {
254	match (self, rhs) {
255	(Self::No(reason), _) \| (_, Self::No(reason)) => Self::No(reason),
256	(Self::Yes, Self::Yes) => Self::Yes,
257	(Self::IfAll(mut lhs), Self::IfAll(ref mut rhs)) => {
258	lhs.append(rhs);
259	Self::IfAll(lhs)
260	}
261	(constraint, Self::IfAll(mut constraints))
262	\| (Self::IfAll(mut constraints), constraint) => {
263	constraints.push(constraint);
264	Self::IfAll(constraints)
265	}
266	(lhs, rhs) => Self::IfAll(vec![lhs, rhs]),
267	}
268	}
269
270	pub(crate) fn or(self, rhs: Self) -> Self {
271	match (self, rhs) {
272	(Self::Yes, _) \| (_, Self::Yes) => Self::Yes,
273	(Self::No(lhr), Self::No(rhr)) => Self::No(lhr),
274	(Self::IfAny(mut lhs), Self::IfAny(ref mut rhs)) => {
275	lhs.append(rhs);
276	Self::IfAny(lhs)
277	}
278	(constraint, Self::IfAny(mut constraints))
279	\| (Self::IfAny(mut constraints), constraint) => {
280	constraints.push(constraint);
281	Self::IfAny(constraints)
282	}
283	(lhs, rhs) => Self::IfAny(vec![lhs, rhs]),
284	}
285	}
286	}
287
288	pub fn for_all<R, I, F>(iter: I, f: F) -> Answer<R>
289	where
290	R: layout::Ref,
291	I: IntoIterator,
292	F: FnMut(<I as IntoIterator>::Item) -> Answer<R>,
293	{
294	use std::ops::ControlFlow::{Break, Continue};
295	let (Continue(result) \| Break(result)) =
296	iter.into_iter().map(f).try_fold(Answer::Yes, \|constraints, constraint\| {
297	match constraint.and(constraints) {
298	Answer::No(reason) => Break(Answer::No(reason)),
299	maybe => Continue(maybe),
300	}
301	});
302	result
303	}
304
305	pub fn there_exists<R, I, F>(iter: I, f: F) -> Answer<R>
306	where
307	R: layout::Ref,
308	I: IntoIterator,
309	F: FnMut(<I as IntoIterator>::Item) -> Answer<R>,
310	{
311	use std::ops::ControlFlow::{Break, Continue};
312	let (Continue(result) \| Break(result)) = iter.into_iter().map(f).try_fold(
313	Answer::No(Reason::DstIsBitIncompatible),
314	\|constraints, constraint\| match constraint.or(constraints) {
315	Answer::Yes => Break(Answer::Yes),
316	maybe => Continue(maybe),
317	},
318	);
319	result
320	}