Make proof tree building generic

This commit is contained in:
Michael Goulet 2024-05-17 12:43:05 -04:00
parent 0f528a4c08
commit 6ee22e184f
5 changed files with 111 additions and 93 deletions

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@ -4759,6 +4759,7 @@ name = "rustc_trait_selection"
version = "0.0.0"
dependencies = [
"bitflags 2.5.0",
"derivative",
"itertools 0.12.1",
"rustc_ast",
"rustc_ast_ir",
@ -4778,6 +4779,7 @@ dependencies = [
"rustc_span",
"rustc_target",
"rustc_transmute",
"rustc_type_ir",
"smallvec",
"tracing",
]

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@ -6,6 +6,7 @@ edition = "2021"
[dependencies]
# tidy-alphabetical-start
bitflags = "2.4.1"
derivative = "2.2.0"
itertools = "0.12"
rustc_ast = { path = "../rustc_ast" }
rustc_ast_ir = { path = "../rustc_ast_ir" }
@ -25,6 +26,7 @@ rustc_session = { path = "../rustc_session" }
rustc_span = { path = "../rustc_span" }
rustc_target = { path = "../rustc_target" }
rustc_transmute = { path = "../rustc_transmute", features = ["rustc"] }
rustc_type_ir = { path = "../rustc_type_ir" }
smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }
tracing = "0.1"
# tidy-alphabetical-end

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@ -95,7 +95,7 @@ pub struct EvalCtxt<'a, 'tcx> {
// evaluation code.
tainted: Result<(), NoSolution>,
pub(super) inspect: ProofTreeBuilder<'tcx>,
pub(super) inspect: ProofTreeBuilder<TyCtxt<'tcx>>,
}
#[derive(derivative::Derivative)]
@ -225,7 +225,7 @@ fn enter_canonical<R>(
tcx: TyCtxt<'tcx>,
search_graph: &'a mut search_graph::SearchGraph<'tcx>,
canonical_input: CanonicalInput<'tcx>,
canonical_goal_evaluation: &mut ProofTreeBuilder<'tcx>,
canonical_goal_evaluation: &mut ProofTreeBuilder<TyCtxt<'tcx>>,
f: impl FnOnce(&mut EvalCtxt<'_, 'tcx>, Goal<'tcx, ty::Predicate<'tcx>>) -> R,
) -> R {
let intercrate = match search_graph.solver_mode() {
@ -287,7 +287,7 @@ fn evaluate_canonical_goal(
tcx: TyCtxt<'tcx>,
search_graph: &'a mut search_graph::SearchGraph<'tcx>,
canonical_input: CanonicalInput<'tcx>,
goal_evaluation: &mut ProofTreeBuilder<'tcx>,
goal_evaluation: &mut ProofTreeBuilder<TyCtxt<'tcx>>,
) -> QueryResult<'tcx> {
let mut canonical_goal_evaluation =
goal_evaluation.new_canonical_goal_evaluation(canonical_input);

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@ -9,11 +9,12 @@
use rustc_middle::bug;
use rustc_middle::infer::canonical::CanonicalVarValues;
use rustc_middle::traits::query::NoSolution;
use rustc_middle::traits::solve::{
use rustc_middle::ty::{self, TyCtxt};
use rustc_next_trait_solver::solve::{
CanonicalInput, Certainty, Goal, GoalSource, QueryInput, QueryResult,
};
use rustc_middle::ty::{self, TyCtxt};
use rustc_session::config::DumpSolverProofTree;
use rustc_type_ir::Interner;
use crate::solve::eval_ctxt::canonical;
use crate::solve::{self, inspect, GenerateProofTree};
@ -38,49 +39,51 @@
/// trees. At the end of trait solving `ProofTreeBuilder::finalize`
/// is called to recursively convert the whole structure to a
/// finished proof tree.
pub(in crate::solve) struct ProofTreeBuilder<'tcx> {
state: Option<Box<DebugSolver<'tcx>>>,
pub(in crate::solve) struct ProofTreeBuilder<I: Interner> {
state: Option<Box<DebugSolver<I>>>,
}
/// The current state of the proof tree builder, at most places
/// in the code, only one or two variants are actually possible.
///
/// We simply ICE in case that assumption is broken.
#[derive(Debug)]
enum DebugSolver<'tcx> {
#[derive(derivative::Derivative)]
#[derivative(Debug(bound = ""))]
enum DebugSolver<I: Interner> {
Root,
GoalEvaluation(WipGoalEvaluation<'tcx>),
CanonicalGoalEvaluation(WipCanonicalGoalEvaluation<'tcx>),
GoalEvaluationStep(WipGoalEvaluationStep<'tcx>),
GoalEvaluation(WipGoalEvaluation<I>),
CanonicalGoalEvaluation(WipCanonicalGoalEvaluation<I>),
GoalEvaluationStep(WipGoalEvaluationStep<I>),
}
impl<'tcx> From<WipGoalEvaluation<'tcx>> for DebugSolver<'tcx> {
fn from(g: WipGoalEvaluation<'tcx>) -> DebugSolver<'tcx> {
impl<I: Interner> From<WipGoalEvaluation<I>> for DebugSolver<I> {
fn from(g: WipGoalEvaluation<I>) -> DebugSolver<I> {
DebugSolver::GoalEvaluation(g)
}
}
impl<'tcx> From<WipCanonicalGoalEvaluation<'tcx>> for DebugSolver<'tcx> {
fn from(g: WipCanonicalGoalEvaluation<'tcx>) -> DebugSolver<'tcx> {
impl<I: Interner> From<WipCanonicalGoalEvaluation<I>> for DebugSolver<I> {
fn from(g: WipCanonicalGoalEvaluation<I>) -> DebugSolver<I> {
DebugSolver::CanonicalGoalEvaluation(g)
}
}
impl<'tcx> From<WipGoalEvaluationStep<'tcx>> for DebugSolver<'tcx> {
fn from(g: WipGoalEvaluationStep<'tcx>) -> DebugSolver<'tcx> {
impl<I: Interner> From<WipGoalEvaluationStep<I>> for DebugSolver<I> {
fn from(g: WipGoalEvaluationStep<I>) -> DebugSolver<I> {
DebugSolver::GoalEvaluationStep(g)
}
}
#[derive(Eq, PartialEq, Debug)]
struct WipGoalEvaluation<'tcx> {
pub uncanonicalized_goal: Goal<'tcx, ty::Predicate<'tcx>>,
pub kind: WipGoalEvaluationKind<'tcx>,
pub evaluation: Option<WipCanonicalGoalEvaluation<'tcx>>,
#[derive(derivative::Derivative)]
#[derivative(PartialEq(bound = ""), Eq(bound = ""), Debug(bound = ""))]
struct WipGoalEvaluation<I: Interner> {
pub uncanonicalized_goal: Goal<I, I::Predicate>,
pub kind: WipGoalEvaluationKind<I>,
pub evaluation: Option<WipCanonicalGoalEvaluation<I>>,
}
impl<'tcx> WipGoalEvaluation<'tcx> {
fn finalize(self) -> inspect::GoalEvaluation<TyCtxt<'tcx>> {
impl<I: Interner> WipGoalEvaluation<I> {
fn finalize(self) -> inspect::GoalEvaluation<I> {
inspect::GoalEvaluation {
uncanonicalized_goal: self.uncanonicalized_goal,
kind: match self.kind {
@ -94,21 +97,23 @@ fn finalize(self) -> inspect::GoalEvaluation<TyCtxt<'tcx>> {
}
}
#[derive(Eq, PartialEq, Debug)]
pub(in crate::solve) enum WipGoalEvaluationKind<'tcx> {
Root { orig_values: Vec<ty::GenericArg<'tcx>> },
#[derive(derivative::Derivative)]
#[derivative(PartialEq(bound = ""), Eq(bound = ""), Debug(bound = ""))]
pub(in crate::solve) enum WipGoalEvaluationKind<I: Interner> {
Root { orig_values: Vec<I::GenericArg> },
Nested,
}
#[derive(Eq, PartialEq)]
pub(in crate::solve) enum WipCanonicalGoalEvaluationKind<'tcx> {
#[derive(derivative::Derivative)]
#[derivative(PartialEq(bound = ""), Eq(bound = ""))]
pub(in crate::solve) enum WipCanonicalGoalEvaluationKind<I: Interner> {
Overflow,
CycleInStack,
ProvisionalCacheHit,
Interned { revisions: &'tcx [inspect::GoalEvaluationStep<TyCtxt<'tcx>>] },
Interned { revisions: I::GoalEvaluationSteps },
}
impl std::fmt::Debug for WipCanonicalGoalEvaluationKind<'_> {
impl<I: Interner> std::fmt::Debug for WipCanonicalGoalEvaluationKind<I> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
match self {
Self::Overflow => write!(f, "Overflow"),
@ -119,18 +124,19 @@ fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
}
}
#[derive(Eq, PartialEq, Debug)]
struct WipCanonicalGoalEvaluation<'tcx> {
goal: CanonicalInput<'tcx>,
kind: Option<WipCanonicalGoalEvaluationKind<'tcx>>,
#[derive(derivative::Derivative)]
#[derivative(PartialEq(bound = ""), Eq(bound = ""), Debug(bound = ""))]
struct WipCanonicalGoalEvaluation<I: Interner> {
goal: CanonicalInput<I>,
kind: Option<WipCanonicalGoalEvaluationKind<I>>,
/// Only used for uncached goals. After we finished evaluating
/// the goal, this is interned and moved into `kind`.
revisions: Vec<WipGoalEvaluationStep<'tcx>>,
result: Option<QueryResult<'tcx>>,
revisions: Vec<WipGoalEvaluationStep<I>>,
result: Option<QueryResult<I>>,
}
impl<'tcx> WipCanonicalGoalEvaluation<'tcx> {
fn finalize(self) -> inspect::CanonicalGoalEvaluation<TyCtxt<'tcx>> {
impl<I: Interner> WipCanonicalGoalEvaluation<I> {
fn finalize(self) -> inspect::CanonicalGoalEvaluation<I> {
assert!(self.revisions.is_empty());
let kind = match self.kind.unwrap() {
WipCanonicalGoalEvaluationKind::Overflow => {
@ -151,14 +157,15 @@ fn finalize(self) -> inspect::CanonicalGoalEvaluation<TyCtxt<'tcx>> {
}
}
#[derive(Eq, PartialEq, Debug)]
struct WipAddedGoalsEvaluation<'tcx> {
evaluations: Vec<Vec<WipGoalEvaluation<'tcx>>>,
#[derive(derivative::Derivative)]
#[derivative(PartialEq(bound = ""), Eq(bound = ""), Debug(bound = ""))]
struct WipAddedGoalsEvaluation<I: Interner> {
evaluations: Vec<Vec<WipGoalEvaluation<I>>>,
result: Option<Result<Certainty, NoSolution>>,
}
impl<'tcx> WipAddedGoalsEvaluation<'tcx> {
fn finalize(self) -> inspect::AddedGoalsEvaluation<TyCtxt<'tcx>> {
impl<I: Interner> WipAddedGoalsEvaluation<I> {
fn finalize(self) -> inspect::AddedGoalsEvaluation<I> {
inspect::AddedGoalsEvaluation {
evaluations: self
.evaluations
@ -172,22 +179,23 @@ fn finalize(self) -> inspect::AddedGoalsEvaluation<TyCtxt<'tcx>> {
}
}
#[derive(Eq, PartialEq, Debug)]
struct WipGoalEvaluationStep<'tcx> {
#[derive(derivative::Derivative)]
#[derivative(PartialEq(bound = ""), Eq(bound = ""), Debug(bound = ""))]
struct WipGoalEvaluationStep<I: Interner> {
/// Unlike `EvalCtxt::var_values`, we append a new
/// generic arg here whenever we create a new inference
/// variable.
///
/// This is necessary as we otherwise don't unify these
/// vars when instantiating multiple `CanonicalState`.
var_values: Vec<ty::GenericArg<'tcx>>,
instantiated_goal: QueryInput<'tcx, ty::Predicate<'tcx>>,
var_values: Vec<I::GenericArg>,
instantiated_goal: QueryInput<I, I::Predicate>,
probe_depth: usize,
evaluation: WipProbe<'tcx>,
evaluation: WipProbe<I>,
}
impl<'tcx> WipGoalEvaluationStep<'tcx> {
fn current_evaluation_scope(&mut self) -> &mut WipProbe<'tcx> {
impl<I: Interner> WipGoalEvaluationStep<I> {
fn current_evaluation_scope(&mut self) -> &mut WipProbe<I> {
let mut current = &mut self.evaluation;
for _ in 0..self.probe_depth {
match current.steps.last_mut() {
@ -198,7 +206,7 @@ fn current_evaluation_scope(&mut self) -> &mut WipProbe<'tcx> {
current
}
fn added_goals_evaluation(&mut self) -> &mut WipAddedGoalsEvaluation<'tcx> {
fn added_goals_evaluation(&mut self) -> &mut WipAddedGoalsEvaluation<I> {
let mut current = &mut self.evaluation;
loop {
match current.steps.last_mut() {
@ -209,7 +217,7 @@ fn added_goals_evaluation(&mut self) -> &mut WipAddedGoalsEvaluation<'tcx> {
}
}
fn finalize(self) -> inspect::GoalEvaluationStep<TyCtxt<'tcx>> {
fn finalize(self) -> inspect::GoalEvaluationStep<I> {
let evaluation = self.evaluation.finalize();
match evaluation.kind {
inspect::ProbeKind::Root { .. } => (),
@ -219,16 +227,17 @@ fn finalize(self) -> inspect::GoalEvaluationStep<TyCtxt<'tcx>> {
}
}
#[derive(Eq, PartialEq, Debug)]
struct WipProbe<'tcx> {
#[derive(derivative::Derivative)]
#[derivative(PartialEq(bound = ""), Eq(bound = ""), Debug(bound = ""))]
struct WipProbe<I: Interner> {
initial_num_var_values: usize,
steps: Vec<WipProbeStep<'tcx>>,
kind: Option<inspect::ProbeKind<TyCtxt<'tcx>>>,
final_state: Option<inspect::CanonicalState<TyCtxt<'tcx>, ()>>,
steps: Vec<WipProbeStep<I>>,
kind: Option<inspect::ProbeKind<I>>,
final_state: Option<inspect::CanonicalState<I, ()>>,
}
impl<'tcx> WipProbe<'tcx> {
fn finalize(self) -> inspect::Probe<TyCtxt<'tcx>> {
impl<I: Interner> WipProbe<I> {
fn finalize(self) -> inspect::Probe<I> {
inspect::Probe {
steps: self.steps.into_iter().map(WipProbeStep::finalize).collect(),
kind: self.kind.unwrap(),
@ -237,17 +246,18 @@ fn finalize(self) -> inspect::Probe<TyCtxt<'tcx>> {
}
}
#[derive(Eq, PartialEq, Debug)]
enum WipProbeStep<'tcx> {
AddGoal(GoalSource, inspect::CanonicalState<TyCtxt<'tcx>, Goal<'tcx, ty::Predicate<'tcx>>>),
EvaluateGoals(WipAddedGoalsEvaluation<'tcx>),
NestedProbe(WipProbe<'tcx>),
#[derive(derivative::Derivative)]
#[derivative(PartialEq(bound = ""), Eq(bound = ""), Debug(bound = ""))]
enum WipProbeStep<I: Interner> {
AddGoal(GoalSource, inspect::CanonicalState<I, Goal<I, I::Predicate>>),
EvaluateGoals(WipAddedGoalsEvaluation<I>),
NestedProbe(WipProbe<I>),
MakeCanonicalResponse { shallow_certainty: Certainty },
RecordImplArgs { impl_args: inspect::CanonicalState<TyCtxt<'tcx>, ty::GenericArgsRef<'tcx>> },
RecordImplArgs { impl_args: inspect::CanonicalState<I, I::GenericArgs> },
}
impl<'tcx> WipProbeStep<'tcx> {
fn finalize(self) -> inspect::ProbeStep<TyCtxt<'tcx>> {
impl<I: Interner> WipProbeStep<I> {
fn finalize(self) -> inspect::ProbeStep<I> {
match self {
WipProbeStep::AddGoal(source, goal) => inspect::ProbeStep::AddGoal(source, goal),
WipProbeStep::EvaluateGoals(eval) => inspect::ProbeStep::EvaluateGoals(eval.finalize()),
@ -262,20 +272,21 @@ fn finalize(self) -> inspect::ProbeStep<TyCtxt<'tcx>> {
}
}
impl<'tcx> ProofTreeBuilder<'tcx> {
fn new(state: impl Into<DebugSolver<'tcx>>) -> ProofTreeBuilder<'tcx> {
// FIXME: Genericize this impl.
impl<'tcx> ProofTreeBuilder<TyCtxt<'tcx>> {
fn new(state: impl Into<DebugSolver<TyCtxt<'tcx>>>) -> ProofTreeBuilder<TyCtxt<'tcx>> {
ProofTreeBuilder { state: Some(Box::new(state.into())) }
}
fn nested<T: Into<DebugSolver<'tcx>>>(&self, state: impl FnOnce() -> T) -> Self {
fn nested<T: Into<DebugSolver<TyCtxt<'tcx>>>>(&self, state: impl FnOnce() -> T) -> Self {
ProofTreeBuilder { state: self.state.as_ref().map(|_| Box::new(state().into())) }
}
fn as_mut(&mut self) -> Option<&mut DebugSolver<'tcx>> {
fn as_mut(&mut self) -> Option<&mut DebugSolver<TyCtxt<'tcx>>> {
self.state.as_deref_mut()
}
pub fn take_and_enter_probe(&mut self) -> ProofTreeBuilder<'tcx> {
pub fn take_and_enter_probe(&mut self) -> ProofTreeBuilder<TyCtxt<'tcx>> {
let mut nested = ProofTreeBuilder { state: self.state.take() };
nested.enter_probe();
nested
@ -293,7 +304,7 @@ pub fn finalize(self) -> Option<inspect::GoalEvaluation<TyCtxt<'tcx>>> {
pub fn new_maybe_root(
tcx: TyCtxt<'tcx>,
generate_proof_tree: GenerateProofTree,
) -> ProofTreeBuilder<'tcx> {
) -> ProofTreeBuilder<TyCtxt<'tcx>> {
match generate_proof_tree {
GenerateProofTree::Never => ProofTreeBuilder::new_noop(),
GenerateProofTree::IfEnabled => {
@ -311,11 +322,11 @@ pub fn new_maybe_root(
}
}
pub fn new_root() -> ProofTreeBuilder<'tcx> {
pub fn new_root() -> ProofTreeBuilder<TyCtxt<'tcx>> {
ProofTreeBuilder::new(DebugSolver::Root)
}
pub fn new_noop() -> ProofTreeBuilder<'tcx> {
pub fn new_noop() -> ProofTreeBuilder<TyCtxt<'tcx>> {
ProofTreeBuilder { state: None }
}
@ -325,10 +336,10 @@ pub fn is_noop(&self) -> bool {
pub(in crate::solve) fn new_goal_evaluation(
&mut self,
goal: Goal<'tcx, ty::Predicate<'tcx>>,
goal: Goal<TyCtxt<'tcx>, ty::Predicate<'tcx>>,
orig_values: &[ty::GenericArg<'tcx>],
kind: solve::GoalEvaluationKind,
) -> ProofTreeBuilder<'tcx> {
) -> ProofTreeBuilder<TyCtxt<'tcx>> {
self.nested(|| WipGoalEvaluation {
uncanonicalized_goal: goal,
kind: match kind {
@ -343,8 +354,8 @@ pub(in crate::solve) fn new_goal_evaluation(
pub fn new_canonical_goal_evaluation(
&mut self,
goal: CanonicalInput<'tcx>,
) -> ProofTreeBuilder<'tcx> {
goal: CanonicalInput<TyCtxt<'tcx>>,
) -> ProofTreeBuilder<TyCtxt<'tcx>> {
self.nested(|| WipCanonicalGoalEvaluation {
goal,
kind: None,
@ -371,7 +382,10 @@ pub fn finalize_evaluation(
})
}
pub fn canonical_goal_evaluation(&mut self, canonical_goal_evaluation: ProofTreeBuilder<'tcx>) {
pub fn canonical_goal_evaluation(
&mut self,
canonical_goal_evaluation: ProofTreeBuilder<TyCtxt<'tcx>>,
) {
if let Some(this) = self.as_mut() {
match (this, *canonical_goal_evaluation.state.unwrap()) {
(
@ -386,7 +400,7 @@ pub fn canonical_goal_evaluation(&mut self, canonical_goal_evaluation: ProofTree
}
}
pub fn goal_evaluation_kind(&mut self, kind: WipCanonicalGoalEvaluationKind<'tcx>) {
pub fn goal_evaluation_kind(&mut self, kind: WipCanonicalGoalEvaluationKind<TyCtxt<'tcx>>) {
if let Some(this) = self.as_mut() {
match this {
DebugSolver::CanonicalGoalEvaluation(canonical_goal_evaluation) => {
@ -397,7 +411,7 @@ pub fn goal_evaluation_kind(&mut self, kind: WipCanonicalGoalEvaluationKind<'tcx
}
}
pub fn goal_evaluation(&mut self, goal_evaluation: ProofTreeBuilder<'tcx>) {
pub fn goal_evaluation(&mut self, goal_evaluation: ProofTreeBuilder<TyCtxt<'tcx>>) {
if let Some(this) = self.as_mut() {
match (this, *goal_evaluation.state.unwrap()) {
(
@ -418,8 +432,8 @@ pub fn goal_evaluation(&mut self, goal_evaluation: ProofTreeBuilder<'tcx>) {
pub fn new_goal_evaluation_step(
&mut self,
var_values: CanonicalVarValues<'tcx>,
instantiated_goal: QueryInput<'tcx, ty::Predicate<'tcx>>,
) -> ProofTreeBuilder<'tcx> {
instantiated_goal: QueryInput<TyCtxt<'tcx>, ty::Predicate<'tcx>>,
) -> ProofTreeBuilder<TyCtxt<'tcx>> {
self.nested(|| WipGoalEvaluationStep {
var_values: var_values.var_values.to_vec(),
instantiated_goal,
@ -433,7 +447,7 @@ pub fn new_goal_evaluation_step(
})
}
pub fn goal_evaluation_step(&mut self, goal_evaluation_step: ProofTreeBuilder<'tcx>) {
pub fn goal_evaluation_step(&mut self, goal_evaluation_step: ProofTreeBuilder<TyCtxt<'tcx>>) {
if let Some(this) = self.as_mut() {
match (this, *goal_evaluation_step.state.unwrap()) {
(
@ -510,7 +524,7 @@ pub fn add_normalizes_to_goal(
&mut self,
infcx: &InferCtxt<'tcx>,
max_input_universe: ty::UniverseIndex,
goal: Goal<'tcx, ty::NormalizesTo<'tcx>>,
goal: Goal<TyCtxt<'tcx>, ty::NormalizesTo<'tcx>>,
) {
self.add_goal(
infcx,
@ -525,7 +539,7 @@ pub fn add_goal(
infcx: &InferCtxt<'tcx>,
max_input_universe: ty::UniverseIndex,
source: GoalSource,
goal: Goal<'tcx, ty::Predicate<'tcx>>,
goal: Goal<TyCtxt<'tcx>, ty::Predicate<'tcx>>,
) {
match self.as_mut() {
None => {}
@ -579,7 +593,7 @@ pub fn make_canonical_response(&mut self, shallow_certainty: Certainty) {
}
}
pub fn finish_probe(mut self) -> ProofTreeBuilder<'tcx> {
pub fn finish_probe(mut self) -> ProofTreeBuilder<TyCtxt<'tcx>> {
match self.as_mut() {
None => {}
Some(DebugSolver::GoalEvaluationStep(state)) => {
@ -627,7 +641,7 @@ pub fn evaluate_added_goals_result(&mut self, result: Result<Certainty, NoSoluti
}
}
pub fn query_result(&mut self, result: QueryResult<'tcx>) {
pub fn query_result(&mut self, result: QueryResult<TyCtxt<'tcx>>) {
if let Some(this) = self.as_mut() {
match this {
DebugSolver::CanonicalGoalEvaluation(canonical_goal_evaluation) => {

View File

@ -253,8 +253,8 @@ pub(super) fn with_new_goal(
&mut self,
tcx: TyCtxt<'tcx>,
input: CanonicalInput<'tcx>,
inspect: &mut ProofTreeBuilder<'tcx>,
mut prove_goal: impl FnMut(&mut Self, &mut ProofTreeBuilder<'tcx>) -> QueryResult<'tcx>,
inspect: &mut ProofTreeBuilder<TyCtxt<'tcx>>,
mut prove_goal: impl FnMut(&mut Self, &mut ProofTreeBuilder<TyCtxt<'tcx>>) -> QueryResult<'tcx>,
) -> QueryResult<'tcx> {
// Check for overflow.
let Some(available_depth) = Self::allowed_depth_for_nested(tcx, &self.stack) else {