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Rollup merge of #119613 - gavinleroy:expose-obligations, r=lcnr
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Expose Obligations created during type inference.

This PR is a first pass at exposing the trait obligations generated and solved for during the type-check progress. Exposing these obligations allows for rustc plugins to use the public interface for proof trees (provided by the next gen trait solver).

The changes proposed track *all* obligations during the type-check process, this is desirable to not only look at the trees of failed obligations, but also those of successfully proved obligations. This feature is placed behind an unstable compiler option `track-trait-obligations` which should be used together with the `next-solver` option. I should note that the main interface is the function `inspect_typeck` made public in `rustc_hir_typeck/src/lib.rs` which allows the caller to provide a callback granting access to the `FnCtxt`.

r? `@lcnr`
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@matthiaskrgr
matthiaskrgr authored Jan 20, 2024
2 parents 6f67208 + 130b7e7 commit 2de5ca2
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Showing 5 changed files with 121 additions and 64 deletions.
24 changes: 21 additions & 3 deletions compiler/rustc_hir_typeck/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -60,6 +60,7 @@ use rustc_hir::{HirIdMap, Node};
use rustc_hir_analysis::astconv::AstConv;
use rustc_hir_analysis::check::check_abi;
use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
use rustc_infer::traits::ObligationInspector;
use rustc_middle::query::Providers;
use rustc_middle::traits;
use rustc_middle::ty::{self, Ty, TyCtxt};
Expand Down Expand Up @@ -139,7 +140,7 @@ fn used_trait_imports(tcx: TyCtxt<'_>, def_id: LocalDefId) -> &UnordSet<LocalDef

fn typeck<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> &ty::TypeckResults<'tcx> {
let fallback = move || tcx.type_of(def_id.to_def_id()).instantiate_identity();
typeck_with_fallback(tcx, def_id, fallback)
typeck_with_fallback(tcx, def_id, fallback, None)
}

/// Used only to get `TypeckResults` for type inference during error recovery.
Expand All @@ -149,14 +150,28 @@ fn diagnostic_only_typeck<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> &ty::T
let span = tcx.hir().span(tcx.local_def_id_to_hir_id(def_id));
Ty::new_error_with_message(tcx, span, "diagnostic only typeck table used")
};
typeck_with_fallback(tcx, def_id, fallback)
typeck_with_fallback(tcx, def_id, fallback, None)
}

#[instrument(level = "debug", skip(tcx, fallback), ret)]
/// Same as `typeck` but `inspect` is invoked on evaluation of each root obligation.
/// Inspecting obligations only works with the new trait solver.
/// This function is *only to be used* by external tools, it should not be
/// called from within rustc. Note, this is not a query, and thus is not cached.
pub fn inspect_typeck<'tcx>(
tcx: TyCtxt<'tcx>,
def_id: LocalDefId,
inspect: ObligationInspector<'tcx>,
) -> &'tcx ty::TypeckResults<'tcx> {
let fallback = move || tcx.type_of(def_id.to_def_id()).instantiate_identity();
typeck_with_fallback(tcx, def_id, fallback, Some(inspect))
}

#[instrument(level = "debug", skip(tcx, fallback, inspector), ret)]
fn typeck_with_fallback<'tcx>(
tcx: TyCtxt<'tcx>,
def_id: LocalDefId,
fallback: impl Fn() -> Ty<'tcx> + 'tcx,
inspector: Option<ObligationInspector<'tcx>>,
) -> &'tcx ty::TypeckResults<'tcx> {
// Closures' typeck results come from their outermost function,
// as they are part of the same "inference environment".
Expand All @@ -178,6 +193,9 @@ fn typeck_with_fallback<'tcx>(
let param_env = tcx.param_env(def_id);

let inh = Inherited::new(tcx, def_id);
if let Some(inspector) = inspector {
inh.infcx.attach_obligation_inspector(inspector);
}
let mut fcx = FnCtxt::new(&inh, param_env, def_id);

if let Some(hir::FnSig { header, decl, .. }) = fn_sig {
Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_infer/src/infer/at.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -90,6 +90,7 @@ impl<'tcx> InferCtxt<'tcx> {
universe: self.universe.clone(),
intercrate,
next_trait_solver: self.next_trait_solver,
obligation_inspector: self.obligation_inspector.clone(),
}
}
}
Expand Down
16 changes: 15 additions & 1 deletion compiler/rustc_infer/src/infer/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,9 @@ use rustc_middle::infer::unify_key::{ConstVidKey, EffectVidKey};
use self::opaque_types::OpaqueTypeStorage;
pub(crate) use self::undo_log::{InferCtxtUndoLogs, Snapshot, UndoLog};

use crate::traits::{self, ObligationCause, PredicateObligations, TraitEngine, TraitEngineExt};
use crate::traits::{
self, ObligationCause, ObligationInspector, PredicateObligations, TraitEngine, TraitEngineExt,
};

use rustc_data_structures::fx::FxIndexMap;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
Expand Down Expand Up @@ -334,6 +336,8 @@ pub struct InferCtxt<'tcx> {
pub intercrate: bool,

next_trait_solver: bool,

pub obligation_inspector: Cell<Option<ObligationInspector<'tcx>>>,
}

impl<'tcx> ty::InferCtxtLike for InferCtxt<'tcx> {
Expand Down Expand Up @@ -708,6 +712,7 @@ impl<'tcx> InferCtxtBuilder<'tcx> {
universe: Cell::new(ty::UniverseIndex::ROOT),
intercrate,
next_trait_solver,
obligation_inspector: Cell::new(None),
}
}
}
Expand Down Expand Up @@ -1718,6 +1723,15 @@ impl<'tcx> InferCtxt<'tcx> {
}
}
}

/// Attach a callback to be invoked on each root obligation evaluated in the new trait solver.
pub fn attach_obligation_inspector(&self, inspector: ObligationInspector<'tcx>) {
debug_assert!(
self.obligation_inspector.get().is_none(),
"shouldn't override a set obligation inspector"
);
self.obligation_inspector.set(Some(inspector));
}
}

impl<'tcx> TypeErrCtxt<'_, 'tcx> {
Expand Down
8 changes: 8 additions & 0 deletions compiler/rustc_infer/src/traits/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,12 +13,15 @@ use std::hash::{Hash, Hasher};

use hir::def_id::LocalDefId;
use rustc_hir as hir;
use rustc_middle::traits::query::NoSolution;
use rustc_middle::traits::solve::Certainty;
use rustc_middle::ty::error::{ExpectedFound, TypeError};
use rustc_middle::ty::{self, Const, ToPredicate, Ty, TyCtxt};
use rustc_span::Span;

pub use self::ImplSource::*;
pub use self::SelectionError::*;
use crate::infer::InferCtxt;

pub use self::engine::{TraitEngine, TraitEngineExt};
pub use self::project::MismatchedProjectionTypes;
Expand Down Expand Up @@ -116,6 +119,11 @@ pub type PredicateObligations<'tcx> = Vec<PredicateObligation<'tcx>>;

pub type Selection<'tcx> = ImplSource<'tcx, PredicateObligation<'tcx>>;

/// A callback that can be provided to `inspect_typeck`. Invoked on evaluation
/// of root obligations.
pub type ObligationInspector<'tcx> =
fn(&InferCtxt<'tcx>, &PredicateObligation<'tcx>, Result<Certainty, NoSolution>);

pub struct FulfillmentError<'tcx> {
pub obligation: PredicateObligation<'tcx>,
pub code: FulfillmentErrorCode<'tcx>,
Expand Down
136 changes: 76 additions & 60 deletions compiler/rustc_trait_selection/src/solve/fulfill.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -11,7 +11,7 @@ use rustc_middle::ty;
use rustc_middle::ty::error::{ExpectedFound, TypeError};

use super::eval_ctxt::GenerateProofTree;
use super::{Certainty, InferCtxtEvalExt};
use super::{Certainty, Goal, InferCtxtEvalExt};

/// A trait engine using the new trait solver.
///
Expand Down Expand Up @@ -43,6 +43,21 @@ impl<'tcx> FulfillmentCtxt<'tcx> {
);
FulfillmentCtxt { obligations: Vec::new(), usable_in_snapshot: infcx.num_open_snapshots() }
}

fn inspect_evaluated_obligation(
&self,
infcx: &InferCtxt<'tcx>,
obligation: &PredicateObligation<'tcx>,
result: &Result<(bool, Certainty, Vec<Goal<'tcx, ty::Predicate<'tcx>>>), NoSolution>,
) {
if let Some(inspector) = infcx.obligation_inspector.get() {
let result = match result {
Ok((_, c, _)) => Ok(*c),
Err(NoSolution) => Err(NoSolution),
};
(inspector)(infcx, &obligation, result);
}
}
}

impl<'tcx> TraitEngine<'tcx> for FulfillmentCtxt<'tcx> {
Expand Down Expand Up @@ -100,65 +115,66 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentCtxt<'tcx> {
let mut has_changed = false;
for obligation in mem::take(&mut self.obligations) {
let goal = obligation.clone().into();
let (changed, certainty, nested_goals) =
match infcx.evaluate_root_goal(goal, GenerateProofTree::IfEnabled).0 {
Ok(result) => result,
Err(NoSolution) => {
errors.push(FulfillmentError {
obligation: obligation.clone(),
code: match goal.predicate.kind().skip_binder() {
ty::PredicateKind::Clause(ty::ClauseKind::Projection(_)) => {
FulfillmentErrorCode::ProjectionError(
// FIXME: This could be a `Sorts` if the term is a type
MismatchedProjectionTypes { err: TypeError::Mismatch },
)
}
ty::PredicateKind::NormalizesTo(..) => {
FulfillmentErrorCode::ProjectionError(
MismatchedProjectionTypes { err: TypeError::Mismatch },
)
}
ty::PredicateKind::AliasRelate(_, _, _) => {
FulfillmentErrorCode::ProjectionError(
MismatchedProjectionTypes { err: TypeError::Mismatch },
)
}
ty::PredicateKind::Subtype(pred) => {
let (a, b) = infcx.instantiate_binder_with_placeholders(
goal.predicate.kind().rebind((pred.a, pred.b)),
);
let expected_found = ExpectedFound::new(true, a, b);
FulfillmentErrorCode::SubtypeError(
expected_found,
TypeError::Sorts(expected_found),
)
}
ty::PredicateKind::Coerce(pred) => {
let (a, b) = infcx.instantiate_binder_with_placeholders(
goal.predicate.kind().rebind((pred.a, pred.b)),
);
let expected_found = ExpectedFound::new(false, a, b);
FulfillmentErrorCode::SubtypeError(
expected_found,
TypeError::Sorts(expected_found),
)
}
ty::PredicateKind::Clause(_)
| ty::PredicateKind::ObjectSafe(_)
| ty::PredicateKind::Ambiguous => {
FulfillmentErrorCode::SelectionError(
SelectionError::Unimplemented,
)
}
ty::PredicateKind::ConstEquate(..) => {
bug!("unexpected goal: {goal:?}")
}
},
root_obligation: obligation,
});
continue;
}
};
let result = infcx.evaluate_root_goal(goal, GenerateProofTree::IfEnabled).0;
self.inspect_evaluated_obligation(infcx, &obligation, &result);
let (changed, certainty, nested_goals) = match result {
Ok(result) => result,
Err(NoSolution) => {
errors.push(FulfillmentError {
obligation: obligation.clone(),
code: match goal.predicate.kind().skip_binder() {
ty::PredicateKind::Clause(ty::ClauseKind::Projection(_)) => {
FulfillmentErrorCode::ProjectionError(
// FIXME: This could be a `Sorts` if the term is a type
MismatchedProjectionTypes { err: TypeError::Mismatch },
)
}
ty::PredicateKind::NormalizesTo(..) => {
FulfillmentErrorCode::ProjectionError(
MismatchedProjectionTypes { err: TypeError::Mismatch },
)
}
ty::PredicateKind::AliasRelate(_, _, _) => {
FulfillmentErrorCode::ProjectionError(
MismatchedProjectionTypes { err: TypeError::Mismatch },
)
}
ty::PredicateKind::Subtype(pred) => {
let (a, b) = infcx.instantiate_binder_with_placeholders(
goal.predicate.kind().rebind((pred.a, pred.b)),
);
let expected_found = ExpectedFound::new(true, a, b);
FulfillmentErrorCode::SubtypeError(
expected_found,
TypeError::Sorts(expected_found),
)
}
ty::PredicateKind::Coerce(pred) => {
let (a, b) = infcx.instantiate_binder_with_placeholders(
goal.predicate.kind().rebind((pred.a, pred.b)),
);
let expected_found = ExpectedFound::new(false, a, b);
FulfillmentErrorCode::SubtypeError(
expected_found,
TypeError::Sorts(expected_found),
)
}
ty::PredicateKind::Clause(_)
| ty::PredicateKind::ObjectSafe(_)
| ty::PredicateKind::Ambiguous => {
FulfillmentErrorCode::SelectionError(
SelectionError::Unimplemented,
)
}
ty::PredicateKind::ConstEquate(..) => {
bug!("unexpected goal: {goal:?}")
}
},
root_obligation: obligation,
});
continue;
}
};
// Push any nested goals that we get from unifying our canonical response
// with our obligation onto the fulfillment context.
self.obligations.extend(nested_goals.into_iter().map(|goal| {
Expand Down

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