Clean up dropck code a bit

- Remove `Result` that couldn't be Err on valid compilation.
- Always compute errors on failure.

Author: matthewjasper

compiler/rustc_borrowck/src/type_check/liveness/trace.rs

@@ -4,6 +4,7 @@ use rustc_index::interval::IntervalSet;
 use rustc_infer::infer::canonical::QueryRegionConstraints;
 use rustc_infer::infer::outlives::for_liveness;
 use rustc_middle::mir::{BasicBlock, Body, ConstraintCategory, HasLocalDecls, Local, Location};
+use rustc_middle::span_bug;
 use rustc_middle::traits::query::DropckOutlivesResult;
 use rustc_middle::ty::relate::Relate;
 use rustc_middle::ty::{Ty, TyCtxt, TypeVisitable, TypeVisitableExt};
@@ -613,23 +614,22 @@ impl<'tcx> LivenessContext<'_, '_, '_, 'tcx> {
                 // can't rely on the the `ErrorGuaranteed` from `fully_perform` here
                 // because it comes from delay_span_bug.
                 let ocx = ObligationCtxt::new_with_diagnostics(&typeck.infcx);
-                let errors = match dropck_outlives::compute_dropck_outlives_with_errors(
-                    &ocx, op, span, true,
-                ) {
-                    Ok(_) => ocx.select_all_or_error(),
-                    Err(e) => {
-                        if e.is_empty() {
-                            ocx.select_all_or_error()
-                        } else {
-                            e
+                let errors =
+                    match dropck_outlives::compute_dropck_outlives_with_errors(&ocx, op, span) {
+                        Ok(_) => ocx.select_all_or_error(),
+                        Err(e) => {
+                            if e.is_empty() {
+                                ocx.select_all_or_error()
+                            } else {
+                                e
+                            }
                         }
-                    }
-                };
+                    };
 
                 if !errors.is_empty() {
                     typeck.infcx.err_ctxt().report_fulfillment_errors(errors);
                 } else {
-                    rustc_middle::span_bug!(span, "Rerunning drop data query produced no error.");
+                    span_bug!(span, "Rerunning drop data query produced no error.");
                 }
                 DropData { dropck_result: Default::default(), region_constraint_data: None }
             }

compiler/rustc_middle/src/query/mod.rs

@@ -802,7 +802,7 @@ rustc_queries! {
 
     query adt_dtorck_constraint(
         key: DefId
-    ) -> Result<&'tcx DropckConstraint<'tcx>, NoSolution> {
+    ) -> &'tcx DropckConstraint<'tcx> {
         desc { |tcx| "computing drop-check constraints for `{}`", tcx.def_path_str(key) }
     }
 

compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs

@@ -94,7 +94,7 @@ pub fn compute_dropck_outlives_inner<'tcx>(
     goal: ParamEnvAnd<'tcx, DropckOutlives<'tcx>>,
     span: Span,
 ) -> Result<DropckOutlivesResult<'tcx>, NoSolution> {
-    match compute_dropck_outlives_with_errors(ocx, goal, span, false) {
+    match compute_dropck_outlives_with_errors(ocx, goal, span) {
         Ok(r) => Ok(r),
         Err(_) => Err(NoSolution),
     }
@@ -104,7 +104,6 @@ pub fn compute_dropck_outlives_with_errors<'tcx, E>(
     ocx: &ObligationCtxt<'_, 'tcx, E>,
     goal: ParamEnvAnd<'tcx, DropckOutlives<'tcx>>,
     span: Span,
-    report_errors: bool,
 ) -> Result<DropckOutlivesResult<'tcx>, Vec<E>>
 where
     E: FromSolverError<'tcx, NextSolverError<'tcx>>,
@@ -162,17 +161,14 @@ where
             result.overflows.len(),
             ty_stack.len()
         );
-        match dtorck_constraint_for_ty_inner(
+        dtorck_constraint_for_ty_inner(
             tcx,
             ocx.infcx.typing_env(param_env),
             span,
             depth,
             ty,
             &mut constraints,
-        ) {
-            Err(_) => return Err(Vec::new()),
-            _ => (),
-        };
+        );
 
         // "outlives" represent types/regions that may be touched
         // by a destructor.
@@ -192,24 +188,19 @@ where
         // do not themselves define a destructor", more or less. We have
         // to push them onto the stack to be expanded.
         for ty in constraints.dtorck_types.drain(..) {
-            let ty = if report_errors {
-                let normalized_ty = ocx.deeply_normalize(&cause, param_env, ty)?;
-
-                let errors = ocx.select_where_possible();
-                if !errors.is_empty() {
-                    debug!("failed to normalize dtorck type: {ty} ~> {errors:#?}");
-                    return Err(errors);
-                }
-                normalized_ty
-            } else if let Ok(Normalized { value: ty, obligations }) =
+            let ty = if let Ok(Normalized { value: ty, obligations }) =
                 ocx.infcx.at(&cause, param_env).query_normalize(ty)
             {
                 ocx.register_obligations(obligations);
 
                 debug!("dropck_outlives: ty from dtorck_types = {:?}", ty);
                 ty
             } else {
-                return Err(Vec::new());
+                ocx.deeply_normalize(&cause, param_env, ty)?;
+
+                let errors = ocx.select_where_possible();
+                debug!("normalize errors: {ty} ~> {errors:#?}");
+                return Err(errors);
             };
 
             match ty.kind() {
@@ -246,14 +237,14 @@ pub fn dtorck_constraint_for_ty_inner<'tcx>(
     depth: usize,
     ty: Ty<'tcx>,
     constraints: &mut DropckConstraint<'tcx>,
-) -> Result<(), NoSolution> {
+) {
     if !tcx.recursion_limit().value_within_limit(depth) {
         constraints.overflows.push(ty);
-        return Ok(());
+        return;
     }
 
     if trivial_dropck_outlives(tcx, ty) {
-        return Ok(());
+        return;
     }
 
     match ty.kind() {
@@ -277,22 +268,20 @@ pub fn dtorck_constraint_for_ty_inner<'tcx>(
             // single-element containers, behave like their element
             rustc_data_structures::stack::ensure_sufficient_stack(|| {
                 dtorck_constraint_for_ty_inner(tcx, typing_env, span, depth + 1, *ety, constraints)
-            })?;
+            });
         }
 
         ty::Tuple(tys) => rustc_data_structures::stack::ensure_sufficient_stack(|| {
             for ty in tys.iter() {
-                dtorck_constraint_for_ty_inner(tcx, typing_env, span, depth + 1, ty, constraints)?;
+                dtorck_constraint_for_ty_inner(tcx, typing_env, span, depth + 1, ty, constraints);
             }
-            Ok::<_, NoSolution>(())
-        })?,
+        }),
 
         ty::Closure(_, args) => rustc_data_structures::stack::ensure_sufficient_stack(|| {
             for ty in args.as_closure().upvar_tys() {
-                dtorck_constraint_for_ty_inner(tcx, typing_env, span, depth + 1, ty, constraints)?;
+                dtorck_constraint_for_ty_inner(tcx, typing_env, span, depth + 1, ty, constraints);
             }
-            Ok::<_, NoSolution>(())
-        })?,
+        }),
 
         ty::CoroutineClosure(_, args) => {
             rustc_data_structures::stack::ensure_sufficient_stack(|| {
@@ -304,10 +293,9 @@ pub fn dtorck_constraint_for_ty_inner<'tcx>(
                         depth + 1,
                         ty,
                         constraints,
-                    )?;
+                    );
                 }
-                Ok::<_, NoSolution>(())
-            })?
+            })
         }
 
         ty::Coroutine(_, args) => {
@@ -346,7 +334,7 @@ pub fn dtorck_constraint_for_ty_inner<'tcx>(
 
         ty::Adt(def, args) => {
             let DropckConstraint { dtorck_types, outlives, overflows } =
-                tcx.at(span).adt_dtorck_constraint(def.did())?;
+                tcx.at(span).adt_dtorck_constraint(def.did());
             // FIXME: we can try to recursively `dtorck_constraint_on_ty`
             // there, but that needs some way to handle cycles.
             constraints
@@ -379,9 +367,7 @@ pub fn dtorck_constraint_for_ty_inner<'tcx>(
         ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) | ty::Error(_) => {
             // By the time this code runs, all type variables ought to
             // be fully resolved.
-            return Err(NoSolution);
+            tcx.dcx().span_delayed_bug(span, format!("Unresolved type in dropck: {:?}.", ty));
         }
     }
-
-    Ok(())
 }

compiler/rustc_traits/src/dropck_outlives.rs

@@ -33,7 +33,7 @@ fn dropck_outlives<'tcx>(
 pub(crate) fn adt_dtorck_constraint(
     tcx: TyCtxt<'_>,
     def_id: DefId,
-) -> Result<&DropckConstraint<'_>, NoSolution> {
+) -> &DropckConstraint<'_> {
     let def = tcx.adt_def(def_id);
     let span = tcx.def_span(def_id);
     let typing_env = ty::TypingEnv::non_body_analysis(tcx, def_id);
@@ -52,20 +52,20 @@ pub(crate) fn adt_dtorck_constraint(
             overflows: vec![],
         };
         debug!("dtorck_constraint: {:?} => {:?}", def, result);
-        return Ok(tcx.arena.alloc(result));
+        return tcx.arena.alloc(result);
     }
 
     let mut result = DropckConstraint::empty();
     for field in def.all_fields() {
         let fty = tcx.type_of(field.did).instantiate_identity();
-        dtorck_constraint_for_ty_inner(tcx, typing_env, span, 0, fty, &mut result)?;
+        dtorck_constraint_for_ty_inner(tcx, typing_env, span, 0, fty, &mut result);
     }
     result.outlives.extend(tcx.destructor_constraints(def));
     dedup_dtorck_constraint(&mut result);
 
     debug!("dtorck_constraint: {:?} => {:?}", def, result);
 
-    Ok(tcx.arena.alloc(result))
+    tcx.arena.alloc(result)
 }
 
 fn dedup_dtorck_constraint(c: &mut DropckConstraint<'_>) {