Rollup merge of rust-lang#127508 - lcnr:search-graph-prep, r=compiler-errors

small search graph refactor

small improvements which shouldn't impact behavior.

r? ```@compiler-errors```

Author: matthiaskrgr

compiler/rustc_next_trait_solver/src/solve/mod.rs

@@ -48,12 +48,20 @@ enum GoalEvaluationKind {
     Nested,
 }
 
+// FIXME(trait-system-refactor-initiative#117): we don't detect whether a response
+// ended up pulling down any universes.
 fn has_no_inference_or_external_constraints<I: Interner>(
     response: ty::Canonical<I, Response<I>>,
 ) -> bool {
-    response.value.external_constraints.region_constraints.is_empty()
-        && response.value.var_values.is_identity()
-        && response.value.external_constraints.opaque_types.is_empty()
+    let ExternalConstraintsData {
+        ref region_constraints,
+        ref opaque_types,
+        ref normalization_nested_goals,
+    } = *response.value.external_constraints;
+    response.value.var_values.is_identity()
+        && region_constraints.is_empty()
+        && opaque_types.is_empty()
+        && normalization_nested_goals.is_empty()
 }
 
 impl<'a, D, I> EvalCtxt<'a, D>

compiler/rustc_next_trait_solver/src/solve/search_graph.rs

@@ -71,7 +71,7 @@ struct StackEntry<I: Interner> {
     /// C :- D
     /// D :- C
     /// ```
-    cycle_participants: HashSet<CanonicalInput<I>>,
+    nested_goals: HashSet<CanonicalInput<I>>,
     /// Starts out as `None` and gets set when rerunning this
     /// goal in case we encounter a cycle.
     provisional_result: Option<QueryResult<I>>,
@@ -139,18 +139,11 @@ impl<I: Interner> SearchGraph<I> {
         self.mode
     }
 
-    /// Pops the highest goal from the stack, lazily updating the
-    /// the next goal in the stack.
-    ///
-    /// Directly popping from the stack instead of using this method
-    /// would cause us to not track overflow and recursion depth correctly.
-    fn pop_stack(&mut self) -> StackEntry<I> {
-        let elem = self.stack.pop().unwrap();
-        if let Some(last) = self.stack.raw.last_mut() {
-            last.reached_depth = last.reached_depth.max(elem.reached_depth);
-            last.encountered_overflow |= elem.encountered_overflow;
+    fn update_parent_goal(&mut self, reached_depth: StackDepth, encountered_overflow: bool) {
+        if let Some(parent) = self.stack.raw.last_mut() {
+            parent.reached_depth = parent.reached_depth.max(reached_depth);
+            parent.encountered_overflow |= encountered_overflow;
         }
-        elem
     }
 
     pub(super) fn is_empty(&self) -> bool {
@@ -222,8 +215,8 @@ impl<I: Interner> SearchGraph<I> {
         let current_cycle_root = &mut stack[current_root.as_usize()];
         for entry in cycle_participants {
             entry.non_root_cycle_participant = entry.non_root_cycle_participant.max(Some(head));
-            current_cycle_root.cycle_participants.insert(entry.input);
-            current_cycle_root.cycle_participants.extend(mem::take(&mut entry.cycle_participants));
+            current_cycle_root.nested_goals.insert(entry.input);
+            current_cycle_root.nested_goals.extend(mem::take(&mut entry.nested_goals));
         }
     }
 
@@ -342,7 +335,7 @@ impl<I: Interner> SearchGraph<I> {
                 non_root_cycle_participant: None,
                 encountered_overflow: false,
                 has_been_used: HasBeenUsed::empty(),
-                cycle_participants: Default::default(),
+                nested_goals: Default::default(),
                 provisional_result: None,
             };
             assert_eq!(self.stack.push(entry), depth);
@@ -364,14 +357,16 @@ impl<I: Interner> SearchGraph<I> {
             }
 
             debug!("canonical cycle overflow");
-            let current_entry = self.pop_stack();
+            let current_entry = self.stack.pop().unwrap();
             debug_assert!(current_entry.has_been_used.is_empty());
             let result = Self::response_no_constraints(cx, input, Certainty::overflow(false));
             (current_entry, result)
         });
 
         let proof_tree = inspect.finalize_canonical_goal_evaluation(cx);
 
+        self.update_parent_goal(final_entry.reached_depth, final_entry.encountered_overflow);
+
         // We're now done with this goal. In case this goal is involved in a larger cycle
         // do not remove it from the provisional cache and update its provisional result.
         // We only add the root of cycles to the global cache.
@@ -394,15 +389,15 @@ impl<I: Interner> SearchGraph<I> {
             //
             // We must not use the global cache entry of a root goal if a cycle
             // participant is on the stack. This is necessary to prevent unstable
-            // results. See the comment of `StackEntry::cycle_participants` for
+            // results. See the comment of `StackEntry::nested_goals` for
             // more details.
             self.global_cache(cx).insert(
                 cx,
                 input,
                 proof_tree,
                 reached_depth,
                 final_entry.encountered_overflow,
-                final_entry.cycle_participants,
+                final_entry.nested_goals,
                 dep_node,
                 result,
             )
@@ -441,14 +436,9 @@ impl<I: Interner> SearchGraph<I> {
             }
         }
 
-        // Update the reached depth of the current goal to make sure
-        // its state is the same regardless of whether we've used the
-        // global cache or not.
+        // Adjust the parent goal as if we actually computed this goal.
         let reached_depth = self.stack.next_index().plus(additional_depth);
-        if let Some(last) = self.stack.raw.last_mut() {
-            last.reached_depth = last.reached_depth.max(reached_depth);
-            last.encountered_overflow |= encountered_overflow;
-        }
+        self.update_parent_goal(reached_depth, encountered_overflow);
 
         Some(result)
     }
@@ -477,7 +467,7 @@ impl<I: Interner> SearchGraph<I> {
         F: FnMut(&mut Self, &mut ProofTreeBuilder<D>) -> QueryResult<I>,
     {
         let result = prove_goal(self, inspect);
-        let stack_entry = self.pop_stack();
+        let stack_entry = self.stack.pop().unwrap();
         debug_assert_eq!(stack_entry.input, input);
 
         // If the current goal is not the root of a cycle, we are done.
@@ -554,27 +544,27 @@ impl<I: Interner> SearchGraph<I> {
                 non_root_cycle_participant,
                 encountered_overflow: _,
                 has_been_used,
-                ref cycle_participants,
+                ref nested_goals,
                 provisional_result,
             } = *entry;
             let cache_entry = provisional_cache.get(&entry.input).unwrap();
             assert_eq!(cache_entry.stack_depth, Some(depth));
             if let Some(head) = non_root_cycle_participant {
                 assert!(head < depth);
-                assert!(cycle_participants.is_empty());
+                assert!(nested_goals.is_empty());
                 assert_ne!(stack[head].has_been_used, HasBeenUsed::empty());
 
                 let mut current_root = head;
                 while let Some(parent) = stack[current_root].non_root_cycle_participant {
                     current_root = parent;
                 }
-                assert!(stack[current_root].cycle_participants.contains(&input));
+                assert!(stack[current_root].nested_goals.contains(&input));
             }
 
-            if !cycle_participants.is_empty() {
+            if !nested_goals.is_empty() {
                 assert!(provisional_result.is_some() || !has_been_used.is_empty());
                 for entry in stack.iter().take(depth.as_usize()) {
-                    assert_eq!(cycle_participants.get(&entry.input), None);
+                    assert_eq!(nested_goals.get(&entry.input), None);
                 }
             }
         }