Auto merge of #130281 - matthiaskrgr:rollup-1b2ibs8, r=matthiaskrgr

Rollup of 5 pull requests

Successful merges:

 - #130101 (some const cleanup: remove unnecessary attributes, add const-hack indications)
 - #130208 (Introduce `'ra` lifetime name.)
 - #130263 (coverage: Simplify creation of sum counters)
 - #130273 (more eagerly discard constraints on overflow)
 - #130276 (Add test for nalgebra hang in coherence)

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

compiler/rustc_mir_transform/src/coverage/counters.rs

@@ -155,12 +155,14 @@ impl CoverageCounters {
         BcbCounter::Expression { id }
     }
 
-    /// Variant of `make_expression` that makes `lhs` optional and assumes [`Op::Add`].
+    /// Creates a counter that is the sum of the given counters.
     ///
-    /// This is useful when using [`Iterator::fold`] to build an arbitrary-length sum.
-    fn make_sum_expression(&mut self, lhs: Option<BcbCounter>, rhs: BcbCounter) -> BcbCounter {
-        let Some(lhs) = lhs else { return rhs };
-        self.make_expression(lhs, Op::Add, rhs)
+    /// Returns `None` if the given list of counters was empty.
+    fn make_sum(&mut self, counters: &[BcbCounter]) -> Option<BcbCounter> {
+        counters
+            .iter()
+            .copied()
+            .reduce(|accum, counter| self.make_expression(accum, Op::Add, counter))
     }
 
     pub(super) fn num_counters(&self) -> usize {
@@ -315,20 +317,17 @@ impl<'a> MakeBcbCounters<'a> {
         // For each out-edge other than the one that was chosen to get an expression,
         // ensure that it has a counter (existing counter/expression or a new counter),
         // and accumulate the corresponding counters into a single sum expression.
-        let sum_of_all_other_out_edges: BcbCounter = {
-            let _span = debug_span!("sum_of_all_other_out_edges", ?expression_to_bcb).entered();
-            successors
-                .iter()
-                .copied()
-                // Skip the chosen edge, since we'll calculate its count from this sum.
-                .filter(|&to_bcb| to_bcb != expression_to_bcb)
-                .fold(None, |accum, to_bcb| {
-                    let _span = debug_span!("to_bcb", ?accum, ?to_bcb).entered();
-                    let edge_counter = self.get_or_make_edge_counter(from_bcb, to_bcb);
-                    Some(self.coverage_counters.make_sum_expression(accum, edge_counter))
-                })
-                .expect("there must be at least one other out-edge")
-        };
+        let other_out_edge_counters = successors
+            .iter()
+            .copied()
+            // Skip the chosen edge, since we'll calculate its count from this sum.
+            .filter(|&to_bcb| to_bcb != expression_to_bcb)
+            .map(|to_bcb| self.get_or_make_edge_counter(from_bcb, to_bcb))
+            .collect::<Vec<_>>();
+        let sum_of_all_other_out_edges: BcbCounter = self
+            .coverage_counters
+            .make_sum(&other_out_edge_counters)
+            .expect("there must be at least one other out-edge");
 
         // Now create an expression for the chosen edge, by taking the counter
         // for its source node and subtracting the sum of its sibling out-edges.
@@ -375,20 +374,15 @@ impl<'a> MakeBcbCounters<'a> {
 
         // A BCB with multiple incoming edges can compute its count by ensuring that counters
         // exist for each of those edges, and then adding them up to get a total count.
-        let sum_of_in_edges: BcbCounter = {
-            let _span = debug_span!("sum_of_in_edges", ?bcb).entered();
-            // We avoid calling `self.bcb_predecessors` here so that we can
-            // call methods on `&mut self` inside the fold.
-            self.basic_coverage_blocks.predecessors[bcb]
-                .iter()
-                .copied()
-                .fold(None, |accum, from_bcb| {
-                    let _span = debug_span!("from_bcb", ?accum, ?from_bcb).entered();
-                    let edge_counter = self.get_or_make_edge_counter(from_bcb, bcb);
-                    Some(self.coverage_counters.make_sum_expression(accum, edge_counter))
-                })
-                .expect("there must be at least one in-edge")
-        };
+        let in_edge_counters = self.basic_coverage_blocks.predecessors[bcb]
+            .iter()
+            .copied()
+            .map(|from_bcb| self.get_or_make_edge_counter(from_bcb, bcb))
+            .collect::<Vec<_>>();
+        let sum_of_in_edges: BcbCounter = self
+            .coverage_counters
+            .make_sum(&in_edge_counters)
+            .expect("there must be at least one in-edge");
 
         debug!("{bcb:?} gets a new counter (sum of predecessor counters): {sum_of_in_edges:?}");
         self.coverage_counters.set_bcb_counter(bcb, sum_of_in_edges)

compiler/rustc_mir_transform/src/pass_manager.rs

@@ -42,7 +42,7 @@ fn to_profiler_name(type_name: &'static str) -> &'static str {
 
 // const wrapper for `if let Some((_, tail)) = name.rsplit_once(':') { tail } else { name }`
 const fn c_name(name: &'static str) -> &'static str {
-    // FIXME Simplify the implementation once more `str` methods get const-stable.
+    // FIXME(const-hack) Simplify the implementation once more `str` methods get const-stable.
     // and inline into call site
     let bytes = name.as_bytes();
     let mut i = bytes.len();
@@ -61,7 +61,7 @@ const fn c_name(name: &'static str) -> &'static str {
 /// loop that goes over each available MIR and applies `run_pass`.
 pub(super) trait MirPass<'tcx> {
     fn name(&self) -> &'static str {
-        // FIXME Simplify the implementation once more `str` methods get const-stable.
+        // FIXME(const-hack) Simplify the implementation once more `str` methods get const-stable.
         // See copypaste in `MirLint`
         const {
             let name = std::any::type_name::<Self>();
@@ -89,7 +89,7 @@ pub(super) trait MirPass<'tcx> {
 /// disabled (via the `Lint` adapter).
 pub(super) trait MirLint<'tcx> {
     fn name(&self) -> &'static str {
-        // FIXME Simplify the implementation once more `str` methods get const-stable.
+        // FIXME(const-hack) Simplify the implementation once more `str` methods get const-stable.
         // See copypaste in `MirPass`
         const {
             let name = std::any::type_name::<Self>();

compiler/rustc_next_trait_solver/src/solve/eval_ctxt/canonical.rs

@@ -122,6 +122,21 @@ where
             (certainty, NestedNormalizationGoals::empty())
         };
 
+        if let Certainty::Maybe(cause @ MaybeCause::Overflow { .. }) = certainty {
+            // If we have overflow, it's probable that we're substituting a type
+            // into itself infinitely and any partial substitutions in the query
+            // response are probably not useful anyways, so just return an empty
+            // query response.
+            //
+            // This may prevent us from potentially useful inference, e.g.
+            // 2 candidates, one ambiguous and one overflow, which both
+            // have the same inference constraints.
+            //
+            // Changing this to retain some constraints in the future
+            // won't be a breaking change, so this is good enough for now.
+            return Ok(self.make_ambiguous_response_no_constraints(cause));
+        }
+
         let external_constraints =
             self.compute_external_query_constraints(certainty, normalization_nested_goals);
         let (var_values, mut external_constraints) = (self.var_values, external_constraints)

compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs

@@ -17,7 +17,7 @@ use crate::delegate::SolverDelegate;
 use crate::solve::inspect::{self, ProofTreeBuilder};
 use crate::solve::search_graph::SearchGraph;
 use crate::solve::{
-    CanonicalInput, CanonicalResponse, Certainty, Goal, GoalEvaluationKind, GoalSource, MaybeCause,
+    CanonicalInput, CanonicalResponse, Certainty, Goal, GoalEvaluationKind, GoalSource,
     NestedNormalizationGoals, NoSolution, PredefinedOpaquesData, QueryResult, SolverMode,
     FIXPOINT_STEP_LIMIT,
 };
@@ -370,20 +370,19 @@ where
             canonical_goal,
             &mut goal_evaluation,
         );
-        let canonical_response = match canonical_response {
+        let response = match canonical_response {
             Err(e) => {
                 self.inspect.goal_evaluation(goal_evaluation);
                 return Err(e);
             }
             Ok(response) => response,
         };
 
-        let (normalization_nested_goals, certainty, has_changed) = self
-            .instantiate_response_discarding_overflow(
-                goal.param_env,
-                orig_values,
-                canonical_response,
-            );
+        let has_changed = !response.value.var_values.is_identity_modulo_regions()
+            || !response.value.external_constraints.opaque_types.is_empty();
+
+        let (normalization_nested_goals, certainty) =
+            self.instantiate_and_apply_query_response(goal.param_env, orig_values, response);
         self.inspect.goal_evaluation(goal_evaluation);
         // FIXME: We previously had an assert here that checked that recomputing
         // a goal after applying its constraints did not change its response.
@@ -398,24 +397,6 @@ where
         Ok((normalization_nested_goals, has_changed, certainty))
     }
 
-    fn instantiate_response_discarding_overflow(
-        &mut self,
-        param_env: I::ParamEnv,
-        original_values: Vec<I::GenericArg>,
-        response: CanonicalResponse<I>,
-    ) -> (NestedNormalizationGoals<I>, Certainty, bool) {
-        if let Certainty::Maybe(MaybeCause::Overflow { .. }) = response.value.certainty {
-            return (NestedNormalizationGoals::empty(), response.value.certainty, false);
-        }
-
-        let has_changed = !response.value.var_values.is_identity_modulo_regions()
-            || !response.value.external_constraints.opaque_types.is_empty();
-
-        let (normalization_nested_goals, certainty) =
-            self.instantiate_and_apply_query_response(param_env, original_values, response);
-        (normalization_nested_goals, certainty, has_changed)
-    }
-
     fn compute_goal(&mut self, goal: Goal<I, I::Predicate>) -> QueryResult<I> {
         let Goal { param_env, predicate } = goal;
         let kind = predicate.kind();