Auto merge of rust-lang#108861 - b-naber:eager-nll-type-relating, r=lcnr

Make NLL Type Relating Eager

We previously instantiated bound regions in nll type relating lazily. Making this eager is more consistent with how we handle type relating in [`higher_ranked_sub`](https://github.com/rust-lang/rust/blob/0a3b557d528dd7c8a88ceca6f7dc0699b89a3ef4/compiler/rustc_infer/src/infer/higher_ranked/mod.rs#L28) and should allow us to short circuit in case there's structural equality.

Author: bors

compiler/rustc_borrowck/src/lib.rs

@@ -510,16 +510,11 @@ impl<'cx, 'tcx> BorrowckInferCtxt<'cx, 'tcx> {
             .as_var()
             .unwrap_or_else(|| bug!("expected RegionKind::RegionVar on {:?}", next_region));
 
-        if cfg!(debug_assertions) {
+        if cfg!(debug_assertions) && !self.inside_canonicalization_ctxt() {
             debug!("inserting vid {:?} with origin {:?} into var_to_origin", vid, origin);
             let ctxt = get_ctxt_fn();
             let mut var_to_origin = self.reg_var_to_origin.borrow_mut();
-            let prev = var_to_origin.insert(vid, ctxt);
-
-            // This only makes sense if not called in a canonicalization context. If this
-            // ever changes we either want to get rid of `BorrowckInferContext::reg_var_to_origin`
-            // or modify how we track nll region vars for that map.
-            assert!(matches!(prev, None));
+            var_to_origin.insert(vid, ctxt);
         }
 
         next_region
@@ -539,16 +534,11 @@ impl<'cx, 'tcx> BorrowckInferCtxt<'cx, 'tcx> {
             .as_var()
             .unwrap_or_else(|| bug!("expected RegionKind::RegionVar on {:?}", next_region));
 
-        if cfg!(debug_assertions) {
+        if cfg!(debug_assertions) && !self.inside_canonicalization_ctxt() {
             debug!("inserting vid {:?} with origin {:?} into var_to_origin", vid, origin);
             let ctxt = get_ctxt_fn();
             let mut var_to_origin = self.reg_var_to_origin.borrow_mut();
-            let prev = var_to_origin.insert(vid, ctxt);
-
-            // This only makes sense if not called in a canonicalization context. If this
-            // ever changes we either want to get rid of `BorrowckInferContext::reg_var_to_origin`
-            // or modify how we track nll region vars for that map.
-            assert!(matches!(prev, None));
+            var_to_origin.insert(vid, ctxt);
         }
 
         next_region

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -256,11 +256,12 @@ fn sccs_info<'cx, 'tcx>(
 
     let mut var_to_origin_sorted = var_to_origin.clone().into_iter().collect::<Vec<_>>();
     var_to_origin_sorted.sort_by_key(|vto| vto.0);
-    let mut debug_str = "region variables to origins:\n".to_string();
+
+    let mut reg_vars_to_origins_str = "region variables to origins:\n".to_string();
     for (reg_var, origin) in var_to_origin_sorted.into_iter() {
-        debug_str.push_str(&format!("{:?}: {:?}\n", reg_var, origin));
+        reg_vars_to_origins_str.push_str(&format!("{:?}: {:?}\n", reg_var, origin));
     }
-    debug!(debug_str);
+    debug!("{}", reg_vars_to_origins_str);
 
     let num_components = sccs.scc_data().ranges().len();
     let mut components = vec![FxIndexSet::default(); num_components];
@@ -275,12 +276,12 @@ fn sccs_info<'cx, 'tcx>(
     for (scc_idx, reg_vars_origins) in components.iter().enumerate() {
         let regions_info = reg_vars_origins.clone().into_iter().collect::<Vec<_>>();
         components_str.push_str(&format!(
-            "{:?}: {:?})",
+            "{:?}: {:?},\n)",
             ConstraintSccIndex::from_usize(scc_idx),
             regions_info,
         ))
     }
-    debug!(components_str);
+    debug!("{}", components_str);
 
     // calculate the best representative for each component
     let components_representatives = components

compiler/rustc_borrowck/src/type_check/relate_tys.rs

@@ -132,9 +132,12 @@ impl<'tcx> TypeRelatingDelegate<'tcx> for NllTypeRelatingDelegate<'_, '_, 'tcx>
 
         let reg_var =
             reg.as_var().unwrap_or_else(|| bug!("expected region {:?} to be of kind ReVar", reg));
-        let mut var_to_origin = self.type_checker.infcx.reg_var_to_origin.borrow_mut();
-        let prev = var_to_origin.insert(reg_var, RegionCtxt::Placeholder(reg_info));
-        assert!(matches!(prev, None));
+
+        if cfg!(debug_assertions) && !self.type_checker.infcx.inside_canonicalization_ctxt() {
+            let mut var_to_origin = self.type_checker.infcx.reg_var_to_origin.borrow_mut();
+            debug!(?reg_var);
+            var_to_origin.insert(reg_var, RegionCtxt::Placeholder(reg_info));
+        }
 
         reg
     }
@@ -149,14 +152,9 @@ impl<'tcx> TypeRelatingDelegate<'tcx> for NllTypeRelatingDelegate<'_, '_, 'tcx>
         let reg_var =
             reg.as_var().unwrap_or_else(|| bug!("expected region {:?} to be of kind ReVar", reg));
 
-        if cfg!(debug_assertions) {
+        if cfg!(debug_assertions) && !self.type_checker.infcx.inside_canonicalization_ctxt() {
             let mut var_to_origin = self.type_checker.infcx.reg_var_to_origin.borrow_mut();
-            let prev = var_to_origin.insert(reg_var, RegionCtxt::Existential(None));
-
-            // It only makes sense to track region vars in non-canonicalization contexts. If this
-            // ever changes we either want to get rid of `BorrowckInferContext::reg_var_to_origin`
-            // or modify how we track nll region vars for that map.
-            assert!(matches!(prev, None));
+            var_to_origin.insert(reg_var, RegionCtxt::Existential(None));
         }
 
         reg

compiler/rustc_infer/src/infer/at.rs

@@ -30,6 +30,8 @@ use super::*;
 use rustc_middle::ty::relate::{Relate, TypeRelation};
 use rustc_middle::ty::{Const, ImplSubject};
 
+use std::cell::Cell;
+
 /// Whether we should define opaque types or just treat them opaquely.
 ///
 /// Currently only used to prevent predicate matching from matching anything
@@ -82,6 +84,7 @@ impl<'tcx> InferCtxt<'tcx> {
             in_snapshot: self.in_snapshot.clone(),
             universe: self.universe.clone(),
             intercrate: self.intercrate,
+            inside_canonicalization_ctxt: Cell::new(self.inside_canonicalization_ctxt()),
         }
     }
 }

compiler/rustc_infer/src/infer/canonical/canonicalizer.rs

@@ -561,6 +561,8 @@ impl<'cx, 'tcx> Canonicalizer<'cx, 'tcx> {
     where
         V: TypeFoldable<TyCtxt<'tcx>>,
     {
+        let _inside_canonical_ctxt_guard = infcx.set_canonicalization_ctxt();
+
         let needs_canonical_flags = if canonicalize_region_mode.any() {
             TypeFlags::NEEDS_INFER |
             TypeFlags::HAS_FREE_REGIONS | // `HAS_RE_PLACEHOLDER` implies `HAS_FREE_REGIONS`

compiler/rustc_infer/src/infer/mod.rs

@@ -39,6 +39,7 @@ use rustc_span::Span;
 
 use std::cell::{Cell, RefCell};
 use std::fmt;
+use std::ops::Drop;
 
 use self::combine::CombineFields;
 use self::error_reporting::TypeErrCtxt;
@@ -342,6 +343,11 @@ pub struct InferCtxt<'tcx> {
     /// there is no type that the user could *actually name* that
     /// would satisfy it. This avoids crippling inference, basically.
     pub intercrate: bool,
+
+    /// Flag that is set when we enter canonicalization. Used for debugging to ensure
+    /// that we only collect region information for `BorrowckInferCtxt::reg_var_to_origin`
+    /// inside non-canonicalization contexts.
+    inside_canonicalization_ctxt: Cell<bool>,
 }
 
 /// See the `error_reporting` module for more details.
@@ -633,6 +639,7 @@ impl<'tcx> InferCtxtBuilder<'tcx> {
             skip_leak_check: Cell::new(false),
             universe: Cell::new(ty::UniverseIndex::ROOT),
             intercrate,
+            inside_canonicalization_ctxt: Cell::new(false),
         }
     }
 }
@@ -1728,6 +1735,31 @@ impl<'tcx> InferCtxt<'tcx> {
             }
         }
     }
+
+    pub fn inside_canonicalization_ctxt(&self) -> bool {
+        self.inside_canonicalization_ctxt.get()
+    }
+
+    pub fn set_canonicalization_ctxt(&self) -> CanonicalizationCtxtGuard<'_, 'tcx> {
+        let prev_ctxt = self.inside_canonicalization_ctxt();
+        self.inside_canonicalization_ctxt.set(true);
+        CanonicalizationCtxtGuard { prev_ctxt, infcx: self }
+    }
+
+    fn set_canonicalization_ctxt_to(&self, ctxt: bool) {
+        self.inside_canonicalization_ctxt.set(ctxt);
+    }
+}
+
+pub struct CanonicalizationCtxtGuard<'cx, 'tcx> {
+    prev_ctxt: bool,
+    infcx: &'cx InferCtxt<'tcx>,
+}
+
+impl<'cx, 'tcx> Drop for CanonicalizationCtxtGuard<'cx, 'tcx> {
+    fn drop(&mut self) {
+        self.infcx.set_canonicalization_ctxt_to(self.prev_ctxt)
+    }
 }
 
 impl<'tcx> TypeErrCtxt<'_, 'tcx> {