Merge #4947

4947: Replace `impls_in_trait` query with smarter use of `CrateImplDefs` r=matklad a=jonas-schievink

`impls_in_trait` was allocating a whopping ~400 MB of RAM when running analysis-stats on r-a itself.

Remove it, instead adding a query that computes a summary `CrateImplDefs` map for all transitive dependencies. This can probably still be made more efficient, but this already reduces the peak memory usage by 25% without much performance impact on analysis-stats.

**Before**:

```
Total: 34.962107188s, 2083mb allocated 2141mb resident
   422mb ImplsForTraitQuery (deps)
   250mb CrateDefMapQueryQuery
   147mb MacroArgQuery
   140mb TraitSolveQuery (deps)
    68mb InferQueryQuery (deps)
    62mb ImplDatumQuery (deps)
```

**After**:

```
Total: 35.261100358s, 1520mb allocated 1569mb resident
   250mb CrateDefMapQueryQuery
   147mb MacroArgQuery
   144mb TraitSolveQuery (deps)
    68mb InferQueryQuery (deps)
    61mb ImplDatumQuery (deps)
    45mb BodyQuery
    45mb ImplDatumQuery
```

Co-authored-by: Jonas Schievink <[email protected]>

1 files changed, 61 insertions, 8 deletions

diff --git a/crates/ra_hir_ty/src/method_resolution.rs b/crates/ra_hir_ty/src/method_resolution.rs
index e83b39456..ed638c195 100644
--- a/crates/ra_hir_ty/src/method_resolution.rs
+++ b/crates/ra_hir_ty/src/method_resolution.rs
@@ -38,18 +38,53 @@ impl TyFingerprint {
     }
 }
 
+/// A queryable and mergeable collection of impls.
 #[derive(Debug, PartialEq, Eq)]
 pub struct CrateImplDefs {
-    impls: FxHashMap<TyFingerprint, Vec<ImplId>>,
+    inherent_impls: FxHashMap<TyFingerprint, Vec<ImplId>>,
     impls_by_trait: FxHashMap<TraitId, FxHashMap<Option<TyFingerprint>, Vec<ImplId>>>,
 }
 
 impl CrateImplDefs {
     pub(crate) fn impls_in_crate_query(db: &dyn HirDatabase, krate: CrateId) -> Arc<CrateImplDefs> {
         let _p = profile("impls_in_crate_query");
-        let mut res =
-            CrateImplDefs { impls: FxHashMap::default(), impls_by_trait: FxHashMap::default() };
+        let mut res = CrateImplDefs {
+            inherent_impls: FxHashMap::default(),
+            impls_by_trait: FxHashMap::default(),
+        };
+        res.fill(db, krate);
+
+        Arc::new(res)
+    }
+
+    /// Collects all impls from transitive dependencies of `krate` that may be used by `krate`.
+    ///
+    /// The full set of impls that can be used by `krate` is the returned map plus all the impls
+    /// from `krate` itself.
+    pub(crate) fn impls_from_deps_query(
+        db: &dyn HirDatabase,
+        krate: CrateId,
+    ) -> Arc<CrateImplDefs> {
+        let _p = profile("impls_from_deps_query");
+        let crate_graph = db.crate_graph();
+        let mut res = CrateImplDefs {
+            inherent_impls: FxHashMap::default(),
+            impls_by_trait: FxHashMap::default(),
+        };
 
+        // For each dependency, calculate `impls_from_deps` recursively, then add its own
+        // `impls_in_crate`.
+        // As we might visit crates multiple times, `merge` has to deduplicate impls to avoid
+        // wasting memory.
+        for dep in &crate_graph[krate].dependencies {
+            res.merge(&db.impls_from_deps(dep.crate_id));
+            res.merge(&db.impls_in_crate(dep.crate_id));
+        }
+
+        Arc::new(res)
+    }
+
+    fn fill(&mut self, db: &dyn HirDatabase, krate: CrateId) {
         let crate_def_map = db.crate_def_map(krate);
         for (_module_id, module_data) in crate_def_map.modules.iter() {
             for impl_id in module_data.scope.impls() {
@@ -57,7 +92,7 @@ impl CrateImplDefs {
                     Some(tr) => {
                         let self_ty = db.impl_self_ty(impl_id);
                         let self_ty_fp = TyFingerprint::for_impl(&self_ty.value);
-                        res.impls_by_trait
+                        self.impls_by_trait
                             .entry(tr.value.trait_)
                             .or_default()
                             .entry(self_ty_fp)
@@ -67,18 +102,36 @@ impl CrateImplDefs {
                     None => {
                         let self_ty = db.impl_self_ty(impl_id);
                         if let Some(self_ty_fp) = TyFingerprint::for_impl(&self_ty.value) {
-                            res.impls.entry(self_ty_fp).or_default().push(impl_id);
+                            self.inherent_impls.entry(self_ty_fp).or_default().push(impl_id);
                         }
                     }
                 }
             }
         }
+    }
 
-        Arc::new(res)
+    fn merge(&mut self, other: &Self) {
+        for (fp, impls) in &other.inherent_impls {
+            let vec = self.inherent_impls.entry(*fp).or_default();
+            vec.extend(impls);
+            vec.sort();
+            vec.dedup();
+        }
+
+        for (trait_, other_map) in &other.impls_by_trait {
+            let map = self.impls_by_trait.entry(*trait_).or_default();
+            for (fp, impls) in other_map {
+                let vec = map.entry(*fp).or_default();
+                vec.extend(impls);
+                vec.sort();
+                vec.dedup();
+            }
+        }
     }
+
     pub fn lookup_impl_defs(&self, ty: &Ty) -> impl Iterator<Item = ImplId> + '_ {
         let fingerprint = TyFingerprint::for_impl(ty);
-        fingerprint.and_then(|f| self.impls.get(&f)).into_iter().flatten().copied()
+        fingerprint.and_then(|f| self.inherent_impls.get(&f)).into_iter().flatten().copied()
     }
 
     pub fn lookup_impl_defs_for_trait(&self, tr: TraitId) -> impl Iterator<Item = ImplId> + '_ {
@@ -110,7 +163,7 @@ impl CrateImplDefs {
     }
 
     pub fn all_impls<'a>(&'a self) -> impl Iterator<Item = ImplId> + 'a {
-        self.impls
+        self.inherent_impls
             .values()
             .chain(self.impls_by_trait.values().flat_map(|m| m.values()))
             .flatten()