7 files changed, 99 insertions, 6 deletions

diff --git a/crates/hir_def/src/data.rs b/crates/hir_def/src/data.rs
index a04f73352..d2bb381be 100644
--- a/crates/hir_def/src/data.rs
+++ b/crates/hir_def/src/data.rs
@@ -22,6 +22,7 @@ pub struct FunctionData {
     pub name: Name,
     pub params: Vec<Interned<TypeRef>>,
     pub ret_type: Interned<TypeRef>,
+    pub async_ret_type: Option<Interned<TypeRef>>,
     pub attrs: Attrs,
     pub visibility: RawVisibility,
     pub abi: Option<Interned<str>>,
@@ -63,6 +64,7 @@ impl FunctionData {
                 })
                 .collect(),
             ret_type: func.ret_type.clone(),
+            async_ret_type: func.async_ret_type.clone(),
             attrs: item_tree.attrs(db, krate, ModItem::from(loc.id.value).into()),
             visibility: item_tree[func.visibility].clone(),
             abi: func.abi.clone(),
diff --git a/crates/hir_def/src/item_tree.rs b/crates/hir_def/src/item_tree.rs
index c4d20c416..227337a8d 100644
--- a/crates/hir_def/src/item_tree.rs
+++ b/crates/hir_def/src/item_tree.rs
@@ -580,6 +580,7 @@ pub struct Function {
     pub abi: Option<Interned<str>>,
     pub params: IdRange<Param>,
     pub ret_type: Interned<TypeRef>,
+    pub async_ret_type: Option<Interned<TypeRef>>,
     pub ast_id: FileAstId<ast::Fn>,
     pub(crate) flags: FnFlags,
 }
diff --git a/crates/hir_def/src/item_tree/lower.rs b/crates/hir_def/src/item_tree/lower.rs
index b83adec46..6208facd5 100644
--- a/crates/hir_def/src/item_tree/lower.rs
+++ b/crates/hir_def/src/item_tree/lower.rs
@@ -356,12 +356,13 @@ impl<'a> Ctx<'a> {
             _ => TypeRef::unit(),
         };
 
-        let ret_type = if func.async_token().is_some() {
+        let (ret_type, async_ret_type) = if func.async_token().is_some() {
+            let async_ret_type = ret_type.clone();
             let future_impl = desugar_future_path(ret_type);
             let ty_bound = Interned::new(TypeBound::Path(future_impl));
-            TypeRef::ImplTrait(vec![ty_bound])
+            (TypeRef::ImplTrait(vec![ty_bound]), Some(async_ret_type))
         } else {
-            ret_type
+            (ret_type, None)
         };
 
         let abi = func.abi().map(lower_abi);
@@ -395,6 +396,7 @@ impl<'a> Ctx<'a> {
             abi,
             params,
             ret_type: Interned::new(ret_type),
+            async_ret_type: async_ret_type.map(Interned::new),
             ast_id,
             flags,
         };
diff --git a/crates/hir_def/src/item_tree/pretty.rs b/crates/hir_def/src/item_tree/pretty.rs
index d1ee697cb..cc9944a22 100644
--- a/crates/hir_def/src/item_tree/pretty.rs
+++ b/crates/hir_def/src/item_tree/pretty.rs
@@ -235,6 +235,7 @@ impl<'a> Printer<'a> {
                     abi,
                     params,
                     ret_type,
+                    async_ret_type: _,
                     ast_id: _,
                     flags,
                 } = &self.tree[it];
diff --git a/crates/hir_def/src/nameres/collector.rs b/crates/hir_def/src/nameres/collector.rs
index 4296c6304..d9d6c91a8 100644
--- a/crates/hir_def/src/nameres/collector.rs
+++ b/crates/hir_def/src/nameres/collector.rs
@@ -477,16 +477,21 @@ impl DefCollector<'_> {
     /// going out of sync with what the build system sees (since we resolve using VFS state, but
     /// Cargo builds only on-disk files). We could and probably should add diagnostics for that.
     fn export_proc_macro(&mut self, def: ProcMacroDef, ast_id: AstId<ast::Fn>) {
+        let kind = def.kind.to_basedb_kind();
         self.exports_proc_macros = true;
         let macro_def = match self.proc_macros.iter().find(|(n, _)| n == &def.name) {
             Some((_, expander)) => MacroDefId {
                 krate: self.def_map.krate,
-                kind: MacroDefKind::ProcMacro(*expander, ast_id),
+                kind: MacroDefKind::ProcMacro(*expander, kind, ast_id),
                 local_inner: false,
             },
             None => MacroDefId {
                 krate: self.def_map.krate,
-                kind: MacroDefKind::ProcMacro(ProcMacroExpander::dummy(self.def_map.krate), ast_id),
+                kind: MacroDefKind::ProcMacro(
+                    ProcMacroExpander::dummy(self.def_map.krate),
+                    kind,
+                    ast_id,
+                ),
                 local_inner: false,
             },
         };
diff --git a/crates/hir_def/src/nameres/proc_macro.rs b/crates/hir_def/src/nameres/proc_macro.rs
index 156598f19..3f095d623 100644
--- a/crates/hir_def/src/nameres/proc_macro.rs
+++ b/crates/hir_def/src/nameres/proc_macro.rs
@@ -18,6 +18,16 @@ pub(super) enum ProcMacroKind {
     Attr,
 }
 
+impl ProcMacroKind {
+    pub(super) fn to_basedb_kind(&self) -> base_db::ProcMacroKind {
+        match self {
+            ProcMacroKind::CustomDerive { .. } => base_db::ProcMacroKind::CustomDerive,
+            ProcMacroKind::FnLike => base_db::ProcMacroKind::FuncLike,
+            ProcMacroKind::Attr => base_db::ProcMacroKind::Attr,
+        }
+    }
+}
+
 impl Attrs {
     #[rustfmt::skip]
     pub(super) fn parse_proc_macro_decl(&self, func_name: &Name) -> Option<ProcMacroDef> {
diff --git a/crates/hir_def/src/nameres/tests/incremental.rs b/crates/hir_def/src/nameres/tests/incremental.rs
index d884a6eb4..7bf152e26 100644
--- a/crates/hir_def/src/nameres/tests/incremental.rs
+++ b/crates/hir_def/src/nameres/tests/incremental.rs
@@ -1,6 +1,8 @@
 use std::sync::Arc;
 
-use base_db::SourceDatabaseExt;
+use base_db::{salsa::SweepStrategy, SourceDatabaseExt};
+
+use crate::{AdtId, ModuleDefId};
 
 use super::*;
 
@@ -163,3 +165,73 @@ m!(Z);
         assert_eq!(n_reparsed_macros, 0);
     }
 }
+
+#[test]
+fn item_tree_prevents_reparsing() {
+    // The `ItemTree` is used by both name resolution and the various queries in `adt.rs` and
+    // `data.rs`. After computing the `ItemTree` and deleting the parse tree, we should be able to
+    // run those other queries without triggering a reparse.
+
+    let (db, pos) = TestDB::with_position(
+        r#"
+pub struct S;
+pub union U {}
+pub enum E {
+    Variant,
+}
+pub fn f(_: S) { $0 }
+pub trait Tr {}
+impl Tr for () {}
+pub const C: u8 = 0;
+pub static ST: u8 = 0;
+pub type Ty = ();
+"#,
+    );
+    let krate = db.test_crate();
+    {
+        let events = db.log_executed(|| {
+            db.file_item_tree(pos.file_id.into());
+        });
+        let n_calculated_item_trees = events.iter().filter(|it| it.contains("item_tree")).count();
+        assert_eq!(n_calculated_item_trees, 1);
+        let n_parsed_files = events.iter().filter(|it| it.contains("parse(")).count();
+        assert_eq!(n_parsed_files, 1);
+    }
+
+    // Delete the parse tree.
+    let sweep = SweepStrategy::default().discard_values().sweep_all_revisions();
+    base_db::ParseQuery.in_db(&db).sweep(sweep);
+
+    {
+        let events = db.log_executed(|| {
+            let crate_def_map = db.crate_def_map(krate);
+            let (_, module_data) = crate_def_map.modules.iter().last().unwrap();
+            assert_eq!(module_data.scope.resolutions().count(), 8);
+            assert_eq!(module_data.scope.impls().count(), 1);
+
+            for imp in module_data.scope.impls() {
+                db.impl_data(imp);
+            }
+
+            for (_, res) in module_data.scope.resolutions() {
+                match res.values.or(res.types).unwrap().0 {
+                    ModuleDefId::FunctionId(f) => drop(db.function_data(f)),
+                    ModuleDefId::AdtId(adt) => match adt {
+                        AdtId::StructId(it) => drop(db.struct_data(it)),
+                        AdtId::UnionId(it) => drop(db.union_data(it)),
+                        AdtId::EnumId(it) => drop(db.enum_data(it)),
+                    },
+                    ModuleDefId::ConstId(it) => drop(db.const_data(it)),
+                    ModuleDefId::StaticId(it) => drop(db.static_data(it)),
+                    ModuleDefId::TraitId(it) => drop(db.trait_data(it)),
+                    ModuleDefId::TypeAliasId(it) => drop(db.type_alias_data(it)),
+                    ModuleDefId::EnumVariantId(_)
+                    | ModuleDefId::ModuleId(_)
+                    | ModuleDefId::BuiltinType(_) => unreachable!(),
+                }
+            }
+        });
+        let n_reparsed_files = events.iter().filter(|it| it.contains("parse(")).count();
+        assert_eq!(n_reparsed_files, 0);
+    }
+}