yet another db api

crates/libanalysis/src/db/imp.rs

@@ -0,0 +1,155 @@
+use std::{
+    sync::Arc,
+    any::Any,
+    hash::{Hash, Hasher},
+    collections::hash_map::{DefaultHasher, HashMap},
+    iter,
+};
+use salsa;
+use {FileId, imp::FileResolverImp};
+use super::{State, Query, QueryCtx};
+
+pub(super) type Data = Arc<Any + Send + Sync + 'static>;
+
+#[derive(Debug)]
+pub(super) struct Db {
+    names: Arc<HashMap<salsa::QueryTypeId, &'static str>>,
+    pub(super) imp: salsa::Db<State, Data>,
+}
+
+impl Db {
+    pub(super) fn new(mut reg: QueryRegistry) -> Db {
+        let config = reg.config.take().unwrap();
+        Db {
+            names: Arc::new(reg.names),
+            imp: salsa::Db::new(config, State::default())
+        }
+    }
+    pub(crate) fn with_changes(&self, new_state: State, changed_files: &[FileId], resolver_changed: bool) -> Db {
+        let names = self.names.clone();
+        let mut invalidations = salsa::Invalidations::new();
+        invalidations.invalidate(FILE_TEXT, changed_files.iter().map(hash).map(salsa::InputFingerprint));
+        if resolver_changed {
+            invalidations.invalidate(FILE_SET, iter::once(salsa::InputFingerprint(hash(&()))));
+        } else {
+            invalidations.invalidate(FILE_SET, iter::empty());
+        }
+        let imp = self.imp.with_ground_data(
+            new_state,
+            invalidations,
+        );
+        Db { names, imp }
+    }
+    pub(super) fn extract_trace(&self, ctx: &salsa::QueryCtx<State, Data>) -> Vec<&'static str> {
+        ctx.trace().into_iter().map(|it| self.names[&it]).collect()
+    }
+}
+
+pub(crate) trait EvalQuery {
+    type Params;
+    type Output;
+    fn query_type(&self) -> salsa::QueryTypeId;
+    fn f(&self) -> salsa::QueryFn<State, Data>;
+    fn get(&self, &QueryCtx, Self::Params) -> Arc<Self::Output>;
+}
+
+impl<T, R> EvalQuery for Query<T, R>
+where
+    T: Hash + Send + Sync + 'static,
+    R: Hash + Send + Sync + 'static,
+{
+    type Params = T;
+    type Output = R;
+    fn query_type(&self) -> salsa::QueryTypeId {
+        salsa::QueryTypeId(self.0)
+    }
+    fn f(&self) -> salsa::QueryFn<State, Data> {
+        let f = self.1;
+        Box::new(move |ctx, data| {
+            let ctx = QueryCtx { imp: ctx };
+            let data: &T = data.downcast_ref().unwrap();
+            let res = f(ctx, data);
+            let h = hash(&res);
+            (Arc::new(res), salsa::OutputFingerprint(h))
+        })
+    }
+    fn get(&self, ctx: &QueryCtx, params: Self::Params) -> Arc<Self::Output> {
+        let query_id = salsa::QueryId(
+            self.query_type(),
+            salsa::InputFingerprint(hash(&params)),
+        );
+        let res = ctx.imp.get(query_id, Arc::new(params));
+        res.downcast().unwrap()
+    }
+}
+
+pub(super) struct QueryRegistry {
+    config: Option<salsa::QueryConfig<State, Data>>,
+    names: HashMap<salsa::QueryTypeId, &'static str>,
+}
+
+impl QueryRegistry {
+    pub(super) fn new() -> QueryRegistry {
+        let mut config = salsa::QueryConfig::<State, Data>::new();
+        config = config.with_ground_query(
+            FILE_TEXT, Box::new(|state, params| {
+                let file_id: &FileId = params.downcast_ref().unwrap();
+                let res = state.file_map[file_id].clone();
+                let fingerprint = salsa::OutputFingerprint(hash(&res));
+                (res, fingerprint)
+            })
+        );
+        config = config.with_ground_query(
+            FILE_SET, Box::new(|state, _params| {
+                let file_ids: Vec<FileId> = state.file_map.keys().cloned().collect();
+                let hash = hash(&file_ids);
+                let file_resolver = state.file_resolver.clone();
+                let res = (file_ids, file_resolver);
+                let fingerprint = salsa::OutputFingerprint(hash);
+                (Arc::new(res), fingerprint)
+            })
+        );
+        let mut names = HashMap::new();
+        names.insert(FILE_TEXT, "FILE_TEXT");
+        names.insert(FILE_SET, "FILE_SET");
+        QueryRegistry { config: Some(config), names }
+    }
+    pub(super) fn add<Q: EvalQuery>(&mut self, q: Q, name: &'static str) {
+        let id = q.query_type();
+        let prev = self.names.insert(id, name);
+        assert!(prev.is_none(), "duplicate query: {:?}", id);
+        let config = self.config.take().unwrap();
+        let config = config.with_query(id, q.f());
+        self.config= Some(config);
+    }
+    pub(super) fn finish(mut self) -> salsa::QueryConfig<State, Data> {
+        self.config.take().unwrap()
+    }
+}
+
+fn hash<T: Hash>(x: &T) -> u64 {
+    let mut hasher = DefaultHasher::new();
+    x.hash(&mut hasher);
+    hasher.finish()
+}
+
+const FILE_TEXT: salsa::QueryTypeId = salsa::QueryTypeId(0);
+pub(super) fn file_text(ctx: QueryCtx, file_id: FileId) -> Arc<String> {
+    let query_id = salsa::QueryId(
+        FILE_TEXT,
+        salsa::InputFingerprint(hash(&file_id)),
+    );
+    let res = ctx.imp.get(query_id, Arc::new(file_id));
+    res.downcast().unwrap()
+}
+
+const FILE_SET: salsa::QueryTypeId = salsa::QueryTypeId(1);
+pub(super) fn file_set(ctx: QueryCtx) -> Arc<(Vec<FileId>, FileResolverImp)> {
+    let query_id = salsa::QueryId(
+        FILE_SET,
+        salsa::InputFingerprint(hash(&())),
+    );
+    let res = ctx.imp.get(query_id, Arc::new(()));
+    res.downcast().unwrap()
+}
+

crates/libanalysis/src/db/mod.rs

@@ -1,195 +1,99 @@
-mod queries;
+mod imp;
 
 use std::{
-    hash::{Hash},
     sync::Arc,
-    fmt::Debug,
-    any::Any,
-    iter,
 };
 use im;
 use salsa;
-use {
+use {FileId, imp::FileResolverImp};
-    FileId,
-    imp::{FileResolverImp},
-};
 
-
+#[derive(Debug, Default, Clone)]
-#[derive(Clone, Default)]
 pub(crate) struct State {
-    pub(crate) resolver: FileResolverImp,
+    pub(crate) file_map: im::HashMap<FileId, Arc<String>>,
-    pub(crate) file_map: im::HashMap<FileId, Arc<str>>,
+    pub(crate) file_resolver: FileResolverImp
-}
-
-type Data = Arc<Any + Send + Sync + 'static>;
-
-pub(crate) struct QueryCtx<'a> {
-    inner: &'a salsa::QueryCtx<State, Data>
 }
 
+#[derive(Debug)]
 pub(crate) struct Db {
-    inner: salsa::Db<State, Data>
+    imp: imp::Db,
 }
 
-struct GroundQuery<T, R> {
+#[derive(Clone, Copy)]
-    id: u16,
+pub(crate) struct QueryCtx<'a> {
-    f: fn(&State, &T) -> R,
+    imp: &'a salsa::QueryCtx<State, imp::Data>,
-    h: fn(&R) -> u64,
 }
 
-pub(crate) struct Query<T, R> {
+pub(crate) struct Query<T, R>(pub(crate) u16, pub(crate) fn(QueryCtx, &T) -> R);
-    pub(crate) id: u16,
+
-    pub(crate) f: fn(QueryCtx, &T) -> R,
+pub(crate) struct QueryRegistry {
+    imp: imp::QueryRegistry,
 }
 
 impl Db {
     pub(crate) fn new() -> Db {
-        let state = Default::default();
+        let reg = QueryRegistry::new();
-        Db { inner: salsa::Db::new(query_config(), state) }
+        Db { imp: imp::Db::new(reg.imp) }
     }
     pub(crate) fn state(&self) -> &State {
-        self.inner.ground_data()
+        self.imp.imp.ground_data()
     }
-    pub(crate) fn with_state(
+    pub(crate) fn with_changes(&self, new_state: State, changed_files: &[FileId], resolver_changed: bool) -> Db {
-        &self,
+        Db { imp: self.imp.with_changes(new_state, changed_files, resolver_changed) }
-        new_state: State,
-        updated_files: &[FileId],
-        file_set_changed: bool,
-    ) -> Db {
-        let mut inv = salsa::Invalidations::new();
-        if file_set_changed {
-            inv.invalidate(
-                salsa::QueryTypeId(queries::FILE_SET.id),
-                iter::once(salsa::InputFingerprint(hash(&()))),
-            );
-        } else {
-            inv.invalidate(
-                salsa::QueryTypeId(queries::FILE_SET.id),
-                iter::empty(),
-            );
     }
-        inv.invalidate(
+    pub(crate) fn make_query<F: FnOnce(QueryCtx) -> R, R>(&self, f: F) -> R {
-            salsa::QueryTypeId(queries::FILE_TEXT.id),
+        let ctx = QueryCtx { imp: &self.imp.imp.query_ctx() };
-            updated_files.iter().map(hash).map(salsa::InputFingerprint),
+        f(ctx)
-        );
-        Db { inner: self.inner.with_ground_data(new_state, inv) }
     }
-    pub(crate) fn get<T, R>(&self, q: Query<T, R>, params: T) -> (Arc<R>, Vec<u16>)
+    pub(crate) fn trace_query<F: FnOnce(QueryCtx) -> R, R>(&self, f: F) -> (R, Vec<&'static str>) {
-    where
+        let ctx = QueryCtx { imp: &self.imp.imp.query_ctx() };
-        T: Hash + Send + Sync + 'static,
+        let res = f(ctx);
-        R: Send + Sync + 'static,
+        let trace = self.imp.extract_trace(ctx.imp);
-    {
+        (res, trace)
-        let query_id = salsa::QueryId(
-            salsa::QueryTypeId(q.id),
-            salsa::InputFingerprint(hash(&params)),
-        );
-        let params = Arc::new(params);
-        let (res, events) = self.inner.get(query_id, params);
-        let res = res.downcast().unwrap();
-        let events = events.into_iter().map(|it| it.0).collect();
-        (res, events)
     }
-
 }
 
 impl<'a> QueryCtx<'a> {
-    fn get_g<T, R>(&self, q: GroundQuery<T, R>, params: T) -> Arc<R>
+    pub(crate) fn get<Q: imp::EvalQuery>(&self, q: Q, params: Q::Params) -> Arc<Q::Output> {
-    where
+        q.get(self, params)
-        T: Hash + Send + Sync + 'static,
-        R: Send + Sync + 'static,
-     {
-        let query_id = salsa::QueryId(
-            salsa::QueryTypeId(q.id),
-            salsa::InputFingerprint(hash(&params)),
-        );
-        let res = self.inner.get(query_id, Arc::new(params));
-        res.downcast().unwrap()
-    }
-    pub(crate) fn get<T, R>(&self, q: Query<T, R>, params: T) -> Arc<R>
-    where
-        T: Hash + Send + Sync + 'static,
-        R: Send + Sync + 'static,
-     {
-        let query_id = salsa::QueryId(
-            salsa::QueryTypeId(q.id),
-            salsa::InputFingerprint(hash(&params)),
-        );
-        let res = self.inner.get(query_id, Arc::new(params));
-        res.downcast().unwrap()
     }
 }
 
-fn query_config() -> salsa::QueryConfig<State, Data> {
+pub(crate) fn file_text(ctx: QueryCtx, file_id: FileId) -> Arc<String> {
-    let mut res = salsa::QueryConfig::new();
+    imp::file_text(ctx, file_id)
-    let queries: Vec<BoxedGroundQuery> = vec![
-        queries::FILE_TEXT.into(),
-        queries::FILE_SET.into(),
-    ];
-    for q in queries {
-        res = res.with_ground_query(q.query_type, q.f)
-    }
-    let mut queries: Vec<BoxedQuery> = vec![
-        queries::FILE_SYNTAX.into(),
-    ];
-    ::module_map_db::queries(&mut queries);
-    for q in queries {
-        res = res.with_query(q.query_type, q.f);
-    }
-    res
 }
 
-struct BoxedGroundQuery {
+pub(crate) fn file_set(ctx: QueryCtx) -> Arc<(Vec<FileId>, FileResolverImp)> {
-    query_type: salsa::QueryTypeId,
+    imp::file_set(ctx)
-    f: Box<Fn(&State, &Data) -> (Data, salsa::OutputFingerprint) + Send + Sync + 'static>,
+}
+pub(crate) use self::queries::file_syntax;
+
+mod queries {
+    use libsyntax2::File;
+    use {FileId};
+    use super::{Query, QueryCtx, QueryRegistry, file_text};
+
+    pub(crate) fn register_queries(reg: &mut QueryRegistry) {
+        reg.add(FILE_SYNTAX, "FILE_SYNTAX")
     }
 
-impl<T, R> From<GroundQuery<T, R>> for BoxedGroundQuery
+    pub(crate) fn file_syntax(ctx: QueryCtx, file_id: FileId) -> File {
-where
+        (&*ctx.get(FILE_SYNTAX, file_id)).clone()
-    T: Send + Sync + 'static,
-    R: Send + Sync + 'static,
-{
-    fn from(q: GroundQuery<T, R>) -> BoxedGroundQuery
-    {
-        BoxedGroundQuery {
-            query_type: salsa::QueryTypeId(q.id),
-            f: Box::new(move |state, data| {
-                let data: &T = data.downcast_ref().unwrap();
-                let res = (q.f)(state, data);
-                let h = (q.h)(&res);
-                (Arc::new(res), salsa::OutputFingerprint(h))
-            })
-        }
-    }
     }
 
-pub(crate) struct BoxedQuery {
+    pub(super) const FILE_SYNTAX: Query<FileId, File> = Query(16, |ctx, file_id: &FileId| {
-    query_type: salsa::QueryTypeId,
+        let text = file_text(ctx, *file_id);
-    f: Box<Fn(&salsa::QueryCtx<State, Data>, &Data) -> (Data, salsa::OutputFingerprint) + Send + Sync + 'static>,
+        File::parse(&*text)
+    });
 }
 
-impl<T, R> From<Query<T, R>> for BoxedQuery
+impl QueryRegistry {
-where
+    fn new() -> QueryRegistry {
-    T: Hash + Send + Sync + 'static,
+        let mut reg = QueryRegistry { imp: imp::QueryRegistry::new() };
-    R: Hash + Send + Sync + 'static,
+        queries::register_queries(&mut reg);
-{
+        ::module_map_db::register_queries(&mut reg);
-    fn from(q: Query<T, R>) -> BoxedQuery
+        reg
-    {
+    }
-        BoxedQuery {
+    pub(crate) fn add<Q: imp::EvalQuery>(&mut self, q: Q, name: &'static str) {
-            query_type: salsa::QueryTypeId(q.id),
+        self.imp.add(q, name)
-            f: Box::new(move |ctx, data| {
-                let ctx = QueryCtx { inner: ctx };
-                let data: &T = data.downcast_ref().unwrap();
-                let res = (q.f)(ctx, data);
-                let h = hash(&res);
-                (Arc::new(res), salsa::OutputFingerprint(h))
-            })
     }
 }
-}
-
-fn hash<T: ::std::hash::Hash>(x: &T) -> u64 {
-    use std::hash::Hasher;
-    let mut hasher = ::std::collections::hash_map::DefaultHasher::new();
-    ::std::hash::Hash::hash(x, &mut hasher);
-    hasher.finish()
-}

crates/libanalysis/src/db/queries.rs

@@ -1,43 +0,0 @@
-use std::sync::Arc;
-use libsyntax2::{File};
-use {
-    FileId, FileResolverImp,
-    db::{Query, GroundQuery, QueryCtx, hash},
-};
-
-
-impl<'a> QueryCtx<'a> {
-    pub(crate) fn file_set(&self) -> Arc<(Vec<FileId>, FileResolverImp)> {
-        self.get_g(FILE_SET, ())
-    }
-    pub(crate) fn file_text(&self, file_id: FileId) -> Arc<str> {
-        Arc::clone(&*self.get_g(FILE_TEXT, file_id))
-    }
-    pub(crate) fn file_syntax(&self, file_id: FileId) -> File {
-        (&*self.get(FILE_SYNTAX, file_id)).clone()
-    }
-}
-
-pub(super) const FILE_TEXT: GroundQuery<FileId, Arc<str>> = GroundQuery {
-    id: 10,
-    f: |state, id| state.file_map[&id].clone(),
-    h: hash,
-};
-
-pub(super) const FILE_SET: GroundQuery<(), (Vec<FileId>, FileResolverImp)> = GroundQuery {
-    id: 11,
-    f: |state, &()| {
-        let files = state.file_map.keys().cloned().collect();
-        let resolver = state.resolver.clone();
-        (files, resolver)
-    },
-    h: |(files, _)| hash(files),
-};
-
-pub(super) const FILE_SYNTAX: Query<FileId, File> = Query {
-    id: 20,
-    f: |ctx, file_id: &FileId| {
-        let text = ctx.file_text(*file_id);
-        File::parse(&*text)
-    }
-};

crates/libanalysis/src/module_map_db/mod.rs

@@ -4,15 +4,16 @@ use std::sync::Arc;
 use {
     FileId,
     db::{
-        BoxedQuery, Query, QueryCtx
+        Query, QueryRegistry, QueryCtx,
+        file_syntax, file_set
     },
     module_map::resolve_submodule,
 };
 
-pub(crate) fn queries(acc: &mut Vec<BoxedQuery>) {
+pub(crate) fn register_queries(reg: &mut QueryRegistry) {
-    acc.push(MODULE_DESCR.into());
+    reg.add(MODULE_DESCR, "MODULE_DESCR");
-    acc.push(RESOLVE_SUBMODULE.into());
+    reg.add(RESOLVE_SUBMODULE, "RESOLVE_SUBMODULE");
-    acc.push(PARENT_MODULE.into());
+    reg.add(PARENT_MODULE, "PARENT_MODULE");
 }
 
 impl<'a> QueryCtx<'a> {
@@ -24,26 +25,18 @@ impl<'a> QueryCtx<'a> {
     }
 }
 
-pub(crate) const MODULE_DESCR: Query<FileId, descr::ModuleDescr> = Query {
+const MODULE_DESCR: Query<FileId, descr::ModuleDescr> = Query(30, |ctx, &file_id| {
-    id: 30,
+    let file = file_syntax(ctx, file_id);
-    f: |ctx, &file_id| {
-        let file = ctx.file_syntax(file_id);
     descr::ModuleDescr::new(file.ast())
-    }
+});
-};
 
-pub(crate) const RESOLVE_SUBMODULE: Query<(FileId, descr::Submodule), Vec<FileId>> = Query {
+const RESOLVE_SUBMODULE: Query<(FileId, descr::Submodule), Vec<FileId>> = Query(31, |ctx, params| {
-    id: 31,
+    let files = file_set(ctx);
-    f: |ctx, params| {
-        let files = ctx.file_set();
     resolve_submodule(params.0, &params.1.name, &files.1).0
-    }
+});
-};
 
-pub(crate) const PARENT_MODULE: Query<FileId, Vec<FileId>> = Query {
+const PARENT_MODULE: Query<FileId, Vec<FileId>> = Query(40, |ctx, file_id| {
-    id: 40,
+    let files = file_set(ctx);
-    f: |ctx, file_id| {
-        let files = ctx.file_set();
     let res = files.0.iter()
         .map(|&parent_id| (parent_id, ctx.module_descr(parent_id)))
         .filter(|(parent_id, descr)| {
@@ -57,8 +50,7 @@ pub(crate) const PARENT_MODULE: Query<FileId, Vec<FileId>> = Query {
         .map(|(id, _)| id)
         .collect();
     res
-    }
+});
-};
 
 #[cfg(test)]
 mod tests {
@@ -107,34 +99,36 @@ mod tests {
             self.next_file_id += 1;
             self.fm.insert(file_id, RelativePathBuf::from(&path[1..]));
             let mut new_state = self.db.state().clone();
-            new_state.file_map.insert(file_id, text.to_string().into_boxed_str().into());
+            new_state.file_map.insert(file_id, Arc::new(text.to_string()));
-            new_state.resolver = FileResolverImp::new(
+            new_state.file_resolver = FileResolverImp::new(
                 Arc::new(FileMap(self.fm.clone()))
             );
-            self.db = self.db.with_state(new_state, &[file_id], true);
+            self.db = self.db.with_changes(new_state, &[file_id], true);
             file_id
         }
         fn remove_file(&mut self, file_id: FileId) {
             self.fm.remove(&file_id);
             let mut new_state = self.db.state().clone();
             new_state.file_map.remove(&file_id);
-            new_state.resolver = FileResolverImp::new(
+            new_state.file_resolver = FileResolverImp::new(
                 Arc::new(FileMap(self.fm.clone()))
             );
-            self.db = self.db.with_state(new_state, &[file_id], true);
+            self.db = self.db.with_changes(new_state, &[file_id], true);
         }
         fn change_file(&mut self, file_id: FileId, new_text: &str) {
             let mut new_state = self.db.state().clone();
-            new_state.file_map.insert(file_id, new_text.to_string().into_boxed_str().into());
+            new_state.file_map.insert(file_id, Arc::new(new_text.to_string()));
-            self.db = self.db.with_state(new_state, &[file_id], false);
+            self.db = self.db.with_changes(new_state, &[file_id], false);
         }
         fn check_parent_modules(
             &self,
             file_id: FileId,
             expected: &[FileId],
-            queries: &[(u16, u64)]
+            queries: &[(&'static str, u64)]
         ) {
-            let (actual, events) = self.db.get(PARENT_MODULE, file_id);
+            let (actual, events) = self.db.trace_query(|ctx| {
+                ctx.get(PARENT_MODULE, file_id)
+            });
             assert_eq!(actual.as_slice(), expected);
             let mut counts = HashMap::new();
             events.into_iter()
@@ -156,25 +150,25 @@ mod tests {
     fn test_parent_module() {
         let mut f = Fixture::new();
         let foo = f.add_file("/foo.rs", "");
-        f.check_parent_modules(foo, &[], &[(MODULE_DESCR.id, 1)]);
+        f.check_parent_modules(foo, &[], &[("MODULE_DESCR", 1)]);
 
         let lib = f.add_file("/lib.rs", "mod foo;");
-        f.check_parent_modules(foo, &[lib], &[(MODULE_DESCR.id, 1)]);
+        f.check_parent_modules(foo, &[lib], &[("MODULE_DESCR", 1)]);
-        f.check_parent_modules(foo, &[lib], &[(MODULE_DESCR.id, 0)]);
+        f.check_parent_modules(foo, &[lib], &[("MODULE_DESCR", 0)]);
 
         f.change_file(lib, "");
-        f.check_parent_modules(foo, &[], &[(MODULE_DESCR.id, 1)]);
+        f.check_parent_modules(foo, &[], &[("MODULE_DESCR", 1)]);
 
         f.change_file(lib, "mod foo;");
-        f.check_parent_modules(foo, &[lib], &[(MODULE_DESCR.id, 1)]);
+        f.check_parent_modules(foo, &[lib], &[("MODULE_DESCR", 1)]);
 
         f.change_file(lib, "mod bar;");
-        f.check_parent_modules(foo, &[], &[(MODULE_DESCR.id, 1)]);
+        f.check_parent_modules(foo, &[], &[("MODULE_DESCR", 1)]);
 
         f.change_file(lib, "mod foo;");
-        f.check_parent_modules(foo, &[lib], &[(MODULE_DESCR.id, 1)]);
+        f.check_parent_modules(foo, &[lib], &[("MODULE_DESCR", 1)]);
 
         f.remove_file(lib);
-        f.check_parent_modules(foo, &[], &[(MODULE_DESCR.id, 0)]);
+        f.check_parent_modules(foo, &[], &[("MODULE_DESCR", 0)]);
     }
 }

crates/salsa/src/lib.rs

@@ -8,8 +8,8 @@ use std::{
 };
 use parking_lot::Mutex;
 
-type GroundQueryFn<T, D> = Box<Fn(&T, &D) -> (D, OutputFingerprint) + Send + Sync + 'static>;
+pub type GroundQueryFn<T, D> = Box<Fn(&T, &D) -> (D, OutputFingerprint) + Send + Sync + 'static>;
-type QueryFn<T, D> = Box<Fn(&QueryCtx<T, D>, &D) -> (D, OutputFingerprint) + Send + Sync + 'static>;
+pub type QueryFn<T, D> = Box<Fn(&QueryCtx<T, D>, &D) -> (D, OutputFingerprint) + Send + Sync + 'static>;
 
 #[derive(Debug)]
 pub struct Db<T, D> {
@@ -118,6 +118,9 @@ where
         self.record_dep(query_id, output_fingerprint);
         res
     }
+    pub fn trace(&self) -> Vec<QueryTypeId> {
+        ::std::mem::replace(&mut *self.executed.borrow_mut(), Vec::new())
+    }
 
     fn get_inner(
         &self,
@@ -261,12 +264,15 @@ where
             query_config: Arc::clone(&self.query_config)
         }
     }
+    pub fn query_ctx(&self) -> QueryCtx<T, D> {
+        QueryCtx::new(self)
+    }
     pub fn get(
         &self,
         query_id: QueryId,
         params: D,
     ) -> (D, Vec<QueryTypeId>) {
-        let ctx = QueryCtx::new(self);
+        let ctx = self.query_ctx();
         let res = ctx.get(query_id, params.into());
         let executed = ::std::mem::replace(&mut *ctx.executed.borrow_mut(), Vec::new());
         (res, executed)