introduce macro_arg intermediate query

Currently, when expanding macros, we look at the source code
directly (we invoke ast_id_to_node query via to_node method).

This is less then ideal, because it make us re-expand macros after
every source change.

This commit establishes a salsa-firewall: a query to get macro call's
token tree. Unlike the syntax tree, token tree changes only if we
actually modify the macro itself.

1 files changed, 4 insertions, 1 deletions

diff --git a/crates/ra_hir/src/db.rs b/crates/ra_hir/src/db.rs
index 8af0a3176..f88ae61bb 100644
--- a/crates/ra_hir/src/db.rs
+++ b/crates/ra_hir/src/db.rs
@@ -42,7 +42,10 @@ pub trait DefDatabase: SourceDatabase {
     #[salsa::invoke(crate::ids::macro_def_query)]
     fn macro_def(&self, macro_id: MacroDefId) -> Option<Arc<mbe::MacroRules>>;
 
-    #[salsa::invoke(HirFileId::hir_parse_query)]
+    #[salsa::invoke(crate::ids::macro_arg_query)]
+    fn macro_arg(&self, macro_call: ids::MacroCallId) -> Option<Arc<tt::Subtree>>;
+
+    #[salsa::invoke(crate::ids::HirFileId::hir_parse_query)]
     fn hir_parse(&self, file_id: HirFileId) -> TreeArc<SourceFile>;
 
     #[salsa::invoke(crate::adt::StructData::struct_data_query)]