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.

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)]

crates/ra_hir/src/expr.rs

@@ -826,22 +826,21 @@ where
                     .with_file_id(self.current_file_id);
 
                 if let Some(call_id) = self.resolver.resolve_macro_call(self.db, path, ast_id) {
-                    if let Some(expr) = expand_macro_to_expr(self.db, call_id, e.token_tree()) {
+                    if let Some(arg) = self.db.macro_arg(call_id) {
+                        if let Some(expr) = expand_macro_to_expr(self.db, call_id, &arg) {
                             log::debug!("macro expansion {}", expr.syntax().debug_dump());
                             let old_file_id =
                                 std::mem::replace(&mut self.current_file_id, call_id.into());
                             let id = self.collect_expr(&expr);
                             self.current_file_id = old_file_id;
-                        id
+                            return id;
-                    } else {
+                        }
+                    }
+                }
                 // FIXME: Instead of just dropping the error from expansion
                 // report it
                 self.alloc_expr(Expr::Missing, syntax_ptr)
             }
-                } else {
-                    self.alloc_expr(Expr::Missing, syntax_ptr)
-                }
-            }
         }
     }
 
@@ -1002,14 +1001,10 @@ where
 fn expand_macro_to_expr(
     db: &impl HirDatabase,
     macro_call: MacroCallId,
-    args: Option<&ast::TokenTree>,
+    arg: &tt::Subtree,
 ) -> Option<TreeArc<ast::Expr>> {
     let rules = db.macro_def(macro_call.loc(db).def)?;
-
+    let expanded = rules.expand(&arg).ok()?;
-    let args = mbe::ast_to_token_tree(args?)?.0;
-
-    let expanded = rules.expand(&args).ok()?;
-
     mbe::token_tree_to_expr(&expanded).ok()
 }
 

crates/ra_hir/src/ids.rs

@@ -86,11 +86,7 @@ fn parse_macro(
     macro_call_id: MacroCallId,
 ) -> Result<TreeArc<SourceFile>, String> {
     let loc = macro_call_id.loc(db);
-    let macro_call = loc.ast_id.to_node(db);
+    let macro_arg = db.macro_arg(macro_call_id).ok_or("Fail to args in to tt::TokenTree")?;
-    let (macro_arg, _) = macro_call
-        .token_tree()
-        .and_then(mbe::ast_to_token_tree)
-        .ok_or("Fail to args in to tt::TokenTree")?;
 
     let macro_rules = db.macro_def(loc.def).ok_or("Fail to find macro definition")?;
     let tt = macro_rules.expand(&macro_arg).map_err(|err| format!("{:?}", err))?;
@@ -139,6 +135,14 @@ pub(crate) fn macro_def_query(db: &impl DefDatabase, id: MacroDefId) -> Option<A
     Some(Arc::new(rules))
 }
 
+pub(crate) fn macro_arg_query(db: &impl DefDatabase, id: MacroCallId) -> Option<Arc<tt::Subtree>> {
+    let loc = id.loc(db);
+    let macro_call = loc.ast_id.to_node(db);
+    let arg = macro_call.token_tree()?;
+    let (tt, _) = mbe::ast_to_token_tree(arg)?;
+    Some(Arc::new(tt))
+}
+
 macro_rules! impl_intern_key {
     ($name:ident) => {
         impl salsa::InternKey for $name {