9 files changed, 44 insertions, 4 deletions

diff --git a/crates/hir_def/src/db.rs b/crates/hir_def/src/db.rs
index 7eadc8e0d..c977971cd 100644
--- a/crates/hir_def/src/db.rs
+++ b/crates/hir_def/src/db.rs
@@ -51,6 +51,9 @@ pub trait InternDatabase: SourceDatabase {
 
 #[salsa::query_group(DefDatabaseStorage)]
 pub trait DefDatabase: InternDatabase + AstDatabase + Upcast<dyn AstDatabase> {
+    #[salsa::input]
+    fn enable_proc_attr_macros(&self) -> bool;
+
     #[salsa::invoke(ItemTree::file_item_tree_query)]
     fn file_item_tree(&self, file_id: HirFileId) -> Arc<ItemTree>;
 
diff --git a/crates/hir_def/src/nameres/collector.rs b/crates/hir_def/src/nameres/collector.rs
index 874a4ebb1..b2ce739bd 100644
--- a/crates/hir_def/src/nameres/collector.rs
+++ b/crates/hir_def/src/nameres/collector.rs
@@ -1067,6 +1067,10 @@ impl DefCollector<'_> {
                         }
                     }
 
+                    if !self.db.enable_proc_attr_macros() {
+                        return true;
+                    }
+
                     // Not resolved to a derive helper, so try to resolve as a macro.
                     match attr_macro_as_call_id(
                         ast_id,
diff --git a/crates/hir_def/src/test_db.rs b/crates/hir_def/src/test_db.rs
index e840fe5e8..b20b066e2 100644
--- a/crates/hir_def/src/test_db.rs
+++ b/crates/hir_def/src/test_db.rs
@@ -30,12 +30,19 @@ use crate::{
     crate::db::InternDatabaseStorage,
     crate::db::DefDatabaseStorage
 )]
-#[derive(Default)]
 pub(crate) struct TestDB {
     storage: salsa::Storage<TestDB>,
     events: Mutex<Option<Vec<salsa::Event>>>,
 }
 
+impl Default for TestDB {
+    fn default() -> Self {
+        let mut this = Self { storage: Default::default(), events: Default::default() };
+        this.set_enable_proc_attr_macros(true);
+        this
+    }
+}
+
 impl Upcast<dyn AstDatabase> for TestDB {
     fn upcast(&self) -> &(dyn AstDatabase + 'static) {
         &*self
diff --git a/crates/ide_db/src/lib.rs b/crates/ide_db/src/lib.rs
index 1f900aef4..105607dca 100644
--- a/crates/ide_db/src/lib.rs
+++ b/crates/ide_db/src/lib.rs
@@ -93,6 +93,7 @@ impl RootDatabase {
         db.set_crate_graph_with_durability(Default::default(), Durability::HIGH);
         db.set_local_roots_with_durability(Default::default(), Durability::HIGH);
         db.set_library_roots_with_durability(Default::default(), Durability::HIGH);
+        db.set_enable_proc_attr_macros(Default::default());
         db.update_lru_capacity(lru_capacity);
         db
     }
diff --git a/crates/rust-analyzer/src/config.rs b/crates/rust-analyzer/src/config.rs
index c33cdb740..d1f3c1b06 100644
--- a/crates/rust-analyzer/src/config.rs
+++ b/crates/rust-analyzer/src/config.rs
@@ -126,6 +126,9 @@ config_data! {
         /// and a blue icon in the `Problems Panel`.
         diagnostics_warningsAsInfo: Vec<String> = "[]",
 
+        /// Expand attribute macros.
+        experimental_procAttrMacros: bool = "false",
+
         /// Controls file watching implementation.
         files_watcher: String = "\"client\"",
         /// These directories will be ignored by rust-analyzer.
@@ -546,6 +549,9 @@ impl Config {
         let path = self.data.procMacro_server.clone().or_else(|| std::env::current_exe().ok())?;
         Some((path, vec!["proc-macro".into()]))
     }
+    pub fn expand_proc_attr_macros(&self) -> bool {
+        self.data.experimental_procAttrMacros
+    }
     pub fn files(&self) -> FilesConfig {
         FilesConfig {
             watcher: match self.data.files_watcher.as_str() {
diff --git a/crates/rust-analyzer/src/global_state.rs b/crates/rust-analyzer/src/global_state.rs
index ea9dbf7fc..582a89667 100644
--- a/crates/rust-analyzer/src/global_state.rs
+++ b/crates/rust-analyzer/src/global_state.rs
@@ -119,12 +119,12 @@ impl GlobalState {
 
         let analysis_host = AnalysisHost::new(config.lru_capacity());
         let (flycheck_sender, flycheck_receiver) = unbounded();
-        GlobalState {
+        let mut this = GlobalState {
             sender,
             req_queue: ReqQueue::default(),
             task_pool,
             loader,
-            config: Arc::new(config),
+            config: Arc::new(config.clone()),
             analysis_host,
             diagnostics: Default::default(),
             mem_docs: FxHashMap::default(),
@@ -151,7 +151,10 @@ impl GlobalState {
 
             fetch_build_data_queue: OpQueue::default(),
             latest_requests: Default::default(),
-        }
+        };
+        // Apply any required database inputs from the config.
+        this.update_configuration(config);
+        this
     }
 
     pub(crate) fn process_changes(&mut self) -> bool {
diff --git a/crates/rust-analyzer/src/reload.rs b/crates/rust-analyzer/src/reload.rs
index 93b5ff55f..bd31d1d13 100644
--- a/crates/rust-analyzer/src/reload.rs
+++ b/crates/rust-analyzer/src/reload.rs
@@ -2,6 +2,7 @@
 use std::{mem, sync::Arc};
 
 use flycheck::{FlycheckConfig, FlycheckHandle};
+use hir::db::DefDatabase;
 use ide::Change;
 use ide_db::base_db::{CrateGraph, SourceRoot, VfsPath};
 use project_model::{BuildDataCollector, BuildDataResult, ProcMacroClient, ProjectWorkspace};
@@ -47,6 +48,11 @@ impl GlobalState {
         } else if self.config.flycheck() != old_config.flycheck() {
             self.reload_flycheck();
         }
+
+        // Apply experimental feature flags.
+        self.analysis_host
+            .raw_database_mut()
+            .set_enable_proc_attr_macros(self.config.expand_proc_attr_macros());
     }
     pub(crate) fn maybe_refresh(&mut self, changes: &[(AbsPathBuf, ChangeKind)]) {
         if !changes.iter().any(|(path, kind)| is_interesting(path, *kind)) {
diff --git a/docs/user/generated_config.adoc b/docs/user/generated_config.adoc
index 7f405b4d7..4eec8455d 100644
--- a/docs/user/generated_config.adoc
+++ b/docs/user/generated_config.adoc
@@ -181,6 +181,11 @@ List of warnings that should be displayed with info severity.
 The warnings will be indicated by a blue squiggly underline in code
 and a blue icon in the `Problems Panel`.
 --
+[[rust-analyzer.experimental.procAttrMacros]]rust-analyzer.experimental.procAttrMacros (default: `false`)::
++
+--
+Expand attribute macros.
+--
 [[rust-analyzer.files.watcher]]rust-analyzer.files.watcher (default: `"client"`)::
 +
 --
diff --git a/editors/code/package.json b/editors/code/package.json
index 4a5070d02..bffc1e05b 100644
--- a/editors/code/package.json
+++ b/editors/code/package.json
@@ -617,6 +617,11 @@
                         "type": "string"
                     }
                 },
+                "rust-analyzer.experimental.procAttrMacros": {
+                    "markdownDescription": "Expand attribute macros.",
+                    "default": false,
+                    "type": "boolean"
+                },
                 "rust-analyzer.files.watcher": {
                     "markdownDescription": "Controls file watching implementation.",
                     "default": "client",