3 files changed, 75 insertions, 0 deletions

diff --git a/crates/ra_hir_def/src/db.rs b/crates/ra_hir_def/src/db.rs
index e87bd525a..1481868d0 100644
--- a/crates/ra_hir_def/src/db.rs
+++ b/crates/ra_hir_def/src/db.rs
@@ -10,6 +10,7 @@ use crate::{
     attr::Attrs,
     body::{scope::ExprScopes, Body, BodySourceMap},
     data::{ConstData, FunctionData, ImplData, TraitData, TypeAliasData},
+    docs::Documentation,
     generics::GenericParams,
     lang_item::{LangItemTarget, LangItems},
     nameres::{
@@ -101,4 +102,9 @@ pub trait DefDatabase2: InternDatabase + AstDatabase {
 
     #[salsa::invoke(LangItems::lang_item_query)]
     fn lang_item(&self, start_crate: CrateId, item: SmolStr) -> Option<LangItemTarget>;
+
+    // FIXME(https://github.com/rust-analyzer/rust-analyzer/issues/2148#issuecomment-550519102)
+    // Remove this query completely, in favor of `Attrs::docs` method
+    #[salsa::invoke(Documentation::documentation_query)]
+    fn documentation(&self, def: AttrDefId) -> Option<Documentation>;
 }
diff --git a/crates/ra_hir_def/src/docs.rs b/crates/ra_hir_def/src/docs.rs
new file mode 100644
index 000000000..1b5c85437
--- /dev/null
+++ b/crates/ra_hir_def/src/docs.rs
@@ -0,0 +1,68 @@
+//! FIXME: write short doc here
+
+use std::sync::Arc;
+
+use hir_expand::either::Either;
+use ra_syntax::ast;
+
+use crate::{db::DefDatabase2, AdtId, AstItemDef, AttrDefId, HasChildSource, HasSource, Lookup};
+
+/// Holds documentation
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Documentation(Arc<str>);
+
+impl Into<String> for Documentation {
+    fn into(self) -> String {
+        self.as_str().to_owned()
+    }
+}
+
+impl Documentation {
+    fn new(s: &str) -> Documentation {
+        Documentation(s.into())
+    }
+
+    pub fn as_str(&self) -> &str {
+        &*self.0
+    }
+
+    pub(crate) fn documentation_query(
+        db: &impl DefDatabase2,
+        def: AttrDefId,
+    ) -> Option<Documentation> {
+        match def {
+            AttrDefId::ModuleId(module) => {
+                let def_map = db.crate_def_map(module.krate);
+                let src = def_map[module.module_id].declaration_source(db)?;
+                docs_from_ast(&src.value)
+            }
+            AttrDefId::StructFieldId(it) => {
+                let src = it.parent.child_source(db);
+                match &src.value[it.local_id] {
+                    Either::A(_tuple) => None,
+                    Either::B(record) => docs_from_ast(record),
+                }
+            }
+            AttrDefId::AdtId(it) => match it {
+                AdtId::StructId(it) => docs_from_ast(&it.0.source(db).value),
+                AdtId::EnumId(it) => docs_from_ast(&it.source(db).value),
+                AdtId::UnionId(it) => docs_from_ast(&it.0.source(db).value),
+            },
+            AttrDefId::EnumVariantId(it) => {
+                let src = it.parent.child_source(db);
+                docs_from_ast(&src.value[it.local_id])
+            }
+            AttrDefId::StaticId(it) => docs_from_ast(&it.source(db).value),
+            AttrDefId::TraitId(it) => docs_from_ast(&it.source(db).value),
+            AttrDefId::MacroDefId(it) => docs_from_ast(&it.ast_id.to_node(db)),
+            AttrDefId::ConstId(it) => docs_from_ast(&it.lookup(db).source(db).value),
+            AttrDefId::FunctionId(it) => docs_from_ast(&it.lookup(db).source(db).value),
+            AttrDefId::TypeAliasId(it) => docs_from_ast(&it.lookup(db).source(db).value),
+            AttrDefId::ImplId(_) => None,
+        }
+    }
+}
+
+pub(crate) fn docs_from_ast(node: &impl ast::DocCommentsOwner) -> Option<Documentation> {
+    node.doc_comment_text().map(|it| Documentation::new(&it))
+}
diff --git a/crates/ra_hir_def/src/lib.rs b/crates/ra_hir_def/src/lib.rs
index 899510be4..1ba7c7ee3 100644
--- a/crates/ra_hir_def/src/lib.rs
+++ b/crates/ra_hir_def/src/lib.rs
@@ -20,6 +20,7 @@ pub mod generics;
 pub mod resolver;
 pub mod data;
 pub mod lang_item;
+pub mod docs;
 
 mod trace;