1 files changed, 102 insertions, 0 deletions

diff --git a/crates/ra_hir/src/lang_item.rs b/crates/ra_hir/src/lang_item.rs
new file mode 100644
index 000000000..adcc682a2
--- /dev/null
+++ b/crates/ra_hir/src/lang_item.rs
@@ -0,0 +1,102 @@
+use std::sync::Arc;
+use rustc_hash::FxHashMap;
+
+use ra_syntax::{SmolStr, ast::AttrsOwner};
+
+use crate::{
+    Crate, DefDatabase, Enum, Function, HirDatabase, ImplBlock, Module, Static, Struct, Trait
+};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum LangItemTarget {
+    Enum(Enum),
+    Function(Function),
+    Impl(ImplBlock),
+    Static(Static),
+    Struct(Struct),
+    Trait(Trait),
+}
+
+impl LangItemTarget {
+    pub(crate) fn krate(&self, db: &impl HirDatabase) -> Option<Crate> {
+        match self {
+            LangItemTarget::Enum(e) => e.module(db).krate(db),
+            LangItemTarget::Function(f) => f.module(db).krate(db),
+            LangItemTarget::Impl(i) => i.module().krate(db),
+            LangItemTarget::Static(s) => s.module(db).krate(db),
+            LangItemTarget::Struct(s) => s.module(db).krate(db),
+            LangItemTarget::Trait(t) => t.module(db).krate(db),
+        }
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct LangItems {
+    items: FxHashMap<SmolStr, LangItemTarget>,
+}
+
+impl LangItems {
+    pub fn target<'a>(&'a self, item: &str) -> Option<&'a LangItemTarget> {
+        self.items.get(item)
+    }
+
+    /// Salsa query. This will query a specific crate for lang items.
+    pub(crate) fn lang_items_query(db: &impl DefDatabase, krate: Crate) -> Arc<LangItems> {
+        let mut lang_items = LangItems { items: FxHashMap::default() };
+
+        if let Some(module) = krate.root_module(db) {
+            lang_items.collect_lang_items_recursive(db, &module);
+        }
+
+        Arc::new(lang_items)
+    }
+
+    fn collect_lang_items_recursive(&mut self, db: &impl DefDatabase, module: &Module) {
+        // Look for impl targets
+        let (impl_blocks, source_map) = db.impls_in_module_with_source_map(module.clone());
+        let source = module.definition_source(db).1;
+        for (impl_id, _) in impl_blocks.impls.iter() {
+            let impl_block = source_map.get(&source, impl_id);
+            let lang_item_name = impl_block
+                .attrs()
+                .filter_map(|a| a.as_key_value())
+                .filter(|(key, _)| key == "lang")
+                .map(|(_, val)| val)
+                .nth(0);
+            if let Some(lang_item_name) = lang_item_name {
+                let imp = ImplBlock::from_id(*module, impl_id);
+                self.items.entry(lang_item_name).or_insert(LangItemTarget::Impl(imp));
+            }
+        }
+
+        // FIXME we should look for the other lang item targets (traits, structs, ...)
+
+        // Look for lang items in the children
+        for child in module.children(db) {
+            self.collect_lang_items_recursive(db, &child);
+        }
+    }
+}
+
+/// Look for a lang item, starting from the specified crate and recursively traversing its
+/// dependencies.
+pub(crate) fn lang_item_lookup(
+    db: &impl DefDatabase,
+    start_krate: Crate,
+    item: &str,
+) -> Option<LangItemTarget> {
+    let lang_items = db.lang_items(start_krate);
+    let start_krate_target = lang_items.items.get(item);
+    if start_krate_target.is_some() {
+        start_krate_target.map(|t| *t)
+    } else {
+        for dep in start_krate.dependencies(db) {
+            let dep_krate = dep.krate;
+            let dep_target = lang_item_lookup(db, dep_krate, item);
+            if dep_target.is_some() {
+                return dep_target;
+            }
+        }
+        None
+    }
+}