8 files changed, 166 insertions, 7 deletions

diff --git a/crates/ra_hir/src/db.rs b/crates/ra_hir/src/db.rs
index 18627bbc2..8af0a3176 100644
--- a/crates/ra_hir/src/db.rs
+++ b/crates/ra_hir/src/db.rs
@@ -1,6 +1,6 @@
 use std::sync::Arc;
 
-use ra_syntax::{SyntaxNode, TreeArc, SourceFile, ast};
+use ra_syntax::{SyntaxNode, TreeArc, SourceFile, SmolStr, ast};
 use ra_db::{SourceDatabase, salsa};
 
 use crate::{
@@ -16,6 +16,7 @@ use crate::{
     generics::{GenericParams, GenericDef},
     type_ref::TypeRef,
     traits::TraitData, Trait, ty::TraitRef,
+    lang_item::{LangItems, LangItemTarget},
     ids
 };
 
@@ -100,6 +101,12 @@ pub trait DefDatabase: SourceDatabase {
 
     #[salsa::invoke(crate::ConstSignature::static_signature_query)]
     fn static_signature(&self, konst: Static) -> Arc<ConstSignature>;
+
+    #[salsa::invoke(crate::lang_item::LangItems::lang_items_query)]
+    fn lang_items(&self, krate: Crate) -> Arc<LangItems>;
+
+    #[salsa::invoke(crate::lang_item::LangItems::lang_item_query)]
+    fn lang_item(&self, start_crate: Crate, item: SmolStr) -> Option<LangItemTarget>;
 }
 
 #[salsa::query_group(HirDatabaseStorage)]
diff --git a/crates/ra_hir/src/lang_item.rs b/crates/ra_hir/src/lang_item.rs
new file mode 100644
index 000000000..5f3f91cba
--- /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),
+    ImplBlock(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::ImplBlock(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 look for lang items in a specific crate.
+    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)
+    }
+
+    /// Salsa query. Look for a lang item, starting from the specified crate and recursively
+    /// traversing its dependencies.
+    pub(crate) fn lang_item_query(
+        db: &impl DefDatabase,
+        start_crate: Crate,
+        item: SmolStr,
+    ) -> Option<LangItemTarget> {
+        let lang_items = db.lang_items(start_crate);
+        let start_crate_target = lang_items.items.get(&item);
+        if let Some(target) = start_crate_target {
+            Some(*target)
+        } else {
+            for dep in start_crate.dependencies(db) {
+                let dep_crate = dep.krate;
+                let dep_target = db.lang_item(dep_crate, item.clone());
+                if dep_target.is_some() {
+                    return dep_target;
+                }
+            }
+            None
+        }
+    }
+
+    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::ImplBlock(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);
+        }
+    }
+}
diff --git a/crates/ra_hir/src/lib.rs b/crates/ra_hir/src/lib.rs
index 9292de1b5..4411715de 100644
--- a/crates/ra_hir/src/lib.rs
+++ b/crates/ra_hir/src/lib.rs
@@ -36,6 +36,7 @@ mod type_ref;
 mod ty;
 mod impl_block;
 mod expr;
+mod lang_item;
 mod generics;
 mod docs;
 mod resolve;
diff --git a/crates/ra_hir/src/nameres.rs b/crates/ra_hir/src/nameres.rs
index 0eddfab12..39152360c 100644
--- a/crates/ra_hir/src/nameres.rs
+++ b/crates/ra_hir/src/nameres.rs
@@ -202,6 +202,10 @@ impl CrateDefMap {
         Arc::new(def_map)
     }
 
+    pub(crate) fn krate(&self) -> Crate {
+        self.krate
+    }
+
     pub(crate) fn root(&self) -> CrateModuleId {
         self.root
     }
diff --git a/crates/ra_hir/src/resolve.rs b/crates/ra_hir/src/resolve.rs
index 685f4b8b1..f2c85eb66 100644
--- a/crates/ra_hir/src/resolve.rs
+++ b/crates/ra_hir/src/resolve.rs
@@ -5,13 +5,15 @@ use rustc_hash::FxHashMap;
 
 use crate::{
     ModuleDef,
+    code_model_api::Crate,
     db::HirDatabase,
     name::{Name, KnownName},
     nameres::{PerNs, CrateDefMap, CrateModuleId},
     generics::GenericParams,
     expr::{scope::{ExprScopes, ScopeId}, PatId},
     impl_block::ImplBlock,
-    path::Path, Trait
+    path::Path,
+    Trait
 };
 
 #[derive(Debug, Clone, Default)]
@@ -197,6 +199,10 @@ impl Resolver {
             _ => None,
         })
     }
+
+    pub(crate) fn krate(&self) -> Option<Crate> {
+        self.module().map(|t| t.0.krate())
+    }
 }
 
 impl Resolver {
diff --git a/crates/ra_hir/src/ty/infer.rs b/crates/ra_hir/src/ty/infer.rs
index 7ca1ff595..c7772a7f6 100644
--- a/crates/ra_hir/src/ty/infer.rs
+++ b/crates/ra_hir/src/ty/infer.rs
@@ -462,6 +462,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
         let remaining_index = remaining_index.unwrap_or(path.segments.len());
         let mut actual_def_ty: Option<Ty> = None;
 
+        let krate = resolver.krate()?;
         // resolve intermediate segments
         for (i, segment) in path.segments[remaining_index..].iter().enumerate() {
             let ty = match resolved {
@@ -500,9 +501,10 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             // Attempt to find an impl_item for the type which has a name matching
             // the current segment
             log::debug!("looking for path segment: {:?}", segment);
+
             actual_def_ty = Some(ty.clone());
 
-            let item: crate::ModuleDef = ty.iterate_impl_items(self.db, |item| {
+            let item: crate::ModuleDef = ty.iterate_impl_items(self.db, krate, |item| {
                 let matching_def: Option<crate::ModuleDef> = match item {
                     crate::ImplItem::Method(func) => {
                         let sig = func.signature(self.db);
diff --git a/crates/ra_hir/src/ty/method_resolution.rs b/crates/ra_hir/src/ty/method_resolution.rs
index 667b66095..ea6e0dc0f 100644
--- a/crates/ra_hir/src/ty/method_resolution.rs
+++ b/crates/ra_hir/src/ty/method_resolution.rs
@@ -14,6 +14,7 @@ use crate::{
     resolve::Resolver,
     traits::TraitItem,
     generics::HasGenericParams,
+    ty::primitive::{UncertainIntTy, UncertainFloatTy}
 };
 use super::{TraitRef, Substs};
 
@@ -110,10 +111,19 @@ impl CrateImplBlocks {
     }
 }
 
-fn def_crate(db: &impl HirDatabase, ty: &Ty) -> Option<Crate> {
+fn def_crate(db: &impl HirDatabase, cur_crate: Crate, ty: &Ty) -> Option<Crate> {
     match ty {
         Ty::Apply(a_ty) => match a_ty.ctor {
             TypeCtor::Adt(def_id) => def_id.krate(db),
+            TypeCtor::Bool => db.lang_item(cur_crate, "bool".into())?.krate(db),
+            TypeCtor::Char => db.lang_item(cur_crate, "char".into())?.krate(db),
+            TypeCtor::Float(UncertainFloatTy::Known(f)) => {
+                db.lang_item(cur_crate, f.ty_to_string().into())?.krate(db)
+            }
+            TypeCtor::Int(UncertainIntTy::Known(i)) => {
+                db.lang_item(cur_crate, i.ty_to_string().into())?.krate(db)
+            }
+            TypeCtor::Str => db.lang_item(cur_crate, "str".into())?.krate(db),
             _ => None,
         },
         _ => None,
@@ -150,8 +160,11 @@ impl Ty {
         // find in the end takes &self, we still do the autoderef step (just as
         // rustc does an autoderef and then autoref again).
 
+        let krate = resolver.krate()?;
         for derefed_ty in self.autoderef(db) {
-            if let Some(result) = derefed_ty.iterate_inherent_methods(db, name, &mut callback) {
+            if let Some(result) =
+                derefed_ty.iterate_inherent_methods(db, name, krate, &mut callback)
+            {
                 return Some(result);
             }
             if let Some(result) =
@@ -208,9 +221,10 @@ impl Ty {
         &self,
         db: &impl HirDatabase,
         name: Option<&Name>,
+        krate: Crate,
         mut callback: impl FnMut(&Ty, Function) -> Option<T>,
     ) -> Option<T> {
-        let krate = match def_crate(db, self) {
+        let krate = match def_crate(db, krate, self) {
             Some(krate) => krate,
             None => return None,
         };
@@ -239,9 +253,10 @@ impl Ty {
     pub fn iterate_impl_items<T>(
         self,
         db: &impl HirDatabase,
+        krate: Crate,
         mut callback: impl FnMut(ImplItem) -> Option<T>,
     ) -> Option<T> {
-        let krate = def_crate(db, &self)?;
+        let krate = def_crate(db, krate, &self)?;
         let impls = db.impls_in_crate(krate);
 
         for impl_block in impls.lookup_impl_blocks(&self) {
diff --git a/crates/ra_hir/src/ty/tests.rs b/crates/ra_hir/src/ty/tests.rs
index 8d8a0eaaa..86f18b487 100644
--- a/crates/ra_hir/src/ty/tests.rs
+++ b/crates/ra_hir/src/ty/tests.rs
@@ -627,6 +627,28 @@ fn test(a: A) {
 }
 
 #[test]
+fn infer_inherent_method_str() {
+    assert_snapshot_matches!(
+        infer(r#"
+#[lang = "str"]
+impl str {
+    fn foo(&self) -> i32 {}
+}
+
+fn test() {
+    "foo".foo();
+}
+"#),
+        @r###"
+[40; 44) 'self': &str
+[53; 55) '{}': ()
+[69; 89) '{     ...o(); }': ()
+[75; 80) '"foo"': &str
+[75; 86) '"foo".foo()': i32"###
+    );
+}
+
+#[test]
 fn infer_tuple() {
     assert_snapshot_matches!(
         infer(r#"