7 files changed, 175 insertions, 30 deletions

diff --git a/crates/ra_hir/src/db.rs b/crates/ra_hir/src/db.rs
index 18627bbc2..b27efcbe3 100644
--- a/crates/ra_hir/src/db.rs
+++ b/crates/ra_hir/src/db.rs
@@ -16,6 +16,7 @@ use crate::{
     generics::{GenericParams, GenericDef},
     type_ref::TypeRef,
     traits::TraitData, Trait, ty::TraitRef,
+    lang_item::LangItems,
     ids
 };
 
@@ -100,6 +101,9 @@ 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::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..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
+    }
+}
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..61925e832 100644
--- a/crates/ra_hir/src/resolve.rs
+++ b/crates/ra_hir/src/resolve.rs
@@ -190,7 +190,7 @@ impl Resolver {
             .flatten()
     }
 
-    fn module(&self) -> Option<(&CrateDefMap, CrateModuleId)> {
+    pub(crate) fn module(&self) -> Option<(&CrateDefMap, CrateModuleId)> {
         self.scopes.iter().rev().find_map(|scope| match scope {
             Scope::ModuleScope(m) => Some((&*m.crate_def_map, m.module_id)),
 
diff --git a/crates/ra_hir/src/ty/infer.rs b/crates/ra_hir/src/ty/infer.rs
index 7ca1ff595..2275ac151 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.module().map(|t| t.0.krate());
         // resolve intermediate segments
         for (i, segment) in path.segments[remaining_index..].iter().enumerate() {
             let ty = match resolved {
@@ -500,38 +501,41 @@ 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 matching_def: Option<crate::ModuleDef> = match item {
-                    crate::ImplItem::Method(func) => {
-                        let sig = func.signature(self.db);
-                        if segment.name == *sig.name() {
-                            Some(func.into())
-                        } else {
-                            None
+            let item: crate::ModuleDef = krate.and_then(|k| {
+                ty.iterate_impl_items(self.db, k, |item| {
+                    let matching_def: Option<crate::ModuleDef> = match item {
+                        crate::ImplItem::Method(func) => {
+                            let sig = func.signature(self.db);
+                            if segment.name == *sig.name() {
+                                Some(func.into())
+                            } else {
+                                None
+                            }
                         }
-                    }
 
-                    crate::ImplItem::Const(konst) => {
-                        let sig = konst.signature(self.db);
-                        if segment.name == *sig.name() {
-                            Some(konst.into())
-                        } else {
-                            None
+                        crate::ImplItem::Const(konst) => {
+                            let sig = konst.signature(self.db);
+                            if segment.name == *sig.name() {
+                                Some(konst.into())
+                            } else {
+                                None
+                            }
                         }
-                    }
 
-                    // FIXME: Resolve associated types
-                    crate::ImplItem::TypeAlias(_) => None,
-                };
-                match matching_def {
-                    Some(_) => {
-                        self.write_assoc_resolution(id, item);
-                        return matching_def;
+                        // FIXME: Resolve associated types
+                        crate::ImplItem::TypeAlias(_) => None,
+                    };
+                    match matching_def {
+                        Some(_) => {
+                            self.write_assoc_resolution(id, item);
+                            return matching_def;
+                        }
+                        None => None,
                     }
-                    None => None,
-                }
+                })
             })?;
 
             resolved = Resolution::Def(item.into());
diff --git a/crates/ra_hir/src/ty/method_resolution.rs b/crates/ra_hir/src/ty/method_resolution.rs
index 667b66095..ba516313c 100644
--- a/crates/ra_hir/src/ty/method_resolution.rs
+++ b/crates/ra_hir/src/ty/method_resolution.rs
@@ -14,6 +14,8 @@ use crate::{
     resolve::Resolver,
     traits::TraitItem,
     generics::HasGenericParams,
+    lang_item::lang_item_lookup,
+    ty::primitive::{UncertainIntTy, UncertainFloatTy}
 };
 use super::{TraitRef, Substs};
 
@@ -110,10 +112,33 @@ impl CrateImplBlocks {
     }
 }
 
-fn def_crate(db: &impl HirDatabase, ty: &Ty) -> Option<Crate> {
+/// Rudimentary check whether an impl exists for a given type and trait; this
+/// will actually be done by chalk.
+pub(crate) fn implements(db: &impl HirDatabase, trait_ref: TraitRef) -> bool {
+    // FIXME use all trait impls in the whole crate graph
+    let krate = trait_ref.trait_.module(db).krate(db);
+    let krate = match krate {
+        Some(krate) => krate,
+        None => return false,
+    };
+    let crate_impl_blocks = db.impls_in_crate(krate);
+    let mut impl_blocks = crate_impl_blocks.lookup_impl_blocks_for_trait(&trait_ref.trait_);
+    impl_blocks.any(|impl_block| &impl_block.target_ty(db) == trait_ref.self_ty())
+}
+
+fn def_crate(db: &impl HirDatabase, cur_krate: 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 => lang_item_lookup(db, cur_krate, "bool")?.krate(db),
+            TypeCtor::Char => lang_item_lookup(db, cur_krate, "char")?.krate(db),
+            TypeCtor::Float(UncertainFloatTy::Known(f)) => {
+                lang_item_lookup(db, cur_krate, f.ty_to_string())?.krate(db)
+            }
+            TypeCtor::Int(UncertainIntTy::Known(i)) => {
+                lang_item_lookup(db, cur_krate, i.ty_to_string())?.krate(db)
+            }
+            TypeCtor::Str => lang_item_lookup(db, cur_krate, "str")?.krate(db),
             _ => None,
         },
         _ => None,
@@ -150,8 +175,11 @@ 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.module().map(|t| t.0.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 +236,10 @@ 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 +268,10 @@ 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) {