Merge #1040

1040: Trait beginnings r=matklad a=flodiebold

This adds some very simple trait method resolution, going through traits in scope, looking for methods of the given name, and checking very naively whether there's an impl for the given type and trait.

Co-authored-by: Florian Diebold <[email protected]>

3 files changed, 84 insertions, 26 deletions

diff --git a/crates/ra_hir/src/ty/infer.rs b/crates/ra_hir/src/ty/infer.rs
index 5fd602a9e..573115321 100644
--- a/crates/ra_hir/src/ty/infer.rs
+++ b/crates/ra_hir/src/ty/infer.rs
@@ -821,7 +821,8 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             }
             Expr::MethodCall { receiver, args, method_name, generic_args } => {
                 let receiver_ty = self.infer_expr(*receiver, &Expectation::none());
-                let resolved = receiver_ty.clone().lookup_method(self.db, method_name);
+                let resolved =
+                    receiver_ty.clone().lookup_method(self.db, method_name, &self.resolver);
                 let (derefed_receiver_ty, method_ty, def_generics) = match resolved {
                     Some((ty, func)) => {
                         self.write_method_resolution(tgt_expr, func);
diff --git a/crates/ra_hir/src/ty/method_resolution.rs b/crates/ra_hir/src/ty/method_resolution.rs
index b1684acf9..3ac8dc46b 100644
--- a/crates/ra_hir/src/ty/method_resolution.rs
+++ b/crates/ra_hir/src/ty/method_resolution.rs
@@ -8,12 +8,12 @@ use rustc_hash::FxHashMap;
 
 use crate::{
     HirDatabase, Module, Crate, Name, Function, Trait,
-    ids::TraitId,
     impl_block::{ImplId, ImplBlock, ImplItem},
     ty::{Ty, TypeCtor},
-    nameres::CrateModuleId,
+    nameres::CrateModuleId, resolve::Resolver, traits::TraitItem
 
 };
+use super::{ TraitRef, Substs};
 
 /// This is used as a key for indexing impls.
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
@@ -38,7 +38,7 @@ pub struct CrateImplBlocks {
     /// To make sense of the CrateModuleIds, we need the source root.
     krate: Crate,
     impls: FxHashMap<TyFingerprint, Vec<(CrateModuleId, ImplId)>>,
-    impls_by_trait: FxHashMap<TraitId, Vec<(CrateModuleId, ImplId)>>,
+    impls_by_trait: FxHashMap<Trait, Vec<(CrateModuleId, ImplId)>>,
 }
 
 impl CrateImplBlocks {
@@ -56,8 +56,7 @@ impl CrateImplBlocks {
         &'a self,
         tr: &Trait,
     ) -> impl Iterator<Item = ImplBlock> + 'a {
-        let id = tr.id;
-        self.impls_by_trait.get(&id).into_iter().flat_map(|i| i.iter()).map(
+        self.impls_by_trait.get(&tr).into_iter().flat_map(|i| i.iter()).map(
             move |(module_id, impl_id)| {
                 let module = Module { krate: self.krate, module_id: *module_id };
                 ImplBlock::from_id(module, *impl_id)
@@ -73,18 +72,18 @@ impl CrateImplBlocks {
 
             let target_ty = impl_block.target_ty(db);
 
-            if let Some(target_ty_fp) = TyFingerprint::for_impl(&target_ty) {
-                self.impls
-                    .entry(target_ty_fp)
-                    .or_insert_with(Vec::new)
-                    .push((module.module_id, impl_id));
-            }
-
             if let Some(tr) = impl_block.target_trait(db) {
                 self.impls_by_trait
-                    .entry(tr.id)
+                    .entry(tr)
                     .or_insert_with(Vec::new)
                     .push((module.module_id, impl_id));
+            } else {
+                if let Some(target_ty_fp) = TyFingerprint::for_impl(&target_ty) {
+                    self.impls
+                        .entry(target_ty_fp)
+                        .or_insert_with(Vec::new)
+                        .push((module.module_id, impl_id));
+                }
             }
         }
 
@@ -109,6 +108,20 @@ impl CrateImplBlocks {
     }
 }
 
+/// 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, ty: &Ty) -> Option<Crate> {
     match ty {
         Ty::Apply(a_ty) => match a_ty.ctor {
@@ -120,20 +133,64 @@ fn def_crate(db: &impl HirDatabase, ty: &Ty) -> Option<Crate> {
 }
 
 impl Ty {
-    // FIXME: cache this as a query?
-    // - if so, what signature? (TyFingerprint, Name)?
-    // - or maybe cache all names and def_ids of methods per fingerprint?
     /// Look up the method with the given name, returning the actual autoderefed
     /// receiver type (but without autoref applied yet).
-    pub fn lookup_method(self, db: &impl HirDatabase, name: &Name) -> Option<(Ty, Function)> {
-        self.iterate_methods(db, |ty, f| {
+    pub fn lookup_method(
+        self,
+        db: &impl HirDatabase,
+        name: &Name,
+        resolver: &Resolver,
+    ) -> Option<(Ty, Function)> {
+        // FIXME: trait methods should be used before autoderefs
+        let inherent_method = self.clone().iterate_methods(db, |ty, f| {
             let sig = f.signature(db);
             if sig.name() == name && sig.has_self_param() {
                 Some((ty.clone(), f))
             } else {
                 None
             }
-        })
+        });
+        inherent_method.or_else(|| self.lookup_trait_method(db, name, resolver))
+    }
+
+    fn lookup_trait_method(
+        self,
+        db: &impl HirDatabase,
+        name: &Name,
+        resolver: &Resolver,
+    ) -> Option<(Ty, Function)> {
+        let mut candidates = Vec::new();
+        for t in resolver.traits_in_scope() {
+            let data = t.trait_data(db);
+            for item in data.items() {
+                match item {
+                    &TraitItem::Function(m) => {
+                        let sig = m.signature(db);
+                        if sig.name() == name && sig.has_self_param() {
+                            candidates.push((t, m));
+                        }
+                    }
+                    _ => {}
+                }
+            }
+        }
+        // FIXME:
+        //  - we might not actually be able to determine fully that the type
+        //    implements the trait here; it's enough if we (well, Chalk) determine
+        //    that it's possible.
+        //  - when the trait method is picked, we need to register an
+        //    'obligation' somewhere so that we later check that it's really
+        //    implemented
+        //  - both points go for additional requirements from where clauses as
+        //    well (in fact, the 'implements' condition could just be considered a
+        //    'where Self: Trait' clause)
+        candidates.retain(|(t, _m)| {
+            let trait_ref = TraitRef { trait_: *t, substs: Substs::single(self.clone()) };
+            db.implements(trait_ref)
+        });
+        // FIXME if there's multiple candidates here, that's an ambiguity error
+        let (_chosen_trait, chosen_method) = candidates.first()?;
+        Some((self.clone(), *chosen_method))
     }
 
     // This would be nicer if it just returned an iterator, but that runs into
diff --git a/crates/ra_hir/src/ty/tests.rs b/crates/ra_hir/src/ty/tests.rs
index 3aedba243..655f3c522 100644
--- a/crates/ra_hir/src/ty/tests.rs
+++ b/crates/ra_hir/src/ty/tests.rs
@@ -1272,8 +1272,8 @@ fn test() {
 [241; 252) 'Struct::FOO': u32
 [262; 263) 'y': u32
 [266; 275) 'Enum::BAR': u32
-[285; 286) 'z': u32
-[289; 302) 'TraitTest::ID': u32"###
+[285; 286) 'z': {unknown}
+[289; 302) 'TraitTest::ID': {unknown}"###
     );
 }
 
@@ -1918,9 +1918,9 @@ fn test() {
 [110; 114) 'self': &{unknown}
 [170; 228) '{     ...i128 }': ()
 [176; 178) 'S1': S1
-[176; 187) 'S1.method()': {unknown}
+[176; 187) 'S1.method()': u32
 [203; 205) 'S2': S2
-[203; 214) 'S2.method()': {unknown}"###
+[203; 214) 'S2.method()': i128"###
     );
 }
 
@@ -1964,10 +1964,10 @@ mod bar_test {
 [169; 173) 'self': &{unknown}
 [300; 337) '{     ...     }': ()
 [310; 311) 'S': S
-[310; 320) 'S.method()': {unknown}
+[310; 320) 'S.method()': u32
 [416; 454) '{     ...     }': ()
 [426; 427) 'S': S
-[426; 436) 'S.method()': {unknown}"###
+[426; 436) 'S.method()': i128"###
     );
 }