Add trait obligations for where clauses when calling functions/methods

E.g. if we call `foo<T: Into<u32>>(x)`, that adds an obligation that `x:
Into<u32>`, etc.

4 files changed, 140 insertions, 30 deletions

diff --git a/crates/ra_hir/src/ty/infer.rs b/crates/ra_hir/src/ty/infer.rs
index a23daabc2..f5d8cd4b1 100644
--- a/crates/ra_hir/src/ty/infer.rs
+++ b/crates/ra_hir/src/ty/infer.rs
@@ -849,8 +849,19 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
     fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
         if let Ty::Apply(a_ty) = callable_ty {
             if let TypeCtor::FnDef(def) = a_ty.ctor {
+                let generic_predicates = self.db.generic_predicates(match def {
+                    // TODO add helper function
+                    CallableDef::Function(f) => f.into(),
+                    CallableDef::Struct(s) => s.into(),
+                    CallableDef::EnumVariant(_e) => unimplemented!(),
+                });
+                for predicate in generic_predicates.iter() {
+                    let predicate = predicate.clone().subst(&a_ty.parameters);
+                    if let Some(obligation) = Obligation::from_predicate(predicate) {
+                        self.obligations.push(obligation);
+                    }
+                }
                 // add obligation for trait implementation, if this is a trait method
-                // FIXME also register obligations from where clauses from the trait or impl and method
                 match def {
                     CallableDef::Function(f) => {
                         if let Some(trait_) = f.parent_trait(self.db) {
@@ -992,7 +1003,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                         (Vec::new(), Ty::Unknown)
                     }
                 };
-                // FIXME register obligations from where clauses from the function
+                self.register_obligations_for_call(&callee_ty);
                 let param_iter = param_tys.into_iter().chain(repeat(Ty::Unknown));
                 for (arg, param) in args.iter().zip(param_iter) {
                     self.infer_expr(*arg, &Expectation::has_type(param));
diff --git a/crates/ra_hir/src/ty/lower.rs b/crates/ra_hir/src/ty/lower.rs
index 8b1b2a7f9..24755c6aa 100644
--- a/crates/ra_hir/src/ty/lower.rs
+++ b/crates/ra_hir/src/ty/lower.rs
@@ -318,15 +318,13 @@ pub(crate) fn type_for_field(db: &impl HirDatabase, field: StructField) -> Ty {
 }
 
 /// Resolve the where clause(s) of an item with generics.
-pub(crate) fn generic_predicates(
+pub(crate) fn generic_predicates_query(
     db: &impl HirDatabase,
     def: GenericDef,
 ) -> Arc<[GenericPredicate]> {
     let resolver = def.resolver(db);
-    let generic_params = def.generic_params(db);
-    let predicates = generic_params
-        .where_predicates
-        .iter()
+    let predicates = resolver
+        .where_predicates_in_scope()
         .map(|pred| {
             TraitRef::for_where_predicate(db, &resolver, pred)
                 .map_or(GenericPredicate::Error, GenericPredicate::Implemented)
@@ -336,7 +334,7 @@ pub(crate) fn generic_predicates(
 }
 
 /// Resolve the default type params from generics
-pub(crate) fn generic_defaults(db: &impl HirDatabase, def: GenericDef) -> Substs {
+pub(crate) fn generic_defaults_query(db: &impl HirDatabase, def: GenericDef) -> Substs {
     let resolver = def.resolver(db);
     let generic_params = def.generic_params(db);
 
diff --git a/crates/ra_hir/src/ty/tests.rs b/crates/ra_hir/src/ty/tests.rs
index 20fa74fb4..aacd94a26 100644
--- a/crates/ra_hir/src/ty/tests.rs
+++ b/crates/ra_hir/src/ty/tests.rs
@@ -2232,16 +2232,18 @@ fn test() {
 }
 "#),
         @r###"
-[86; 87) 't': T
-[92; 94) '{}': ()
-[105; 144) '{     ...(s); }': ()
-[115; 116) 's': S<{unknown}>
-[119; 120) 'S': S<{unknown}>(T) -> S<T>
-[119; 129) 'S(unknown)': S<{unknown}>
-[121; 128) 'unknown': {unknown}
-[135; 138) 'foo': fn foo<S<{unknown}>>(T) -> ()
-[135; 141) 'foo(s)': ()
-[139; 140) 's': S<{unknown}>"###
+   ⋮
+   ⋮[86; 87) 't': T
+   ⋮[92; 94) '{}': ()
+   ⋮[105; 144) '{     ...(s); }': ()
+   ⋮[115; 116) 's': S<u32>
+   ⋮[119; 120) 'S': S<u32>(T) -> S<T>
+   ⋮[119; 129) 'S(unknown)': S<u32>
+   ⋮[121; 128) 'unknown': u32
+   ⋮[135; 138) 'foo': fn foo<S<u32>>(T) -> ()
+   ⋮[135; 141) 'foo(s)': ()
+   ⋮[139; 140) 's': S<u32>
+    "###
     );
 }
 
@@ -2259,17 +2261,19 @@ fn test() {
 }
 "#),
         @r###"
-[87; 88) 't': T
-[98; 100) '{}': ()
-[111; 163) '{     ...(s); }': ()
-[121; 122) 's': S<{unknown}>
-[125; 126) 'S': S<{unknown}>(T) -> S<T>
-[125; 135) 'S(unknown)': S<{unknown}>
-[127; 134) 'unknown': {unknown}
-[145; 146) 'x': u32
-[154; 157) 'foo': fn foo<u32, S<{unknown}>>(T) -> U
-[154; 160) 'foo(s)': u32
-[158; 159) 's': S<{unknown}>"###
+   ⋮
+   ⋮[87; 88) 't': T
+   ⋮[98; 100) '{}': ()
+   ⋮[111; 163) '{     ...(s); }': ()
+   ⋮[121; 122) 's': S<u32>
+   ⋮[125; 126) 'S': S<u32>(T) -> S<T>
+   ⋮[125; 135) 'S(unknown)': S<u32>
+   ⋮[127; 134) 'unknown': u32
+   ⋮[145; 146) 'x': u32
+   ⋮[154; 157) 'foo': fn foo<u32, S<u32>>(T) -> U
+   ⋮[154; 160) 'foo(s)': u32
+   ⋮[158; 159) 's': S<u32>
+    "###
     );
 }
 
@@ -2822,6 +2826,94 @@ fn test(s: S) {
     assert_eq!(t, "{unknown}");
 }
 
+#[test]
+fn obligation_from_function_clause() {
+    let t = type_at(
+        r#"
+//- /main.rs
+struct S;
+
+trait Trait<T> {}
+impl Trait<u32> for S {}
+
+fn foo<T: Trait<U>, U>(t: T) -> U {}
+
+fn test(s: S) {
+    foo(s)<|>;
+}
+"#,
+    );
+    assert_eq!(t, "u32");
+}
+
+#[test]
+fn obligation_from_method_clause() {
+    let t = type_at(
+        r#"
+//- /main.rs
+struct S;
+
+trait Trait<T> {}
+impl Trait<isize> for S {}
+
+struct O;
+impl O {
+    fn foo<T: Trait<U>, U>(&self, t: T) -> U {}
+}
+
+fn test() {
+    O.foo(S)<|>;
+}
+"#,
+    );
+    assert_eq!(t, "isize");
+}
+
+#[test]
+fn obligation_from_self_method_clause() {
+    let t = type_at(
+        r#"
+//- /main.rs
+struct S;
+
+trait Trait<T> {}
+impl Trait<i64> for S {}
+
+impl S {
+    fn foo<U>(&self) -> U where Self: Trait<U> {}
+}
+
+fn test() {
+    S.foo()<|>;
+}
+"#,
+    );
+    assert_eq!(t, "i64");
+}
+
+#[test]
+fn obligation_from_impl_clause() {
+    let t = type_at(
+        r#"
+//- /main.rs
+struct S;
+
+trait Trait<T> {}
+impl Trait<&str> for S {}
+
+struct O<T>;
+impl<U, T: Trait<U>> O<T> {
+    fn foo(&self) -> U {}
+}
+
+fn test(o: O<S>) {
+    o.foo()<|>;
+}
+"#,
+    );
+    assert_eq!(t, "&str");
+}
+
 fn type_at_pos(db: &MockDatabase, pos: FilePosition) -> String {
     let file = db.parse(pos.file_id).ok().unwrap();
     let expr = algo::find_node_at_offset::<ast::Expr>(file.syntax(), pos.offset).unwrap();
diff --git a/crates/ra_hir/src/ty/traits.rs b/crates/ra_hir/src/ty/traits.rs
index cff4de316..23a26a971 100644
--- a/crates/ra_hir/src/ty/traits.rs
+++ b/crates/ra_hir/src/ty/traits.rs
@@ -7,7 +7,7 @@ use parking_lot::Mutex;
 use ra_prof::profile;
 use rustc_hash::FxHashSet;
 
-use super::{Canonical, ProjectionTy, TraitRef, Ty};
+use super::{Canonical, GenericPredicate, ProjectionTy, TraitRef, Ty};
 use crate::{db::HirDatabase, Crate, ImplBlock, Trait};
 
 use self::chalk::{from_chalk, ToChalk};
@@ -78,6 +78,15 @@ pub enum Obligation {
     // Projection(ProjectionPredicate),
 }
 
+impl Obligation {
+    pub fn from_predicate(predicate: GenericPredicate) -> Option<Obligation> {
+        match predicate {
+            GenericPredicate::Implemented(trait_ref) => Some(Obligation::Trait(trait_ref)),
+            GenericPredicate::Error => None,
+        }
+    }
+}
+
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub struct ProjectionPredicate {
     pub projection_ty: ProjectionTy,