Deal better with implicit type parameters and argument lists

crates/ra_hir_ty/src/infer/expr.rs

@@ -647,8 +647,10 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
         generic_args: Option<&GenericArgs>,
         receiver_ty: &Ty,
     ) -> Substs {
-        let (total_len, _parent_len, child_len) =
+        let (parent_params, self_params, type_params, impl_trait_params) =
-            def_generics.as_ref().map_or((0, 0, 0), |g| g.len_split());
+            def_generics.as_ref().map_or((0, 0, 0, 0), |g| g.provenance_split());
+        assert_eq!(self_params, 0); // method shouldn't have another Self param
+        let total_len = parent_params + type_params + impl_trait_params;
         let mut substs = Vec::with_capacity(total_len);
         // Parent arguments are unknown, except for the receiver type
         if let Some(parent_generics) = def_generics.as_ref().map(|p| p.iter_parent()) {
@@ -663,7 +665,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
         // handle provided type arguments
         if let Some(generic_args) = generic_args {
             // if args are provided, it should be all of them, but we can't rely on that
-            for arg in generic_args.args.iter().take(child_len) {
+            for arg in generic_args.args.iter().take(type_params) {
                 match arg {
                     GenericArg::Type(type_ref) => {
                         let ty = self.make_ty(type_ref);

crates/ra_hir_ty/src/lower.rs

@@ -161,15 +161,19 @@ impl Ty {
                     ImplTraitLoweringMode::Variable => {
                         let idx = ctx.impl_trait_counter.get();
                         ctx.impl_trait_counter.set(idx + 1);
-                        let (self_params, list_params, _impl_trait_params) =
+                        let (parent_params, self_params, list_params, _impl_trait_params) =
                             if let Some(def) = ctx.resolver.generic_def() {
                                 let generics = generics(ctx.db, def);
                                 generics.provenance_split()
                             } else {
-                                (0, 0, 0)
+                                (0, 0, 0, 0)
                             };
-                        // assert!((idx as usize) < impl_trait_params); // TODO return position impl trait
+                        Ty::Bound(
-                        Ty::Bound(idx as u32 + self_params as u32 + list_params as u32)
+                            idx as u32
+                                + parent_params as u32
+                                + self_params as u32
+                                + list_params as u32,
+                        )
                     }
                     ImplTraitLoweringMode::Disallowed => {
                         // FIXME: report error
@@ -420,26 +424,23 @@ pub(super) fn substs_from_path_segment(
     ctx: &TyLoweringContext<'_, impl HirDatabase>,
     segment: PathSegment<'_>,
     def_generic: Option<GenericDefId>,
-    add_self_param: bool,
+    _add_self_param: bool,
 ) -> Substs {
     let mut substs = Vec::new();
     let def_generics = def_generic.map(|def| generics(ctx.db, def.into()));
 
-    let (total_len, parent_len, child_len) = def_generics.map_or((0, 0, 0), |g| g.len_split());
+    let (parent_params, self_params, type_params, impl_trait_params) =
-    substs.extend(iter::repeat(Ty::Unknown).take(parent_len));
+        def_generics.map_or((0, 0, 0, 0), |g| g.provenance_split());
-    if add_self_param {
+    substs.extend(iter::repeat(Ty::Unknown).take(parent_params));
-        // FIXME this add_self_param argument is kind of a hack: Traits have the
-        // Self type as an implicit first type parameter, but it can't be
-        // actually provided in the type arguments
-        // (well, actually sometimes it can, in the form of type-relative paths: `<Foo as Default>::default()`)
-        // TODO handle this using type param provenance (if there's a self param, and not one provided, add unknown)
-        substs.push(Ty::Unknown);
-    }
     if let Some(generic_args) = &segment.args_and_bindings {
+        if !generic_args.has_self_type {
+            substs.extend(iter::repeat(Ty::Unknown).take(self_params));
+        }
+        let expected_num =
+            if generic_args.has_self_type { self_params + type_params } else { type_params };
+        let skip = if generic_args.has_self_type && self_params == 0 { 1 } else { 0 };
         // if args are provided, it should be all of them, but we can't rely on that
-        let self_param_correction = if add_self_param { 1 } else { 0 };
+        for arg in generic_args.args.iter().skip(skip).take(expected_num) {
-        let child_len = child_len - self_param_correction;
-        for arg in generic_args.args.iter().take(child_len) {
             match arg {
                 GenericArg::Type(type_ref) => {
                     let ty = Ty::from_hir(ctx, type_ref);
@@ -448,9 +449,9 @@ pub(super) fn substs_from_path_segment(
             }
         }
     }
+    let total_len = parent_params + self_params + type_params + impl_trait_params;
     // add placeholders for args that were not provided
-    let supplied_params = substs.len();
+    for _ in substs.len()..total_len {
-    for _ in supplied_params..total_len {
         substs.push(Ty::Unknown);
     }
     assert_eq!(substs.len(), total_len);

crates/ra_hir_ty/src/tests/traits.rs

@@ -905,6 +905,114 @@ fn test(x: impl Trait<u64>, y: &impl Trait<u32>) {
     );
 }
 
+#[test]
+fn argument_impl_trait_type_args_1() {
+    assert_snapshot!(
+        infer_with_mismatches(r#"
+trait Trait {}
+trait Foo {
+    // this function has an implicit Self param, an explicit type param,
+    // and an implicit impl Trait param!
+    fn bar<T>(x: impl Trait) -> T { loop {} }
+}
+fn foo<T>(x: impl Trait) -> T { loop {} }
+struct S;
+impl Trait for S {}
+struct F;
+impl Foo for F {}
+
+fn test() {
+    Foo::bar(S);
+    <F as Foo>::bar(S);
+    F::bar(S);
+    Foo::bar::<u32>(S);
+    <F as Foo>::bar::<u32>(S);
+
+    foo(S);
+    foo::<u32>(S);
+    foo::<u32, i32>(S); // we should ignore the extraneous i32
+}
+"#, true),
+        @r###"
+    [156; 157) 'x': impl Trait
+    [176; 187) '{ loop {} }': T
+    [178; 185) 'loop {}': !
+    [183; 185) '{}': ()
+    [200; 201) 'x': impl Trait
+    [220; 231) '{ loop {} }': T
+    [222; 229) 'loop {}': !
+    [227; 229) '{}': ()
+    [301; 510) '{     ... i32 }': ()
+    [307; 315) 'Foo::bar': fn bar<{unknown}, {unknown}, S>(S) -> {unknown}
+    [307; 318) 'Foo::bar(S)': {unknown}
+    [316; 317) 'S': S
+    [324; 339) '<F as Foo>::bar': fn bar<F, {unknown}, S>(S) -> {unknown}
+    [324; 342) '<F as ...bar(S)': {unknown}
+    [340; 341) 'S': S
+    [348; 354) 'F::bar': fn bar<F, {unknown}, S>(S) -> {unknown}
+    [348; 357) 'F::bar(S)': {unknown}
+    [355; 356) 'S': S
+    [363; 378) 'Foo::bar::<u32>': fn bar<{unknown}, u32, S>(S) -> u32
+    [363; 381) 'Foo::b...32>(S)': u32
+    [379; 380) 'S': S
+    [387; 409) '<F as ...:<u32>': fn bar<F, u32, S>(S) -> u32
+    [387; 412) '<F as ...32>(S)': u32
+    [410; 411) 'S': S
+    [419; 422) 'foo': fn foo<{unknown}, S>(S) -> {unknown}
+    [419; 425) 'foo(S)': {unknown}
+    [423; 424) 'S': S
+    [431; 441) 'foo::<u32>': fn foo<u32, S>(S) -> u32
+    [431; 444) 'foo::<u32>(S)': u32
+    [442; 443) 'S': S
+    [450; 465) 'foo::<u32, i32>': fn foo<u32, S>(S) -> u32
+    [450; 468) 'foo::<...32>(S)': u32
+    [466; 467) 'S': S
+    "###
+    );
+}
+
+#[test]
+fn argument_impl_trait_type_args_2() {
+    assert_snapshot!(
+        infer_with_mismatches(r#"
+trait Trait {}
+struct S;
+impl Trait for S {}
+struct F<T>;
+impl<T> F<T> {
+    fn foo<U>(self, x: impl Trait) -> (T, U) { loop {} }
+}
+
+fn test() {
+    F.foo(S);
+    F::<u32>.foo(S);
+    F::<u32>.foo::<i32>(S);
+    F::<u32>.foo::<i32, u32>(S); // extraneous argument should be ignored
+}
+"#, true),
+        @r###"
+    [88; 92) 'self': F<T>
+    [94; 95) 'x': impl Trait
+    [119; 130) '{ loop {} }': (T, U)
+    [121; 128) 'loop {}': !
+    [126; 128) '{}': ()
+    [144; 284) '{     ...ored }': ()
+    [150; 151) 'F': F<{unknown}>
+    [150; 158) 'F.foo(S)': ({unknown}, {unknown})
+    [156; 157) 'S': S
+    [164; 172) 'F::<u32>': F<u32>
+    [164; 179) 'F::<u32>.foo(S)': (u32, {unknown})
+    [177; 178) 'S': S
+    [185; 193) 'F::<u32>': F<u32>
+    [185; 207) 'F::<u3...32>(S)': (u32, i32)
+    [205; 206) 'S': S
+    [213; 221) 'F::<u32>': F<u32>
+    [213; 240) 'F::<u3...32>(S)': (u32, i32)
+    [238; 239) 'S': S
+    "###
+    );
+}
+
 #[test]
 #[ignore]
 fn impl_trait() {

crates/ra_hir_ty/src/utils.rs

@@ -145,8 +145,9 @@ impl Generics {
         (parent + child, parent, child)
     }
 
-    /// (self, type param list, impl trait)
+    /// (parent total, self param, type param list, impl trait)
-    pub(crate) fn provenance_split(&self) -> (usize, usize, usize) {
+    pub(crate) fn provenance_split(&self) -> (usize, usize, usize, usize) {
+        let parent = self.parent_generics.as_ref().map_or(0, |p| p.len());
         let self_params = self
             .params
             .types
@@ -165,7 +166,7 @@ impl Generics {
             .iter()
             .filter(|(_, p)| p.provenance == TypeParamProvenance::ArgumentImplTrait)
             .count();
-        (self_params, list_params, impl_trait_params)
+        (parent, self_params, list_params, impl_trait_params)
     }
 
     pub(crate) fn param_idx(&self, param: TypeParamId) -> Option<u32> {