9 files changed, 226 insertions, 20 deletions

diff --git a/crates/hir_ty/src/diagnostics.rs b/crates/hir_ty/src/diagnostics.rs
index 84fc8ce14..7598e2193 100644
--- a/crates/hir_ty/src/diagnostics.rs
+++ b/crates/hir_ty/src/diagnostics.rs
@@ -8,12 +8,14 @@ use std::{any::Any, fmt};
 
 use base_db::CrateId;
 use hir_def::{DefWithBodyId, ModuleDefId};
-use hir_expand::diagnostics::{Diagnostic, DiagnosticCode, DiagnosticSink};
 use hir_expand::{name::Name, HirFileId, InFile};
 use stdx::format_to;
 use syntax::{ast, AstPtr, SyntaxNodePtr};
 
-use crate::db::HirDatabase;
+use crate::{
+    db::HirDatabase,
+    diagnostics_sink::{Diagnostic, DiagnosticCode, DiagnosticSink},
+};
 
 pub use crate::diagnostics::expr::{record_literal_missing_fields, record_pattern_missing_fields};
 
@@ -446,15 +448,13 @@ impl Diagnostic for ReplaceFilterMapNextWithFindMap {
 mod tests {
     use base_db::{fixture::WithFixture, FileId, SourceDatabase, SourceDatabaseExt};
     use hir_def::{db::DefDatabase, AssocItemId, ModuleDefId};
-    use hir_expand::{
-        db::AstDatabase,
-        diagnostics::{Diagnostic, DiagnosticSinkBuilder},
-    };
+    use hir_expand::db::AstDatabase;
     use rustc_hash::FxHashMap;
     use syntax::{TextRange, TextSize};
 
     use crate::{
         diagnostics::{validate_body, validate_module_item},
+        diagnostics_sink::{Diagnostic, DiagnosticSinkBuilder},
         test_db::TestDB,
     };
 
diff --git a/crates/hir_ty/src/diagnostics/decl_check.rs b/crates/hir_ty/src/diagnostics/decl_check.rs
index 075dc4131..ef982cbcd 100644
--- a/crates/hir_ty/src/diagnostics/decl_check.rs
+++ b/crates/hir_ty/src/diagnostics/decl_check.rs
@@ -19,10 +19,7 @@ use hir_def::{
     src::HasSource,
     AdtId, AttrDefId, ConstId, EnumId, FunctionId, Lookup, ModuleDefId, StaticId, StructId,
 };
-use hir_expand::{
-    diagnostics::DiagnosticSink,
-    name::{AsName, Name},
-};
+use hir_expand::name::{AsName, Name};
 use stdx::{always, never};
 use syntax::{
     ast::{self, NameOwner},
@@ -32,6 +29,7 @@ use syntax::{
 use crate::{
     db::HirDatabase,
     diagnostics::{decl_check::case_conv::*, CaseType, IdentType, IncorrectCase},
+    diagnostics_sink::DiagnosticSink,
 };
 
 mod allow {
diff --git a/crates/hir_ty/src/diagnostics/expr.rs b/crates/hir_ty/src/diagnostics/expr.rs
index d1f113e7f..86f82e3fa 100644
--- a/crates/hir_ty/src/diagnostics/expr.rs
+++ b/crates/hir_ty/src/diagnostics/expr.rs
@@ -5,7 +5,7 @@
 use std::sync::Arc;
 
 use hir_def::{expr::Statement, path::path, resolver::HasResolver, AssocItemId, DefWithBodyId};
-use hir_expand::{diagnostics::DiagnosticSink, name};
+use hir_expand::name;
 use rustc_hash::FxHashSet;
 use syntax::{ast, AstPtr};
 
@@ -16,6 +16,7 @@ use crate::{
         MismatchedArgCount, MissingFields, MissingMatchArms, MissingOkOrSomeInTailExpr,
         MissingPatFields, RemoveThisSemicolon,
     },
+    diagnostics_sink::DiagnosticSink,
     AdtId, InferenceResult, Interner, TyExt, TyKind,
 };
 
diff --git a/crates/hir_ty/src/diagnostics/unsafe_check.rs b/crates/hir_ty/src/diagnostics/unsafe_check.rs
index 5d13bddea..c3c483425 100644
--- a/crates/hir_ty/src/diagnostics/unsafe_check.rs
+++ b/crates/hir_ty/src/diagnostics/unsafe_check.rs
@@ -9,10 +9,10 @@ use hir_def::{
     resolver::{resolver_for_expr, ResolveValueResult, ValueNs},
     DefWithBodyId,
 };
-use hir_expand::diagnostics::DiagnosticSink;
 
 use crate::{
-    db::HirDatabase, diagnostics::MissingUnsafe, InferenceResult, Interner, TyExt, TyKind,
+    db::HirDatabase, diagnostics::MissingUnsafe, diagnostics_sink::DiagnosticSink, InferenceResult,
+    Interner, TyExt, TyKind,
 };
 
 pub(super) struct UnsafeValidator<'a, 'b: 'a> {
diff --git a/crates/hir_ty/src/diagnostics_sink.rs b/crates/hir_ty/src/diagnostics_sink.rs
new file mode 100644
index 000000000..084fa8b06
--- /dev/null
+++ b/crates/hir_ty/src/diagnostics_sink.rs
@@ -0,0 +1,109 @@
+//! Semantic errors and warnings.
+//!
+//! The `Diagnostic` trait defines a trait object which can represent any
+//! diagnostic.
+//!
+//! `DiagnosticSink` struct is used as an emitter for diagnostic. When creating
+//! a `DiagnosticSink`, you supply a callback which can react to a `dyn
+//! Diagnostic` or to any concrete diagnostic (downcasting is used internally).
+//!
+//! Because diagnostics store file offsets, it's a bad idea to store them
+//! directly in salsa. For this reason, every hir subsytem defines it's own
+//! strongly-typed closed set of diagnostics which use hir ids internally, are
+//! stored in salsa and do *not* implement the `Diagnostic` trait. Instead, a
+//! subsystem provides a separate, non-query-based API which can walk all stored
+//! values and transform them into instances of `Diagnostic`.
+
+use std::{any::Any, fmt};
+
+use hir_expand::InFile;
+use syntax::SyntaxNodePtr;
+
+#[derive(Copy, Clone, Debug, PartialEq)]
+pub struct DiagnosticCode(pub &'static str);
+
+impl DiagnosticCode {
+    pub fn as_str(&self) -> &str {
+        self.0
+    }
+}
+
+pub trait Diagnostic: Any + Send + Sync + fmt::Debug + 'static {
+    fn code(&self) -> DiagnosticCode;
+    fn message(&self) -> String;
+    /// Source element that triggered the diagnostics.
+    ///
+    /// Note that this should reflect "semantics", rather than specific span we
+    /// want to highlight. When rendering the diagnostics into an error message,
+    /// the IDE will fetch the `SyntaxNode` and will narrow the span
+    /// appropriately.
+    fn display_source(&self) -> InFile<SyntaxNodePtr>;
+    fn as_any(&self) -> &(dyn Any + Send + 'static);
+    fn is_experimental(&self) -> bool {
+        false
+    }
+}
+
+pub struct DiagnosticSink<'a> {
+    callbacks: Vec<Box<dyn FnMut(&dyn Diagnostic) -> Result<(), ()> + 'a>>,
+    filters: Vec<Box<dyn FnMut(&dyn Diagnostic) -> bool + 'a>>,
+    default_callback: Box<dyn FnMut(&dyn Diagnostic) + 'a>,
+}
+
+impl<'a> DiagnosticSink<'a> {
+    pub fn push(&mut self, d: impl Diagnostic) {
+        let d: &dyn Diagnostic = &d;
+        self._push(d);
+    }
+
+    fn _push(&mut self, d: &dyn Diagnostic) {
+        for filter in &mut self.filters {
+            if !filter(d) {
+                return;
+            }
+        }
+        for cb in &mut self.callbacks {
+            match cb(d) {
+                Ok(()) => return,
+                Err(()) => (),
+            }
+        }
+        (self.default_callback)(d)
+    }
+}
+
+pub struct DiagnosticSinkBuilder<'a> {
+    callbacks: Vec<Box<dyn FnMut(&dyn Diagnostic) -> Result<(), ()> + 'a>>,
+    filters: Vec<Box<dyn FnMut(&dyn Diagnostic) -> bool + 'a>>,
+}
+
+impl<'a> DiagnosticSinkBuilder<'a> {
+    pub fn new() -> Self {
+        Self { callbacks: Vec::new(), filters: Vec::new() }
+    }
+
+    pub fn filter<F: FnMut(&dyn Diagnostic) -> bool + 'a>(mut self, cb: F) -> Self {
+        self.filters.push(Box::new(cb));
+        self
+    }
+
+    pub fn on<D: Diagnostic, F: FnMut(&D) + 'a>(mut self, mut cb: F) -> Self {
+        let cb = move |diag: &dyn Diagnostic| match diag.as_any().downcast_ref::<D>() {
+            Some(d) => {
+                cb(d);
+                Ok(())
+            }
+            None => Err(()),
+        };
+        self.callbacks.push(Box::new(cb));
+        self
+    }
+
+    pub fn build<F: FnMut(&dyn Diagnostic) + 'a>(self, default_callback: F) -> DiagnosticSink<'a> {
+        DiagnosticSink {
+            callbacks: self.callbacks,
+            filters: self.filters,
+            default_callback: Box::new(default_callback),
+        }
+    }
+}
diff --git a/crates/hir_ty/src/display.rs b/crates/hir_ty/src/display.rs
index 637bbc634..44f843bf3 100644
--- a/crates/hir_ty/src/display.rs
+++ b/crates/hir_ty/src/display.rs
@@ -778,8 +778,10 @@ fn write_bounds_like_dyn_trait(
             }
             WhereClause::AliasEq(alias_eq) if is_fn_trait => {
                 is_fn_trait = false;
-                write!(f, " -> ")?;
-                alias_eq.ty.hir_fmt(f)?;
+                if !alias_eq.ty.is_unit() {
+                    write!(f, " -> ")?;
+                    alias_eq.ty.hir_fmt(f)?;
+                }
             }
             WhereClause::AliasEq(AliasEq { ty, alias }) => {
                 // in types in actual Rust, these will always come
diff --git a/crates/hir_ty/src/infer.rs b/crates/hir_ty/src/infer.rs
index db3c937ff..8cefd80f3 100644
--- a/crates/hir_ty/src/infer.rs
+++ b/crates/hir_ty/src/infer.rs
@@ -28,13 +28,14 @@ use hir_def::{
     AdtId, AssocItemId, DefWithBodyId, EnumVariantId, FieldId, FunctionId, HasModule, Lookup,
     TraitId, TypeAliasId, VariantId,
 };
-use hir_expand::{diagnostics::DiagnosticSink, name::name};
+use hir_expand::name::name;
 use la_arena::ArenaMap;
 use rustc_hash::FxHashMap;
 use stdx::impl_from;
 use syntax::SmolStr;
 
 use super::{DomainGoal, InEnvironment, ProjectionTy, TraitEnvironment, TraitRef, Ty};
+use crate::diagnostics_sink::DiagnosticSink;
 use crate::{
     db::HirDatabase, fold_tys, infer::diagnostics::InferenceDiagnostic,
     lower::ImplTraitLoweringMode, to_assoc_type_id, AliasEq, AliasTy, Goal, Interner, Substitution,
@@ -578,9 +579,14 @@ impl<'a> InferenceContext<'a> {
     }
 
     fn resolve_ops_try_ok(&self) -> Option<TypeAliasId> {
+        // FIXME resolve via lang_item once try v2 is stable
         let path = path![core::ops::Try];
         let trait_ = self.resolver.resolve_known_trait(self.db.upcast(), &path)?;
-        self.db.trait_data(trait_).associated_type_by_name(&name![Ok])
+        let trait_data = self.db.trait_data(trait_);
+        trait_data
+            // FIXME remove once try v2 is stable
+            .associated_type_by_name(&name![Ok])
+            .or_else(|| trait_data.associated_type_by_name(&name![Output]))
     }
 
     fn resolve_ops_neg_output(&self) -> Option<TypeAliasId> {
@@ -793,11 +799,11 @@ impl std::ops::BitOrAssign for Diverges {
 
 mod diagnostics {
     use hir_def::{expr::ExprId, DefWithBodyId};
-    use hir_expand::diagnostics::DiagnosticSink;
 
     use crate::{
         db::HirDatabase,
         diagnostics::{BreakOutsideOfLoop, NoSuchField},
+        diagnostics_sink::DiagnosticSink,
     };
 
     #[derive(Debug, PartialEq, Eq, Clone)]
diff --git a/crates/hir_ty/src/lib.rs b/crates/hir_ty/src/lib.rs
index ef021978a..50e0d6333 100644
--- a/crates/hir_ty/src/lib.rs
+++ b/crates/hir_ty/src/lib.rs
@@ -21,6 +21,7 @@ mod utils;
 mod walk;
 pub mod db;
 pub mod diagnostics;
+pub mod diagnostics_sink;
 pub mod display;
 pub mod method_resolution;
 pub mod primitive;
diff --git a/crates/hir_ty/src/tests/traits.rs b/crates/hir_ty/src/tests/traits.rs
index a5a2df54c..6ad96bfe3 100644
--- a/crates/hir_ty/src/tests/traits.rs
+++ b/crates/hir_ty/src/tests/traits.rs
@@ -161,6 +161,43 @@ mod result {
 }
 
 #[test]
+fn infer_tryv2() {
+    check_types(
+        r#"
+//- /main.rs crate:main deps:core
+fn test() {
+    let r: Result<i32, u64> = Result::Ok(1);
+    let v = r?;
+    v;
+} //^ i32
+
+//- /core.rs crate:core
+#[prelude_import] use ops::*;
+mod ops {
+    trait Try {
+        type Output;
+        type Residual;
+    }
+}
+
+#[prelude_import] use result::*;
+mod result {
+    enum Infallible {}
+    enum Result<O, E> {
+        Ok(O),
+        Err(E)
+    }
+
+    impl<O, E> crate::ops::Try for Result<O, E> {
+        type Output = O;
+        type Error = Result<Infallible, E>;
+    }
+}
+"#,
+    );
+}
+
+#[test]
 fn infer_for_loop() {
     check_types(
         r#"
@@ -3041,7 +3078,7 @@ fn infer_fn_trait_arg() {
 
 #[test]
 fn infer_box_fn_arg() {
-    // The type mismatch is a bug
+    // The type mismatch is because we don't define Unsize and CoerceUnsized
     check_infer_with_mismatches(
         r#"
 //- /lib.rs deps:std
@@ -3101,7 +3138,7 @@ fn foo() {
             555..557 'ps': {unknown}
             559..561 '{}': ()
             568..569 'f': Box<dyn FnOnce(&Option<i32>)>
-            568..573 'f(&s)': FnOnce::Output<dyn FnOnce(&Option<i32>), (&Option<i32>,)>
+            568..573 'f(&s)': ()
             570..572 '&s': &Option<i32>
             571..572 's': Option<i32>
             549..562: expected Box<dyn FnOnce(&Option<i32>)>, got Box<|{unknown}| -> ()>
@@ -3571,3 +3608,55 @@ fn main() {
         "#]],
     )
 }
+
+#[test]
+fn fn_returning_unit() {
+    check_infer_with_mismatches(
+        r#"
+#[lang = "fn_once"]
+trait FnOnce<Args> {
+    type Output;
+}
+
+fn test<F: FnOnce()>(f: F) {
+    let _: () = f();
+}"#,
+        expect![[r#"
+            82..83 'f': F
+            88..112 '{     ...f(); }': ()
+            98..99 '_': ()
+            106..107 'f': F
+            106..109 'f()': ()
+        "#]],
+    );
+}
+
+#[test]
+fn trait_in_scope_of_trait_impl() {
+    check_infer(
+        r#"
+mod foo {
+    pub trait Foo {
+        fn foo(self);
+        fn bar(self) -> usize { 0 }
+    }
+}
+impl foo::Foo for u32 {
+    fn foo(self) {
+        let _x = self.bar();
+    }
+}
+    "#,
+        expect![[r#"
+            45..49 'self': Self
+            67..71 'self': Self
+            82..87 '{ 0 }': usize
+            84..85 '0': usize
+            131..135 'self': u32
+            137..173 '{     ...     }': ()
+            151..153 '_x': usize
+            156..160 'self': u32
+            156..166 'self.bar()': usize
+        "#]],
+    );
+}