3 files changed, 159 insertions, 17 deletions

diff --git a/crates/hir/src/diagnostics.rs b/crates/hir/src/diagnostics.rs
index 26dbcd86a..8a7c3a4fd 100644
--- a/crates/hir/src/diagnostics.rs
+++ b/crates/hir/src/diagnostics.rs
@@ -11,9 +11,8 @@ use hir_expand::{name::Name, HirFileId, InFile};
 use stdx::format_to;
 use syntax::{ast, AstPtr, SyntaxNodePtr, TextRange};
 
-pub use hir_ty::{
-    diagnostics::IncorrectCase,
-    diagnostics_sink::{Diagnostic, DiagnosticCode, DiagnosticSink, DiagnosticSinkBuilder},
+pub use crate::diagnostics_sink::{
+    Diagnostic, DiagnosticCode, DiagnosticSink, DiagnosticSinkBuilder,
 };
 
 // Diagnostic: unresolved-module
@@ -578,3 +577,33 @@ impl Diagnostic for InternalBailedOut {
         self
     }
 }
+
+pub use hir_ty::diagnostics::IncorrectCase;
+
+impl Diagnostic for IncorrectCase {
+    fn code(&self) -> DiagnosticCode {
+        DiagnosticCode("incorrect-ident-case")
+    }
+
+    fn message(&self) -> String {
+        format!(
+            "{} `{}` should have {} name, e.g. `{}`",
+            self.ident_type,
+            self.ident_text,
+            self.expected_case.to_string(),
+            self.suggested_text
+        )
+    }
+
+    fn display_source(&self) -> InFile<SyntaxNodePtr> {
+        InFile::new(self.file, self.ident.clone().into())
+    }
+
+    fn as_any(&self) -> &(dyn Any + Send + 'static) {
+        self
+    }
+
+    fn is_experimental(&self) -> bool {
+        true
+    }
+}
diff --git a/crates/hir/src/diagnostics_sink.rs b/crates/hir/src/diagnostics_sink.rs
new file mode 100644
index 000000000..084fa8b06
--- /dev/null
+++ b/crates/hir/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/src/lib.rs b/crates/hir/src/lib.rs
index dd5515c2b..2468c0dc6 100644
--- a/crates/hir/src/lib.rs
+++ b/crates/hir/src/lib.rs
@@ -27,6 +27,7 @@ mod attrs;
 mod has_source;
 
 pub mod diagnostics;
+pub mod diagnostics_sink;
 pub mod db;
 
 mod display;
@@ -35,13 +36,6 @@ use std::{iter, sync::Arc};
 
 use arrayvec::ArrayVec;
 use base_db::{CrateDisplayName, CrateId, Edition, FileId};
-use diagnostics::{
-    BreakOutsideOfLoop, InactiveCode, InternalBailedOut, MacroError, MismatchedArgCount,
-    MissingFields, MissingOkOrSomeInTailExpr, MissingPatFields, MissingUnsafe, NoSuchField,
-    RemoveThisSemicolon, ReplaceFilterMapNextWithFindMap, UnimplementedBuiltinMacro,
-    UnresolvedExternCrate, UnresolvedImport, UnresolvedMacroCall, UnresolvedModule,
-    UnresolvedProcMacro,
-};
 use either::Either;
 use hir_def::{
     adt::{ReprKind, VariantData},
@@ -64,8 +58,7 @@ use hir_ty::{
     consteval::ConstExt,
     could_unify,
     diagnostics::BodyValidationDiagnostic,
-    diagnostics_sink::DiagnosticSink,
-    method_resolution::{self, def_crates, TyFingerprint},
+    method_resolution::{self, TyFingerprint},
     primitive::UintTy,
     subst_prefix,
     traits::FnTrait,
@@ -87,7 +80,14 @@ use tt::{Ident, Leaf, Literal, TokenTree};
 
 use crate::{
     db::{DefDatabase, HirDatabase},
-    diagnostics::MissingMatchArms,
+    diagnostics::{
+        BreakOutsideOfLoop, InactiveCode, InternalBailedOut, MacroError, MismatchedArgCount,
+        MissingFields, MissingMatchArms, MissingOkOrSomeInTailExpr, MissingPatFields,
+        MissingUnsafe, NoSuchField, RemoveThisSemicolon, ReplaceFilterMapNextWithFindMap,
+        UnimplementedBuiltinMacro, UnresolvedExternCrate, UnresolvedImport, UnresolvedMacroCall,
+        UnresolvedModule, UnresolvedProcMacro,
+    },
+    diagnostics_sink::DiagnosticSink,
 };
 
 pub use crate::{
@@ -361,7 +361,9 @@ impl ModuleDef {
             None => return,
         };
 
-        hir_ty::diagnostics::validate_module_item(db, module.id.krate(), id, sink)
+        for diag in hir_ty::diagnostics::validate_module_item(db, module.id.krate(), id) {
+            sink.push(diag)
+        }
     }
 }
 
@@ -1225,7 +1227,9 @@ impl Function {
             }
         }
 
-        hir_ty::diagnostics::validate_module_item(db, krate, self.id.into(), sink);
+        for diag in hir_ty::diagnostics::validate_module_item(db, krate, self.id.into()) {
+            sink.push(diag)
+        }
     }
 
     /// Whether this function declaration has a definition.
@@ -1944,7 +1948,7 @@ impl Impl {
     }
 
     pub fn all_for_type(db: &dyn HirDatabase, Type { krate, ty, .. }: Type) -> Vec<Impl> {
-        let def_crates = match def_crates(db, &ty, krate) {
+        let def_crates = match method_resolution::def_crates(db, &ty, krate) {
             Some(def_crates) => def_crates,
             None => return Vec::new(),
         };
@@ -2350,7 +2354,7 @@ impl Type {
         krate: Crate,
         mut callback: impl FnMut(AssocItem) -> Option<T>,
     ) -> Option<T> {
-        for krate in def_crates(db, &self.ty, krate.id)? {
+        for krate in method_resolution::def_crates(db, &self.ty, krate.id)? {
             let impls = db.inherent_impls_in_crate(krate);
 
             for impl_def in impls.for_self_ty(&self.ty) {