internal: move diagnostics to hir

The idea here is to eventually get rid of `dyn Diagnostic` and
`DiagnosticSink` infrastructure altogether, and just have a `enum
hir::Diagnostic` instead.

The problem with `dyn Diagnostic` is that it is defined in the lowest
level of the stack (hir_expand), but is used by the highest level (ide).

As a first step, we free hir_expand and hir_def from `dyn Diagnostic`
and kick the can up to `hir_ty`, as an intermediate state. The plan is
then to move DiagnosticSink similarly to the hir crate, and, as final
third step, remove its usage from the ide.

One currently unsolved problem is testing. You can notice that the test
which checks precise diagnostic ranges, unresolved_import_in_use_tree,
was moved to the ide layer. Logically, only IDE should have the infra to
render a specific range.

At the same time, the range is determined with the data produced in
hir_def and hir crates, so this layering is rather unfortunate. Working
on hir_def shouldn't require compiling `ide` for testing.

7 files changed, 125 insertions, 15 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/infer.rs b/crates/hir_ty/src/infer.rs
index db3c937ff..174b7471e 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,
@@ -793,11 +794,11 @@ 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;