Add API to emit type-checking diagnostics (#12988)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

crates/red_knot_python_semantic/src/db.rs

@@ -1,15 +1,18 @@
+use ruff_db::files::File;
 use ruff_db::{Db as SourceDb, Upcast};
 
 /// Database giving access to semantic information about a Python program.
 #[salsa::db]
-pub trait Db: SourceDb + Upcast<dyn SourceDb> {}
+pub trait Db: SourceDb + Upcast<dyn SourceDb> {
+    fn is_file_open(&self, file: File) -> bool;
+}
 
 #[cfg(test)]
 pub(crate) mod tests {
     use std::sync::Arc;
 
     use crate::module_resolver::vendored_typeshed_stubs;
-    use ruff_db::files::Files;
+    use ruff_db::files::{File, Files};
     use ruff_db::system::{DbWithTestSystem, System, TestSystem};
     use ruff_db::vendored::VendoredFileSystem;
     use ruff_db::{Db as SourceDb, Upcast};
@@ -91,7 +94,11 @@ pub(crate) mod tests {
     }
 
     #[salsa::db]
-    impl Db for TestDb {}
+    impl Db for TestDb {
+        fn is_file_open(&self, file: File) -> bool {
+            !file.path(self).is_vendored_path()
+        }
+    }
 
     #[salsa::db]
     impl salsa::Database for TestDb {

crates/red_knot_python_semantic/src/semantic_index.rs

@@ -154,6 +154,10 @@ impl<'db> SemanticIndex<'db> {
         &self.scopes[id]
     }
 
+    pub(crate) fn scope_ids(&self) -> impl Iterator<Item = ScopeId> {
+        self.scope_ids_by_scope.iter().copied()
+    }
+
     /// Returns the id of the parent scope.
     pub(crate) fn parent_scope_id(&self, scope_id: FileScopeId) -> Option<FileScopeId> {
         let scope = self.scope(scope_id);

crates/red_knot_python_semantic/src/types.rs

@@ -5,21 +5,37 @@ use crate::builtins::builtins_scope;
 use crate::semantic_index::definition::Definition;
 use crate::semantic_index::symbol::{ScopeId, ScopedSymbolId};
 use crate::semantic_index::{
-    global_scope, symbol_table, use_def_map, DefinitionWithConstraints,
+    global_scope, semantic_index, symbol_table, use_def_map, DefinitionWithConstraints,
     DefinitionWithConstraintsIterator,
 };
 use crate::types::narrow::narrowing_constraint;
 use crate::{Db, FxOrderSet};
 
+pub(crate) use self::builder::{IntersectionBuilder, UnionBuilder};
+pub(crate) use self::diagnostic::TypeCheckDiagnostics;
+pub(crate) use self::infer::{
+    infer_definition_types, infer_expression_types, infer_scope_types, TypeInference,
+};
+
 mod builder;
+mod diagnostic;
 mod display;
 mod infer;
 mod narrow;
 
-pub(crate) use self::builder::{IntersectionBuilder, UnionBuilder};
-pub(crate) use self::infer::{
-    infer_definition_types, infer_expression_types, infer_scope_types, TypeInference,
-};
+pub fn check_types(db: &dyn Db, file: File) -> TypeCheckDiagnostics {
+    let _span = tracing::trace_span!("check_types", file=?file.path(db)).entered();
+
+    let index = semantic_index(db, file);
+    let mut diagnostics = TypeCheckDiagnostics::new();
+
+    for scope_id in index.scope_ids() {
+        let result = infer_scope_types(db, scope_id);
+        diagnostics.extend(result.diagnostics());
+    }
+
+    diagnostics
+}
 
 /// Infer the public type of a symbol (its type as seen from outside its scope).
 pub(crate) fn symbol_ty<'db>(
@@ -333,3 +349,48 @@ pub struct IntersectionType<'db> {
     /// directly in intersections rather than as a separate type.
     negative: FxOrderSet<Type<'db>>,
 }
+
+#[cfg(test)]
+mod tests {
+    use anyhow::Context;
+
+    use ruff_db::files::system_path_to_file;
+    use ruff_db::system::{DbWithTestSystem, SystemPathBuf};
+
+    use crate::db::tests::TestDb;
+    use crate::{Program, ProgramSettings, PythonVersion, SearchPathSettings};
+
+    #[test]
+    fn check_types() -> anyhow::Result<()> {
+        let mut db = TestDb::new();
+
+        db.write_file("src/foo.py", "import bar\n")
+            .context("Failed to write foo.py")?;
+
+        Program::from_settings(
+            &db,
+            ProgramSettings {
+                target_version: PythonVersion::default(),
+                search_paths: SearchPathSettings {
+                    extra_paths: Vec::new(),
+                    src_root: SystemPathBuf::from("/src"),
+                    site_packages: vec![],
+                    custom_typeshed: None,
+                },
+            },
+        )
+        .expect("Valid search path settings");
+
+        let foo = system_path_to_file(&db, "src/foo.py").context("Failed to resolve foo.py")?;
+
+        let diagnostics = super::check_types(&db, foo);
+
+        assert_eq!(diagnostics.len(), 1);
+        assert_eq!(
+            diagnostics[0].message(),
+            "Import 'bar' could not be resolved."
+        );
+
+        Ok(())
+    }
+}

crates/red_knot_python_semantic/src/types/diagnostic.rs

@@ -0,0 +1,111 @@
+use ruff_db::files::File;
+use ruff_text_size::{Ranged, TextRange};
+use std::fmt::Formatter;
+use std::ops::Deref;
+use std::sync::Arc;
+
+#[derive(Debug, Eq, PartialEq)]
+pub struct TypeCheckDiagnostic {
+    // TODO: Don't use string keys for rules
+    pub(super) rule: String,
+    pub(super) message: String,
+    pub(super) range: TextRange,
+    pub(super) file: File,
+}
+
+impl TypeCheckDiagnostic {
+    pub fn rule(&self) -> &str {
+        &self.rule
+    }
+
+    pub fn message(&self) -> &str {
+        &self.message
+    }
+
+    pub fn file(&self) -> File {
+        self.file
+    }
+}
+
+impl Ranged for TypeCheckDiagnostic {
+    fn range(&self) -> TextRange {
+        self.range
+    }
+}
+
+/// A collection of type check diagnostics.
+///
+/// The diagnostics are wrapped in an `Arc` because they need to be cloned multiple times
+/// when going from `infer_expression` to `check_file`. We could consider
+/// making [`TypeCheckDiagnostic`] a Salsa struct to have them Arena-allocated (once the Tables refactor is done).
+/// Using Salsa struct does have the downside that it leaks the Salsa dependency into diagnostics and
+/// each Salsa-struct comes with an overhead.
+#[derive(Default, Eq, PartialEq)]
+pub struct TypeCheckDiagnostics {
+    inner: Vec<std::sync::Arc<TypeCheckDiagnostic>>,
+}
+
+impl TypeCheckDiagnostics {
+    pub fn new() -> Self {
+        Self { inner: Vec::new() }
+    }
+
+    pub(super) fn push(&mut self, diagnostic: TypeCheckDiagnostic) {
+        self.inner.push(Arc::new(diagnostic));
+    }
+
+    pub(crate) fn shrink_to_fit(&mut self) {
+        self.inner.shrink_to_fit();
+    }
+}
+
+impl Extend<TypeCheckDiagnostic> for TypeCheckDiagnostics {
+    fn extend<T: IntoIterator<Item = TypeCheckDiagnostic>>(&mut self, iter: T) {
+        self.inner.extend(iter.into_iter().map(std::sync::Arc::new));
+    }
+}
+
+impl Extend<std::sync::Arc<TypeCheckDiagnostic>> for TypeCheckDiagnostics {
+    fn extend<T: IntoIterator<Item = Arc<TypeCheckDiagnostic>>>(&mut self, iter: T) {
+        self.inner.extend(iter);
+    }
+}
+
+impl<'a> Extend<&'a std::sync::Arc<TypeCheckDiagnostic>> for TypeCheckDiagnostics {
+    fn extend<T: IntoIterator<Item = &'a Arc<TypeCheckDiagnostic>>>(&mut self, iter: T) {
+        self.inner
+            .extend(iter.into_iter().map(std::sync::Arc::clone));
+    }
+}
+
+impl std::fmt::Debug for TypeCheckDiagnostics {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        self.inner.fmt(f)
+    }
+}
+
+impl Deref for TypeCheckDiagnostics {
+    type Target = [std::sync::Arc<TypeCheckDiagnostic>];
+
+    fn deref(&self) -> &Self::Target {
+        &self.inner
+    }
+}
+
+impl IntoIterator for TypeCheckDiagnostics {
+    type Item = Arc<TypeCheckDiagnostic>;
+    type IntoIter = std::vec::IntoIter<std::sync::Arc<TypeCheckDiagnostic>>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.inner.into_iter()
+    }
+}
+
+impl<'a> IntoIterator for &'a TypeCheckDiagnostics {
+    type Item = &'a Arc<TypeCheckDiagnostic>;
+    type IntoIter = std::slice::Iter<'a, std::sync::Arc<TypeCheckDiagnostic>>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.inner.iter()
+    }
+}

crates/red_knot_python_semantic/src/types/infer.rs

@@ -29,7 +29,8 @@ use salsa::plumbing::AsId;
 use ruff_db::files::File;
 use ruff_db::parsed::parsed_module;
 use ruff_python_ast as ast;
-use ruff_python_ast::{Expr, ExprContext};
+use ruff_python_ast::{AnyNodeRef, ExprContext};
+use ruff_text_size::Ranged;
 
 use crate::builtins::builtins_scope;
 use crate::module_name::ModuleName;
@@ -40,6 +41,7 @@ use crate::semantic_index::expression::Expression;
 use crate::semantic_index::semantic_index;
 use crate::semantic_index::symbol::{FileScopeId, NodeWithScopeKind, NodeWithScopeRef, ScopeId};
 use crate::semantic_index::SemanticIndex;
+use crate::types::diagnostic::{TypeCheckDiagnostic, TypeCheckDiagnostics};
 use crate::types::{
     builtins_symbol_ty_by_name, definitions_ty, global_symbol_ty_by_name, ClassType, FunctionType,
     Name, Type, UnionBuilder,
@@ -123,13 +125,16 @@ pub(crate) enum InferenceRegion<'db> {
 }
 
 /// The inferred types for a single region.
-#[derive(Debug, Eq, PartialEq, Default, Clone)]
+#[derive(Debug, Eq, PartialEq, Default)]
 pub(crate) struct TypeInference<'db> {
     /// The types of every expression in this region.
     expressions: FxHashMap<ScopedExpressionId, Type<'db>>,
 
     /// The types of every definition in this region.
     definitions: FxHashMap<Definition<'db>, Type<'db>>,
+
+    /// The diagnostics for this region.
+    diagnostics: TypeCheckDiagnostics,
 }
 
 impl<'db> TypeInference<'db> {
@@ -142,9 +147,14 @@ impl<'db> TypeInference<'db> {
         self.definitions[&definition]
     }
 
+    pub(crate) fn diagnostics(&self) -> &[std::sync::Arc<TypeCheckDiagnostic>] {
+        &self.diagnostics
+    }
+
     fn shrink_to_fit(&mut self) {
         self.expressions.shrink_to_fit();
         self.definitions.shrink_to_fit();
+        self.diagnostics.shrink_to_fit();
     }
 }
 
@@ -235,6 +245,7 @@ impl<'db> TypeInferenceBuilder<'db> {
     fn extend(&mut self, inference: &TypeInference<'db>) {
         self.types.definitions.extend(inference.definitions.iter());
         self.types.expressions.extend(inference.expressions.iter());
+        self.types.diagnostics.extend(&inference.diagnostics);
     }
 
     /// Infers types in the given [`InferenceRegion`].
@@ -855,7 +866,7 @@ impl<'db> TypeInferenceBuilder<'db> {
             asname: _,
         } = alias;
 
-        let module_ty = self.module_ty_from_name(ModuleName::new(name));
+        let module_ty = self.module_ty_from_name(ModuleName::new(name), alias.into());
         self.types.definitions.insert(definition, module_ty);
     }
 
@@ -953,7 +964,7 @@ impl<'db> TypeInferenceBuilder<'db> {
             ModuleName::new(module_name)
         };
 
-        let module_ty = self.module_ty_from_name(module_name);
+        let module_ty = self.module_ty_from_name(module_name, import_from.into());
 
         let ast::Alias {
             range: _,
@@ -984,10 +995,26 @@ impl<'db> TypeInferenceBuilder<'db> {
         }
     }
 
-    fn module_ty_from_name(&self, module_name: Option<ModuleName>) -> Type<'db> {
-        module_name
-            .and_then(|module_name| resolve_module(self.db, module_name))
-            .map_or(Type::Unknown, |module| Type::Module(module.file()))
+    fn module_ty_from_name(
+        &mut self,
+        module_name: Option<ModuleName>,
+        node: AnyNodeRef,
+    ) -> Type<'db> {
+        let Some(module_name) = module_name else {
+            return Type::Unknown;
+        };
+
+        if let Some(module) = resolve_module(self.db, module_name.clone()) {
+            Type::Module(module.file())
+        } else {
+            self.add_diagnostic(
+                node,
+                "unresolved-import",
+                format_args!("Import '{module_name}' could not be resolved."),
+            );
+
+            Type::Unknown
+        }
     }
 
     fn infer_decorator(&mut self, decorator: &ast::Decorator) -> Type<'db> {
@@ -1059,7 +1086,7 @@ impl<'db> TypeInferenceBuilder<'db> {
             ast::Expr::Yield(yield_expression) => self.infer_yield_expression(yield_expression),
             ast::Expr::YieldFrom(yield_from) => self.infer_yield_from_expression(yield_from),
             ast::Expr::Await(await_expression) => self.infer_await_expression(await_expression),
-            Expr::IpyEscapeCommand(_) => todo!("Implement Ipy escape command support"),
+            ast::Expr::IpyEscapeCommand(_) => todo!("Implement Ipy escape command support"),
         };
 
         let expr_id = expression.scoped_ast_id(self.db, self.scope);
@@ -1706,6 +1733,28 @@ impl<'db> TypeInferenceBuilder<'db> {
         }
     }
 
+    /// Adds a new diagnostic.
+    ///
+    /// The diagnostic does not get added if the rule isn't enabled for this file.
+    fn add_diagnostic(&mut self, node: AnyNodeRef, rule: &str, message: std::fmt::Arguments) {
+        if !self.db.is_file_open(self.file) {
+            return;
+        }
+
+        // TODO: Don't emit the diagnostic if:
+        // * The enclosing node contains any syntax errors
+        // * The rule is disabled for this file. We probably want to introduce a new query that
+        //   returns a rule selector for a given file that respects the package's settings,
+        //   any global pragma comments in the file, and any per-file-ignores.
+
+        self.types.diagnostics.push(TypeCheckDiagnostic {
+            file: self.file,
+            rule: rule.to_string(),
+            message: message.to_string(),
+            range: node.range(),
+        });
+    }
+
     pub(super) fn finish(mut self) -> TypeInference<'db> {
         self.infer_region();
         self.types.shrink_to_fit();

crates/red_knot_wasm/src/lib.rs

@@ -109,7 +109,7 @@ impl Workspace {
     pub fn check_file(&self, file_id: &FileHandle) -> Result<Vec<String>, Error> {
         let result = self.db.check_file(file_id.file).map_err(into_error)?;
 
-        Ok(result.to_vec())
+        Ok(result.clone())
     }
 
     /// Checks all open files

crates/red_knot_wasm/tests/api.rs

@@ -17,5 +17,8 @@ fn check() {
 
     let result = workspace.check_file(&test).expect("Check to succeed");
 
-    assert_eq!(result, vec!["/test.py:1:8: Unresolved import 'random22'"]);
+    assert_eq!(
+        result,
+        vec!["/test.py:1:8: Import 'random22' could not be resolved.",]
+    );
 }

crates/red_knot_workspace/src/db.rs

@@ -11,7 +11,6 @@ use ruff_db::{Db as SourceDb, Upcast};
 use salsa::plumbing::ZalsaDatabase;
 use salsa::{Cancelled, Event};
 
-use crate::lint::Diagnostics;
 use crate::workspace::{check_file, Workspace, WorkspaceMetadata};
 
 mod changes;
@@ -61,7 +60,7 @@ impl RootDatabase {
         self.with_db(|db| db.workspace().check(db))
     }
 
-    pub fn check_file(&self, file: File) -> Result<Diagnostics, Cancelled> {
+    pub fn check_file(&self, file: File) -> Result<Vec<String>, Cancelled> {
         self.with_db(|db| check_file(db, file))
     }
 
@@ -115,7 +114,15 @@ impl Upcast<dyn SourceDb> for RootDatabase {
 }
 
 #[salsa::db]
-impl SemanticDb for RootDatabase {}
+impl SemanticDb for RootDatabase {
+    fn is_file_open(&self, file: File) -> bool {
+        let Some(workspace) = &self.workspace else {
+            return false;
+        };
+
+        workspace.is_file_open(self, file)
+    }
+}
 
 #[salsa::db]
 impl SourceDb for RootDatabase {
@@ -242,7 +249,12 @@ pub(crate) mod tests {
     }
 
     #[salsa::db]
-    impl red_knot_python_semantic::Db for TestDb {}
+    impl red_knot_python_semantic::Db for TestDb {
+        fn is_file_open(&self, file: ruff_db::files::File) -> bool {
+            !file.path(self).is_vendored_path()
+        }
+    }
+
     #[salsa::db]
     impl Db for TestDb {}
 

crates/red_knot_workspace/src/lint.rs

@@ -1,5 +1,4 @@
 use std::cell::RefCell;
-use std::ops::Deref;
 use std::time::Duration;
 
 use tracing::debug_span;
@@ -22,7 +21,7 @@ use crate::db::Db;
 pub(crate) fn unwind_if_cancelled(db: &dyn Db) {}
 
 #[salsa::tracked(return_ref)]
-pub(crate) fn lint_syntax(db: &dyn Db, file_id: File) -> Diagnostics {
+pub(crate) fn lint_syntax(db: &dyn Db, file_id: File) -> Vec<String> {
     #[allow(clippy::print_stdout)]
     if std::env::var("RED_KNOT_SLOW_LINT").is_ok() {
         for i in 0..10 {
@@ -64,7 +63,7 @@ pub(crate) fn lint_syntax(db: &dyn Db, file_id: File) -> Diagnostics {
         }));
     }
 
-    Diagnostics::from(diagnostics)
+    diagnostics
 }
 
 fn lint_lines(source: &str, diagnostics: &mut Vec<String>) {
@@ -86,7 +85,7 @@ fn lint_lines(source: &str, diagnostics: &mut Vec<String>) {
 
 #[allow(unreachable_pub)]
 #[salsa::tracked(return_ref)]
-pub fn lint_semantic(db: &dyn Db, file_id: File) -> Diagnostics {
+pub fn lint_semantic(db: &dyn Db, file_id: File) -> Vec<String> {
     let _span = debug_span!("lint_semantic", file=%file_id.path(db)).entered();
 
     let source = source_text(db.upcast(), file_id);
@@ -94,7 +93,7 @@ pub fn lint_semantic(db: &dyn Db, file_id: File) -> Diagnostics {
     let semantic = SemanticModel::new(db.upcast(), file_id);
 
     if !parsed.is_valid() {
-        return Diagnostics::Empty;
+        return vec![];
     }
 
     let context = SemanticLintContext {
@@ -106,7 +105,7 @@ pub fn lint_semantic(db: &dyn Db, file_id: File) -> Diagnostics {
 
     SemanticVisitor { context: &context }.visit_body(parsed.suite());
 
-    Diagnostics::from(context.diagnostics.take())
+    context.diagnostics.take()
 }
 
 fn format_diagnostic(context: &SemanticLintContext, message: &str, start: TextSize) -> String {
@@ -116,48 +115,13 @@ fn format_diagnostic(context: &SemanticLintContext, message: &str, start: TextSi
         .source_location(start, context.source_text());
     format!(
         "{}:{}:{}: {}",
-        context.semantic.file_path().as_str(),
+        context.semantic.file_path(),
         source_location.row,
         source_location.column,
         message,
     )
 }
 
-fn lint_unresolved_imports(context: &SemanticLintContext, import: AnyImportRef) {
-    // TODO: this treats any symbol with `Type::Unknown` as an unresolved import,
-    // which isn't really correct: if it exists but has `Type::Unknown` in the
-    // module we're importing it from, we shouldn't really emit a diagnostic here,
-    // but currently do.
-    match import {
-        AnyImportRef::Import(import) => {
-            for alias in &import.names {
-                let ty = alias.ty(&context.semantic);
-
-                if ty.is_unknown() {
-                    context.push_diagnostic(format_diagnostic(
-                        context,
-                        &format!("Unresolved import '{}'", &alias.name),
-                        alias.start(),
-                    ));
-                }
-            }
-        }
-        AnyImportRef::ImportFrom(import) => {
-            for alias in &import.names {
-                let ty = alias.ty(&context.semantic);
-
-                if ty.is_unknown() {
-                    context.push_diagnostic(format_diagnostic(
-                        context,
-                        &format!("Unresolved import '{}'", &alias.name),
-                        alias.start(),
-                    ));
-                }
-            }
-        }
-    }
-}
-
 fn lint_maybe_undefined(context: &SemanticLintContext, name: &ast::ExprName) {
     if !matches!(name.ctx, ast::ExprContext::Load) {
         return;
@@ -280,17 +244,8 @@ struct SemanticVisitor<'a> {
 
 impl Visitor<'_> for SemanticVisitor<'_> {
     fn visit_stmt(&mut self, stmt: &ast::Stmt) {
-        match stmt {
-            ast::Stmt::ClassDef(class) => {
-                lint_bad_override(self.context, class);
-            }
-            ast::Stmt::Import(import) => {
-                lint_unresolved_imports(self.context, AnyImportRef::Import(import));
-            }
-            ast::Stmt::ImportFrom(import) => {
-                lint_unresolved_imports(self.context, AnyImportRef::ImportFrom(import));
-            }
-            _ => {}
+        if let ast::Stmt::ClassDef(class) = stmt {
+            lint_bad_override(self.context, class);
         }
 
         walk_stmt(self, stmt);
@@ -308,53 +263,6 @@ impl Visitor<'_> for SemanticVisitor<'_> {
     }
 }
 
-#[derive(Debug, Clone, PartialEq, Eq)]
-pub enum Diagnostics {
-    Empty,
-    List(Vec<String>),
-}
-
-impl Diagnostics {
-    pub fn as_slice(&self) -> &[String] {
-        match self {
-            Diagnostics::Empty => &[],
-            Diagnostics::List(list) => list.as_slice(),
-        }
-    }
-}
-
-impl Deref for Diagnostics {
-    type Target = [String];
-    fn deref(&self) -> &Self::Target {
-        self.as_slice()
-    }
-}
-
-impl From<Vec<String>> for Diagnostics {
-    fn from(value: Vec<String>) -> Self {
-        if value.is_empty() {
-            Diagnostics::Empty
-        } else {
-            Diagnostics::List(value)
-        }
-    }
-}
-
-#[derive(Copy, Clone, Debug)]
-enum AnyImportRef<'a> {
-    Import(&'a ast::StmtImport),
-    ImportFrom(&'a ast::StmtImportFrom),
-}
-
-impl Ranged for AnyImportRef<'_> {
-    fn range(&self) -> ruff_text_size::TextRange {
-        match self {
-            AnyImportRef::Import(import) => import.range(),
-            AnyImportRef::ImportFrom(import) => import.range(),
-        }
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use red_knot_python_semantic::{Program, ProgramSettings, PythonVersion, SearchPathSettings};
@@ -363,7 +271,7 @@ mod tests {
 
     use crate::db::tests::TestDb;
 
-    use super::{lint_semantic, Diagnostics};
+    use super::lint_semantic;
 
     fn setup_db() -> TestDb {
         setup_db_with_root(SystemPathBuf::from("/src"))
@@ -409,9 +317,9 @@ mod tests {
         .unwrap();
 
         let file = system_path_to_file(&db, "/src/a.py").expect("file to exist");
-        let Diagnostics::List(messages) = lint_semantic(&db, file) else {
-            panic!("expected some diagnostics");
-        };
+        let messages = lint_semantic(&db, file);
+
+        assert_ne!(messages, &[] as &[String], "expected some diagnostics");
 
         assert_eq!(
             *messages,

crates/red_knot_workspace/src/workspace.rs

@@ -4,17 +4,19 @@ use rustc_hash::{FxBuildHasher, FxHashSet};
 use salsa::{Durability, Setter as _};
 
 pub use metadata::{PackageMetadata, WorkspaceMetadata};
-use ruff_db::source::{source_text, SourceDiagnostic};
+use red_knot_python_semantic::types::check_types;
+use ruff_db::source::{line_index, source_text, SourceDiagnostic};
 use ruff_db::{
     files::{system_path_to_file, File},
     system::{walk_directory::WalkState, SystemPath, SystemPathBuf},
 };
 use ruff_python_ast::{name::Name, PySourceType};
+use ruff_text_size::Ranged;
 
 use crate::workspace::files::{Index, Indexed, PackageFiles};
 use crate::{
     db::Db,
-    lint::{lint_semantic, lint_syntax, Diagnostics},
+    lint::{lint_semantic, lint_syntax},
 };
 
 mod files;
@@ -92,8 +94,8 @@ pub struct Package {
     root_buf: SystemPathBuf,
 
     /// The files that are part of this package.
-    #[return_ref]
     #[default]
+    #[return_ref]
     file_set: PackageFiles,
     // TODO: Add the loaded settings.
 }
@@ -249,6 +251,23 @@ impl Workspace {
             FxHashSet::default()
         }
     }
+
+    /// Returns `true` if the file is open in the workspace.
+    ///
+    /// A file is considered open when:
+    /// * explicitly set as an open file using [`open_file`](Self::open_file)
+    /// * It has a [`SystemPath`] and belongs to a package's `src` files
+    /// * It has a [`SystemVirtualPath`](ruff_db::system::SystemVirtualPath)
+    pub fn is_file_open(self, db: &dyn Db, file: File) -> bool {
+        if let Some(open_files) = self.open_files(db) {
+            open_files.contains(&file)
+        } else if let Some(system_path) = file.path(db).as_system_path() {
+            self.package(db, system_path)
+                .map_or(false, |package| package.contains_file(db, file))
+        } else {
+            file.path(db).is_system_virtual_path()
+        }
+    }
 }
 
 #[salsa::tracked]
@@ -309,8 +328,12 @@ impl Package {
                 let _entered =
                     tracing::debug_span!("index_package_files", package = %self.name(db)).entered();
 
-                tracing::debug!("Indexing files for package {}", self.name(db));
                 let files = discover_package_files(db, self.root(db));
+                tracing::info!(
+                    "Indexed {} files for package '{}'",
+                    files.len(),
+                    self.name(db)
+                );
                 vacant.set(files)
             }
             Index::Indexed(indexed) => indexed,
@@ -348,7 +371,7 @@ impl Package {
 }
 
 #[salsa::tracked]
-pub(super) fn check_file(db: &dyn Db, file: File) -> Diagnostics {
+pub(super) fn check_file(db: &dyn Db, file: File) -> Vec<String> {
     let path = file.path(db);
     let _span = tracing::debug_span!("check_file", file=%path).entered();
     tracing::debug!("Checking file {path}");
@@ -364,13 +387,25 @@ pub(super) fn check_file(db: &dyn Db, file: File) -> Diagnostics {
     );
 
     // Abort checking if there are IO errors.
-    if source_text(db.upcast(), file).has_read_error() {
-        return Diagnostics::from(diagnostics);
+    let source = source_text(db.upcast(), file);
+
+    if source.has_read_error() {
+        return diagnostics;
+    }
+
+    for diagnostic in check_types(db.upcast(), file) {
+        let index = line_index(db.upcast(), diagnostic.file());
+        let location = index.source_location(diagnostic.start(), source.as_str());
+        diagnostics.push(format!(
+            "{path}:{location}: {message}",
+            path = file.path(db),
+            message = diagnostic.message()
+        ));
     }
 
     diagnostics.extend_from_slice(lint_syntax(db, file));
     diagnostics.extend_from_slice(lint_semantic(db, file));
-    Diagnostics::from(diagnostics)
+    diagnostics
 }
 
 fn discover_package_files(db: &dyn Db, path: &SystemPath) -> FxHashSet<File> {
@@ -424,7 +459,7 @@ mod tests {
     use ruff_db::testing::assert_function_query_was_not_run;
 
     use crate::db::tests::TestDb;
-    use crate::lint::{lint_syntax, Diagnostics};
+    use crate::lint::lint_syntax;
     use crate::workspace::check_file;
 
     #[test]
@@ -442,9 +477,7 @@ mod tests {
         assert_eq!(source_text(&db, file).as_str(), "");
         assert_eq!(
             check_file(&db, file),
-            Diagnostics::List(vec![
-                "Failed to read file: No such file or directory".to_string()
-            ])
+            vec!["Failed to read file: No such file or directory".to_string()]
         );
 
         let events = db.take_salsa_events();
@@ -455,7 +488,7 @@ mod tests {
         db.write_file(path, "").unwrap();
 
         assert_eq!(source_text(&db, file).as_str(), "");
-        assert_eq!(check_file(&db, file), Diagnostics::Empty);
+        assert_eq!(check_file(&db, file), vec![] as Vec<String>);
 
         Ok(())
     }

crates/ruff_benchmark/benches/red_knot.rs

@@ -18,6 +18,7 @@ struct Case {
 }
 
 const TOMLLIB_312_URL: &str = "https://raw.githubusercontent.com/python/cpython/8e8a4baf652f6e1cee7acde9d78c4b6154539748/Lib/tomllib";
+const EXPECTED_DIAGNOSTICS: usize = 27;
 
 fn get_test_file(name: &str) -> TestFile {
     let path = format!("tomllib/{name}");
@@ -89,7 +90,7 @@ fn benchmark_incremental(criterion: &mut Criterion) {
                 let Case { db, parser, .. } = case;
                 let result = db.check_file(*parser).unwrap();
 
-                assert_eq!(result.len(), 34);
+                assert_eq!(result.len(), EXPECTED_DIAGNOSTICS);
             },
             BatchSize::SmallInput,
         );
@@ -104,7 +105,7 @@ fn benchmark_cold(criterion: &mut Criterion) {
                 let Case { db, parser, .. } = case;
                 let result = db.check_file(*parser).unwrap();
 
-                assert_eq!(result.len(), 34);
+                assert_eq!(result.len(), EXPECTED_DIAGNOSTICS);
             },
             BatchSize::SmallInput,
         );

crates/ruff_source_file/src/lib.rs

@@ -254,6 +254,12 @@ impl Debug for SourceLocation {
     }
 }
 
+impl std::fmt::Display for SourceLocation {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{row}:{column}", row = self.row, column = self.column)
+    }
+}
+
 #[derive(Debug, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
 pub enum SourceRow {
     /// A row within a cell in a Jupyter Notebook.